CN110021955B - Photovoltaic power generation system integrating energy storage function and method for dynamically balancing electric energy - Google Patents
Photovoltaic power generation system integrating energy storage function and method for dynamically balancing electric energy Download PDFInfo
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- H—ELECTRICITY
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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Abstract
The invention relates to a photovoltaic power generation system with an integrated energy storage function and a method for dynamically balancing electric energy. The photovoltaic power generation system comprises a plurality of photovoltaic modules and a plurality of voltage converters connected in series, wherein each voltage converter converts electric energy extracted from a corresponding photovoltaic module into output power. There are inverters that perform power conversion on output power supplied from a multistage voltage converter and generate alternating current, and the respective output voltages of the voltage converters are superimposed on a direct current bus as a bus voltage. The energy storage part feeds electric energy to the direct current bus when the sum of the power provided by the multi-stage photovoltaic modules is lower than a preset power value required by the alternating current, and the energy storage part draws the electric energy from the direct current bus when the sum of the power provided by the multi-stage photovoltaic modules is higher than the preset power value required by the alternating current. The power grid demand is quickly diagnosed, and the energy flowing direction of the energy storage part is judged, so that accurate electric energy compensation is provided for the power grid.
Description
Technical Field
The invention mainly relates to the technical field of photovoltaic power generation, in particular to a method for providing power energy storage and grid connection in an application occasion containing a photovoltaic cell, which can quickly diagnose the power grid requirement according to the actual situation and judge the energy flow direction of an energy storage part so as to provide accurate electric energy compensation for the power grid.
Background
The energy is indispensable resource for human production and life, and the energy is also a contradiction point which is obvious between the current actual demand of human and the consumption of natural resources. Along with the non-regenerability of traditional chemical energy sources such as petroleum, coal, natural gas and the like, the traditional chemical energy sources are increasingly exhausted and simultaneously cause serious environmental problems such as air pollution, greenhouse effect and the like. Energy is an important material basis for the existence and development of human society, and along with the development and the gradual reduction of energy of the society, solar energy is rapidly developed as one of important energy with the advantages of inexhaustibility, no pollution and the like. However, solar energy has the defects of intermittence, instability, poor controllability and the like. In order to ensure the balance and continuity of power supply, the energy storage device becomes a key matching component of the photovoltaic power generation system. The energy storage systems are various, and although the application technologies of lead-acid batteries, lithium batteries, sodium-sulfur batteries, vanadium redox flow batteries and the like are different in maturity, the high-capacity energy storage is easy to realize. The charging and discharging speed, the charging and discharging times and the like of the battery energy storage are limited by the characteristics of the battery, and the battery energy storage can not be used for realizing rapid dynamic power compensation, inhibiting dynamic oscillation and smoothing rapid change of wind power generation output. The problem to be solved urgently is to provide a photovoltaic energy storage power station which can be charged and discharged quickly and has the charging and discharging times automatically adaptive to power compensation. The photovoltaic energy storage power station comprises a solar panel for converting solar energy into electric energy, a DC/DC converter for converting direct current output by the solar panel into stable direct current, an energy storage system, and a controller for charging the energy storage system by using the DC-DC converter, and the photovoltaic energy storage power station further comprises an inverter for converting direct current output by the DC converter into alternating current. The photovoltaic energy storage power station aims to quickly respond to charging and discharging requirements, can absorb frequent weak illumination and meet the characteristic point that the energy storage power station has high efficiency, rapid energy storage and ultra-long cycle life.
Solar energy has the characteristics of wide distribution and almost endless use, and the problem of using a solar photovoltaic power generation system is that photovoltaic energy also has the characteristics of intermittency and uncertainty, and is difficult to provide continuous and stable power supply for a load. Based on improving the energy management efficiency of the photovoltaic power generation system, a battery management system is usually arranged to manage the photovoltaic power generation system, the charging and discharging conditions of the battery module are simply controlled, along with the increase of components of the photovoltaic power generation system and the extension of function diversification, the charging and discharging of the battery are simply controlled, the defects of low efficiency, slow response, poor control accuracy and the like are increasingly shown, and the charging and discharging control cannot be carried out according to the parameters of the load and the battery module, so that the energy utilization efficiency is low. Solar photovoltaic power generation systems have been widely used in present industrial and civil power systems as one of the many sources of solar energy. In addition to grid-connected photovoltaic power generation systems in the conventional sense, off-grid systems of photovoltaic are also relatively common systems that utilize solar power generation. A photovoltaic off-grid system generally includes a photovoltaic cell module, an ac-to-dc charger connected to the photovoltaic cell module, a battery pack connected to an output terminal of the ac-to-dc charger, an inverter connected to an output terminal of the storage battery pack and configured to convert dc power to ac power, an ac load, and the like. The photovoltaic cell module converts solar energy into electric energy under the condition of illumination, and the electric storage battery pack is charged through the charging device; and in the absence of illumination, the alternating current load is supplied with power by the storage battery pack through the inverter. The existing off-grid system of photovoltaic needs to modify the equipment design of the whole energy storage system to expand the battery assembly if the modification of the established capacity of the battery assembly is attempted, or needs to replace the battery under the condition of cutting off the power output, and performs the modification operation of the battery capacity under the extremely inconvenient condition. There is therefore a need to provide an improved photovoltaic power generation system and its energy storage system to solve the above problems.
Disclosure of Invention
The present application provides in one embodiment a photovoltaic power generation system integrated with energy storage functionality, comprising: each stage of voltage converter converts electric energy captured from a corresponding photovoltaic module into output power; an inverter that performs power conversion on output power provided from the multi-level voltage converter and generates alternating current; the output voltages of the multi-level voltage converters are superposed on a direct current bus and used as bus voltages; the energy storage part dynamically balances the electric energy on the direct current bus, and feeds the electric energy to the direct current bus when the sum of the external power provided by the multi-stage photovoltaic assembly is lower than a preset power value required by the alternating current, or the energy storage part draws the electric energy from the direct current bus when the sum of the external power provided by the multi-stage photovoltaic assembly is higher than the preset power value required by the alternating current.
The photovoltaic power generation system integrating the energy storage function is characterized in that: each stage of the voltage converter is also used for setting the output current and the output voltage of the corresponding photovoltaic module at the maximum power point.
The photovoltaic power generation system integrating the energy storage function is characterized in that: the energy storage part comprises a bidirectional direct current converter and an electric storage battery, and the energy storage part feeds electric energy onto the direct current bus by taking the electric energy stored by the electric storage battery as an energy supply source, or stores the electric energy absorbed by the energy storage part in the electric storage battery.
The photovoltaic power generation system with the integrated energy storage function is characterized in that: and a value obtained by dividing the given reference power of the electric storage battery by the set battery voltage of the electric storage battery is defined as a tracking current value of the bidirectional direct current converter, the actual output current of the bidirectional direct current converter is collected in real time, and the actual output current of the bidirectional direct current converter is controlled to tend to be equal to the tracking current value.
The photovoltaic power generation system integrating the energy storage function is characterized in that: the given reference power of the storage battery is equal to the difference between the sum of the external powers supplied by the multi-stage photovoltaic module and the predetermined power value required by the alternating current.
The photovoltaic power generation system integrating the energy storage function is characterized in that: ways to control the actual output current of the bidirectional dc converter to tend to equal the tracking current value include: a pulse width modulation signal generated by a current PI controller established based on the actual output current and the tracking current value of the bidirectional direct current converter is used for driving the bidirectional direct current converter; the PI controller sets the tracking current value as a given instruction value and synchronously adjusts the deviation of the actual output current of the bidirectional direct current converter to the tracking current value, and the pulse width modulation signal generated according to the deviation is used for reducing the deviation in the stage of driving the bidirectional direct current converter.
