A novel photovoltaic grid-connected circuit topology with multiplexing of inverter and chopper

Abstract

The application belongs to the field of photovoltaic new energy grid-connected system and power electronics technology, and discloses a novel photovoltaic grid-connected circuit topology with an inverter and a chopper multiplexing converter, which comprises a high-frequency zigzag transformer, a photovoltaic cell, a three-phase grid-connected inverter and chopper multiplexing converter and a controller; a power grid is connected in series between the primary side and the secondary side of the high-frequency zigzag transformer; the AC side of the three-phase grid-connected inverter and chopper multiplexing converter is connected to the secondary side through a power grid line equivalent resistance, and the DC side is connected to an energy storage battery through a DC bus; the photovoltaic cell is connected between the grounding end of the three-phase grid-connected inverter and chopper multiplexing converter and the grounding end of the energy storage battery; and the three-phase grid-connected inverter and chopper multiplexing converter comprises a three-phase full-bridge circuit composed of IGBT switching tubes Q1-Q6; the controller is used for controlling the on-off of the IGBT switching tubes Q1-Q6, so that the three-phase full-bridge circuit is multiplexed into an inverter and a chopper circuit. The application can reduce the number of devices used in the photovoltaic grid-connected circuit topology and reduce the cost.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic new energy grid-connected systems and power electronics technology, and more specifically, relates to a novel photovoltaic grid-connected circuit topology with an inverter and chopper multiplexing converter. Background Art

[0002] Photovoltaic grid-connected inverter circuit is used to invert the new energy electric energy generated by photovoltaic cells into AC electric energy that can be transmitted to the power grid.

[0003] The current mainstream three-port photovoltaic grid-connected inverter circuit topology can be summarized as follows: based on the original two-port photovoltaic and grid circuit, a DC / DC circuit is added to the DC bus as a chopper converter, forming a "three-port" parallel structure. In this structure, the photovoltaic power supply is connected in parallel at the output of the DC / DC circuit. The chopper converter transfers the power from the DC bus to the energy storage battery. The grid-connected inverter connected between the photovoltaic and grid ports transfers the power from the DC bus to the grid. The circuit topology is clear and simple, the device stress stability is uniform, and the switching error rate is low. However, this "three-port" parallel structure uses a large number of components and is costly. It is not good for the power quality of small users and is prone to problems such as harmonics and power factor imbalance. Summary of the Invention

[0004] In response to the above defects or improvement needs of the prior art, the present invention provides a new photovoltaic grid-connected circuit topology with an inverter and chopper multiplexing converter, the purpose of which is to reduce the number of devices used in the photovoltaic grid-connected circuit topology and reduce costs.

[0005] To achieve the above objectives, according to a first aspect of the present invention, there is provided a novel photovoltaic grid-connected circuit topology with an inverter and chopper multiplexing converter, comprising: a high-frequency zigzag transformer, a photovoltaic cell, a three-phase grid-connected inverter and chopper multiplexing converter, and a controller;

[0006] The high-frequency zigzag transformer includes a primary winding and a secondary winding connected in series; the power grid is connected in series between the primary winding and the secondary winding; the AC side of the three-phase grid-connected inverter and chopper multiplexing converter is connected to the secondary winding via the grid line equivalent resistance, and the DC side is connected to an external energy storage battery via a DC bus; the photovoltaic cell is connected between the ground terminal of the three-phase grid-connected inverter and chopper multiplexing converter and the ground terminal of the energy storage battery; and the three-phase grid-connected inverter and chopper multiplexing converter includes a three-phase full-bridge circuit composed of IGBT switches Q1-Q6;

[0007] The controller is used to control the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted between the power grid and the energy storage battery, the power grid, the secondary winding, the three-phase full-bridge circuit and the energy storage battery form an inverter circuit; wherein the three-phase full-bridge circuit acts as an inverter to realize the inverter function;

[0008] And / or, the controller is further used to control the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted from the photovoltaic cell to the energy storage battery, the photovoltaic cell, the high-frequency zigzag transformer, each phase arm of the three-phase full-bridge circuit and the energy storage battery form a chopper circuit; wherein each phase arm of the three-phase full-bridge circuit serves as a chopper circuit to perform chopping control on the current in the chopper circuit.

[0009] Furthermore, a voltage-stabilizing capacitor is connected in parallel at both ends of the photovoltaic cell; and a voltage-stabilizing capacitor is connected in parallel at both ends of the energy storage battery.

[0010] Furthermore, the high-frequency zigzag transformer further comprises a magnetic column, on which corresponding phase coils of the primary winding and the secondary winding are wound in opposite directions, so that the primary winding and the secondary winding form a zigzag connection in series.

