CN112994100A - Multi-mode control photovoltaic grid-connected inverter based on intelligent distribution transformer terminal - Google Patents

Multi-mode control photovoltaic grid-connected inverter based on intelligent distribution transformer terminal Download PDF

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Publication number
CN112994100A
CN112994100A CN202110253280.7A CN202110253280A CN112994100A CN 112994100 A CN112994100 A CN 112994100A CN 202110253280 A CN202110253280 A CN 202110253280A CN 112994100 A CN112994100 A CN 112994100A
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inverter
photovoltaic
grid
capacitor
resistor
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CN112994100B (en
Inventor
李练兵
刘艳杰
范辉
梁纪峰
李佳祺
李东颖
周文
李铁成
罗蓬
冯慧波
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Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
Hebei University of Technology
State Grid Hebei Electric Power Co Ltd
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Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
Hebei University of Technology
State Grid Hebei Electric Power Co Ltd
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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
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00016—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • 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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    • 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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    • 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
    • Y02E40/30—Reactive power compensation
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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
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    • 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
    • Y02E40/70—Smart grids as climate change mitigation technology in the energy generation sector
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
    • 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
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
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    • Y04S10/12—Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation
    • Y04S10/123—Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation the energy generation units being or involving renewable energy sources
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    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
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Abstract

The invention relates to a multi-mode control photovoltaic grid-connected inverter based on an intelligent distribution transformer terminal. The inverter comprises an intelligent distribution transformer terminal unit, an extended power signal detection module, a photovoltaic inverter, a photovoltaic battery and a capacitor battery; the connection relationship is as follows: the intelligent distribution transformer terminal unit is connected with the extended power signal detection module, the extended power signal detection module is connected with the photovoltaic inverter, and the input side of the photovoltaic inverter is connected with the photovoltaic battery and the capacitor battery. The photovoltaic inverter can solve the problem of insufficient energy efficiency ratio of the existing equipment or method, realize the multifunctional mode conversion of the photovoltaic inverter, effectively solve the line loss problem, obviously improve the energy efficiency ratio of a power grid and improve the active support of the system.

Description

Multi-mode control photovoltaic grid-connected inverter based on intelligent distribution transformer terminal
Technical Field
The invention belongs to the technical field of electrical control, particularly relates to a multi-mode control photovoltaic grid-connected inverter based on an intelligent distribution transformer terminal, and belongs to the field of intelligent distribution transformers.
Background
In recent years, photovoltaic power generation technology is rapidly developed, photovoltaic power generation is accepted by more and more people, and the quality of electric energy at a public connection point is deteriorated due to more and more power electronic equipment used by a user side and the characteristics of nonlinearity, imbalance, reactive power and the like of local loads. Leading to a large amount of harmonic waves to be injected into the power grid, increasing the interference of the power grid and reducing the power factor.
The general photovoltaic grid-connected inverter has a single function, and an additional filtering device and a reactive power compensation device need to be added on the side of a power grid, for example, if a device with a specific function is installed to control the stacking impurities of a plurality of devices. In the prior art, the quality of electric energy at a power grid side is detected by using an acquisition circuit of an inverter, the electric energy is transmitted to a grid-connected inverter, and then the grid-connected inverter performs calculation control. But always some configuration components are added to maintain the stability of the input side voltage of the grid-connected inverter.
Lizhengming et al < grid-connected inverter with harmonic suppression and reactive compensation > (1000-100X (2016)09-0030-05), which is composed of a large power grid, a grid-connected inverter and various loads. The acquisition circuit of the grid-connected inverter is bridged on a large power grid, the output side of the grid-connected inverter is connected to a load, and the load is connected to the power grid through a power line. The generalized instantaneous reactive power current detection method is comprehensively applied, the positive and negative synchronous rotating coordinate system transformation is utilized, the current negative sequence and the fundamental wave reactive power division are effectively detected, and the harmonic suppression and the reactive power compensation are simultaneously carried out. However, when the grid-connected point information is acquired by using the acquisition circuit of the inverter, when the grid-connected inverter is connected with the external expansion component or when a plurality of inverters are connected in parallel, redundancy of the connecting wires is caused, and the complexity of control is increased. The simultaneous implementation of filtering and reactive compensation functions with one control strategy may result in an incomplete role for one function.
In order to solve the situation, a photovoltaic grid-connected inverter based on intelligent distribution transformation terminal multi-mode control is provided.
Disclosure of Invention
The invention aims to provide a photovoltaic grid-connected inverter based on multi-mode control of an intelligent distribution and transformation terminal, aiming at the defects in the prior art. As shown in fig. 1, an extended power signal detection module is added to the PCC point, and the extended power signal detection module is respectively connected to the intelligent distribution terminal unit, the photovoltaic inverter, and the PCC point. The expansion power signal detection module collects voltage and current information of a grid-connected point and state information of the inverter and transmits the voltage and current information and the state information of the inverter to an intelligent distribution terminal unit (TTU) and sends a control instruction to adjust the working mode of the inverter through different control strategies. And a capacitor battery is added on the input side of the photovoltaic inverter to be connected with the photovoltaic inverter.