The photovoltaic power generation system integrating the energy storage function is characterized in that: the positive sign or the negative sign of the difference between the sum of the external power provided by the multi-stage photovoltaic module and the preset power value is multiplied by the magnitude of the tracking current value to define the direction of the tracking current value: when the tracking current value is a negative value, the direction of current in the bidirectional direct current converter is from the storage battery to the direct current bus; when the tracking current value is a positive value, the direction of the current in the bidirectional direct current converter is from the direct current bus to the storage battery.
The photovoltaic power generation system with the integrated energy storage function is characterized in that: the bidirectional direct current converter is provided with a boosting circuit and a voltage reduction circuit, when the tracking current value is a negative value, the bidirectional direct current converter is set to be in a boosting working state, and when the tracking current value is a positive value, the bidirectional direct current converter is set to be in a voltage reduction working state.
The photovoltaic power generation system integrating the energy storage function is characterized in that: the duty ratio of the voltage boosting circuit when the bidirectional direct current converter is in a voltage boosting working state is complementary with the duty ratio of the voltage reducing circuit when the bidirectional direct current converter is in a voltage reducing working state.
The photovoltaic power generation system integrating the energy storage function is characterized in that: the bidirectional direct-current converter is provided with an input capacitor at an input side coupled to the direct-current bus and an output capacitor at an output side coupled to the storage battery; when the voltage drop across the input capacitor is higher than the voltage drop across the output capacitor, the bidirectional DC converter is triggered to store electrical energy into the storage battery, and when the voltage drop across the input capacitor is lower than the voltage drop across the output capacitor, the bidirectional DC converter is triggered to feed electrical energy from the storage battery to the DC bus.
The photovoltaic power generation system integrating the energy storage function is characterized in that: when the voltage drop of the input side of the bidirectional direct current converter coupled to the direct current bus is higher than the voltage drop of the output side of the bidirectional direct current converter coupled to the storage battery, the bidirectional direct current converter is triggered to start the voltage reduction circuit to store the electric energy into the storage battery; and when the voltage drop of the input side of the bidirectional direct current converter coupled to the direct current bus is lower than the voltage drop of the output side of the bidirectional direct current converter coupled to the storage battery, triggering the bidirectional direct current converter to start the boost circuit to feed the electric energy to the direct current bus.
In another embodiment, the present application provides a method for dynamically balancing electrical energy in a photovoltaic power generation system integrated with energy storage, the photovoltaic power generation system having a plurality of photovoltaic modules and a plurality of voltage converters connected in series, each of the plurality of voltage converters converting electrical energy received from a corresponding one of the photovoltaic modules into an output power; the photovoltaic power generation system also has an inverter that performs power conversion on output power supplied from the multi-level voltage converter and generates alternating current, and the respective output voltages of the multi-level voltage converters are superimposed on the direct current bus and thereby serve as a bus voltage; the method comprises the following steps: comparing the sum of external power provided by the multi-stage photovoltaic module with a preset power value required by the alternating current; when the sum of external power provided by the multi-stage photovoltaic module is lower than a preset power value required by the alternating current, feeding electric energy to the direct current bus by using the provided energy storage part; when the condition that the sum of external power provided by the multi-stage photovoltaic module is higher than a preset power value required by alternating current is met, the provided energy storage part is utilized to absorb electric energy from the direct current bus; thereby utilizing the energy storage part to dynamically throughput energy to smooth energy fluctuation on the direct current bus.
The method described above, wherein: each stage of the voltage converter is also used for setting the output current and the output voltage of the corresponding photovoltaic module at the maximum power point.
The method described above, wherein: the energy storage part comprises a bidirectional direct current converter and an electric storage battery, and the method for dynamically handling energy comprises the following steps: the energy storage part stores the drawn electric energy in the storage battery, or the energy storage part feeds the electric energy onto the direct current bus by using the electric energy stored in the storage battery as an energy supply source.
The method described above, wherein: the method for adjusting the size of the power value sucked or fed by the energy storage part in the energy throughput process comprises the following steps: collecting external power provided by each of the multi-stage photovoltaic modules and calculating a difference value between the sum of the external power provided by the multi-stage photovoltaic modules and a preset power value required by alternating current; defining a value calculated by dividing a given reference power of the storage battery by a battery voltage of the storage battery as a tracking current value of the bidirectional dc converter, the given reference power of the storage battery being equal to the difference value; and acquiring the actual output current of the bidirectional direct current converter in real time, and controlling the actual output current of the bidirectional direct current converter to tend to be equal to the tracking current value.
The method described above, wherein: the mode for controlling the actual output current of the bidirectional direct current converter to tend to be equal to the tracking current value comprises the following steps: a pulse width modulation signal generated by a current PI controller established based on the actual output current and the tracking current value of the bidirectional direct current converter is used for driving the bidirectional direct current converter; the current PI controller sets the tracking current value as a given command value and also synchronously adjusts the deviation of the actual output current of the bidirectional DC converter to the tracking current value, and the pulse width modulation signal generated according to the deviation is used for reducing the deviation in the stage of driving the bidirectional DC converter.
The method described above, wherein: defining the direction of the tracking current value by multiplying the positive or negative sign of said difference value by the magnitude of the tracking current value: when the tracking current value is a negative value, the direction of current in the bidirectional direct current converter is from the storage battery to the direct current bus; when the tracking current value is a positive value, the direction of the current in the bidirectional direct current converter is from the direct current bus to the storage battery.
The method described above, wherein: the method comprises the following steps of setting a bidirectional direct current converter to be provided with a boost circuit and a buck circuit at the same time, and judging the mode that the bidirectional direct current converter starts the boost circuit or starts the buck circuit: when the tracking current value is judged to be a negative value, the bidirectional direct current converter is driven to be in a boosting working state; and when the tracking current value is judged to be a positive value, the bidirectional direct current converter is driven to be in a voltage reduction working state.
The method described above, wherein: the bidirectional direct current converter is provided with a boosting circuit and a voltage reduction circuit at the same time, and the duty ratio of the boosting circuit when the bidirectional direct current converter is in a boosting working state and the duty ratio of the voltage reduction circuit when the bidirectional direct current converter is in a voltage reduction working state are complementary to each other.
The method described above, wherein: when the voltage drop of the input side of the bidirectional direct current converter coupled to the direct current bus is higher than the voltage drop of the output side of the bidirectional direct current converter coupled to the storage battery, the bidirectional direct current converter is triggered to start the voltage reduction circuit to store the electric energy into the storage battery; when the voltage drop of the input side of the bidirectional direct current converter coupled to the direct current bus is lower than the voltage drop of the output side of the bidirectional direct current converter coupled to the storage battery, the bidirectional direct current converter is triggered to start the boost circuit to feed electric energy to the direct current bus.
Drawings
To make the above objects, features and advantages more comprehensible, embodiments accompanied with figures are described in detail below, and features and advantages of the present application will become apparent upon reading the following detailed description and upon reference to the following figures.
Fig. 1 is an exemplary schematic diagram of an overall architecture of a multi-level photovoltaic module and a series-connected multi-level voltage converter.
Fig. 2 is a schematic diagram of a multistage voltage converter or an inverter as a charging device for charging an electric storage battery.
Fig. 3 is an exemplary schematic diagram of a bidirectional dc converter incorporated in a photovoltaic power generation system with integrated energy storage.