[0011] According to a second aspect of the present invention, a control method for a novel photovoltaic grid-connected circuit topology is provided. The control method is applied to a controller in the novel photovoltaic grid-connected circuit topology according to any one of the first aspects, comprising:

[0012] Controlling the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted between the grid and the energy storage battery, the grid, the secondary winding, the three-phase full-bridge circuit, and the energy storage battery form an inverter circuit; wherein the three-phase full-bridge circuit operates as an inverter in an inverter mode;

[0013] And / or, the on and off of the IGBT switches Q1-Q6 are also controlled so that when electric energy is transmitted from the photovoltaic cell to the energy storage battery, the photovoltaic cell, the high-frequency zigzag transformer, each phase arm of the three-phase full-bridge circuit and the energy storage battery form a chopper circuit; wherein each phase arm of the three-phase full-bridge circuit operates as a chopper circuit in a chopper conversion mode.

[0014] Furthermore, when the three-phase full-bridge circuit operates as an inverter in the inverter mode, the direction of electric energy transmission between the power grid and the energy storage battery is determined by the following method:

[0015] Based on the voltage and current equations satisfied by the equivalent circuit of the novel photovoltaic grid-connected circuit topology, the duty cycle of the control signal generated by the controller is adjusted to control the on and off of the IGBT switches Q1-Q6, thereby changing the current value of i in the voltage and current equations. d 、i q and Ud 、U q The size of d 、i q are the d-axis and q-axis components of the inverter AC side current after dq transformation, U d 、U q are respectively the d-axis and q-axis components of the AC side voltage of the inverter after dq transformation;

[0016] Based on the current moment i d 、i q and U d 、U q The size of the line is used to calculate the active power transmitted; the direction from the grid to the energy storage battery is set as i d 、i q In the positive direction, when the active power is positive, electric energy is transmitted from the grid to the energy storage battery; otherwise, electric energy is transmitted from the energy storage battery to the grid.

[0017] Furthermore, when the three-phase full-bridge circuit is used as a chopper circuit, the amount of electric energy transmitted from the photovoltaic cell to the energy storage battery is determined in the following manner:

[0018] The voltage ratio K is adjusted to control the on-off of the IGBT switches Q1-Q6 to change the loop current i of each chopper circuit. d2 , thereby changing the amount of electrical energy transmitted from the photovoltaic cell to the energy storage battery; wherein the voltage transformation ratio K satisfies:

[0019]

[0020] Where U PV is the output voltage of the photovoltaic cell, U dl is the output voltage of the energy storage battery, r eq2 is the equivalent resistance of the equivalent circuit of the novel photovoltaic grid-connected circuit topology.

[0021] Furthermore, when the three-phase full-bridge circuit acts as an inverter and a chopper circuit at the same time, the three-phase full-bridge circuit operates in a mixed inverter and chopper conversion mode; at this time, based on the voltage and current equations satisfied by the equivalent circuit of the novel photovoltaic grid-connected circuit topology, the duty cycle of the control signal generated by the controller is adjusted, and the size of the voltage transformation ratio K is adjusted to control the on and off of the IGBT switches Q1-Q6, thereby changing the i in the voltage and current equations at the current moment. d 、i q and U d 、U q The size of each chopper circuit and the loop current i d2 ;

[0022] Based on the current moment id i q and U d U q the size of the current i d i q the positive direction, if the active power is positive, the power is transmitted from the grid to the energy storage battery, otherwise, the power is transmitted from the energy storage battery to the grid;

[0023] According to the loop current i d2 , the size of the power transmitted from the photovoltaic cell to the energy storage battery is changed.

[0024] According to a third aspect of the present application, a controller is provided, comprising a computer readable storage medium and a processor;

[0025] The computer readable storage medium is configured to store executable instructions;

[0026] The processor is configured to read the executable instructions stored in the computer readable storage medium to execute the control method according to any one of the second aspect.

[0027] According to a fourth aspect of the present application, a computer readable storage medium is provided, which stores a computer program, and the program is executed by a processor to implement the control method according to any one of the second aspect.

[0028] According to a fifth aspect of the present application, a computer program product is provided, which comprises a computer program, and when the computer program is executed on a computer, the computer is caused to execute the control method according to any one of the second aspect.

