CN110601256B - Power flow control method - Google Patents

Power flow control method Download PDF

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CN110601256B
CN110601256B CN201910831752.5A CN201910831752A CN110601256B CN 110601256 B CN110601256 B CN 110601256B CN 201910831752 A CN201910831752 A CN 201910831752A CN 110601256 B CN110601256 B CN 110601256B
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power
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CN110601256A (en
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不公告发明人
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BEIJING PICOHOOD TECHNOLOGY Co.,Ltd.
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/66—Regulating electric power
    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Abstract

The invention discloses a power flow control method, which comprises a photovoltaic system, a direct current bidirectional converter, a bidirectional DC/AC converter, a maximum power tracker, a controller, an energy storage system, a direct current load and an alternating current load, wherein the direct current load is connected between the direct current bidirectional converter and the bidirectional DC/AC converter; the method comprises the following steps: establishing a photovoltaic system power tracking model, and solving the maximum tracking current output by the photovoltaic system; solving a harmonic compensation current of the power grid; obtaining the current required by the direct current load and the alternating current load; and controlling the power of the photovoltaic system, the energy storage system and the power grid by the controller according to the obtained maximum tracking current, the harmonic compensation current of the power grid, the direct current load demand current and the alternating current load current, and realizing the rapid power flow control by controlling the direct current bidirectional converter and the bidirectional DC/AC converter. The power supply device and the power supply method can flexibly control the power flow value between a plurality of power supply sources to the load, and conveniently coordinate various different power supplies to carry out matching power supply.

Description

Power flow control method
Technical Field
The invention relates to the technical field of power regulation, in particular to a power flow control method.
Background
In daily life, a plurality of different power supply sources are often encountered, especially for the rapid development of the current microgrid system, a microgrid is matched with a main network to realize power supply for various loads, then, how to control various loads and various power sources to carry out rapid control on power flow, especially under the condition of unstable power supply of a plurality of intermittent power sources in the microgrid, how to ensure that a gap power source is utilized to the maximum extent, and simultaneously, a power flow mode between the power sources and the loads is well controlled, so that the full utilization of power is realized.
At the present stage, many street lamps have used the photovoltaic to supply power, and then how to guarantee that the street lamp is when the photovoltaic supplies power, soft illumination satisfies the road conditions demand, and energy saving simultaneously is one of the difficult problems that need to solve of future control power flow mode.
Disclosure of Invention
The invention provides a power flow control method, which comprises a photovoltaic system, a direct current bidirectional converter, a bidirectional DC/AC converter, a maximum power tracker, a controller, an energy storage system, a direct current load and an alternating current load, wherein the direct current load is connected between the direct current bidirectional converter and the bidirectional DC/AC converter; the method comprises the following steps:
establishing a photovoltaic system power tracking model, and solving the maximum tracking current output by the photovoltaic system;
solving a harmonic compensation current of the power grid;
obtaining the current required by the direct current load and the alternating current load;
and controlling the power of the photovoltaic system, the energy storage system and the power grid by the controller according to the obtained maximum tracking current, the harmonic compensation current of the power grid, the direct current load demand current and the alternating current load current, and realizing the rapid power flow control by controlling the direct current bidirectional converter and the bidirectional DC/AC converter.
In the power flow control method, the bidirectional DC/AC converter includes at least two parallel DC/AC converters, which are standby for each other, and the standby includes two modes:
in the first mode, when one of the two faults is failed, the other one is put into use quickly;
and when the power flow exceeds the using power of the single DC/AC converter, simultaneously putting two DC/AC converters and averaging the circulating power values of the two DC/AC converters.
The power flow control method for realizing the power rapid flow control specifically comprises the following steps: when the output power of the photovoltaic system exceeds the requirement of a direct current load, the exceeding power is transmitted to a power grid through the bidirectional DC/AC converter, and the bidirectional DC/AC converter is in an inversion mode at the moment; when the output power of the photovoltaic system is lower than the direct current load demand, the direct current load electric energy is supplied through the photovoltaic system and the power grid, the bidirectional DC/AC converter is in a rectification mode at the moment, and when the power grid is in power failure or fault, the direct current load is supplied with power through the battery.