Fig. 4 is an exemplary schematic diagram of driving a bi-directional dc converter in a photovoltaic power generation system with integrated energy storage.
Fig. 5 is an exemplary schematic diagram of a bidirectional dc converter with a power switch tube shared by a boost circuit and a buck circuit.
Fig. 6 is an exemplary schematic diagram of a power switch tube of a boost circuit and a buck circuit of a bidirectional dc converter.
Detailed Description
While the technical solutions disclosed in the present application will be described in detail and fully with reference to the specific embodiments, the embodiments described are only illustrative and non-exhaustive of the embodiments used in the present application, and based on the embodiments, those skilled in the art will recognize that any solution obtained without inventive efforts falls within the scope of the present application.
Currently in distributed or centralized photovoltaic plants, the problems of concern are: shadow occlusion causes mismatch between numerous photovoltaic modules; problems are also found in: the battery output characteristics of the photovoltaic module are shown in the fact that output voltage and output current are closely related to external factors such as illumination intensity and ambient temperature, and due to uncertainty of the external factors, the corresponding voltage of the maximum output power and the maximum power point changes along with changes of the external factors. Based on these concerns, achieving maximum power point tracking of photovoltaic modules/cells in view of external factors is one of the objectives of the present application.
Referring to fig. 1, a photovoltaic module array is a basis for converting light energy into electric energy of a photovoltaic power generation system, and a plurality of battery strings are installed in the photovoltaic module array, and each battery string is formed by serially connecting a plurality of photovoltaic modules PV1 to PVN. Each photovoltaic module or cell is equipped with a voltage converter or power optimizer that performs a maximum power tracking algorithm. In a certain string of battery packs, for example, the electric energy generated by the first stage photovoltaic module PV1 is power-converted by the first stage voltage converter CH1 to perform power optimization, the electric energy generated by the second stage photovoltaic module PV2 is power-converted by the second stage voltage converter CH2 to perform power optimization, and so on, until the electric energy generated by the nth stage photovoltaic module PVN is power-converted by the nth stage voltage converter CHN to perform power optimization, N is a natural number not lower than 1. The voltage converters used in this context, also known as maximum power point trackers, typically use a specific type of topological circuit to search for the maximum power point and allow the voltage converter to extract as much maximum power as possible from the photovoltaic module.
Referring to fig. 1, the output voltage V of the first-stage voltage converter CH1 is set O1 Second stage voltage converter CH2 output voltage V O2 … and so on until the voltage converter CHN of the nth stage outputs the voltage V ON . The total string-level voltage on any string of photovoltaic battery strings is about V through calculation O1 +V O2 +…V ON ＝V BUS . Different groups of battery packs are connected in series-parallel between the buses LA and LB: if it is defined that the multistage voltage converters CH1 to CHN constitute a certain link, different ones of the links are connected in parallel between the busbars LA and LB. The total electrical energy provided by the array of photovoltaic modules is transmitted by a dc bus to an energy harvesting device of various types, including at least the inverter INVT of fig. 1, which can invert dc to ac, or a charger, which charges a battery, etc. In fact, the photovoltaic module in fig. 1 is only a specific example as a dc power source, i.e. an optimized object, the voltage converter is not only compatible with the crystalline silicon solar panel, but also can be matched with a part of the thin film battery, the photovoltaic module can be replaced by a chemical battery, a storage battery or a storage battery, etc., and the voltage converter is more in a sense of performing power optimization on different types of dc power sources, such as wind energy, a fuel battery, etc. Any solution in the prior art for maximum power tracking of a dc power supply is equally applicable to the voltage converter of the present application, most preferablyCommon maximum power tracking methods include a constant voltage method, a conductance increment method, a disturbance observation method and the like, and common open-circuit voltage methods, short-circuit current methods and the like belong to relatively simple schemes, but the tracking accuracy is relatively low.
Referring to fig. 1, a voltage converter belongs to a power electronic device, and the main purpose is to realize the function of maximum power point tracking of an individual photovoltaic module. The Buck Buck circuit, the Boost circuit, the Buck-Boost circuit, the other CuK converter circuit and the like are main circuit topologies suitable for the photovoltaic voltage converter. These main circuit topologies are also essentially in the category of SMPS systems, which usually use power semiconductor devices as switching elements, and control the duty ratio of the switching elements to adjust the output voltage by periodically switching on and off the switches. The power conversion realized by the switching power supply is a core part of the switching power supply, in order to meet the requirement of high power density, the converter needs to work in a high-frequency state, and the switching transistor needs to adopt a power switch with high switching speed and short on and off time, such as a power thyristor, a power field effect transistor, an insulated bipolar transistor and the like. The main control modes of the switching converter are pulse width modulation, pulse frequency modulation and the like, and a pulse width modulation scheme is commonly used. The switching power supply converter of the application is embodied by a voltage converter for reducing or boosting direct current to direct current, and after the voltage converter optimizes the maximum power of a single component, energy is transmitted to an inverter for local use or grid connection after direct current to alternating current processing. The inverter INVT may typically be a pure inverter device without maximum power tracking or an inverter device equipped with two-stage maximum power tracking.
Referring to fig. 1, the overall power generation system is illustrated with a number N of photovoltaic modules PV1-PVN and a corresponding number N of series connected voltage converters CH1-CHN and associated inverters INVT as examples. The voltage converter has an input coupled to the photovoltaic module and an output providing an output power. For example, a first input terminal of the input side of the first-stage voltage converter CH1 is coupled to the anode of the first-stage photovoltaic module PV1, and a second input terminal of the input side of the first-stage voltage converter CH1 is coupled to the first stageThe electrical energy received at the negative, input side of the photovoltaic module PV1 is converted into output power at a first output and a second output at the output side of the first stage voltage converter CH 1. The correspondence of the photovoltaic modules PV2-PVN and the voltage converters CH2-CHN has been shown in the figure. The voltage converters CH1-CHN are required to be connected in series as follows: the multi-stage voltage converters CH1-CHN in series provide a total cascode voltage equal to the sum of their respective output voltages. So that: a total cascade voltage V can be provided between the bus LA to which the first stage voltage converter CH1 is coupled and the bus LB to which the nth stage voltage converter CHN is coupled BUS ＝V O1 +V O2 +…V ON . The most important core significance of the power optimizer is that: a certain voltage converter needs to set the output current and the output voltage of a certain dc power supply paired therewith to the maximum power point of the dc power supply, in other words, the voltage converter needs to set its own output current to have no direct correlation with the output current of the dc power supply paired therewith, and the voltage converter needs to set its own output voltage to have no direct correlation with the output voltage of the dc power supply paired therewith.
