CN115360758A - Micro inverter and control method thereof - Google Patents
Micro inverter and control method thereof Download PDFInfo
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- CN115360758A CN115360758A CN202211071105.7A CN202211071105A CN115360758A CN 115360758 A CN115360758 A CN 115360758A CN 202211071105 A CN202211071105 A CN 202211071105A CN 115360758 A CN115360758 A CN 115360758A
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- 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
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- 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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
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- 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
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- 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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- 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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
- H02M3/1582—Buck-boost converters
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- 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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
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- 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
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
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- 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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- 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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
- H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
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- 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
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Abstract
A micro inverter comprises a plurality of pre-stage DC/DC conversion circuits, wherein the input ends of the pre-stage DC/DC conversion circuits are connected with respective photovoltaic cell assemblies, the output ends of the pre-stage DC/DC conversion circuits are connected with a first direct current bus in parallel, and the pre-stage DC/DC conversion circuits control the output voltage of the photovoltaic cell assemblies; a post-stage DC/DC conversion circuit, an input terminal of which is connected in parallel to the first DC bus, and an output terminal of which is connected in parallel to a second DC bus, the post-stage DC/DC conversion circuit controlling a voltage of the first DC bus; and the input end of the DC/AC conversion circuit is connected with the second direct current bus in parallel, and the DC output by the second direct current bus is inverted into AC. The micro inverter reduces the number of isolation transformers, and can achieve higher power density; the efficiency of tracking the maximum power point of the photovoltaic cell can be effectively improved based on the multi-path Boost circuit, and the power generation efficiency of the photovoltaic cell is improved.
Description
Technical Field
The invention belongs to the technical field of inverters, and particularly relates to a micro inverter.
Background
The photovoltaic power generation system is a power generation system which converts solar radiation energy into electric energy by utilizing the photovoltaic effect of a semiconductor material. The energy of the photovoltaic power generation system is derived from inexhaustible solar energy, and is clean, safe and renewable energy.
The micro inverter generally refers to an inverter with low power and module level MPPT in a photovoltaic power generation system, and is called a micro photovoltaic grid-connected inverter. "micro" is with respect to a centralized inverter. The centralized inverter is used for connecting all direct currents generated by all photovoltaic cell assemblies under the irradiation of sunlight in series and in parallel, and then inverting the direct currents into alternating currents through one inverter to be connected into a power grid; the micro-inverter controls each photovoltaic cell assembly independently. The photovoltaic grid-connected inverter has the advantages that independent MPPT control can be carried out on each photovoltaic cell assembly, the overall power generation efficiency can be greatly improved, and meanwhile, the direct-current high voltage, poor weak light effect, barrel effect and the like of a centralized inverter can be avoided.
The photovoltaic micro-inverter can be simultaneously connected with a plurality of photovoltaic cell assemblies, can ensure that each photovoltaic assembly independently realizes the function of tracking the maximum power point, and then converts the energy of all the photovoltaic cell assemblies into alternating current to be accessed into a power grid through one inverter. Compared with a micro inverter which can only be connected with a single photovoltaic cell assembly, the photovoltaic inverter has the advantages of higher conversion efficiency, lower cost, smaller volume, higher power density and the like.
In the prior art, a photovoltaic micro-inverter, which can simultaneously connect a plurality of photovoltaic cell modules, is generally in a two-stage topology.
The first stage is a DC-DC booster circuit connected with a single photovoltaic cell assembly, has the function of MPPT and is connected with a direct current bus at the output. Since the voltage of a single photovoltaic cell assembly does not exceed 60V at most, the stage circuit is usually an isolated DC-DC boost circuit with a transformer to achieve a 10 to 50 times direct current boost ratio. The isolated DC-DC booster circuit adopts a scheme of an interleaved Flyback converter circuit (Flyback), for example, the maximum power of a single Flyback converter circuit (Flyback) is difficult to exceed 300 watts, and therefore the power level is improved to 600 watts by adopting the interleaved Flyback converter circuit (Flyback). When the photovoltaic input power is low, only one Flyback conversion circuit (Flyback) works, and when the power is high, two Flyback conversion circuits (Flyback) work and work in a staggered parallel mode to improve the efficiency.