The invention solves the existing problems by adopting the following technical scheme:
a photovoltaic grid-connected inverter based on intelligent distribution transformer terminal multi-mode control comprises an intelligent distribution transformer terminal unit, an extended power signal detection module, a photovoltaic inverter, a photovoltaic battery and a capacitor battery; the connection relationship is as follows: the intelligent distribution transformer terminal unit is connected with the extended power signal detection module, the extended power signal detection module is connected with the photovoltaic inverter, and the input side of the photovoltaic inverter is connected with the photovoltaic battery and the capacitor battery;
the extended power signal detection module comprises a microprocessor, a signal acquisition circuit, a carrier communication interface and an RS485 communication interface; the microprocessor is respectively connected with the signal acquisition circuit, the carrier communication circuit and the RS485 communication circuit; the signal acquisition circuit is connected with the PCC of the power distribution network, and the RS485 communication is connected with the photovoltaic inverter;
the signal acquisition circuit includes: the input IN is connected with one end of a resistor R2, the other end of the resistor R2 is connected with a pin 3 of an operational amplifier U1A, a capacitor C is connected with the resistor R7 IN parallel, one end of the capacitor C is also connected with the pin 3 of the operational amplifier U1A, and the other ends of the capacitor C and the resistor R7 are grounded; the 2 pin of the operational amplifier U1A is connected with the 1 pin of the chip U1A; the 8 pins of the operational amplifier U1A are respectively connected with a-5V power supply and a capacitor C1, and the other end of the capacitor C1 is grounded; the 4 pins of the operational amplifier U1A are respectively connected with a +5V power supply and a capacitor C5, and the other end of the capacitor C5 is grounded; a pin 1 of the operational amplifier U1A is connected with one end of a resistor R1; the other end of the resistor R1 is respectively connected with a pin 6 of an operational amplifier U1B, a capacitor C2 and a pin 3 of a linear optocoupler; the pin 5 of the operational amplifier U1B is grounded; a pin 7 of the operational amplifier U1B is respectively connected with the other end of the capacitor C2 and one end of the resistor R3; a pin 1 of the linear optocoupler is connected with the other end of the resistor R3, and a pin 2 of the linear optocoupler is connected with a +12V _ SO power supply; 4 pins of the linear optocoupler are grounded; the 6 pins of the linear optical coupler are respectively connected with the 6 pins of the operational amplifier U3B and the end of the resistor R4; a pin 5 of the linear optocoupler is connected with a pin 5 of the operational amplifier U3B and a ground wire respectively; the 4 pins of the operational amplifier U3B are respectively connected with a +5V power supply and one end of a capacitor C7, and the other end of the capacitor C7 is connected with a signal ground wire; a pin 7 of the operational amplifier U3B is respectively connected with one end of the resistor R9 and the other end of the resistor R4; 8 pins of the operational amplifier U3B are respectively connected with a +4V power supply and a capacitor C3, and the other end of the capacitor C3 is connected with a signal ground wire; the pin 3 of the operational amplifier U3A is connected with the other end of the resistor R9; the 2 pins of the operational amplifier U3A are respectively connected with a resistor R5 and a resistor R6; the other end of the resistor R5 is connected with a signal ground wire; a pin 1 of the operational amplifier U3A is connected with the other end of the resistor R6; the pin 1 of the operational amplifier U3A is further connected to one end of a resistor R8, the other end of the resistor R8 is connected to the output OUT and one end of a capacitor C6, respectively, and the other end of the capacitor C6 is connected to a signal ground. The input IN comes from the signal at the place to be collected, i.e. at the grid connection point. Pin OUT is connected to the ad sample port of stm32F 103.
In the photovoltaic inverter, an inverter unit is connected with a power grid through an LCL filter; the inversion unit is also connected with the control unit; a power grid voltage and current sampling circuit of the control unit is directly connected with a power grid, and an intermediate direct current voltage sampling circuit is connected with the power grid through a user;
the control unit of the photovoltaic inverter comprises a middle direct-current voltage sampling circuit, a power grid voltage sampling circuit, an inverter output voltage and current sampling circuit, a microprocessor, a communication module, a control signal and an IGBT main circuit; the intermediate direct-current voltage sampling circuit, the power grid voltage sampling circuit and the inverter output voltage and current sampling circuit are respectively connected with the microprocessor; the communication module and the control signal are respectively connected with the microprocessor to realize mutual control; the output of the microprocessor is connected with the IGBT main circuit.
The microprocessor in the control unit of the photovoltaic inverter is specifically ARM GD32F 407.