[0029] In general, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0030] (1) The novel photovoltaic grid-connected circuit topology designed by the present invention with an inverter and chopper multiplexing converter is realized by adding a high-frequency zigzag transformer with a primary winding and a secondary winding connected in series, and arranging the user-side photovoltaic cell between the ground terminal of the three-phase grid and the three-phase grid-connected inverter and chopper multiplexing converter and the ground terminal of the energy storage battery, and coordinating with a three-phase full-bridge circuit composed of IGBT switches Q1-Q6, so that the three-phase full-bridge circuit has both the inverter and chopper multiplexing functions. Specifically, the three-phase full-bridge circuit composed of IGBT switches Q1-Q6 is generally used as an inverter. If it is used as a chopper circuit, due to the presence of DC current from the user-side photovoltaic cell, the inductance in the three-phase grid will interact to produce a DC magnetization problem, and the zero-sequence current flowing into the three phases will cause the three-phase voltage to fluctuate, resulting in an increase in grid harmonics, thereby reducing the power quality of the entire circuit system. Based on the above considerations, in order to enable the three-phase full-bridge circuit composed of IGBT switches Q1-Q6 to be used as an inverter and a chopper circuit at the same time, the present invention considers introducing a high-frequency zigzag transformer with the primary winding and the secondary winding connected in series, and specifically connecting the user-side photovoltaic cell between the ground terminal of the three-phase power grid and the three-phase grid-connected inverter and chopper multiplexing converter, and the ground terminal of the energy storage battery. In this way, when the three-phase full-bridge circuit is used as a chopping circuit, the zero-sequence magnetic flux generated in the power grid can flow along the magnetic column of the high-frequency zigzag transformer instead of flowing along the leakage magnetic path, thereby suppressing the zero-sequence magnetic flux in the circuit, alleviating the DC magnetization problem, and improving the power quality on the grid side; and, the secondary winding of the high-frequency zigzag transformer and the equivalent resistance of the grid line form an RL filtering effect, further improving the power quality on the grid side. Therefore, the three-phase full-bridge circuit can be used as a chopping circuit, and when it realizes the chopping function, each phase arm of the three-phase full-bridge circuit can be independently used as a chopping circuit, and the three independent chopping circuits jointly chop the DC current output by the photovoltaic cell on the user side. The present invention realizes that the three-phase full-bridge circuit has the functions of both inversion and chopping multiplexing, reduces the number and cost of the components used, and can improve the power quality, avoiding the problems of harmonics and power factor imbalance.

[0031] (2) The topological structure of the present application, because the secondary winding of the high-frequency zigzag transformer is connected to the three-phase grid-connected inverter and the chopping multiplexing converter through the grid line equivalent resistance, when the three-phase grid-connected inverter and the chopping multiplexing converter are used as the chopping circuit, the high-frequency zigzag transformer has a certain inhibitory effect on the current in the three chopping circuits, which can alleviate the problem of uneven heating of semiconductor devices caused by different on and off times of the switch within one switching cycle.

[0032] In summary, the photovoltaic grid-connected circuit topology designed in the present application is a photovoltaic grid-connected circuit topology with an inverter and a chopping multiplexing converter, which has the functions of inverter and chopping multiplexing, can reduce the number of devices used in the photovoltaic grid-connected circuit topology, and reduce the cost. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The figure is a schematic diagram of the new photovoltaic grid-connected circuit topology with an inverter and a chopping multiplexing converter in the embodiments of the present application.

[0034] Figure 2(a) is an equivalent circuit structure diagram of the inverter circuit composed of the three-phase grid-connected inverter and the chopping multiplexing converter as an inverter.

[0035] Figure 2(b) is an equivalent circuit structure diagram of the chopping circuit composed of the three-phase grid-connected inverter and the chopping multiplexing converter as a chopping circuit.

[0036] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0037] 1 - high-frequency zigzag transformer 1, 2 - photovoltaic cell, 3 - three-phase grid-connected inverter and chopping multiplexing converter. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] Embodiment 1

[0040] As Figure 1As shown, an embodiment of the present invention provides a novel photovoltaic grid-connected circuit topology with an inverter and chopper multiplexing converter, which mainly includes: a high-frequency zigzag transformer 1, a photovoltaic cell 2, a three-phase grid-connected inverter and chopper multiplexing converter 3 and a controller.

[0041] The high-frequency zigzag transformer 1 includes a primary winding and a secondary winding connected in series; the three-phase power grid is connected in series between the primary winding and the secondary winding of the high-frequency zigzag transformer 1; the secondary winding of the high-frequency zigzag transformer 1 is connected to the AC side of the three-phase grid-connected inverter and chopper multiplexing converter 3 through the equivalent resistance of the grid line; the DC side of the three-phase grid-connected inverter and chopper multiplexing converter 3 is used to connect an external energy storage battery through a DC bus; a photovoltaic cell 2 is provided between the ground terminal of the three-phase power grid and the three-phase grid-connected inverter and chopper multiplexing converter 3 and the ground terminal of the energy storage battery.