Referring to fig. 1, the voltage converters CH1 to CH10 of which the number N =10 are connected in series as follows: it is considered that the second output terminal of any preceding voltage converter is coupled to the first output terminal of an adjacent succeeding voltage converter via a power line or the like. Take the actual connection relationship as an example: the second output terminal of the first stage voltage converter CH1 is connected to the first output terminal of the second stage voltage converter CH2, and the second output terminal of the second stage voltage converter CH2 is connected to the first output terminal of the adjacent third stage voltage converter CH3, and so on, until the second output terminal of the ninth stage voltage converter CH9 is directly connected to the first output terminal of the tenth stage voltage converter CH 10. It can therefore also be considered that: the cascade voltages provided by the series-connected multistage voltage converters CH1-CH10 are equal to the superposition of their respective output voltages; so that: a total cascade voltage V can be provided between a bus LA coupled to a first output of the first stage voltage converter CH1 and a bus LB coupled to a second output of the tenth stage voltage converter CH10 BUS ＝V O1 +V O2 +…V O10 。
Referring to fig. 1, a conventional series type power optimizer adopts a fixed voltage design concept. The inverter confirms the voltage of a stable direct-current bus according to the alternating-current end voltage, collects the maximum power collected by the power optimizer connected in series, calculates the bus current and transmits the bus current to the power optimizer through a wireless or power carrier signal. The voltage at the output of the power optimizer is equal to the power of the maximum power of the collected component divided by the bus current. If the maximum power collected by the multi-stage voltage converters CH1-CHN is delivered to the inverter INVT, the total power provided by the photovoltaic modules PV1-PVN divided by the fixed voltage of the dc bus of the inverter INVT can calculate the bus current. And after the assembly is shielded, the power optimizer corresponding to the shielded battery re-determines the maximum output power value according to the volt-ampere curve, and transmits the maximum output power value to the inverter through a communication means. And on the premise of maintaining the voltage of the direct current bus unchanged, recalculating the bus current if the bus current becomes small and feeding back the bus current to each voltage converter. At the moment, the power of the shielded photovoltaic module is reduced, and the corresponding voltage converter can also reduce the voltage to confirm that the output current reaches the standard. The voltage converters of other photovoltaic modules which are not shielded can boost the voltage to achieve the standard output current, and the dynamic regulation procedure is the voltage complement process, so that the bus voltage provided for the direct current end of the inverter is stabilized. The output voltage of the voltage converter corresponding to the photovoltaic component which is not shielded easily exceeds the voltage tolerance range of the voltage converter, and the problem becomes more prominent when partial components are shielded more seriously, so that the direct-current voltage of the direct-current bus can be properly and elastically floated.
Referring to fig. 1, the multi-stage voltage converters CH1 to CHN are configured with processors, except that MPPT is performed by the PWM signals output from the processors, the processors and their configured peripheral hardware can also collect various target parameters of the dc power supply or the voltage converter, which is equivalent to a data collector, because it is meaningful for the data collection device to capture the target parameter data, such as calculating the bus current and adjusting the bus voltage based on the total power of each battery string, and transmitting various data to the cloud server as backup or for calling. In an optional embodiment, the peripheral hardware may collect a series of related specified target parameter information such as voltage and current, power, temperature and power generation amount and the like of the photovoltaic module, for example, the voltage parameter is collected by a voltage sensor, the current parameter is collected by a current sensor, the temperature parameter is collected by peripheral hardware such as a temperature sensor, and the like, and the illumination radiation intensity is collected by an illumination sensor. It will be readily appreciated that the more types of peripheral hardware, the more types of parameters that the processor can obtain in relation to the photovoltaic module, but the more costs increase and compromises are required. In a simpler embodiment, the various target parameters may further include data of ambient environmental factors where the photovoltaic module is located, which are detected by an environmental monitor: the environment temperature, humidity, wind speed, illumination intensity, air pressure and the like, and the visible environment monitor is a high-integration-level data acquisition device. The voltage converters may communicate data with each other through wireless communication or carrier communication or the voltage converters and the inverter INVT may communicate data with each other through wireless communication or carrier communication.
Referring to fig. 1, an implementation method for effectively utilizing solar energy includes providing a number N of voltage converters and a number N of photovoltaic modules, wherein the voltage converters CH1-CHN and the photovoltaic modules PV1-PVN perform power conversion in a one-to-one manner, and a natural number N > 1. Providing an inverter INVT for concentrating the output power of the voltage converters CH1-CHN, wherein a bus voltage V for powering the inverter INVT BUS Is equal to the output voltage V of each of the voltage converters O1 +V O2 +…V ON The inverter is a dc-to-ac conversion device. The inverter circuit of the inverter generally performs the inversion of direct current to alternating current under the drive of the drive signal output by the processor, and equivalent devices having the same functions as the processor such as: logic devices, control devices, state machines, controllers, chips, software drives or a plurality of microprocessors, gate arrays. The inverter is provided with a control unit or a processing unit or a processor. The AC power generated by the inverter can be connected to the grid GThe RID is either supplied to the ac load for local use.
Referring to fig. 2, in an embodiment of the present application, an energy storage integrated photovoltaic power generation system is provided, which mainly attempts to absorb electric energy and reversely push the electric energy between the dc buses LA-LB, so that the photovoltaic power generation system has a power regulation function to cope with power instability of a photovoltaic module. The foregoing has already mentioned: external factors such as shadow shielding, assembly aging, illumination intensity and ambient temperature can cause unstable power of the photovoltaic assembly. The real-time power of the photovoltaic module and the corresponding voltage of the maximum power point change along with the change of external factors, so that the alternating current provided by the photovoltaic power generation system is further caused to be not in accordance with safety specifications, and the negative influence is that the power fluctuation impact on the GRID is caused, and the power fluctuation range which can be tolerated by the GRID can be possibly exceeded. Therefore, the most basic problem to be solved by the present application is to add an energy storage part to a conventional photovoltaic power generation system to cope with the intermittent fluctuation of the power of the photovoltaic module. Except for available lead-acid batteries, lithium batteries, sodium-sulfur batteries, vanadium flow batteries and the like, any electric storage battery BAT is suitable for the application. The storage battery is coupled to the dc bus to feed the stored electrical energy onto the dc bus as an energy supply source, or the storage battery is coupled to the dc bus to draw electrical energy on the bus and store it in the storage battery. Lead-acid storage batteries, alkaline storage batteries, lithium batteries and super capacitors are applied to different occasions or products respectively in the application of the storage battery BAT, and the lead-acid storage batteries are most widely applied at present, and a plurality of types of modified storage batteries are derived from the lead-acid storage batteries, such as pregnant solution lead-acid batteries, valve-controlled sealed lead-acid batteries, colloid batteries, lead-carbon batteries and the like. The fastest growing today are lithium battery systems, typically represented by lithium iron phosphate batteries and ternary lithium batteries, i.e., lithium nickel cobalt manganese (Li-Ni-Co-Mn).
Referring to fig. 3, in one embodiment of the present application, the energy storage integrated photovoltaic power generation system has a plurality of photovoltaic modules PV1-PVN and a plurality of voltage converters CH1-CHN connected in series, wherein each voltage converter is connected to a corresponding photovoltaic moduleThe extracted electrical energy is converted into output power, for example, the voltage converter CHN converts the electrical energy extracted from the corresponding photovoltaic module PVN into the output power of the voltage converter CHN itself. The photovoltaic power generation system integrated with the energy storage function is provided with an inverter INVT which performs power conversion on output power provided by the multistage voltage converters CH1 to CHN and generates alternating current. As described above, the output voltages, i.e., V, of the respective multi-stage voltage converters CH1-CHN O1 To V ON Superimposed on the dc bus LA-LB and thereby acting as a bus voltage, which is practically nearly equal to the cascade voltage V BUS ＝V O1 +V O2 +…V ON . Bus capacitor C in one embodiment BUS Connected between two DC buses LA-LB and bus capacitor C BUS The large capacitance capacity of the capacitor can effectively reduce the fluctuation of bus voltage and realize the decoupling between the input constant power and the output fluctuation power. As shown in fig. 3, the photovoltaic power generation system with integrated energy storage function has an energy storage portion for dynamically balancing the electric energy on the dc bus, and the energy storage portion includes a bidirectional dc converter 80 and an electric storage battery BAT. The design scheme for dynamically balancing the electric energy on the direct current bus of the energy storage part is mainly embodied as follows: the energy storage portion feeds electric energy to the dc bus LA-LB with the electric energy stored in the electric storage battery BAT as an energy supply source, or the energy storage portion stores the electric energy drawn from the dc bus in the electric storage battery BAT. The significance of the bidirectional dc converter 80 is therefore that energy is either stored in the storage battery BAT or is fed to the dc bus, the energy or power flowing in both directions on the input side and on the output side of the bidirectional dc converter 80. The bidirectional dc converter 80 also belongs to the category of high-frequency switching power supplies SMPS per se, and a Buck circuit, a Boost circuit, a Buck-Boost circuit, another CUK converter CUK circuit, and the like are also suitable for the bidirectional dc converter 80, but compared with the aforementioned voltage converters CH1-CHN, the bidirectional dc converter and the power optimizer are not consistent in operation mechanism, and the voltage converter functions to realize maximum power point tracking while the bidirectional dc converter functions to realize power bidirectional flow.