The second stage is a grid-connected inverter circuit which converts the direct current of the direct current bus into alternating current and is connected to a power grid. Since the power of the micro-inverter is generally very small, the stage circuit is usually a critical-conduction mode (CRM) inverter circuit to improve the conversion efficiency.
The above-mentioned traditional topological structure of photovoltaic micro-inverter that can connect multichannel photovoltaic module has following several shortcomings:
firstly, the maximum power point voltages of photovoltaic cell assemblies of different models are different and are generally between 30V and 50V, and for an isolated DC-DC booster circuit, the circuit is difficult to be ensured to work in a high conversion efficiency range all the time under the condition of different boosting ratios;
secondly, the maximum power range of photovoltaic cell assemblies of different models is between 200 watts and 800 watts, and for a single isolated DC-DC booster circuit, it is difficult to ensure that the single isolated DC-DC booster circuit works in a maximum conversion efficiency interval in different power sections, and for micro inverters connected with photovoltaic cell assemblies of different models, it is difficult to ensure that the system efficiency is optimal.
And thirdly, the quasi-resonant inverter circuit is suitable for a small power range within 1000 watts, the power level cannot exceed 2000 watts, and if the power level is too high, the quasi-resonant inverter circuit has the problems that grid-connected current harmonic distortion rate is difficult to control, grid-connected inductance is too large in size, cost is too high and the like. These drawbacks have limited the trend of micro-inverters to boost power levels.
Fourthly, the power level is difficult to improve, the scheme of a staggered parallel Flyback conversion circuit (Flyback) is adopted, the photovoltaic power input by a single path is not suitable to exceed 500 watts, and the grid-connected inductor needs to be greatly increased when the grid-connected inverter circuit works in a quasi-resonant mode under the high-power working condition, so that the cost is increased, the volume is increased, the power level is not suitable to exceed 2000 watts, and the number of connectable photovoltaic cell assemblies is limited.
Fifthly, a scheme of interleaving and parallel connection is adopted, and each path of photovoltaic input comprises two power transformers and a plurality of power devices, so that the whole system comprises a plurality of power transformers, the system is large in size, and the system cost is high.
Disclosure of Invention
In view of the above problems, the present invention provides a micro inverter, which can effectively solve the above technical problems.
In order to achieve the purpose, the invention mainly adopts the following technical scheme:
a micro-inverter includes a micro-inverter having a micro-inverter,
a plurality of pre-stage DC/DC conversion circuits, input terminals of the pre-stage DC/DC conversion circuits being connected in parallel with the photovoltaic cell modules, respectively, output terminals of the plurality of pre-stage DC/DC conversion circuits being connected in parallel with the first DC bus, the pre-stage DC/DC conversion circuits controlling output voltages of the photovoltaic cell modules,
a post-stage DC/DC conversion circuit, an input terminal of which is connected in parallel with the first DC bus and an output terminal of which is connected in parallel with a second DC bus, the post-stage DC/DC conversion circuit controlling a voltage of the first DC bus,
and the input end of the DC/AC conversion circuit is connected with the second direct current bus in parallel, and the DC output by the second direct current bus is inverted into AC.
The preceding-stage DC/DC conversion circuit is a BOOST circuit topology.
The post-stage DC/DC conversion circuit is in an isolated circuit topology, and the DC/AC conversion circuit is in a non-isolated circuit topology.
The post-stage DC/DC conversion circuit is in a non-isolated circuit topology, and the DC/AC conversion circuit is in an isolated circuit topology.
The micro inverter further comprises a plurality of second pre-stage DC/DC conversion circuits, wherein the input ends of the second pre-stage DC/DC conversion circuits are respectively connected with the batteries in parallel, and the output ends of the second pre-stage DC/DC conversion circuits are connected with the first direct current bus in parallel.
The second front stage DC/DC conversion circuit, the rear stage DC/DC conversion circuit and the DC/AC conversion circuit are bidirectional conversion circuits.
The micro inverter further comprises a plurality of second pre-stage DC/DC conversion circuits, wherein the input ends of the second pre-stage DC/DC conversion circuits are respectively connected with the batteries in parallel, and the output ends of the second pre-stage DC/DC conversion circuits are connected with the second direct current bus in parallel.
The second pre-stage DC/DC conversion circuit and the DC/AC conversion circuit are bidirectional conversion circuits.