The input side of the photovoltaic inverter is additionally provided with a capacitor battery connected with the photovoltaic inverter. The input side is composed of a photovoltaic array, an MPPT module, a Boost module and a super capacitor battery composite energy storage module, and the super capacitor battery composite energy storage module comprises a capacitor battery and a photovoltaic battery. The connection relationship is as follows: the photovoltaic array is connected with the MPPT module, the MPPT module is connected with the Boost module to Boost, and then the MPPT module is connected with the super capacitor battery composite energy storage module and finally connected to the photovoltaic inverter.
The microprocessor in the extended power signal detection module is specifically ARM stm32F 103.
The signal acquisition circuit uses a linear optical coupler HCNR 200-000E.
The operational amplifiers U1A and 3A and the operational amplifiers U1B and 3B are LM 2904.
The invention has the beneficial effects that:
the invention adds an extended power signal detection module which is respectively connected with the intelligent distribution transformer terminal unit and the photovoltaic inverter, and the convenience and the rapidity of detection can be improved by utilizing power line carrier communication and RS485 communication; a capacitor battery composite energy storage device is added on the input side of the inverter, and the photovoltaic inverter is respectively connected with the photovoltaic battery and the capacitor battery to provide stable voltage for the photovoltaic inverter, so that the reactive power can be adjusted, the impact load can be stabilized, and the active frequency can be supported. Compared with simulation tests, the harmonic content of the current on the power grid side after compensation is greatly reduced, the total harmonic distortion rate is remarkably reduced, the current is smooth, and the total current distortion rate is about 1.6%. After reactive compensation, the voltage is in a stable state, the voltage and the current are in the same phase, and the voltage distortion rate is greatly reduced from about 25% to about 1.5%. The problem of insufficient energy efficiency ratio of the existing equipment or method is solved, multifunctional mode conversion of the photovoltaic inverter is realized, the problem of line loss is effectively solved, the energy efficiency ratio of a power grid is obviously improved, and the active support of the system is improved. The power utilization quality of the user side is effectively guaranteed, the social benefit is remarkable, and the future development prospect is wide.
Drawings
FIG. 1 is a block diagram of a system connection according to the present invention;
FIG. 2 is a block diagram of the components of an extended power signal detection module according to the present invention;
FIG. 3 is a signal acquisition circuit in the extended power signal detection module;
FIG. 4 is a general schematic of a system according to the present invention;
FIG. 5 shows i according to the inventionp-iqStructure block diagram of reactive current detection method；
FIG. 6 is a block diagram of an FFT algorithm for harmonic compensation according to the present invention;
FIG. 7 is a block diagram of the photovoltaic inverter output side according to the present invention;
FIG. 8 is a block diagram illustrating the components of a photovoltaic inverter control unit according to the present invention;
FIG. 9 shows a topology of the input side of a photovoltaic inverter according to the present invention;
FIG. 10 is a current waveform before grid side harmonic compensation;
FIG. 11 is a current waveform after power grid side harmonic compensation;
FIG. 12 is a current voltage waveform before reactive compensation of the power grid side;
FIG. 13 is the current voltage waveform after the reactive compensation of the power grid side;
fig. 14 shows the voltage distortion rate after reactive compensation.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
In the following, embodiments of the invention will be further explained with reference to the drawings, referring to fig. 1, which shows a general flow chart of a system according to the invention,
a photovoltaic grid-connected inverter based on multi-mode control of an intelligent distribution transformer terminal comprises an intelligent distribution transformer terminal unit, an extended power signal detection module, a photovoltaic inverter, a photovoltaic battery and a capacitor battery; the connection relationship is as follows: the intelligent distribution transformer terminal unit is connected with the extended power signal detection module, the extended power signal detection module is connected with the photovoltaic inverter, and the input side of the photovoltaic inverter is connected with the photovoltaic battery and the capacitor battery.
As shown in fig. 2, the extended power signal detection module includes a microprocessor, a signal acquisition circuit, a carrier communication interface, and an RS485 communication interface; the microprocessor is respectively connected with the signal acquisition circuit, the carrier communication circuit and the RS485 communication circuit; wherein signal acquisition circuit links to each other with distribution network PCC, and RS485 communication links to each other with photovoltaic inverter.
The microprocessor is connected with the signal acquisition circuit to receive information and is respectively connected with the carrier communication interface and the RS485 communication interface to realize information transmission.
The microprocessor is specifically ARM stm32F 103.
The signal acquisition circuit is shown in fig. 3. The signal acquisition circuit uses a linear optocoupler HCNR (200-000E), a pin IN is connected with a grid-connected point to acquire a signal, then the signal passes through the front two operational amplifier circuits and is used for forming a voltage follower circuit with a filtering function, the rear two operational amplifier circuits are filtered and followed, and then a pin OUT is connected to an ad sampling port of stm32F 103; the RS485 communication interface is connected to two ports of a usart1 and a usart2 of the microprocessor; the carrier communication interface is connected to the usart4 port of the microprocessor.