Referring to fig. 4, the power input by the inverter is required to be kept constant in general, but the power output by the inverter is low-frequency alternating current because the voltage and the current of the power grid are both low-frequency alternating current, so that the instantaneous power of the inverter stage contains double-frequency pulsating quantity, and the low-frequency pulsating power enables the input current of the inverter stage to contain large alternating current components with double output voltage frequencies, so that the output current of the preceding-stage voltage converter has low-frequency pulsation, and the pulsating power is shared by the filter inductor of the voltage converter and the middle bus capacitor. If one tries to achieve a more optimal decoupling between the constant power of the inverter stage input and the fluctuating power of the output, it is necessary to use an energy storage scheme. In one embodiment of the present application, the operating mechanism of the energy storage portion for dynamically balancing the electric energy on the dc bus is embodied as follows: on the basis of counting the external power provided by each stage of photovoltaic modules PV1-PVN, for example, the external power P1 provided by the first stage of photovoltaic module PV1 is collected, the external power P2 provided by the second stage of photovoltaic module PV2 is collected, and so on until the external power PN provided by the nth stage of photovoltaic module PVN is collected. Without doubt, the sum of the external power provided by the multi-stage PV modules PV1-PVN is equal to P1+ P2+ P3+ … PN = PT, and the rough calculation is that in general the sum of the output power provided by each of the multi-stage voltage converters CH1-CHN is also approximately equal to PT, in practice with a slight power loss. Based on the fact that external factors cause power fluctuations of the photovoltaic module, the sum PT of the external powers as a whole is not always perfectly matched to the input power of the inverter required by the grid, and the countermeasures are generally designed as follows: the energy storage part feeds electric energy onto the direct current bus LA-LB when the sum PT of the external power provided by the multi-stage photovoltaic modules PV1-PVN is lower than a predetermined power value PG required by the alternating current, wherein the predetermined power value PG required by the alternating current is mainly determined by the requirement of a power grid or an alternating current load, and the predetermined power value can be basically determined if the alternating current is determined; when the sum PT of the external power provided by the multi-stage photovoltaic modules PV1-PVN is higher than a preset power value PG required by the alternating current, the energy storage part draws electric energy from the direct current buses LA-LB and stores the electric energy into the storage battery. Considering the instability of photovoltaic power generation in a photovoltaic power station, when the real-time power of photovoltaic modules PV1-PVN suddenly changes or transiently jumps, cloud, tree shadow, building shielding and the like are all inducement factors of the fluctuation and randomness of the output power of the photovoltaic modules, an energy storage part plays a role in real-time compensation and balances the system power, and the input power of an inverter stage is ensured and maintained to be close to the preset power value required by alternating current.
Referring to fig. 4, in one embodiment of the present application, at least the functional blocks included in microprocessor 100 are disclosed as being suitable for use with bi-directional dc converter 80: a value calculated by dividing a given reference power of electric storage battery BAT by battery voltage VB of the electric storage battery is defined as tracking current value IR of bidirectional dc converter 80, so that the given reference power is divided by battery voltage VB by divider DIV to be equal to tracking current value IR. The significance of calculating the tracking current value here is that we need to actively control the bidirectional DC converter 80, i.e., control the actual output current IA of the bidirectional DC/DC converter to tend to be equal to the tracking current value IR. The actual output current IA can be detected by a current sensor and mostly detects the inductor current of the DC/DC converter, and certainly, the current analog detected by the current sensor needs to be processed digitally by a microprocessor, i.e., a/D conversion. In one embodiment of the application, the given reference power of the storage battery is substantially equal to the difference between the sum PT of the external powers provided by the multilevel PV modules PV1-PVN and the predetermined power value PG required by the alternating current, it has been described above that the sum of the external powers provided by the multilevel PV modules PV1-PVN is equal to P1+ P2+ P3+ … PN = PT, and the given reference power is equal to PT minus PG, it must be noted that the sum of the external powers is not continuously greater than or less than the predetermined power value, meaning that the calculation result of PT minus PG should have a positive or negative sign, i.e. a magnitude relationship characterizing PT and PG. Modes in which the microprocessor 100 controls the actual output current IA of the bidirectional dc converter 80 to approach the tracking current value IR include: in order to reduce the error between IA and IR and to try to improve the dynamic response capability in response to the power fluctuation, the main scheme is that the pulse width modulation signal generated by the current PI controller based on the actual output current IA and the tracking current value IR of the bidirectional dc converter 80, which are monitored, is used to drive the bidirectional dc converter 80, the current PI controller with single loop negative feedback sets the tracking current value IR to a given command value and also synchronously adjusts the deviation of the actual output current IA of the bidirectional dc converter 80 from the tracking current value IR, the actual output current is mostly considered as an inductive current, and the pulse width modulation signal PWM generated according to the deviation is used to reduce the deviation at the stage of driving the bidirectional dc converter 80. In the industry, PI controllers/regulators form a control deviation from a given command value and an actual output value, and in the course of the control, the proportional and integral of the deviation are combined linearly to form a so-called control variable, which controls a controlled object, for example the actual output current IA. Wherein the proportion regulation function is as follows: the deviation of the controlled object is reflected in proportion, and once the controlled object has the deviation, the proportion adjustment quick response immediately generates an adjustment function to reduce the deviation. The adoption of a larger proportion effect can accelerate the adjustment and reduce errors, but the stability of the bidirectional direct current converter is reduced and even the converter is unstable due to an overlarge proportion relation. Wherein the integral adjustment functions are as follows: the bidirectional DC converter system eliminates steady-state errors and improves the error-free degree. The so-called proportional, integral and derivative actions are often regarded as a combination with a better regulation law in the industry and constitute either a PI regulator or a PID regulator. The output of the PI regulator or PID regulator is fed to a PWM generation module to generate a desired target PWM signal, which in turn is used to control an actuator of a power stage, such as a power switch of the bi-directional dc converter 80. In the present application, the current PI controller generates an output D according to the deviation, the output D is transmitted to the PWM generating module to generate a PWM signal for driving the bi-directional dc converter 80, and the PWM signal generated according to the deviation is used to reduce the deviation between IA and IR at the stage of driving the bi-directional dc converter 80.