The power flow control method, wherein the establishing of the photovoltaic system power tracking model and the obtaining of the maximum tracking current output by the photovoltaic system specifically comprise: setting a single solar cell model, wherein the current output by the model is as follows:
Figure BDA0002190938570000021
when the model is set to be open-circuit, the open-circuit voltage is Voc, and when the model is open-circuit, i is 0; v ═ VOC，VOC≈C；
Short-circuit when model is short-circuitedSC，
Figure BDA0002190938570000022
Then A is approximately equal to Isc; b and D are determined at the maximum power tracking point; the current at the maximum power tracking point is:
Figure BDA0002190938570000023
wherein I ═ IMPPT，v＝VMPPT；A≈Isc；C≈VOC；IMPPTCurrent for maximum power tracking, VMPPTA voltage that is maximum power tracked;
taking the derivative to obtain:
Figure BDA0002190938570000024
the following equations (2) to (3) can be obtained:
Figure BDA0002190938570000025
Figure BDA0002190938570000026
the output current I of maximum power tracking can be determined by the set modelMPPTAnd voltage VMPPTAnd the output power of maximum power tracking.
The power flow control method comprises the following steps of obtaining current Id by considering a direct current load, obtaining a maximum power output current value of a photovoltaic system according to a harmonic current value of an alternating current load, and obtaining an output current value of a bidirectional DC/AC converter, wherein the calculation mode is as follows:
Pn＝Vn×In(6)
Pp＝Vp×Ip(7)
wherein, PnFor previously output power values, PpFor the currently output power value, Vn、InFor previously varying voltages and currents, Vp、IpIs the current changing voltage and current; setting a reference voltage corresponding to an operation point with initial maximum power as Vref1, when the output voltage of a solar cell of a photovoltaic system is Vref1, setting a power output value as Pmax, taking the reference voltage as a horizontal coordinate and the power output value as a vertical coordinate, establishing a planar rectangular coordinate system, dividing the power output value into a left area and a right area by a straight line formed by taking the reference voltage Vref1 as the horizontal coordinate, wherein the power values corresponding to the left area and the right area are both less than Pmax;
when Pn > Pp, whether the output parameters of the photovoltaic system are ready needs to be determined again;
when Pn is Pp, the photovoltaic system is at the maximum power point;
when Pn < Pp, if Vn > Vp, the operating point of the solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from the left region to the right region, at which time the reference voltage Vref2 corresponding to the maximum power operating point decreases from the left region to the right region; if Vn > Vp, the operating point of the solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from the right region to the left region, at the moment, the reference voltage Vref3 corresponding to the maximum power operating point increases from the left region to the right region;
the reference current output by the bidirectional DC/AC converter of the photovoltaic system is as follows:
Iref＝[KP(Vc *-Vc)+KI∫(Vc *-Vc)dt-(IMPPT-Id)]×sin(wt) (8)
wherein, Vc *Is a reference voltage, KP、KIAs a fixed parameter of the PI controller, IMPPTMaximum tracking current, V, calculated for equation (2)cIs a real-time voltage; id is the direct current load demand current;
the actual output current of the bidirectional DC/AC converter of the photovoltaic system is as follows:
IPWM＝Iref+Ic (9)
where Ic is the compensation current taken to cancel the harmonics,
the grid voltage is defined as:
Figure BDA0002190938570000031
Figure BDA0002190938570000032
wherein Vm is output voltage amplitude of the bidirectional DC/AC converter, Im is output current amplitude of the bidirectional DC/AC converter, and Ir is IL(t) subtracting Imsin (wt) remaining current value; w is the phase angle of the output alternating current of the bidirectional DC/AC converter
The reference value for the compensation current Ic is:
Figure BDA0002190938570000033
determining the current I output by a bidirectional DC/AC converter according to equation (9)PWMThe controller generates PWM wave and outputs the PWM wave to the bidirectional DC/AC converter for switching controlThe bidirectional DC/AC converter outputs alternating current to a power grid, the requirements of grid connection and supply of direct current loads of a photovoltaic system are met, and power flow is controlled.