[0042] In an embodiment of the present invention, the three-phase grid-connected inverter and chopper multiplexing converter 3 includes a three-phase full-bridge circuit composed of IGBT switching tubes Q1-Q6. The DC side of the three-phase full-bridge circuit is the DC side of the three-phase grid-connected inverter and chopper multiplexing converter 3, and the AC side of the three-phase full-bridge circuit is the AC side of the three-phase grid-connected inverter and chopper multiplexing converter 3.

[0043] The controller is used to generate control signals to control the on and off of IGBT switches Q1-Q6 under hybrid SPWM modulation. When energy flows between the grid and the energy storage battery, the grid, the secondary side of the high-frequency zigzag transformer, the three-phase full-bridge circuit, and the energy storage battery on the DC bus side form an inverter circuit. The three-phase full-bridge circuit acts as an inverter to realize the inverter function.

[0044] And / or, the controller is further configured to generate a control signal to control the on / off switching of the IGBT switches Q1-Q6 under hybrid SPWM modulation, so that when energy flows from the user-side photovoltaic cell to the energy storage battery, the user-side photovoltaic cell, the high-frequency zigzag transformer, each phase arm of the three-phase full-bridge circuit, and the energy storage battery on the DC bus side form a chopper circuit, wherein each phase of the three-phase full-bridge circuit serves as an independent chopper circuit to perform chopping control on the current flowing into the chopper circuit, and the sum of the currents in the three chopper circuits is consistent with the output current of the user-side photovoltaic cell.

[0045] In an embodiment of the present invention, a high-frequency zigzag transformer 1 includes: a magnetic column and a primary winding and a secondary winding wound on the magnetic column; wherein the corresponding phase coils of the primary winding and the secondary winding are wound in opposite directions on the phase magnetic column, so that the primary winding and the secondary winding form a zigzag connection in series. Since the high-frequency zigzag transformer operates at a high frequency, its loss is low. The use of the high-frequency zigzag transformer can improve the conversion efficiency of the circuit topology, thereby improving the power quality. In addition, the leakage inductance and distributed capacitance of the high-frequency zigzag transformer can be reduced by optimizing the design and winding process, reducing the voltage spike and current spike when the IGBT switch tube is switched, thereby improving the stability and reliability of the entire system.

[0046] As a preferred implementation method, a voltage-stabilizing capacitor is connected in parallel at both ends of the photovoltaic cell on the user side, and a voltage-stabilizing capacitor Cd is connected in parallel at both ends of the energy storage battery. Specifically, the voltage-stabilizing capacitor and the photovoltaic cell are integrated into a system, which has the functions of buffering and filtering, and can provide a relatively stable photovoltaic voltage. The parallel use of photovoltaic cells and voltage-stabilizing capacitors can achieve more efficient and stable energy management, and has the function of buffering current to prevent damage to the photovoltaic cell on the user side when the reuse circuit is working. The capacitor connected in parallel with the photovoltaic cell has the characteristics of high power density, fast charging and discharging capabilities, long cycle life and high safety. It can absorb or release electrical energy while maintaining voltage, and the photovoltaic cell provides electrical energy input. The mutual cooperation between the two subtly adjusts the energy flow structure in the system, making the power quality control more stable.

[0047] Specifically, after the novel photovoltaic grid-connected circuit with an inverter and chopper multiplexer in the embodiments of the present invention is connected to the grid, energy flows and conversions occur between grid power, user-side photovoltaic battery power, and DC bus-side power. The grid-side and DC bus-side energy storage batteries and user-side photovoltaic batteries form two circuits: an AC / DC power circuit and a DC / DC power circuit.

[0048] The power conversion circuit, also known as the AC / DC power circuit, consists of the grid, the secondary side of the high-frequency zigzag transformer, a three-phase full-bridge circuit, and the energy storage battery on the DC bus side. This circuit exchanges energy between the grid and the energy storage battery on the DC bus side. In this case, the three-phase full-bridge circuit (a three-phase grid-connected inverter and chopper multiplexing converter) acts as an inverter. By varying the duty cycle of the control signal generated by the controller, energy flow between the grid and the energy storage battery on the DC bus side is achieved. The three-phase grid-connected inverter and chopper multiplexing converter acts as an inverter, converting energy between the DC side of the energy storage battery and the AC side of the grid.

[0049] The conversion circuit, also known as the DC / DC power circuit, consists of user-side photovoltaic cells, a high-frequency zigzag transformer, a three-phase full-bridge circuit, and a DC bus-side energy storage battery. This circuit facilitates energy exchange between the user-side photovoltaic cells and the DC bus-side energy storage battery. Each phase arm of the three-phase full-bridge circuit (three-phase grid-connected inverter and chopper converter) functions as a chopper circuit. By varying the duty cycle of the control signal generated by the controller, energy flow from the user side to the DC bus side is achieved. The three-phase grid-connected inverter and chopper converter functions as a chopper circuit to implement chopping control between the user side and the DC bus side. By using different IGBT control methods, the three-phase grid-connected inverter and chopper converter can be equivalent to three independent chopper converters. This allows power from the user side to be transferred to the DC bus while maintaining voltage stability. This reciprocating process allows the circuit system to transfer power from the user side to the grid side.