Referring to fig. 4, as mentioned above, it is described that the calculation result of PT minus PG should have a positive or negative sign, i.e. to characterize the magnitude relationship between PT and PG, in a certain embodiment, the positive or negative sign of the difference between the sum PT of the external powers provided by the multi-stage PV assemblies PV1-PVN and the predetermined power value PG is multiplied by the magnitude value of the tracking current value IR to define the direction of the tracking current value; it can also be considered that a value calculated by dividing the calculation result of PT minus PG by battery voltage VB of power storage battery BAT is defined as tracking current value IR of bidirectional dc converter 80, and the tracking current value naturally has a positive or negative sign of the difference between PT and PG. In summary, the positive or negative sign of the PT/PG difference multiplied by the absolute magnitude of the tracking current value defines the direction of the tracking current value: when the tracking current value IR is a negative value, it means that the direction of the current in the bidirectional dc converter 80 is from the electric storage battery BAT to the dc bus LA-LB, reflecting that energy flows from the electric storage battery to the dc bus; when tracking current value IR is a positive value, it means that the direction of current in bidirectional dc converter 80 is from dc bus LA-LB to electric storage battery BAT, and the reflected energy flows from the dc bus to the electric storage battery BAT.
Referring to fig. 5, the bidirectional DC converter 80, i.e. the DC/DC converter, although belonging to the category of high frequency switching power supplies SMPS, its alternative topology is not limited to a particular kind. The bi-directional dc converter 80 is preferably provided with both a boost circuit and a buck circuit. In alternative embodiments: power switches Q1 and Q2 are connected in series between a first input node of the bidirectional dc-to-dc converter, which is coupled to dc-link LA and a corresponding second input node to dc-link LB, and a second input node of the bidirectional dc-to-dc converter, which is also set such that the first output node of the bidirectional dc-to-dc converter is coupled to the positive pole of the accumulator battery BAT and the second output node of the bidirectional dc-to-dc converter is coupled to the negative pole of the accumulator battery BAT. Note that both power switch Q1 and power switch Q2 are connected to a first interconnection node X1, the inductor device L is connected between the first interconnection node X1 and a first output node of the bidirectional dc converter, and the second input node and the second output node are directly coupled together. In an optional, but not necessary, embodiment: an input capacitor C is connected between the first input node and the second input node 1 An output capacitor C is connected between the first output node and the second output node 2 . The power switch is typically an insulated gate bipolar transistor, a semiconductor field effect transistor, or the like. The bi-directional dc converter 80 preferably incorporates both buck and boost circuits such as: energy flows from a first input node and a second input node on the input side of the converter to a first output node on the output side of the converter andand the second output node, the voltage reduction circuit plays a leading role, the two power switches Q1-Q2 form a voltage reduction single arm of the voltage reduction circuit BUCK, the PWM signal provided by the PWM generation module can be used for driving the two complementary switches Q1-Q2 of the voltage reduction circuit to switch at high frequency but not be allowed to be switched on simultaneously, generally, the duty ratio of the PWM signal for the voltage reduction circuit refers to the duty ratio of the power switch Q1, the power switch Q2 is a synchronous follow current switch, and energy flows from the direct current bus to the storage battery in the embodiment. In other embodiments for comparison, the bi-directional dc converter 80 preferably has both a boost circuit and a buck circuit: energy flows from a first output node and a second output node on the output side of the converter to a first input node and a second input node on the input side of the converter, the Boost circuit plays a leading role, the power switches Q1-Q2 form a Boost single arm of the Boost circuit Boost, the PWM signal provided by the PWM generating module can be used for driving complementary switches Q1-Q2 of the Boost circuit, the switches Q1-Q2 are switched at high frequency but not allowed to be switched simultaneously, the duty ratio of the PWM signal for the Boost circuit is the duty ratio of the power switch Q2, and the power switch Q1 is a synchronous free-wheeling switch, and in the embodiment, the energy flows from the storage battery to the direct current bus. The power switch may include a parasitic anti-parallel diode in its semiconductor structure, and in some embodiments, an external diode may be directly connected in parallel to two ends of the power switch as an equivalent anti-parallel diode, and the anti-parallel diode may also be used as a freewheeling element to provide a freewheeling path for current flowing through the inductive device.
Referring to fig. 5, in an embodiment of the present application, when the tracking current value IR is a negative value, the bidirectional dc converter is set to be in the boost operating state, that is, the power switch Q2 is used as the main switch and the power switch Q1 is used as the freewheeling switch. In another embodiment of the present application, tracking the current value IR to a positive value sets the bidirectional dc converter to be in a step-down operation state, i.e., the power switch Q1 is used as a main switch and the power switch Q2 is used as a freewheeling switch. In an embodiment, the bidirectional DC converter includes a Boost circuit and a Buck circuit, such as the DC/DC converter shown in fig. 5, where a duty ratio of the Boost circuit when the bidirectional DC converter 80 is in the Boost operating state and a duty ratio of the Buck circuit when the bidirectional DC converter 80 is in the Buck operating state are complementary to each other, for example, a duty ratio of the power switch Q2 in the Boost operating state and a duty ratio of the power switch Q1 in the Buck operating state are complementary to each other, that is, a duty ratio of the power switch Q2 in a condition that energy flows from the storage battery to the DC bus and a duty ratio of the power switch Q1 in a condition that energy flows from the DC bus to the storage battery are complementary to each other. It should be noted that the complementary setting of the duty ratio of the power switch Q2 under the step-up condition and the duty ratio of the power switch Q1 under the step-down condition is only an alternative embodiment, but is not a necessary embodiment, for example, if the duty ratio of the power switch Q2 under the step-up condition is 0.7 and the duty ratio of the power switch Q1 under the step-down condition is 0.6, it is obvious that the complementary relationship does not exist between the duty ratio of the power switch Q2 under the step-up condition and the duty ratio of the power switch Q1 under the step-down condition.
Referring to fig. 5, if the DC/DC converter satisfies that the duty ratio of the power switch Q2 under the boost operating condition and the duty ratio of the power switch Q1 under the buck operating condition have a complementary relationship, in an alternative embodiment of the present application, the following scheme may be implemented: when the voltage drop of the input side of the bidirectional direct current converter 80 coupled to the direct current bus LA-LB is higher than the voltage drop of the output side of the bidirectional direct current converter 80 coupled to the electric storage battery BAT, the bidirectional direct current converter is immediately and automatically triggered to start the voltage reduction circuit to store electric energy to the electric storage battery BAT; when the voltage drop at the input side of the bidirectional dc converter 80 coupled to the dc bus is lower than the voltage drop at the output side of the bidirectional dc converter 80 coupled to the electric storage battery BAT, the bidirectional dc converter 80 is automatically triggered immediately to enable the boost circuit to feed electric energy to the dc bus. This has a very quick dynamic response speed for regulating the energy on the dc bus and enables nearly time delay free energy compensation. The voltage drop at the input side of the bidirectional dc converter coupled to dc bus LA-LB is substantially equal to the voltage drop level between the first and second input nodes at the input side, while the voltage drop at the output side of the bidirectional dc converter coupled to electric storage battery BAT is substantially equal to the voltage drop level between the first and second output nodes at the output side.