According to the power flow control method, the direct current load comprises an LED lamp, the controller comprises a brightness detection unit, a direct current load current regulation unit and a PWM generation unit, the brightness detection unit is used for controlling the LED lamp to be turned on according to the detected brightness, and the direct current load current regulation unit regulates the current value Id of the turned-on LED lamp and outputs the Id to the PWM generation unit.
According to the power flow control method, the alternating current load comprises an air conditioner, a refrigerator and a motor.
The controller further comprises a prediction control unit, the prediction control unit predicts a required current value according to the photovoltaic system and the direct current load, generates a PWM control signal, and predicts and controls the flow direction and the output current value of the bidirectional DC/AC converter.
The beneficial technical effects obtained by the invention are as follows: the invention can flexibly control the power flow value between a plurality of power supply sources to the load, and is convenient to coordinate various different power sources for matching power supply. The invention has the main improvement points that the power can be quickly matched between various loads and various power supplies according to a direct current load, an alternating current load, a new energy system, a battery and the like, the energy can be ensured to flow orderly while the new energy is utilized to the maximum extent, and the new energy caused by untimely flow between the powers can be prevented from being fully utilized. The coordination between the load and the power supply ensures that the photovoltaic system is in maximum power tracking, and more preferably, the DC/AC converter can be controlled predictively through the calculated reference value of the output of the photovoltaic system, so that the control efficiency of the converter is improved.
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The invention will be further understood from the following description in conjunction with the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. In the drawings, like reference numerals designate corresponding parts throughout the different views.
Fig. 1 is a schematic diagram of a power flow control method of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments thereof; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Other systems, methods, and/or features of the present embodiments will become apparent to those skilled in the art upon review of the following detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. Additional features of the disclosed embodiments are described in, and will be apparent from, the detailed description that follows.
As shown in fig. 1, a schematic diagram of a power flow control method provided by the present invention includes a photovoltaic system, a DC bidirectional converter, a bidirectional DC/AC converter, a maximum power tracker, a controller, an energy storage system, a DC load, and an AC load, where the DC load is connected between the DC bidirectional converter and the bidirectional DC/AC converter; the method comprises the following steps:
establishing a photovoltaic system power tracking model, and solving the maximum tracking current output by the photovoltaic system;
solving a harmonic compensation current of the power grid;
obtaining the current required by the direct current load and the alternating current load;
and controlling the power of the photovoltaic system, the energy storage system and the power grid by the controller according to the obtained maximum tracking current, the harmonic compensation current of the power grid, the direct current load demand current and the alternating current load current, and realizing the rapid power flow control by controlling the direct current bidirectional converter and the bidirectional DC/AC converter.
In the power flow control method, the bidirectional DC/AC converter includes at least two parallel DC/AC converters, which are standby for each other, and the standby includes two modes:
in the first mode, when one of the two faults is failed, the other one is put into use quickly;
and when the power flow exceeds the using power of the single DC/AC converter, simultaneously putting two DC/AC converters and averaging the circulating power values of the two DC/AC converters.
The power flow control method for realizing the power rapid flow control specifically comprises the following steps: when the output power of the photovoltaic system exceeds the requirement of a direct current load, the exceeding power is transmitted to a power grid through the bidirectional DC/AC converter, and the bidirectional DC/AC converter is in an inversion mode at the moment; when the output power of the photovoltaic system is lower than the direct current load demand, the direct current load electric energy is supplied through the photovoltaic system and the power grid, the bidirectional DC/AC converter is in a rectification mode at the moment, and when the power grid is in power failure or fault, the direct current load is supplied with power through the battery.