[0050] The novel photovoltaic grid-connected circuit topology designed by the present invention, featuring an inverter and chopper multiplexing converter, incorporates a high-frequency zigzag transformer 1 with a primary and secondary winding connected in series, positions the user-side photovoltaic cell between the ground terminals of the three-phase grid and the three-phase grid-connected inverter and chopper multiplexing converter 3, and the ground terminal of the energy storage battery. This circuit, in conjunction with a three-phase full-bridge circuit comprised of IGBT switches Q1-Q6, achieves both inverter and chopper multiplexing functionality. Specifically, the three-phase full-bridge circuit comprised of IGBT switches Q1-Q6 is typically used as an inverter. However, if used as a chopper circuit, the DC current from the user-side photovoltaic cell interacts with the inductance in the three-phase grid, resulting in DC magnetization problems. Furthermore, the zero-sequence current flowing through the three phases causes three-phase voltage fluctuations, increasing grid harmonics and thus degrading the power quality of the entire circuit system. Based on the above considerations, in order to enable the three-phase full-bridge circuit composed of IGBT switching tubes Q1-Q6 to be used as an inverter and also as a chopper circuit, the present invention considers introducing a high-frequency zigzag transformer 1 with the primary side winding and the secondary side winding connected in series, and in particular connecting the user-side photovoltaic cell between the ground terminal of the three-phase power grid and the three-phase grid-connected inverter and chopper multiplexing converter 3, and the ground terminal of the energy storage battery. In this way, when the three-phase full-bridge circuit is used as a chopping circuit, the zero-sequence magnetic flux generated in the power grid can flow along the magnetic column of the high-frequency zigzag transformer 1 instead of flowing along the leakage magnetic path, thereby suppressing the zero-sequence magnetic flux in the circuit, alleviating the DC magnetization problem, and improving the power quality on the grid side; and, the secondary winding of the high-frequency zigzag transformer 1 and the equivalent resistance of the grid line form an RL filtering effect, further improving the power quality on the grid side. Therefore, the three-phase full-bridge circuit can be used as a chopping circuit, and when it realizes the chopping function, each phase arm of the three-phase full-bridge circuit can be independently used as a chopping circuit, and the three independent chopping circuits jointly chop the DC current output by the photovoltaic cell on the user side. The present invention realizes that the three-phase full-bridge circuit has the functions of both inversion and chopping multiplexing, reduces the number and cost of the components used, and can improve the power quality, avoiding the problems of harmonics and power factor imbalance.

[0051] Moreover, in the topological structure of the present invention, since the secondary winding of the high-frequency zigzag transformer 1 is connected to the AC side of the three-phase grid-connected inverter and chopper multiplexing converter 3 through the equivalent resistance of the grid line, when the three-phase grid-connected inverter and chopper multiplexing converter 3 is used as a chopper circuit, the high-frequency zigzag transformer 1 has a certain inhibitory effect on the current in the three chopper circuits, which can alleviate the problem of uneven heating of semiconductor devices caused by different turn-on and turn-off times of the switching tube in a switching cycle.

[0052] The topological structure of the present invention reduces the number of IGBT switches, greatly reducing costs. During the actual installation process, due to the reduction in the number of components, the space occupied by the circuit devices and packaging is reduced, thereby reducing the redundancy of the circuit.

[0053] The system uses a high-frequency zigzag transformer series circuit to achieve high power density and current density. Combined with photovoltaic cells, three-phase grid-connected inverters, and chopper-multiplexed converters, it reduces zero-sequence flux and zero-sequence impedance during circuit operation, ensuring system stability and reliability.

[0054] Example 2

[0055] An embodiment of the present invention further provides a control method for a novel photovoltaic grid-connected circuit topology having an inverter and chopper multiplexing converter. The control method is applied to the controller in the novel photovoltaic grid-connected circuit topology having an inverter and chopper multiplexing converter in the above-mentioned embodiment 1, and includes: controlling the three-phase grid-connected inverter and chopper multiplexing converter 3 to operate in any one of the following three modes:

[0056] 1) Three-phase grid-connected inverter mode:

[0057] Under hybrid SPWM modulation, the controller generates control signals to switch IGBT switches Q1-Q6 on and off, enabling energy to flow between the grid and the energy storage battery. The grid, the secondary side of the high-frequency zigzag transformer, the three-phase full-bridge circuit, and the energy storage battery on the DC bus side form an inverter circuit, with the three-phase full-bridge circuit acting as an inverter. At this point, the IGBTs control the power output from the energy storage battery on the DC bus side, converting it into a three-phase symmetrical voltage and current with a high power factor and minimal harmonics, which is then absorbed by the grid. Alternatively, the AC power output from the grid is converted into DC power by the IGBTs and stored in the energy storage battery on the DC bus side.