Referring to fig. 6, an alternative DC/DC converter for bidirectional energy flow/bidirectional power conversion is a circuit modification based on fig. 5: the power switches Q1 and Q2 are connected in series between a first input node and a second input node, and the power switches Q3 and Q4 using power tubes are connected in series between a first output node and a second output node, wherein the first input node is coupled to the dc bus LA and the corresponding second input node is coupled to the dc bus LB, and it is still further set that the first output node of the bidirectional dc converter is coupled to the positive electrode of the storage battery BAT and the second output node of the bidirectional dc converter is coupled to the negative electrode of the storage battery BAT, and the second input node and the second output node are directly coupled together. Both power switches Q1 and Q2 in the bidirectional DC converter are connected to an interconnection node X1 and both power switches Q3 and Q4 are connected to a further interconnection node X2, and a main inductor L is also connected between the DC/DC converter first and second interconnection nodes X1 and X2. In alternative embodiments: compared with the circuit shown in FIG. 5, the circuit has the power conversion capability of voltage reduction and voltage boosting under the condition that the energy flows from the bus to the storage battery and is in an H-bridge type. If the converter is operated in the BUCK state, the switch Q4 can be directly and continuously turned on, and the switch Q3 can be continuously turned off, only the power switches Q1 and Q2 are driven to be alternately switched on at a high frequency, which means that the power conversion BUCK circuit can independently operate; if the converter is operated in the BOOST state, the switch Q1 can be directly and continuously turned on, and the switch Q2 can be continuously turned off, only the power switches Q3 and Q4 are driven to be alternately switched on at a high frequency, which means that the BOOST circuit of the power conversion can be operated independently.
Referring to fig. 6, in an alternative embodiment: compared with the circuit shown in FIG. 5, the circuit has the power conversion capability of voltage reduction and voltage boosting and is in an H bridge type under the condition that the energy flows from the storage battery to the bus. If the converter is operated in the BUCK state, the switch Q1 can be directly and continuously turned on, and the switch Q2 can be continuously turned off, only the power switches Q4 and Q3 are driven to be alternately switched on at a high frequency, which means that the power conversion BUCK circuit can independently operate; if the converter is operated in the BOOST state, the switch Q4 can be directly and continuously turned on, and the switch Q3 can be continuously turned off, only the power switches Q2 and Q1 are driven to be alternately switched on at a high frequency, which means that the BOOST circuit of the power conversion can be operated independently. The features or solutions described above with respect to fig. 3-5 are also applicable to the bidirectional dc converter of fig. 6.
Referring to fig. 6, in conjunction with the previously described embodiments of fig. 3-5, in an alternative embodiment: the voltage drop of the input side and the voltage drop of the output side of the bidirectional direct current converter need to be detected simultaneously, the sign of the tracking current value IR is determined simultaneously, and the bidirectional direct current converter is triggered to start the voltage reduction circuit to store electric energy into the storage battery only when the voltage drop of the input side of the bidirectional direct current converter 80 coupled to the direct current bus LA-LB is higher than the voltage drop of the output side of the bidirectional direct current converter 80 coupled to the storage battery BAT and the tracking current value IR is positive; or when the voltage drop of the input side of the bidirectional direct current converter 80 coupled to the direct current bus LA-LB is lower than the voltage drop of the output side of the bidirectional direct current converter 80 coupled to the electric storage battery BAT and the tracking current value IR is negative, the bidirectional direct current converter is triggered to start the boost circuit to feed electric energy to the direct current bus; in the above case, the duty ratio of the step-up circuit when the bidirectional dc converter is in the step-up operation state and the duty ratio of the step-down circuit when the bidirectional dc converter is in the step-down operation state may be selected to be complementary to each other. The advantage of this is under the prerequisite of guaranteeing the power change on the quick response direct current bus, avoid the wrong flow direction of power, the wrong power compensation direction on the direct current bus may aggravate the impact of the alternating current of being incorporated into the power networks to the commercial power grid. As a measure to further take a gentle dc bus based on the embodiments of fig. 3-6, each stage of the voltage converters CH1-CHN is a BOOST-BUCK type BUCK-BOOST circuit similar to fig. 6 with positive polarity (i.e., the output voltage and the input voltage have the same polarity). As a solution for dealing with the real-time power output by the photovoltaic modules with relatively large fluctuation and randomness, a measure with high priority must be performed, that is, the operating states of the voltage converters CH1 to CHN are monitored, when any one or more of the voltage converters CH1 to CHN enters the BUCK step-down mode, the energy storage part is triggered to feed electric energy to the direct-current bus immediately, at this moment, the relation between the sum of the external power provided by the multi-stage photovoltaic modules and the predetermined power value required by the alternating current is ignored, and then the following solution is implemented: the energy storage section feeds electric energy onto the direct current bus when the sum PT of the external powers supplied by the multi-stage photovoltaic modules PV1-PVN is lower than a predetermined power value PG required for the alternating current, or draws electric energy from the bus when the sum PT of the external powers supplied by the multi-stage photovoltaic modules PV1-PVN is higher than the predetermined power value PG required for the alternating current. As a scheme for dealing with the fact that real-time power output by the photovoltaic modules has large fluctuation and randomness, a measure with high priority is still implemented, that is, the working states of the voltage converters CH1 to CHN are monitored, when all the voltage converters CH1 to CHN are detected to enter the BOOST mode, the energy storage part is immediately triggered to draw electric energy from the direct current bus in advance, at the moment, the relation between PT of external power provided by the photovoltaic modules and a predetermined power value PG required by alternating current is ignored, and then the following scheme is implemented: the energy storage part feeds electric energy to the direct current bus when the sum PT of the external power provided by the multi-stage photovoltaic modules CH1-CHN is lower than a preset power value PG required by alternating current, or the energy storage part draws electric energy from the direct current bus when the sum PT of the external power provided by the multi-stage photovoltaic modules CH1-CHN is higher than the preset power value PG. The above scheme may be applied to the embodiments of fig. 3-6 and thereby further smooth out the power fluctuations of the dc bus.
Referring to fig. 6, the present application is directed to overcoming the intermittent and uncertain characteristics of light irradiation resources, endeavoring to provide continuous and stable power supply for a load, storing or releasing electric energy by using an energy storage system, reducing negative effects on a photovoltaic power generation system caused by factors such as weather or the quality of the module itself and the position orientation distribution of the photovoltaic module, stably supplying power to power consumers, ensuring the reliability and the quality of the power supply, and improving the energy management efficiency of the photovoltaic power generation system. Because the maximum power output by the photovoltaic module is determined by the sunlight intensity, the output power has randomness and violent fluctuation, and the random uncontrollable characteristic has high probability of causing larger impact on a power grid and possibly causing negative influence on some important load operation. The energy storage device can make up the defect of the photovoltaic power generation system, the energy storage device has a power regulation function in a certain range under the working mechanism of peak clipping, valley filling and flat wave suppression on the output power of the photovoltaic power supply, and when the generated energy is greater than the power consumption, the residual electric energy is charged to the energy storage device and is stored; when the generated energy is not enough, the energy storage device is called again and the stored electric energy can be released to supplement the shortage of power generation. When photovoltaic power generation suddenly changes, the energy storage device can also play a role in real-time compensation, and the output power of the system is balanced.
While the foregoing specification teaches, with reference to the specific embodiments provided above, and illustrated in the accompanying drawings, certain preferred embodiments of the present invention are shown and described, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to that as illustrated and described herein. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. Therefore, the appended claims should be construed to cover all such variations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.