A control method of a micro inverter comprises the following steps,
step S21 is MPPT control, and the voltage output by the photovoltaic cell assembly is sampled . The current is calculated by using an MPPT algorithm, the reference voltage of the photovoltaic cell assembly is compared with a first set value, the voltage output by the photovoltaic cell assembly is smaller than the first set value, and the preceding-stage DC/DC conversion circuit is controlled to work in a boosting mode; the voltage output by the photovoltaic cell assembly is not less than a first set value, and the preceding-stage DC/DC conversion circuit is controlled to work in a direct-through mode;
step S22 is photovoltaic voltage control, and the voltage output by the photovoltaic cell assembly is sampled . The voltage output by the photovoltaic cell assembly is subjected to adjustment operation after being differed from the reference voltage of the photovoltaic cell assembly to generate a first driving signal, and the driving signal is used for driving a preceding-stage DC/DC conversion circuit connected with the photovoltaic cell assembly;
step S32, calculating the reference of the low-voltage direct-current bus, comparing the reference voltages of all the photovoltaic cell assemblies, selecting the maximum voltage, if the maximum value is larger than a first set value, selecting the maximum value as the reference voltage of the first direct-current bus, and if the maximum value is smaller than the first set value, selecting the first set value as the reference voltage of the first direct-current bus;
step S33 is low-voltage direct-current bus voltage control, and the reference voltage of the first direct-current bus, the voltage of the first direct-current bus and the voltage of the second direct-current bus are regulated to generate a second driving signal for controlling the rear-stage DC/DC conversion circuit;
step S41 is high-voltage direct-current bus reference calculation, and the reference voltage of a second direct-current bus is calculated;
step S42 is a high-voltage DC bus voltage control, which performs adjustment operation on the reference voltage of the second DC bus, the voltage of the second DC bus, and the voltage output by the DC/AC conversion circuit to generate a third driving signal for controlling the DC/AC conversion circuit.
In step S21, the first set value is the lowest value of the optimal input voltage of the subsequent DC/DC conversion circuit.
The micro inverter reduces the number of isolation transformers, and can achieve higher power density; the efficiency of tracking the maximum power point of the photovoltaic cell can be effectively improved based on the multi-path Boost circuit, and the power generation efficiency of the photovoltaic cell is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings according to the drawings.
Fig. 1 is a schematic block diagram of a first embodiment of a microinverter of the present invention.
Fig. 2 is a block diagram of a control method of the micro-inverter of fig. 1.
Fig. 3 is a schematic diagram of an embodiment of the pre-stage DC/DC conversion circuit in fig. 1.
Fig. 4 is a schematic diagram of an embodiment of the post-DC/DC converter circuit of fig. 1.
Fig. 5 is a schematic diagram of an embodiment of the DC/AC conversion circuit of fig. 1.
Fig. 6 is a schematic block diagram of a second embodiment of a microinverter of the present invention.
Fig. 7 is a schematic block diagram of a micro-inverter according to a third embodiment of the present invention.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without inventive step, are within the scope of protection of the invention.
As shown in fig. 1, the micro inverter of the present invention includes a plurality of preceding stage DC/DC conversion circuits 2, a plurality of following stage DC/DC conversion circuits 3, and a plurality of DC/AC conversion circuits 4, the preceding stage DC/DC conversion circuits 2, i.e., the preceding stage DC/DC conversion circuits 2.1 to the preceding stage DC/DC conversion circuits 2.n in the drawing, the input terminals of the preceding stage DC/DC conversion circuits 2.1 to 2.n are respectively connected in parallel with the photovoltaic cell module 1, and the input terminal of the preceding stage DC/DC conversion circuit 2.1 is connected in parallel with the photovoltaic cell module 1.1 to the input terminal of the preceding stage DC/DC conversion circuit 2.n in parallel with the photovoltaic cell module 1.n. The output ends of the preceding-stage DC/DC conversion circuit 2.1 to the preceding-stage DC/DC conversion circuit 2.n are connected in parallel to a direct current bus. The input end of the rear-stage DC/DC conversion circuit 3 is connected with the direct-current bus bus.L in parallel, the output end of the rear-stage DC/DC conversion circuit 3 is connected with the direct-current bus bus.H in parallel, the input end of the DC/AC conversion circuit 4 is connected with the direct-current bus bus.H in parallel, and the output end of the DC/AC conversion circuit 4 is connected with the alternating current 5 in parallel.