The method specifically comprises the following steps: the input IN is connected with one end of a resistor R2, the other end of the resistor R2 is connected with a pin 3 of an operational amplifier U1A, a capacitor C is connected with the resistor R7 IN parallel, one end of the capacitor C is also connected with the pin 3 of the operational amplifier U1A, and the other ends of the capacitor C and the resistor R7 are grounded; the 2 pin of the operational amplifier U1A is connected with the 1 pin of the chip U1A; the 8 pins of the operational amplifier U1A are respectively connected with a-5V power supply and a capacitor C1, and the other end of the capacitor C1 is grounded; the 4 pins of the operational amplifier U1A are respectively connected with a +5V power supply and a capacitor C5, and the other end of the capacitor C5 is grounded; a pin 1 of the operational amplifier U1A is connected with one end of a resistor R1; the other end of the resistor R1 is respectively connected with a pin 6 of an operational amplifier U1B, a capacitor C2 and a pin 3 of a linear optocoupler; the pin 5 of the operational amplifier U1B is grounded; a pin 7 of the operational amplifier U1B is respectively connected with the other end of the capacitor C2 and one end of the resistor R3; a pin 1 of the linear optocoupler is connected with the other end of the resistor R3, and a pin 2 of the linear optocoupler is connected with a +12V _ SO power supply; 4 pins of the linear optocoupler are grounded; the 6 pins of the linear optical coupler are respectively connected with the 6 pins of the operational amplifier U3B and the end of the resistor R4; a pin 5 of the linear optocoupler is connected with a pin 5 of the operational amplifier U3B and a ground wire respectively; the 4 pins of the operational amplifier U3B are respectively connected with a +5V power supply and one end of a capacitor C7, and the other end of the capacitor C7 is connected with a signal ground wire; a pin 7 of the operational amplifier U3B is respectively connected with one end of the resistor R9 and the other end of the resistor R4; 8 pins of the operational amplifier U3B are respectively connected with a +4V power supply and a capacitor C3, and the other end of the capacitor C3 is connected with a signal ground wire; the pin 3 of the operational amplifier U3A is connected with the other end of the resistor R9; the 2 pins of the operational amplifier U3A are respectively connected with a resistor R5 and a resistor R6; the other end of the resistor R5 is connected with a signal ground wire; a pin 1 of the operational amplifier U3A is connected with the other end of the resistor R6; the pin 1 of the operational amplifier U3A is further connected to one end of a resistor R8, the other end of the resistor R8 is connected to the output OUT and one end of a capacitor C6, respectively, and the other end of the capacitor C6 is connected to a signal ground. The input IN comes from the signal at the place to be collected, i.e. at the grid connection point. Pin OUT is connected to the ad sample port of stm32F 103.
The model of the operational amplifiers U1A and U3A and the model of the operational amplifiers U1B and U3B are LM 2904;
the intelligent distribution terminal is a known device, is an intelligent distribution terminal-based device, and is used for calculating the voltage, the current distortion rate, the power factor and the residual capacity of the photovoltaic inverter of a grid-connected point according to the three-phase voltage and current information acquired by the extended power signal detection module, calculating the reactive power and the harmonic compensation control quantity by the intelligent distribution terminal unit, adjusting the working mode of the photovoltaic inverter, and performing reactive power compensation and harmonic suppression on a public connection point.
The photovoltaic inverter is only connected with a photovoltaic cell originally, and on the basis, a capacitor cell is additionally connected with the photovoltaic inverter, and the photovoltaic cell is connected with the capacitor cell in a parallel connection mode.
Fig. 7 is a working schematic diagram of the photovoltaic inverter, that is, a structural diagram of the output side of the photovoltaic inverter is formed, and the inverter unit is connected with a power grid through an LCL filter; the inversion unit is also connected with the control unit; a power grid voltage and current sampling circuit of the control unit is directly connected with a power grid, and an intermediate direct current voltage sampling circuit is connected with the power grid through a user;
fig. 8 shows a control unit of the photovoltaic inverter, which includes an intermediate dc voltage sampling circuit, a grid voltage sampling circuit, an inverter output voltage and current sampling circuit, a microprocessor, a communication module, a control signal, and an IGBT main circuit. The microprocessor is specifically ARM GD32F 407. The intermediate direct-current voltage sampling circuit, the power grid voltage sampling circuit and the inverter output voltage and current sampling circuit are respectively connected with the microprocessor. The communication module and the control signal are respectively connected with the microprocessor to realize mutual control. The output of the microprocessor is connected with the IGBT main circuit.
Further, the communication module is in communication connection with an RS485 of the extended power signal detection module, and the control signal is connected with the intelligent distribution and transformation terminal unit. According to the control quantity fed back by the intelligent distribution transformer terminal unit, the microprocessor calculates the control quantity through a certain algorithm to control the output of the IGBT main circuit so as to realize the functions of harmonic suppression and reactive compensation.
As shown in fig. 9, a capacitor battery is added to the input side of the photovoltaic inverter according to the present invention. The input side is composed of a photovoltaic array, an MPPT module, a Boost module and a super capacitor battery composite energy storage module, and the super capacitor battery composite energy storage module comprises a capacitor battery and a photovoltaic battery. The connection relationship is as follows: the photovoltaic array is connected with the MPPT module, the MPPT module is connected with the Boost module to Boost, and then the MPPT module is connected with the super capacitor battery composite energy storage module and finally connected to the photovoltaic inverter.