Claims (10)
1. A photovoltaic power generation system integrated with an energy storage function, comprising:
the photovoltaic power generation system comprises a plurality of photovoltaic assemblies and a plurality of voltage converters connected in series, wherein each voltage converter converts electric energy extracted from a corresponding photovoltaic assembly into output power, and is also used for setting the output current and the output voltage of the corresponding photovoltaic assembly at a maximum power point;
an inverter that performs power conversion on output power provided from the multi-level voltage converter and generates alternating current;
the respective output voltages of the multilevel voltage converters are superimposed on the direct current bus and thereby serve as a bus voltage;
the energy storage part dynamically balances the electric energy on the direct current bus, and feeds the electric energy to the direct current bus when the sum of the external power provided by the multi-stage photovoltaic assembly is lower than a preset power value required by alternating current, or absorbs the electric energy from the direct current bus when the sum of the external power provided by the multi-stage photovoltaic assembly is higher than the preset power value required by the alternating current;
the energy storage part comprises a bidirectional direct current converter and an electric storage battery, and the energy storage part feeds electric energy to the direct current bus by taking the electric energy stored by the electric storage battery as an energy supply source or stores the drawn electric energy in the electric storage battery;
and a value obtained by dividing the given reference power of the storage battery by the battery voltage of the storage battery is defined as a tracking current value of the bidirectional direct current converter, the actual output current of the bidirectional direct current converter is controlled to tend to be equal to the tracking current value, and the given reference power of the storage battery is equal to the difference between the sum of the external power provided by the multi-stage photovoltaic module and a preset power value required by the alternating current.
2. The energy storage function integrated photovoltaic power generation system according to claim 1, characterized in that:
the mode for controlling the actual output current of the bidirectional direct current converter to tend to be equal to the tracking current value comprises the following steps: the pulse width modulation signal generated by a current PI controller established based on the actual output current and the tracking current value of the bidirectional direct current converter is used for driving the bidirectional direct current converter;
the current PI controller sets the tracking current value as a given command value and also synchronously adjusts the deviation of the actual output current of the bidirectional DC converter to the tracking current value, and the pulse width modulation signal generated according to the deviation is used for reducing the deviation in the stage of driving the bidirectional DC converter.
3. The energy storage function integrated photovoltaic power generation system according to claim 1, characterized in that:
the positive or negative sign of the difference between the sum of the external power provided by the multi-stage photovoltaic module and the predetermined power value is used for multiplying the magnitude of the tracking current value to define the direction of the tracking current value:
when the tracking current value is a negative value, the direction of current in the bidirectional direct-current converter is from the storage battery to the direct-current bus;
when the tracking current value is a positive value, the direction of the current in the bidirectional direct current converter is from the direct current bus to the storage battery.
4. The energy storage function integrated photovoltaic power generation system according to claim 3, characterized in that:
the bidirectional direct current converter is provided with a boosting circuit and a voltage reduction circuit, when the tracking current value is a negative value, the bidirectional direct current converter is set to be in a boosting working state, and when the tracking current value is a positive value, the bidirectional direct current converter is set to be in a voltage reduction working state.
5. The energy storage function integrated photovoltaic power generation system according to claim 1, characterized in that:
the bidirectional direct current converter is provided with a boosting circuit and a voltage reduction circuit at the same time, and the duty ratio of the boosting circuit when the bidirectional direct current converter is in a boosting working state and the duty ratio of the voltage reduction circuit when the bidirectional direct current converter is in a voltage reduction working state are complementary to each other.
6. The integrated energy storage functional photovoltaic power generation system of claim 5, wherein:
when the voltage drop of the input side of the bidirectional direct current converter coupled to the direct current bus is higher than the voltage drop of the output side of the bidirectional direct current converter coupled to the storage battery, the bidirectional direct current converter is triggered to start the voltage reduction circuit to store the electric energy into the storage battery; and
when the voltage drop of the input side of the bidirectional direct current converter, which is coupled to the direct current bus, is lower than the voltage drop of the output side of the bidirectional direct current converter, which is coupled to the storage battery, the bidirectional direct current converter is triggered to start the boost circuit to feed the electric energy to the direct current bus.
7. A method for dynamically balancing electric energy in a photovoltaic power generation system integrated with energy storage function is characterized in that the photovoltaic power generation system is provided with a plurality of photovoltaic modules and a plurality of voltage converters connected in series, each voltage converter converts the electric energy extracted from a corresponding photovoltaic module into output power, and each voltage converter is also used for setting the output current and the output voltage of the corresponding photovoltaic module at the maximum power point; the photovoltaic power generation system also has an inverter that performs power conversion on output power supplied from the multi-level voltage converter and generates alternating current, and the respective output voltages of the multi-level voltage converters are superimposed on the direct current bus and thereby serve as a bus voltage; the method comprises the following steps:
comparing the sum of external power provided by the multi-stage photovoltaic module with a preset power value required by the alternating current;
when the sum of external power provided by the multi-stage photovoltaic module is lower than a preset power value required by alternating current, feeding electric energy to the direct current bus by using the provided energy storage part; or
When the condition that the sum of external power provided by the multi-stage photovoltaic module is higher than a preset power value required by alternating current is met, the provided energy storage part is utilized to absorb electric energy from the direct current bus; thereby, the device can
Energy fluctuation on a direct current bus is smoothed by dynamically handling energy through the energy storage part;
the energy storage part comprises a bidirectional direct current converter and an electric storage battery, and the method for dynamically handling energy comprises the following steps: the energy storage part stores the drawn electric energy in an electric storage battery, or the energy storage part feeds the electric energy to the direct current bus by taking the electric energy stored in the electric storage battery as an energy supply source;
the method for adjusting the power value of the suction or feed of the energy storage part in the energy throughput process comprises the following steps: collecting external power provided by each of the multi-stage photovoltaic modules and calculating a difference value between the sum of the external power provided by the multi-stage photovoltaic modules and a preset power value required by alternating current; defining a value calculated by dividing a given reference power of the storage battery by a battery voltage of the storage battery as a tracking current value of the bidirectional dc converter, the given reference power of the storage battery being equal to the difference value; the actual output current of the control bidirectional direct current converter tends to be equal to the tracking current value.
8. The method of claim 7, wherein:
the mode for controlling the actual output current of the bidirectional direct current converter to tend to be equal to the tracking current value comprises the following steps: a pulse width modulation signal generated by a current PI controller established based on the actual output current and the tracking current value of the bidirectional direct current converter is used for driving the bidirectional direct current converter;
the current PI controller sets the tracking current value as a given command value and also synchronously adjusts the deviation of the actual output current of the bidirectional DC converter to the tracking current value, and the pulse width modulation signal generated according to the deviation is used for reducing the deviation in the stage of driving the bidirectional DC converter.
9. The method of claim 7, wherein:
defining a direction of the tracking current value by multiplying a positive or negative sign of the difference by a magnitude of the tracking current value:
when the tracking current value is a negative value, the direction of current in the bidirectional direct current converter is from the storage battery to the direct current bus;
when the tracking current value is a positive value, the direction of the current in the bidirectional direct current converter is from the direct current bus to the storage battery.
10. The method of claim 9, wherein:
the method comprises the following steps of setting a bidirectional direct current converter to be provided with a boost circuit and a buck circuit at the same time, and judging the mode that the bidirectional direct current converter starts the boost circuit or starts the buck circuit:
when the tracking current value is judged to be a negative value, the bidirectional direct current converter is driven to be in a boosting working state;
and when the tracking current value is judged to be a positive value, the bidirectional direct current converter is driven to be in a voltage reduction working state.
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| EP3886305A1 (en) * | 2020-03-24 | 2021-09-29 | FRONIUS INTERNATIONAL GmbH | Method for operating an inverter and inverter for executing the method |
| EP4080758A4 (en) * | 2020-08-14 | 2023-03-29 | Huawei Digital Power Technologies Co., Ltd. | Linkage protection system and method for photovoltaic power station |
| CN112994105A (en) * | 2021-03-25 | 2021-06-18 | 华为技术有限公司 | Photovoltaic power generation system, power control device and energy storage system |
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