Each path of photovoltaic cell component 1 is connected with a single preceding-stage DC/DC conversion circuit 2, and the energy of each path of input photovoltaic cell component 1 is transmitted to a direct current bus. The preceding-stage DC/DC conversion circuit 2 has two operation modes: one in a pass-through mode, i.e. the output voltage V of the photovoltaic cell assembly 1 pv Voltage V clamped at bus.l of dc bus bus.L Output voltage V of photovoltaic cell module 1 pv Is directly controlled by the post-stage DC/DC conversion circuit 3; the other is a boosting mode, i.e. the voltage V output by the photovoltaic cell assembly 1 pv Voltage V less than bus.L of DC bus bus.L The output voltage V of the photovoltaic cell module 1 is converted by the preceding-stage DC/DC conversion circuit 2 through voltage boosting pv The output voltage V is transmitted to a direct current bus (Bus.L) and the photovoltaic cell component 1 pv Is directly controlled by the preceding stage DC/DC conversion circuit 2.
The preceding-stage DC/DC conversion circuit 2 of each path has a maximum power point tracking function, and each path of photovoltaic cell assembly 1 is ensured to output maximum power. When the preceding-stage DC/DC conversion circuit 2 operates in the through mode, the input voltage of the preceding-stage DC/DC conversion circuit 2 is equal to the voltage V of the DC bus bus.L Will pass through the control voltage V bus.L To realize the maximum power point tracking of the input of the path; when the preceding DC/DC conversion circuit 2 is operated in the boost mode, the micro-inverter controls the voltage V input to the preceding DC/DC conversion circuit 2 by controlling the driving of the switching device in the preceding DC/DC conversion circuit 2 pv So as to realize maximum power point tracking of the input of the path.
The rear-stage DC/DC conversion circuit 3 transfers energy from the DC bus bus.l to the DC bus bus.h. The direct current bus is a low-voltage direct current bus, and the direct current bus is a high-voltage direct current bus. The micro inverter realizes the voltage V of the bus.L of the direct current bus through a post-stage DC/DC conversion circuit 3 bus.L And (4) controlling.
The DC/AC conversion circuit 4 transmits energy from a direct current bus bus.H to an alternating current power grid 5; the micro inverse DC/AC conversion circuit 4 controls the voltage V of the direct current bus bus.H And active power P transmitted to the AC grid 5 grid Reactive power Q grid And current I grid 。
As shown in fig. 2, the block diagram of the method for controlling the micro-inverter is used to control the micro-inverter shown in fig. 1, and control the 1 st pre-stage DC/DC conversion circuit 2.1 to the i th pre-stage DC/DC conversion circuit 2.i in the pre-stage DC/DC conversion circuit 2 to operate in the boost mode, and the i +1 st pre-stage DC/DC conversion circuit 2.1 to the n th pre-stage DC/DC conversion circuit 2.n in the pre-stage DC/DC conversion circuit 2 to operate in the through mode.
Step S21 is MPPT control, and the voltage V output by the photovoltaic cell component 1 is sampled pv. And current I pv According to voltage V pv. And current I pv.1 Calculation of the basis of a photovoltaic module 1 using the MPPT algorithmQuasi-voltage V pv.ref . Comparison voltage V pv And a first set value V set Voltage V of pv Is less than a first set value V set Controlling the front-stage DC/DC conversion circuit 2 to work in a boosting mode; voltage V pv Greater than a first set value V set And controlling the front-stage DC/DC conversion circuit 2 to work in a through mode. The voltage V output by the 1 st photovoltaic cell assembly 1.1 is sampled as shown in the figure pv. 。 1 And current I pv.1 The voltage V output by the nth photovoltaic cell component 1.i pv。n. And current I pv.n And calculates the 1 st reference voltage V pv.ref.1 To ith reference voltage V pv.ref.n . Wherein the voltage V output by the 1 st photovoltaic cell component 1.1 to the ith photovoltaic cell component 1.i pv Is less than a first set value V set Voltage V output from the (i + 1) th photovoltaic cell assembly 1.I +1 to the (n) th photovoltaic cell assembly 1.n pv. Greater than a first set value V set 。
The first set value V set The optimum input voltage of the post-stage DC/DC conversion circuit is set according to the minimum value.