The carrier communication and RS485 communication of the extended power signal detection module are respectively connected with the intelligent distribution and transformation terminal unit and the communication module of the photovoltaic inverter, and the signal acquisition circuits of the extended power signal detection module are respectively connected with the grid-connected point and the communication module of the photovoltaic inverter.
The expansion power signal detection module collects information, the information is transmitted to an intelligent distribution Transformer Terminal Unit (TTU) in a power line carrier communication mode, the TTU can also access the state of the photovoltaic inverter through power line carrier communication and an RS485 interface to issue an instruction, and the photovoltaic inverter changes the working mode; and the input side of the photovoltaic inverter is additionally provided with a capacitive battery composite energy storage device, so that the photovoltaic inverter has the functions of adjusting reactive and impact loads and supporting active frequency. And moreover, own algorithm strategies are set, and functions of harmonic suppression, reactive compensation and the like are realized through the set control strategies to adjust the power quality of the grid-connected point.
The functions of each part are as follows:
the intelligent distribution transformer terminal unit is connected with the photovoltaic grid-connected inverter controlled in a multi-mode manner to establish contact, receives the collected voltage and current information of a grid-connected Point (PCC) and sends out information for controlling the photovoltaic inverter;
the photovoltaic grid-connected inverter is controlled in a multi-mode, is connected with the intelligent distribution transformer terminal unit to establish contact, and comprises an extended power signal detection module and a photovoltaic inverter;
the extended power signal detection module is connected with the intelligent distribution transformer terminal unit through power line carrier communication to establish contact, and is connected with the photovoltaic inverter through RS485 communication to establish contact;
the photovoltaic inverter is respectively connected with the photovoltaic battery and the capacitor battery, receives the adjusting information and sends an adjusting instruction;
the photovoltaic cell is used for providing photovoltaic inverter input side voltage for the photovoltaic inverter;
and the capacitor battery realizes the charging and discharging of the battery and stabilizes the voltage of the input side of the photovoltaic inverter.
Referring to fig. 4, there is shown a general schematic of a system according to the present invention, comprising the steps of:
the method comprises the following steps: the method comprises the steps that a power signal detection module is expanded in a monitoring period of each intelligent distribution transformer terminal unit to collect state information of a photovoltaic grid-connected inverter and voltage and current data information of a grid-connected point;
step two: the information acquired by the extended power signal detection module transmits the voltage and current information of the inverter and the grid-connected point to an intelligent distribution Transformer Terminal Unit (TTU) through RS485 communication and power line carrier communication (HPLC);
step three: the TTU calculates the voltage, the current harmonic distortion rate, the power factor and the residual capacity of the photovoltaic inverter of the grid-connected point; under the limit of the capacity of the photovoltaic grid-connected inverter, the intelligent distribution transformer terminal unit sends out an inverter control instruction by taking the optimal power quality of the public connection point as a target and then transmits the inverter control instruction to the photovoltaic inverter;
step four: and controlling the output of the photovoltaic inverter according to the information fed back by the TTU unit, adjusting the working mode of the photovoltaic grid-connected inverter, and performing reactive power compensation and harmonic suppression on the public connection point.
In the first step, as shown in fig. 4, an extended power signal detection module is connected near a Point of Common Coupling (PCC), and the extended power signal detection module acquires information on the output side of the inverter through an RS485 interface. And modulating and demodulating the collected signals into identifiable signals through a coupling device at the PCC terminal.
The expansion power signal detection module reads the voltage and current information at the common connection point, and if the reactive power and the harmonic current at the common connection point need to be adjusted, the expansion power signal detection module reads the state of the inverter and compensates after the residual capacity exists. The expansion power signal detection module collects voltage and current to help control the photovoltaic inverter, the states of the photovoltaic inverter and the PCC point are transmitted to the TTU through a carrier, and the TTU controls the photovoltaic inverter through an intelligent power line carrier-to-RS 485 interface. The extended power signal detection module inquires the state of the photovoltaic inverter periodically, the PCC state is collected, the TTU inquires the extended power virtual signal detection module to report the states of the PCC and the photovoltaic inverter, and the TTU calculates a relevant reference value.
Power line carrier communication (HPLC) is adopted between the TTU and the extended power signal detection module, an intelligent RS485 interface converted from power line carrier is adopted between the photovoltaic inverter and the TTU, and RS485 communication is adopted between the photovoltaic inverter and the extended power signal detection module. And a coupling device is arranged on each of the PCC and the TTU sides to realize the transceiving of carrier signals and the transmission of communication information. The power line carrier module is provided with a power line carrier interface which is used for establishing connection between the carrier circuit and external communication, and the communication interface uses RS 485.