[0058] In the embodiment of the present invention, the controller adopts power factor regulation and harmonic control regulation, and the IGBT switches Q1-Q6 adopt SPWM control mode.

[0059] Specifically, the energy flow between the grid-side and DC bus-side energy storage batteries is achieved by changing the duty cycle of the control signal generated by the controller.

[0060] When the three-phase grid-connected inverter and chopper multiplexing converter are used as the inverter, it is assumed that the equivalent voltage of the grid voltage after abc and dq transformation is E d 、E q The equivalent voltage of the three-phase grid-connected inverter and chopper multiplexing converter 3 after abc, dq transformation is U d 、U qBased on the equivalent circuit topology Figure 2(a) at this time, the voltage and current equations of the three-phase grid-connected inverter and chopper multiplexing converter in the dq coordinate system can be listed:

[0061]

[0062] Where, L eq When the three-phase grid-connected inverter and chopper multiplexing converter are used as the inverter, the equivalent inductance of the high-frequency zigzag transformer and the grid transmission line in the photovoltaic grid-connected equivalent circuit is r eq When the three-phase grid-connected inverter and chopper multiplexing converter are used as the inverter, the equivalent resistance of the high-frequency zigzag transformer and the grid transmission line in the photovoltaic grid-connected equivalent circuit; i d 、i q When the three-phase grid-connected inverter and the chopper multiplexing converter are used as the inverter, the d-axis component and q-axis component of the AC side current of the three-phase grid-connected inverter and the chopper multiplexing converter are transformed after dq; ω is the preset electrical angular velocity; t is the current moment; where L eq 、r eq These are Leq and Req in Figure 2(a).

[0063] Based on the above voltage and current equations, the duty cycle of the control signal is adjusted to change the current moment i d 、i q and U d 、U q The size of i based on the current moment d 、i q and U d 、U q Calculate the active power transmitted by the line, and determine the energy flow between the grid side and the DC bus side energy storage battery according to the positive and negative active power transmitted by the line. Specifically, assume that the line from the grid side to the DC bus side is i d 、i q In the positive direction, when the calculated active power transmitted by the line is positive, the electric energy is transmitted from the grid side to the energy storage battery on the DC bus side; when the active power transmitted by the line is negative, the electric energy is transmitted from the energy storage battery on the DC bus side to the grid side.

[0064] 2) User chopping mode:

[0065] Under hybrid SPWM modulation, the controller generates control signals to control the on and off of IGBT switches Q1-Q6. When energy flows from the user-side photovoltaic cells to the energy storage battery, the user-side photovoltaic cells, high-frequency zigzag transformer, three-phase full-bridge circuit and energy storage battery on the DC bus side form a chopper circuit. The three-phase bridge arms of the three-phase full-bridge circuit act as three independent chopper circuits to achieve chopper control.

[0066] In the three-phase grid-connected inverter mode, it is only assumed that the grid side and the DC bus side exchange electric energy. However, in the embodiment of the present invention, the circuit topology includes user-side photovoltaic cells, and the photovoltaic cells and the DC bus side implement a DC chopping function through a multiplexing converter. Unlike the multiplexing converter as an inverter, the control strategy of the six IGBTs Q1-Q6 in this case is not to turn on each other in turn as in three-phase inverter, but to perform control based on the DC voltage of the user-side photovoltaic cells.

[0067] When the three-phase grid-connected inverter and chopper multiplexing converter is used as a chopper circuit, based on the equivalent circuit topology Figure 2(b) at this time, the voltage and current equations of the three-phase grid-connected inverter and chopper multiplexing converter can be listed as follows:

[0068]

[0069] Where, L eq2 is the equivalent series inductance in the photovoltaic grid-connected equivalent circuit when the three-phase grid-connected inverter and chopper multiplexing converter is used as the chopper circuit, r eq2 is the equivalent resistance of the photovoltaic grid-connected equivalent circuit when the three-phase grid-connected inverter and chopper multiplexing converter is used as the chopper circuit; i d2 is the loop current of each chopping circuit. Ideally, the currents in the three chopping circuits are equal, and the sum of the currents in the three chopping circuits is consistent with the output current of the photovoltaic cell on the user side; U PV is the photovoltaic cell voltage; U2 is the output voltage of the AC side of the three-phase grid-connected inverter and chopper multiplexing converter when the three-phase grid-connected inverter and chopper multiplexing converter is used as a chopper circuit. eq2 、r eq2 These are Leq2 and Req2 in Figure 2(b).