If the direct mode is adopted, the MPPT controller of the path can close the driving of the photovoltaic DC-DC conversion circuit of the path. The voltage V output by the photovoltaic cell component 1 pv Voltage V clamped at bus.L of DC bus bus.L While the voltage V output by the photovoltaic cell module 1 pv And controlling the DC/DC conversion circuit of the later stage.
Step S22 is photovoltaic voltage control, and the voltage V output by the photovoltaic cell component 1 is sampled pv And current I pv Voltage V output by the photovoltaic cell module 1 pv And a reference voltage V of the photovoltaic cell assembly pv.ref After the difference is made, an adjustment operation, such as a PI or PID adjustment operation, is performed to generate the drive signal P2. After the above calculation is performed in steps S22.1 to S22.I, the driving signals P2.1 to P2.I are generated to control the main power switches in the 1 st to i th preceding DC/DC conversion circuits 2.1 to 2.i, respectively. Thereby realizing the function of tracking the maximum power point of the photovoltaic cell assembly 1.
Step S32 is a low-voltage DC bus reference meterCalculating and comparing the reference voltage V of each path of the photovoltaic cell assembly 1 pv.ref Selecting the maximum value, if the maximum value is greater than the first set value V set Then it is selected as the reference voltage V of the first DC bus Ref.bus.L If the maximum value is less than the first set value V set Then, select the first setting value V set As a reference voltage for the first dc bus.
Step S33 is the voltage control of the low voltage DC bus, and the low voltage DC bus controller will control the voltage according to the reference voltage V Ref.bus.L Simultaneously according to the low-voltage DC bus voltage V bus.L And the high-voltage direct-current bus voltage V bus.L Generating a driving signal through a low-voltage direct-current bus voltage control algorithm to control a second stage of a topological structure of the micro inverter, namely a DC-DC boost conversion circuit for converting a low-voltage bus into a high-voltage bus, so as to realize the control of the voltage of the low-voltage direct-current bus and transmit energy from the low-voltage direct-current bus to a high-voltage direct-current bus;
step S41 is high-voltage direct-current bus reference calculation, and the control system of the micro inverter calculates to obtain reference voltage V according to the actual working state of the micro inverter system and the state of the alternating-current power grid Ref.bus.H . For example, selecting a reference voltage V Ref.bus.H Not less than the peak value of the alternating current 5. Step S42 is a high voltage DC bus voltage control, according to which the high voltage DC bus controller will be based Ref.bus.H And the high voltage DC bus voltage V bus.H Voltage of the grid V grid And a grid-connected current I grid When the information is equal, the grid voltage V is controlled by a high-voltage direct-current bus control algorithm grid The fundamental component obtained by phase locking is multiplied by the output of the voltage loop and then is multiplied by the grid-connected current I grid Compensating and amplifying the difference to generate a driving signal for controlling the third stage of the topological structure of the micro inverter, namely a DC-AC grid-connected inverter circuit, so as to realize the voltage V of the high-voltage direct-current bus bus.H And grid-connected active power P grid Grid-connected reactive power Q grid And a grid-connected current I grid The control function of (2);
the micro-inverter as shown in FIG. 2According to the voltage V output by each photovoltaic cell module 1 pv Making a judgment if all the voltages V output by the photovoltaic cell assemblies 1 pv Are all lower than a first set value V set Controlling all the preceding-stage DC/DC conversion circuits 2 to work in a boosting mode;
if there is one or more voltage V output by the photovoltaic cell component 1 pv Is higher than a first set value V set According to the voltage V output by the photovoltaic cell component 1 pv Assuming that the input of the a-th path is the maximum, the output voltage is V pv.a Controlling the corresponding preceding-stage DC/DC conversion circuit 2.a to work in a through mode, and controlling the preceding-stage DC/DC conversion circuit 2 of the other circuit to work in a boost mode;
optimized if there is a voltage V output by other photovoltaic cell assemblies 1 pv Is equal to or close to the maximum value V pv.a Controlling the front-stage DC/DC conversion circuits 2 corresponding to the circuits to work in a through mode, and controlling the front-stage DC/DC conversion circuits 2 of other circuits to work in a boosting mode;
optimally, if the change of the voltage reference voltage of the low-voltage direct-current bus causes that the photovoltaic input of a certain path working in the direct-through mode can not reach the maximum power point, the control system of the micro inverter commands the photovoltaic DC-DC conversion circuit to exit the direct-through mode and change the mode into the boosting mode.