In the second step, because the photovoltaic inverter is close to the PCC point, the photovoltaic inverter is connected with the expansion power signal detection module through a lead, and the state of the photovoltaic inverter and the state of the PCC point are both sent to the TTU through the carrier circuit. A power line carrier module is provided with a coupling device at a grid-connected point side and a TTU side respectively for transmitting and receiving signals collected by an expanded power signal detection module, the coupling device uses a capacitive coupling mode to isolate strong current and weak current and provide a high-frequency signal path to prevent power frequency current from entering a weak current system, a frequency spectrum is moved in the power line carrier path, the conversion mode is modulation, and a coder and a modulator are integrated in a transmitting device.
And in the third step, according to the voltage and current information collected in the first step, the voltage and current harmonic distortion rate, the power factor and the residual capacity of the photovoltaic inverter of the grid-connected point are calculated, and the intelligent distribution terminal unit calculates.
And the third step is to calculate the distortion rate of the voltage and the current of the grid-connected point. And the expanded power signal detection module of the grid-connected point detects voltage and current information in real time, calculates the voltage harmonic distortion rate and the harmonic current according to an instantaneous reactive power method, calculates the power factor and the residual capacity of the photovoltaic inverter, and the TTU forms control information and sends a control command. And the TTU analyzes the state of a grid-connected point according to the received information, gives a certain control instruction to control the working mode of the inverter and make an adjusting action.
The calculation formula of the voltage-current distortion rate in the third step is as follows:
Figure BDA0002963045070000081
in the formula un-the effective value of the nth harmonic voltage, u1Is the effective value of the fundamental voltage, THDuIs the voltage distortion rate.
Figure BDA0002963045070000091
In the formula In-the effective value of the nth harmonic current, I1Effective value of fundamental current, THDiIs the current distortion rate.
Remaining capacity calculation of the inverter:
Pr＝(P-Pe)×95％
in the above formula PrFor the residual capacity of the photovoltaic inverter, P is the rated power of the inverter，PeIs the grid-connected power of the inverter. And realizing compensation of the system according to the residual capacity of the inverter.
Calculating the power factor of the grid-connected point:
Figure BDA0002963045070000092
p-active power of grid-connected point, Q-reactive power of grid-connected point, PbIs the power factor of the point of grid connection. P and Q are found by the instantaneous reactive power method.
When the harmonic distortion rate of the voltage and the current of the grid-connected point exceeds the limit value required by the system and the power factor does not meet the requirement of the system, the TTU enables the photovoltaic inverter to make regulation through power line carrier communication. The photovoltaic inverter suppresses harmonic waves and compensates reactive power according to the residual capacity of the photovoltaic inverter. And actively performing function conversion according to the voltage amplitude of the photovoltaic grid-connected point and the capacity limit of the photovoltaic inverter and the energy storage.
In the fourth step, as shown in fig. 5 and 6, the photovoltaic inverter receives feedback information from the TTU through power line carrier communication, and the photovoltaic inverter sends out a corresponding output value to control the output current of the photovoltaic inverter to realize harmonic suppression and reactive compensation, thereby realizing time division multiplexing of the photovoltaic inverter and realizing the functions of regulating voltage, preventing voltage from exceeding the limit and regulating active and reactive power.
Through RS485 communication between intelligent power line carrier 485 conversion interface and the photovoltaic inverter, using ModBus communication protocol, TTU can generate control instruction to control the photovoltaic inverter to improve the power quality of the power grid according to the information detected by the grid-connected point.
Referring to FIG. 5, i according to the present inventionp-iqA structural block diagram of a reactive current detection method;
the invention adopts a reactive current detection method based on instantaneous reactive power, directly takes the reactive current required by a grid connection point as a part of instruction current, and realizes dynamic real-time compensation of the reactive power by controlling the magnitude and the phase of fundamental voltage or current. Using ip-iqThe method only needs to carry out coordinate transformation processing on the current signal to directly obtain a corresponding reactive current signal. According to the requirement for ipAnd iqTo carry out the inverseThe corresponding reactive current and harmonic current signals can be obtained through conversion. Directly converting reactive component i generated by grid-connected pointLqAfter reversed polarity, the command current is used as the reactive current output by the photovoltaic inverter
Figure BDA0002963045070000093
And is compared with the current i actually output by the photovoltaic inverterqAnd comparing, sending the comparison result to a PI controller, tracking the command current, driving a pulse generator by the control quantity, and controlling the on-off of a switch of the photovoltaic inverter.
Fig. 6 is a block diagram of an FFT algorithm for harmonic compensation according to the present invention, further implementing the calculation of the filtering current by using an FFT method:
and carrying out FFT decomposition according to the acquired current value of one period to obtain the amplitude and the phase coefficient of each harmonic, and then carrying out FFT inverse transformation to synthesize the total harmonic. The inverter outputs corresponding current to suppress harmonics.