The power flow control method, wherein the establishing of the photovoltaic system power tracking model and the obtaining of the maximum tracking current output by the photovoltaic system specifically comprise: setting a single solar cell model, wherein the current output by the model is as follows:
Figure BDA0002190938570000051
when the model is set to be open-circuit, the open-circuit voltage is Voc, and when the model is open-circuit, i is 0; v ═ VOC，VOC≈C；
Short-circuit when model is short-circuitedSC，i＝ISC；v＝0；
Figure BDA0002190938570000052
Then A is approximately equal to Isc; b and D are determined at the maximum power tracking point; the current at the maximum power tracking point is:
Figure BDA0002190938570000061
wherein I ═ IMPPT，v＝VMPPT；A≈Isc；C≈VOC；IMPPTCurrent for maximum power tracking, VMPPTA voltage that is maximum power tracked;
taking the derivative to obtain:
Figure BDA0002190938570000062
the following equations (2) to (3) can be obtained:
Figure BDA0002190938570000063
Figure BDA0002190938570000064
the output current I of maximum power tracking can be determined by the set modelMPPTAnd voltage VMPPTAnd the output power of maximum power tracking.
The power flow control method comprises the following steps of obtaining current Id by considering a direct current load, obtaining a maximum power output current value of a photovoltaic system according to a harmonic current value of an alternating current load, and obtaining an output current value of a bidirectional DC/AC converter, wherein the calculation mode is as follows:
Pn＝Vn×In(6)
Pp＝Vp×Ip(7)
wherein, PnFor previously output power values, PpFor the currently output power value, Vn、InFor previously varying voltages and currents, Vp、IpIs the current changing voltage and current; setting a reference voltage corresponding to an operation point with initial maximum power as Vref1, when the output voltage of a solar cell of a photovoltaic system is Vref1, setting a power output value as Pmax, taking the reference voltage as a horizontal coordinate and the power output value as a vertical coordinate, establishing a planar rectangular coordinate system, dividing the power output value into a left area and a right area by a straight line formed by taking the reference voltage Vref1 as the horizontal coordinate, wherein the power values corresponding to the left area and the right area are both less than Pmax;
when Pn > Pp, whether the output parameters of the photovoltaic system are ready needs to be determined again;
when Pn is Pp, the photovoltaic system is at the maximum power point;
when Pn < Pp, if Vn > Vp, the operating point of the solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from the left region to the right region, at which time the reference voltage Vref2 corresponding to the maximum power operating point decreases from the left region to the right region; if Vn > Vp, the operating point of the solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from the right region to the left region, at the moment, the reference voltage Vref3 corresponding to the maximum power operating point increases from the left region to the right region;
the reference current output by the bidirectional DC/AC converter of the photovoltaic system is as follows:
Iref＝[KP(Vc *-Vc)+KI∫(V* c-Vc)dt-(IMPPT-Id)]×sin(wt) (8)
wherein, Vc *Is a reference voltage, KP、KIAs a fixed parameter of the PI controller, IMPPTMaximum tracking current, V, calculated for equation (2)cIs a real-time voltage; id is the direct current load demand current;
the actual output current of the bidirectional DC/AC converter of the photovoltaic system is as follows:
IPWM＝Iref+Ic (9)
where Ic is the compensation current taken to cancel the harmonics,
the grid voltage is defined as:
Figure BDA0002190938570000071
Figure BDA0002190938570000072
wherein Vm is a bidirectional DC/AC converter outputThe output voltage amplitude value Im is the output current amplitude value of the bidirectional DC/AC converter, and Ir is IL(t) subtracting Imsin (wt) remaining current value; w is the phase angle of the output alternating current of the bidirectional DC/AC converter
The reference value for the compensation current Ic is:
Figure BDA0002190938570000073
determining the current I output by a bidirectional DC/AC converter according to equation (9)PWMThe controller generates PWM waves and outputs the PWM waves to the bidirectional DC/AC converter for switching control, and the bidirectional DC/AC converter outputs alternating current to a power grid to meet the requirements of grid connection and supply of direct current loads of a photovoltaic system and control power flow.
According to the power flow control method, the direct current load comprises an LED lamp, the controller comprises a brightness detection unit, a direct current load current regulation unit and a PWM generation unit, the brightness detection unit is used for controlling the LED lamp to be turned on according to the detected brightness, and the direct current load current regulation unit regulates the current value Id of the turned-on LED lamp and outputs the Id to the PWM generation unit.