As shown in fig. 3, a specific embodiment of the preceding stage DC/DC conversion circuit 2 is, for example, a Boost circuit topology. The Boost circuit can work in a direct mode and a boosting mode.
When the preceding stage DC/DC conversion circuit 2 has no drive signal, the switch operates in the through mode. If the voltage V is pv Not lower than voltage V bus.L Then voltage V pv Will be clamped at voltage V by diode D1 bus.L So that the voltage V is pv Is equal to voltage V bus.L Voltage V of bus.L Will be controlled by the post-stage DC/DC converter circuit 3.
When the preceding stage DC/DC conversion circuit 2 has a drive signal, it operates in a boost mode. Voltage V pv Controlled by the preceding DC/DC converter circuit 2.
The power grade of the Boost circuit topology is larger, the photovoltaic cell modules with different models and different power grades are easier to be compatible, and the conversion efficiency is higher; the Boost circuit topology has fewer power devices and does not need an isolation transformer, so that the volume is smaller and the power density is higher; the photovoltaic voltage control strategy based on the multi-path Boost circuit topology can effectively improve the efficiency of tracking the maximum power point of the photovoltaic cell, namely, the power generation efficiency of the photovoltaic cell.
As shown in fig. 4, in an embodiment of the post-stage DC/DC conversion circuit 3, for example, an LLC resonant circuit topology is adopted, and the post-stage DC/DC conversion circuit 3 transmits energy of the DC bus bus.l to the DC bus bus.h and is responsible for controlling voltage of the DC bus bus.l.
Compared with an isolated DC-DC booster circuit which is separately equipped for each path of photovoltaic battery component 1 in a two-stage topology of the prior art, the invention outputs the voltage V output by each path of photovoltaic battery component 1 to the respective front-stage DC/DC conversion circuit 2 through each path of photovoltaic battery component 1 pv Voltage V to be boosted to uniform bus.L of direct current bus bus.L And then, a low-voltage direct current is boosted to a high-voltage direct current through an independent DC-DC isolation boosting circuit, and when the number of the photovoltaic cell assemblies 1 is more, the number of the isolation transformers is saved more, the reduced volume is larger, the power density is higher, and the cost is reduced more. Voltage V of bus.L due to DC bus.L Voltage V output relative to photovoltaic cell module 1 pv And the DC/DC conversion circuit 3 at the back stage can work at a fixed step-up ratio all the time, so that the DC/DC conversion circuit can work in a high conversion efficiency range for a long time.
As shown in fig. 5, a specific embodiment of the DC/AC conversion circuit 4, for example, adopts a logic circuit topology. The stage circuit is responsible for converting direct current of the direct current bus bus.H into alternating current and connecting the alternating current to a power grid, and is also responsible for controlling the voltage of the direct current bus bus.H.
The above embodiment is only an exemplary specific example of the present invention, and the present invention is not limited thereto, for example, the post-stage DC/DC conversion circuit 3 may also adopt circuit topologies such as a non-isolated LLC, an isolated phase-shifted full bridge, and a non-isolated phase-shifted full bridge. The DC/AC conversion circuit 4 may adopt a circuit topology such as CRM inversion, heric inversion, or the like. When the power level of the micro inverter is low, the DC/AC conversion circuit 4 can adopt a CRM inverter circuit to improve the conversion efficiency; when the power level of the micro inverter is high, the DC/AC conversion circuit 4 may be connected to a single-phase power grid by using a full-bridge inverter or a Heric inverter circuit topology, or connected to a three-phase power grid by using a three-level inverter or other circuit topologies, so as to increase the power level.
When the post-stage DC/DC conversion circuit 3 adopts a non-isolated DC-DC boost circuit topology, circuits related to signal isolation inside the system can be reduced, and the design of circuits such as a sampling circuit, a driving circuit, a control circuit and the like inside the system can be optimized, and when the post-stage DC/DC conversion circuit 3 adopts a non-isolated DC-DC boost circuit topology, the DC/AC conversion circuit 4 adopts an inverter circuit capable of effectively suppressing leakage current, such as a Heric circuit and the like.