And if the grid connection point contains higher harmonics, Fourier decomposition is carried out on the higher harmonics, fundamental wave components of voltage of the grid are obtained, and the amplitude and phase conditions of the higher harmonics can be obtained. The expression is as follows:
Figure BDA0002963045070000101
wherein (n ═ 1, 2, 3)
In the formula: u. of(t)Is a fundamental component of voltage, a0For each harmonic amplitude, n ω0Frequency of the respective harmonic wave, AnIs the amplitude of the nth harmonic, phi0Is the ratio of phase, harmonic frequency and fundamental frequency
Figure BDA0002963045070000102
Referred to as harmonic order.
Fig. 9 shows the input side of a photovoltaic inverter according to the invention. The photovoltaic energy storage system is composed of an MPPT module, a Boost module and a super capacitor battery composite energy storage module, has the function of adjusting reactive power and impact load, and improves the energy efficiency ratio of a photovoltaic system and the stability of a power grid.
In the case of the example 1, the following examples are given,
the photovoltaic grid-connected inverter based on the intelligent distribution terminal multi-mode control of the invention is described in the following by specific embodiments. In order to verify the effectiveness of the device, a multi-mode control photovoltaic grid-connected inverter simulation experiment platform is built on Matlab/Simulink, a simulation model takes three phases of 380V, 0 phase and 50Hz as the state of a power grid side, the switching frequency is 10KHz, and the direct-current bus voltage U is setdc800V DC bus side capacitor Cdc2500 muF, inverter side capacitance Cf＝600μF、L 1500 muh. In order to verify the harmonic suppression and reactive compensation capabilities of the invention, specific load harmonic and reactive sources were simulated on the load side. The photovoltaic inverter is a 10KW photovoltaic inverter, high-order harmonics and reactive power are added in simulation, and the whole system device obtains a good expected effect by switching operation modes with different functions.
In fig. 10, to verify the ability of harmonic suppression, a load was added at the grid output side to create a source of interference. The current waveform before harmonic compensation at the power grid side is intercepted and contains a large amount of harmonic waves, the amplitude of the visible current waveform is unstable, and the visible current contains many higher harmonic waves and cannot form a sine characteristic, so that damage is easily caused.
Fig. 11 shows the current waveform after the power grid side harmonic compensation using the FFT harmonic detection algorithm, the power grid side current harmonic content after compensation is greatly reduced, the current is smooth, and the total harmonic distortion is significantly reduced.
Comparing fig. 10 and fig. 11, when higher harmonics are injected into the grid-connected inverter control system, the waveform of the grid-connected current filtered by the device is smooth, and the sinusoidal characteristic is obviously better than the waveform of the grid-connected current before compensation.
In fig. 12, the upper column is the current-voltage waveform before reactive power compensation on the grid side, the middle column is the compensation current waveform, and the lower column is the disturbance current waveform. The current amplitude before compensation is unstable and not sinusoidal, the voltage amplitude is weak, the voltage and the current have phase difference and are obviously in an advanced state, and the damage to a power grid and users is easily caused.
The upper column of FIG. 13 is using ip-iqAnd measuring the voltage waveform of the power grid after the reactive current detection method. Reactive compensationThe compensated voltage is in a stable state, the phase difference is completely compensated, and the compensated voltage is in a sine wave shape.
In fig. 14, the uppermost curve after 0.06s is the voltage distortion rate before compensation, and the lower curve is the voltage distortion rate after compensation, and it can be seen from the graph that the voltage distortion rate is reduced from about 0.25 to about 0.015, and the photovoltaic inverter completely improves the power quality.
It should be emphasized that the examples described herein are illustrative and not restrictive, and thus the present invention includes, but is not limited to, those examples described in this detailed description, as well as other embodiments that can be derived from the teachings of the present invention by those skilled in the art and that are within the scope of the present invention.
The invention is not the best known technology.

Claims (10)

1. A photovoltaic grid-connected inverter based on intelligent distribution transformer terminal multi-mode control is characterized in that the inverter comprises an intelligent distribution transformer terminal unit, an extended power signal detection module, a photovoltaic inverter, a photovoltaic battery and a capacitor battery; the connection relationship is as follows: the intelligent distribution transformer terminal unit is connected with the extended power signal detection module, the extended power signal detection module is connected with the photovoltaic inverter, and the input side of the photovoltaic inverter is connected with the photovoltaic battery and the capacitor battery.
2. The intelligent distribution transformer terminal-based multi-mode control photovoltaic grid-connected inverter as claimed in claim 1, wherein the extended power signal detection module comprises a microprocessor, a signal acquisition circuit, a carrier communication interface, and an RS485 communication interface; wherein, microprocessor links to each other with signal acquisition circuit, carrier communication, RS485 communication respectively.