The brightness detection unit is used for detecting the brightness information of the environment, comparing the detected brightness information with a preset threshold value, outputting a series of pulse signals to the direct current load starting unit when the detected brightness information is lower than the preset threshold value and used for starting the direct current load, adjusting the current value under the control of the direct current load current adjustment unit after the direct current load receives the starting signals, and adjusting the operation mode of the direct current load according to the adjusted current value, such as the brightness of the LED lighting.
According to the power flow control method, the alternating current load comprises an air conditioner, a refrigerator and a motor.
The controller further comprises a prediction control unit, the prediction control unit predicts a required current value according to the photovoltaic system and the direct current load, generates a PWM control signal, and predicts and controls the flow direction and the output current value of the bidirectional DC/AC converter.
The beneficial technical effects obtained by the invention are as follows: the invention can flexibly control the power flow value between a plurality of power supply sources to the load, and is convenient to coordinate various different power sources for matching power supply. The invention has the main improvement points that the power can be quickly matched between various loads and various power supplies according to a direct current load, an alternating current load, a new energy system, a battery and the like, the energy can be ensured to flow orderly while the new energy is utilized to the maximum extent, and the new energy caused by untimely flow between the powers can be prevented from being fully utilized. The coordination between the load and the power supply ensures that the photovoltaic system is in maximum power tracking, and more preferably, the DC/AC converter can be controlled predictively through the calculated reference value of the output of the photovoltaic system, so that the control efficiency of the converter is improved.
The photovoltaic system is connected with a direct current bidirectional converter, a bidirectional DC/AC converter and a power grid in sequence, the maximum power tracker is connected between the photovoltaic system and the controller, the energy storage system and the direct current load are connected between the direct current bidirectional converter and the bidirectional DC/AC converter, and the alternating current load is connected with the power grid.
Although the invention has been described above with reference to various embodiments, it should be understood that many changes and modifications may be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention. The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.

Claims (4)

1. A power flow control method is characterized by comprising a photovoltaic system, a direct current bidirectional converter, a bidirectional DC/AC converter, a maximum power tracker, a controller, an energy storage system, a direct current load and an alternating current load, wherein the direct current load is connected between the direct current bidirectional converter and the bidirectional DC/AC converter; the method comprises the following steps:
establishing a photovoltaic system power tracking model, and solving the maximum tracking current output by the photovoltaic system;
solving a harmonic compensation current of the power grid;
obtaining the current required by the direct current load and the alternating current load;
according to the obtained maximum tracking current, the harmonic compensation current of the power grid, the direct current load demand current and the alternating current load current, the controller controls the power of the photovoltaic system, the energy storage system and the power grid, and the power rapid flow control is realized by controlling the direct current bidirectional converter and the bidirectional DC/AC converter; the bidirectional DC/AC converter comprises at least two DC/AC converters which are connected in parallel and are mutually standby, and the standby comprises two modes:
in the first mode, when one of the two faults is failed, the other one is put into use quickly;
when the power flow does not exceed the use power of the single DC/AC converter, selecting any DC/AC converter to perform power flow, and when the power flow exceeds the use power of the single DC/AC converter, simultaneously inputting two DC/AC converters, and averaging the circulating power values of the two DC/AC converters; the implementation of the power fast flow control specifically includes: when the output power of the photovoltaic system exceeds the requirement of a direct current load, the exceeding power is transmitted to a power grid through the bidirectional DC/AC converter, and the bidirectional DC/AC converter is in an inversion mode at the moment; when the output power of the photovoltaic system is lower than the direct-current load demand, the direct-current load electric energy is supplied through the photovoltaic system and the power grid, the bidirectional DC/AC converter is in a rectification mode at the moment, and when the power grid is in power failure or fault, the direct-current load is supplied with power through the battery; the establishing of the photovoltaic system power tracking model and the solving of the maximum tracking current output by the photovoltaic system specifically comprise: setting a single solar cell model, wherein the current output by the model is as follows:
Figure FDA0002573643890000011
wherein, when the model is set to be open-circuit, the open-circuit voltage is Voc, and when the model is open-circuit，i＝0；v＝VOC，VOC≈C；
When the model is short-circuited, the short-circuit current is ISC，i＝ISC；v＝0；
Figure FDA0002573643890000012
Then A ≈ ISC(ii) a B and D are determined at the maximum power tracking point; the current at the maximum power tracking point is:
Figure FDA0002573643890000013
wherein I ═ IMPPT，v＝VMPPT；A≈ISC；C≈VOC；IMPPTCurrent for maximum power tracking, VMPPTA voltage that is maximum power tracked;
taking the derivative to obtain:
Figure FDA0002573643890000021
the following equations (2) to (3) can be obtained:
Figure FDA0002573643890000022
Figure FDA0002573643890000023
the output current I of maximum power tracking can be determined by the set modelMPPTAnd voltage VMPPTAnd the output power of maximum power tracking.