As shown in fig. 6, unlike fig. 1, the present embodiment further includes a battery BT6 and a preceding DC/DC converter circuit 7, and the preceding DC/DC converter circuit 7 performs charge/discharge management for the battery BT6. In the embodiment, the multi-battery BT6, the battery BT6.1, the battery BT6.2 to bt6.M, and the corresponding preceding-stage DC/DC conversion circuit 7.1 to the preceding-stage DC/DC conversion circuit 7.m are included. One end of the preceding-stage DC/DC conversion circuit 7 is connected with the battery BT6, and the other end of the preceding-stage DC/DC conversion circuit 7 is connected with other preceding-stage DC/DC conversion circuits 7 in parallel and then is connected with a direct-current bus.
In this embodiment, the photovoltaic cell module 1 transmits electric energy to the preceding-stage DC/DC conversion circuit 7 through the preceding-stage DC/DC conversion circuit 2, and the preceding-stage DC/DC conversion circuit 7 charges the battery BT 6; or the alternating current 5 transmits electric energy to the front-stage DC/DC conversion circuit 7 through the DC/AC conversion circuit 4 and the rear-stage DC/DC conversion circuit 3, and the front-stage DC/DC conversion circuit 7 charges the battery BT 6; or the battery BT6 supplies electric energy to the alternating current 5 through the preceding stage DC/DC conversion circuit 7, the subsequent stage DC/DC conversion circuit 3, and the DC/AC conversion circuit 4.
In this embodiment, the front stage DC/DC conversion circuit 7, the rear stage DC/DC conversion circuit 3, and the DC/AC conversion circuit 4 are all bidirectional conversion circuits, and support bidirectional flow of electric energy.
As shown in fig. 7, unlike fig. 1, the present embodiment further includes a battery BT6 and a preceding DC/DC converter circuit 7, and the preceding DC/DC converter circuit 7 performs charge/discharge management for the battery BT6. In this embodiment, the multi-stage DC/DC converter includes a plurality of batteries BT6, BT6.1, BT6.2 to bt6.M, and corresponding preceding DC/DC converters 7.1 to 7.m. One end of the preceding-stage DC/DC conversion circuit 7 is connected with the battery BT6, and the other end is connected with the other preceding-stage DC/DC conversion circuit 7 in parallel and then connected with the direct-current bus.
In this embodiment, the photovoltaic cell module 1 transmits electric energy to the front-stage DC/DC conversion circuit 7 through the front-stage DC/DC conversion circuit 2 and the rear-stage DC/DC conversion circuit 3, and the front-stage DC/DC conversion circuit 7 charges the battery BT 6; or the alternating current 5 transmits electric energy to the front-stage DC/DC conversion circuit 7 through the DC/AC conversion circuit 4, and the front-stage DC/DC conversion circuit 7 charges the battery BT 6; or the battery BT6 supplies electric energy to the alternating current 5 through the DC/AC conversion circuit 4 of the preceding stage DC/DC conversion circuit 7.
In the present embodiment, the pre-stage DC/DC conversion circuit 7 and the DC/AC conversion circuit 4 are both bidirectional conversion circuits, and support bidirectional flow of electric energy.
It should be understood that the detailed description of the present invention is only for illustrating the present invention and is not limited by the technical solutions described in the embodiments of the present invention, and those skilled in the art should understand that the present invention can be modified or substituted equally to achieve the same technical effects; as long as the use requirements are met, the method is within the protection scope of the invention.
Claims (10)
1. A micro-inverter, comprising,
a plurality of first preceding-stage DC/DC conversion circuits, input terminals of the first preceding-stage DC/DC conversion circuits being connected to respective photovoltaic cell modules, output terminals of the plurality of first preceding-stage DC/DC conversion circuits being connected in parallel to a first DC bus, the first preceding-stage DC/DC conversion circuits controlling output voltages of the photovoltaic cell modules,
a post-stage DC/DC conversion circuit having an input terminal connected in parallel to the first DC bus and an output terminal connected in parallel to a second DC bus, the post-stage DC/DC conversion circuit controlling a voltage of the first DC bus,
and the input end of the DC/AC conversion circuit is connected with the second direct current bus in parallel, and the DC output by the second direct current bus is inverted into AC.