[0070] Due to the modulation effect of the IGBT switch tube, the output voltage of the photovoltaic cell on the user side will maintain a ratio with the output voltage of the energy storage battery on the DC bus side, which is recorded as K. The voltage on the DC bus side is known to be U dl , then:

[0071] U2=KU dl (3)

[0072] From formula (2), we can get:

[0073]

[0074] It can be concluded that K can change the DC voltage and current, U PV with U dlThe ratio of will affect the DC power regulation range. The IGBT control with multiplexing function can accurately control the value of K, so that the voltage at both ends of the multiplexing converter remains stable while realizing the flow of energy from the user side to the DC bus side. That is, by adjusting the size of the voltage ratio K, the loop current i of each chopper circuit is changed. d2 , thereby changing the amount of power transmitted from the user side to the DC bus side energy storage battery; wherein, the voltage transformation ratio K is used to reflect the change in the duty cycle of the control signal generated by the controller. d2 It is generally positive, so the energy is generally from the user's photovoltaic side to the DC bus to measure the energy storage battery.

[0075] 3) Inverter and chopper hybrid conversion mode

[0076] From the first two operating modes, we can know that the different regulation of the IGBT switch tube of the multiplexed converter can realize the inverter and chopping functions of the converter. When the modulation wave superposition of the inverter and chopping is adopted in the control circuit, it is reflected in the on-off state of the IGBT. Specifically, the simultaneous multiplexing of the inverter and chopping functions is realized by introducing the current control amount superposition operation in the control stage. That is, based on the voltage and current equation group shown in the above formula (1), the duty cycle of the control signal generated by the controller is adjusted to change the current moment i d 、i q and U d 、U q The size of i based on the current moment d 、i q and U d 、U q Calculate the active power transmitted by the line, and determine the energy flow between the grid side and the energy storage battery on the DC bus side based on the positive and negative active power transmitted by the line; at the same time, adjust the size of the voltage transformation ratio K to change the loop current i of each chopper circuit d2 , thereby changing the amount of electric energy transmitted from the user side to the energy storage battery on the DC bus side; in this way, the inverter and chopper hybrid conversion mode is realized at the same time.

[0077] Example 3

[0078] An embodiment of the present invention provides a controller including a memory and a processor. The memory stores a computer program, and the processor implements the steps of the control method in the above-mentioned embodiment 2 when executing the computer program.

[0079] The relevant technical solutions are the same as above and will not be repeated here.

[0080] Example 4

[0081] The embodiment of the present application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to realize the steps of the control method in the above embodiment 2.

[0082] The related technical solutions are the same as above, and will not be repeated here.

[0083] Embodiment 5

[0084] The embodiment of the present application provides a computer program product, which comprises a computer program, and when the computer program runs on a computer, the computer program makes the computer execute the steps of the control method in the above embodiment 2.

[0085] The related technical solutions are the same as above, and will not be repeated here.

[0086] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A novel photovoltaic grid-connected circuit topology with an inverter and chopper multiplexed converter, characterized in that: include: High-frequency zigzag transformers, photovoltaic cells, three-phase grid-connected inverters and chopper multiplexing converters and controllers; The high-frequency zigzag transformer includes a primary winding and a secondary winding connected in series; the power grid is connected in series between the primary winding and the secondary winding; the AC side of the three-phase grid-connected inverter and chopper multiplexing converter is connected to the secondary winding via the grid line equivalent resistance, and the DC side is connected to an external energy storage battery via a DC bus; the photovoltaic cell is connected between the ground terminal of the three-phase grid-connected inverter and chopper multiplexing converter and the ground terminal of the energy storage battery; and the three-phase grid-connected inverter and chopper multiplexing converter includes a three-phase full-bridge circuit composed of IGBT switches Q1-Q6; The controller is used to control the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted between the power grid and the energy storage battery, the power grid, the secondary winding, the three-phase full-bridge circuit and the energy storage battery form an inverter circuit; wherein the three-phase full-bridge circuit acts as an inverter to realize the inverter function; And / or, the controller is further used to control the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted from the photovoltaic cell to the energy storage battery, the photovoltaic cell, the high-frequency zigzag transformer, each phase arm of the three-phase full-bridge circuit and the energy storage battery form a chopper circuit; wherein each phase arm of the three-phase full-bridge circuit serves as a chopper circuit to perform chopping control on the current in the chopper circuit.