3. The intelligent distribution transformer terminal-based multimode control photovoltaic grid-connected inverter as claimed in claim 2, wherein the signal acquisition circuit comprises: the input IN is connected with one end of a resistor R2, the other end of the resistor R2 is connected with a pin 3 of an operational amplifier U1A, a capacitor C is connected with the resistor R7 IN parallel, one end of the capacitor C is also connected with the pin 3 of the operational amplifier U1A, and the other ends of the capacitor C and the resistor R7 are grounded; the 2 pin of the operational amplifier U1A is connected with the 1 pin of the chip U1A; the 8 pins of the operational amplifier U1A are respectively connected with a-5V power supply and a capacitor C1, and the other end of the capacitor C1 is grounded; the 4 pins of the operational amplifier U1A are respectively connected with a +5V power supply and a capacitor C5, and the other end of the capacitor C5 is grounded; a pin 1 of the operational amplifier U1A is connected with one end of a resistor R1; the other end of the resistor R1 is respectively connected with a pin 6 of an operational amplifier U1B, a capacitor C2 and a pin 3 of a linear optocoupler; the pin 5 of the operational amplifier U1B is grounded; a pin 7 of the operational amplifier U1B is respectively connected with the other end of the capacitor C2 and one end of the resistor R3; a pin 1 of the linear optocoupler is connected with the other end of the resistor R3, and a pin 2 of the linear optocoupler is connected with a +12V _ SO power supply; 4 pins of the linear optocoupler are grounded; the 6 pins of the linear optical coupler are respectively connected with the 6 pins of the operational amplifier U3B and the end of the resistor R4; a pin 5 of the linear optocoupler is connected with a pin 5 of the operational amplifier U3B and a ground wire respectively; the 4 pins of the operational amplifier U3B are respectively connected with a +5V power supply and one end of a capacitor C7, and the other end of the capacitor C7 is connected with a signal ground wire; a pin 7 of the operational amplifier U3B is respectively connected with one end of the resistor R9 and the other end of the resistor R4; 8 pins of the operational amplifier U3B are respectively connected with a +4V power supply and a capacitor C3, and the other end of the capacitor C3 is connected with a signal ground wire; the pin 3 of the operational amplifier U3A is connected with the other end of the resistor R9; the 2 pins of the operational amplifier U3A are respectively connected with a resistor R5 and a resistor R6; the other end of the resistor R5 is connected with a signal ground wire; a pin 1 of the operational amplifier U3A is connected with the other end of the resistor R6; the pin 1 of the operational amplifier U3A is further connected to one end of a resistor R8, the other end of the resistor R8 is connected to the output OUT and one end of a capacitor C6, respectively, the other end of the capacitor C6 is connected to a signal ground, the input IN is a signal from a place to be collected, that is, at a grid-connected point, the pin OUT is connected to the ad sampling port of stm32F 103.
4. The intelligent distribution transformer terminal-based multimode control photovoltaic grid-connected inverter as claimed in claim 1, wherein in the photovoltaic inverter, an inverter unit is connected with a power grid through an LCL filter; the inversion unit is also connected with the control unit; the grid voltage and current sampling circuit of the control unit is directly connected with the grid, and the intermediate direct current voltage sampling circuit is connected with the grid through a user.
5. The photovoltaic grid-connected inverter based on the intelligent distribution terminal multi-mode control of claim 4, wherein the control unit of the photovoltaic inverter comprises an intermediate direct-current voltage sampling circuit, a grid voltage sampling circuit, an inverter output voltage and current sampling circuit, a microprocessor, a communication module, a control signal and an IGBT main circuit; the intermediate direct-current voltage sampling circuit, the power grid voltage sampling circuit and the inverter output voltage and current sampling circuit are respectively connected with the microprocessor; the communication module and the control signal are respectively connected with the microprocessor to realize mutual control; the output of the microprocessor is connected with the IGBT main circuit.
6. The intelligent distribution terminal-based multimode controlled photovoltaic grid-connected inverter as claimed in claim 5, characterized in that the microprocessor in the control unit of the photovoltaic inverter is specifically ARM GD32F 407.
7. The intelligent distribution transformer terminal-based multi-mode control photovoltaic grid-connected inverter as claimed in claim 1, wherein a capacitive battery is added at an input side of the photovoltaic inverter and connected with the photovoltaic inverter, the input side is composed of a photovoltaic array, an MPPT module, a Boost module and a super capacitive battery composite energy storage module, the super capacitive battery composite energy storage module comprises a capacitive battery and a photovoltaic battery, and the connection relationship is as follows: the photovoltaic array is connected with the MPPT module, the MPPT module is connected with the Boost module to Boost, and then the MPPT module is connected with the super capacitor battery composite energy storage module and finally connected to the photovoltaic inverter.
8. The intelligent distribution transformer terminal-based multimode control photovoltaic grid-connected inverter as claimed in claim 2, wherein the microprocessor in the extended power signal detection module is specifically ARM stm32F 103.
9. The intelligent distribution transformer terminal-based multimode control photovoltaic grid-connected inverter as claimed in claim 3, wherein the signal acquisition circuit uses a linear optical coupler HCNR 200-000E.
10. The intelligent distribution transformer terminal-based multimode control photovoltaic grid-connected inverter as claimed in claim 3, wherein the operational amplifiers U1A and U3A and U1B and U3B are LM 2904.
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