2. The power flow control method according to claim 1, wherein the current Id obtained from the DC load is considered, the maximum power output current value of the photovoltaic system is obtained according to the harmonic current value of the AC load, and the output current value of the bidirectional DC/AC converter is obtained by the following calculation method:
Pn＝Vn×In(6)
Pp＝Vp×Ip(7)
wherein, PnFor previously output power values, PpFor the currently output power value, Vn、InFor previously varying voltages and currents, Vp、IpIs the current changing voltage and current; setting a reference voltage corresponding to an operation point with initial maximum power as Vref1, when the output voltage of a solar cell of a photovoltaic system is Vref1, setting a power output value as Pmax, taking the reference voltage as a horizontal coordinate and the power output value as a vertical coordinate, establishing a planar rectangular coordinate system, dividing the power output value into a left area and a right area by a straight line formed by taking the reference voltage Vref1 as the horizontal coordinate, wherein the power values corresponding to the left area and the right area are both less than Pmax;
when Pn is larger than Pp, whether the output parameters of the photovoltaic system are ready needs to be determined again;
when Pn is Pp, the photovoltaic system is at the maximum power point;
when Pn is less than Pp, if Vn is more than Vp, the operating point of a solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from a left area to a right area, and at the moment, the first reference voltage Vref2 corresponding to the maximum power operating point is reduced from the left area to the right area; if Vn is less than Vp, the operating point of the solar cell array in the photovoltaic system exceeds the maximum power operating point, and the power output point moves from the right region to the left region, at the moment, the second reference voltage Vref3 corresponding to the maximum power operating point increases from the left region to the right region;
the reference current output by the bidirectional DC/AC converter of the photovoltaic system is as follows:
Iref＝[KP(Vc *-Vc)+KI∫(Vc *-Vc)dt-(IMPPT-Id)]×sin(wt) (8)
wherein, Vc *Is a third reference voltage, KP、KIAs a fixed parameter of the PI controller, IMPPTMaximum tracking power calculated for equation (2)Flow, VcIs a real-time voltage; id is the direct current load demand current;
the actual output current of the bidirectional DC/AC converter of the photovoltaic system is as follows:
IPWM＝Iref+Ic (9)
where Ic is the compensation current taken to cancel the harmonics,
the grid voltage is defined as:
Figure FDA0002573643890000031
Figure FDA0002573643890000032
wherein Im is the output current amplitude of the bidirectional DC/AC converter, and Ir is IL(t) subtracting Imsin (wt) remaining current value; w is the phase angle of the output alternating current of the bidirectional DC/AC converter
The reference value for the compensation current Ic is:
Figure FDA0002573643890000033
determining the current I output by a bidirectional DC/AC converter according to equation (9)PWMThe controller generates PWM waves and outputs the PWM waves to the bidirectional DC/AC converter for switching control, and the bidirectional DC/AC converter outputs alternating current to a power grid to meet the requirements of grid connection and supply of direct current loads of a photovoltaic system and control power flow.
3. The power flow control method according to claim 2, wherein the dc load includes an LED lamp, the controller includes a brightness detection unit for controlling the LED lamp to be turned on according to the detected brightness, a dc load current adjustment unit for adjusting a current value Id of the turned-on LED lamp and outputting Id to the PWM generation unit, and a PWM generation unit.
4. The power flow control method of claim 3, wherein the AC load includes an air conditioner, a refrigerator, and a motor.
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