2. The microinverter of claim 1, wherein the first pre-stage DC/DC conversion circuit is a BOOST circuit topology.
3. The micro-inverter of claim 2, wherein the post-stage DC/DC conversion circuit is an isolated circuit topology and the DC/AC conversion circuit is a non-isolated circuit topology.
4. The micro-inverter of claim 2, wherein the post-stage DC/DC conversion circuit is a non-isolated circuit topology and the DC/AC conversion circuit is an isolated circuit topology.
5. The microinverter of claim 1, further comprising a plurality of second pre-stage DC/DC conversion circuits, wherein the input terminals of the second pre-stage DC/DC conversion circuits are connected in parallel to the battery, respectively, and the output terminals of the plurality of second pre-stage DC/DC conversion circuits are connected in parallel to the first DC bus.
6. The microinverter of claim 5, wherein the second preceding stage DC/DC conversion circuit, the subsequent stage DC/DC conversion circuit, and the DC/AC conversion circuit are bidirectional conversion circuits.
7. The microinverter of claim 1, further comprising a plurality of second pre-stage DC/DC conversion circuits, wherein the input terminals of the second pre-stage DC/DC conversion circuits are connected in parallel to the battery, respectively, and the output terminals of the plurality of second pre-stage DC/DC conversion circuits are connected in parallel to the second DC bus.
8. The microinverter of claim 7, wherein the second pre-stage DC/DC conversion circuit and the DC/AC conversion circuit are bidirectional conversion circuits.
9. A control method for controlling a micro-inverter according to any one of claims 1 to 8, comprising,
step S21 is MPPT control, and the voltage output by the photovoltaic cell assembly is sampled . The current is calculated by using an MPPT algorithm, the reference voltage of the photovoltaic cell assembly is compared with a first set value, the voltage output by the photovoltaic cell assembly is smaller than the first set value, and the preceding-stage DC/DC conversion circuit is controlled to work in a boosting mode; the voltage output by the photovoltaic cell assembly is not less than a first set value, and the preceding-stage DC/DC conversion circuit is controlled to work in a direct-through mode;
step S22 is photovoltaic voltage control, and the voltage output by the photovoltaic cell assembly is sampled . And the current is used for calculating power, and the voltage output by the photovoltaic cell assembly is subjected to adjustment operation after being differed with the reference voltage of the photovoltaic cell assembly to generate a first driving signal, wherein the driving signal is used for driving a preceding-stage DC/DC conversion circuit connected with the photovoltaic cell assembly;
step S32, calculating the reference of the low-voltage direct-current bus, comparing the reference voltages of all the photovoltaic cell assemblies, selecting the maximum voltage, if the maximum value is larger than a first set value, selecting the maximum value as the reference voltage of the first direct-current bus, and if the maximum value is smaller than the first set value, selecting the first set value as the reference voltage of the first direct-current bus;
step S33 is low-voltage direct-current bus voltage control, and the reference voltage of the first direct-current bus, the voltage of the first direct-current bus and the voltage of the second direct-current bus are regulated to generate a second driving signal for controlling the rear-stage DC/DC conversion circuit;
step S41 is high-voltage direct-current bus reference calculation, and the reference voltage of a second direct-current bus is calculated;
step S42 is a high-voltage DC bus voltage control, which performs adjustment operation on the reference voltage of the second DC bus, the voltage of the second DC bus, and the voltage output by the DC/AC conversion circuit to generate a third driving signal for controlling the DC/AC conversion circuit.
10. The method according to claim 9, wherein in step S21, the first set value is a lowest value of an optimal input voltage of the subsequent DC/DC conversion circuit.
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| CN115882745A (en) * | 2023-02-22 | 2023-03-31 | 江西清华泰豪三波电机有限公司 | Electric energy router and control method thereof |
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| CN115882745A (en) * | 2023-02-22 | 2023-03-31 | 江西清华泰豪三波电机有限公司 | Electric energy router and control method thereof |
| CN115882745B (en) * | 2023-02-22 | 2023-05-16 | 江西清华泰豪三波电机有限公司 | Electric energy router and control method thereof |
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