2. The novel photovoltaic grid-connected circuit topology according to claim 1, characterized in that: A voltage-stabilizing capacitor is connected in parallel at both ends of the photovoltaic cell; and a voltage-stabilizing capacitor is connected in parallel at both ends of the energy storage battery.

3. The novel photovoltaic grid-connected circuit topology according to claim 1 or 2, characterized in that: The high frequency zigzag transformer further comprises a magnetic column, on which corresponding phase coils of the primary winding and the secondary winding are wound in opposite directions, so that the primary winding and the secondary winding form a zigzag connection in series.

4. A novel control method for photovoltaic grid-connected circuit topology, characterized in that: The control method is applied to a controller in a novel photovoltaic grid-connected circuit topology according to any one of claims 1 to 3, comprising: Controlling the on and off of the IGBT switches Q1-Q6 so that when electric energy is transmitted between the grid and the energy storage battery, the grid, the secondary winding, the three-phase full-bridge circuit, and the energy storage battery form an inverter circuit; wherein the three-phase full-bridge circuit operates as an inverter in an inverter mode; And / or, the on and off of the IGBT switches Q1-Q6 are also controlled so that when electric energy is transmitted from the photovoltaic cell to the energy storage battery, the photovoltaic cell, the high-frequency zigzag transformer, each phase arm of the three-phase full-bridge circuit and the energy storage battery form a chopper circuit; wherein each phase arm of the three-phase full-bridge circuit operates as a chopper circuit in a chopper conversion mode.

5. The control method according to claim 4, characterized in that: When the three-phase full-bridge circuit operates as an inverter in the inverter mode, the direction of electric energy transmission between the grid and the energy storage battery is determined in the following manner: Based on the voltage and current equations satisfied by the equivalent circuit of the novel photovoltaic grid-connected circuit topology, the duty cycle of the control signal generated by the controller is adjusted to control the on and off of the IGBT switches Q1-Q6, thereby changing the current value of i in the voltage and current equations. d 、i q and U d 、U q The size of d 、i q are the d-axis and q-axis components of the inverter AC side current after dq transformation, U d 、U q are respectively the d-axis and q-axis components of the AC side voltage of the inverter after dq transformation; Based on the current moment i d 、i q and U d 、U q The size of the line is used to calculate the active power transmitted; the direction from the grid to the energy storage battery is set as i d 、i q In the positive direction, when the active power is positive, electric energy is transmitted from the grid to the energy storage battery; otherwise, electric energy is transmitted from the energy storage battery to the grid.

6. The control method according to claim 5, characterized in that: When the three-phase full-bridge circuit is used as a chopper circuit, the amount of electric energy transmitted from the photovoltaic cell to the energy storage battery is determined in the following manner: The voltage ratio K is adjusted to control the on-off of the IGBT switches Q1-Q6 to change the loop current i of each chopper circuit. d2 , thereby changing the amount of electrical energy transmitted from the photovoltaic cell to the energy storage battery; wherein the voltage transformation ratio K satisfies: Where U PV is the output voltage of the photovoltaic cell, U dl is the output voltage of the energy storage battery, r eq2 is the equivalent resistance of the equivalent circuit of the novel photovoltaic grid-connected circuit topology.

7. The control method according to claim 6, characterized in that: When the three-phase full-bridge circuit acts as an inverter and a chopper circuit at the same time, the three-phase full-bridge circuit operates in an inverter and chopper hybrid conversion mode; at this time, based on the voltage and current equations satisfied by the equivalent circuit of the novel photovoltaic grid-connected circuit topology, the duty cycle of the control signal generated by the controller is adjusted, and the size of the voltage transformation ratio K is adjusted to control the on and off of the IGBT switches Q1-Q6, thereby changing the i in the voltage and current equations at the current moment. d 、i q and U d 、U q The size of each chopper circuit and the loop current i d2 ; Based on the current moment i d 、i q and U d 、U q The size of the line is used to calculate the active power transmitted; the direction from the grid to the energy storage battery is set as i d 、i q In the positive direction, when the active power is positive, electric energy is transmitted from the grid to the energy storage battery; otherwise, electric energy is transmitted from the energy storage battery to the grid; According to the loop current i of each chopper circuit d2 , changing the amount of electrical energy transmitted from photovoltaic cells to energy storage batteries.

8. A controller, characterized in that: comprising a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read the executable instructions stored in the computer-readable storage medium to execute the control method according to any one of claims 4 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the control method according to any one of claims 4 to 7 is implemented.

10. A computer program product, characterized in that The invention comprises a computer program, which, when running on a computer, enables the computer to execute the control method according to any one of claims 4 to 7.

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