Control method and control system of photovoltaic grid-connected power generation system

Abstract

The invention discloses a control method and a control system of a photovoltaic grid-connected power generation system. The method comprises the following steps: a first selection switch determines a first control signal of each switch tube based on a first output signal generated by a trigger at the stage of a current period of power grid voltage; the arithmetic unit calculates the difference between the reference working voltage and the direct-current voltage of the photovoltaic panel to obtain a first voltage; the proportional-integral controller and the coordinate transformation unit sequentially process the first voltage to obtain a grid-connected current reference value; the first multiplier multiplies the direct-current voltage and the inductive current determined by the second switching tube and then inputs the product into the integrator; the second multiplier multiplies the grid-connected current reference value and the voltage of the power grid; when the output of the integrator is greater than or equal to the output of the second multiplier, the comparator generates a high-level input signal; the trigger generates a second output signal based on the high-level input signal; and the first selection switch determines a second control signal corresponding to each switching tube based on the stage of the current period and the second output signal.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic grid-connected power generation system control, and specifically to a control method and control system for a photovoltaic grid-connected power generation system. Background Art

[0002] Solar power generation, as one of the most valuable renewable energy sources, has been applied in many fields. Its main utilization method is photovoltaic cell power generation, such as large-scale photovoltaic power stations, photovoltaic charging equipment, photovoltaic building integration, etc.

[0003] At present, photovoltaic power generation applications are increasingly inclined to the primary structure, mainly referring to the single-stage grid-connected system structure. In this structure, the system only contains a primary power conversion device, namely the grid-connected inverter. Since there is only one primary power conversion device, the system structure is relatively simple, fewer devices are required, the energy loss in the intermediate links is reduced, and the overall efficiency of the system is improved. However, although the system structure is simplified, it is more sensitive to environmental factors such as light. In fact, in the process of converting solar energy into electrical energy, the direct current output by the photovoltaic panel contains a certain low-frequency pulsation. When the environment changes, such as partial shading or uneven light, this pulsation is more obvious. The traditional system mainly relies on the capacitor before the inverter for filtering, but it cannot be completely filtered out. The larger the capacitance, the larger its physical size and weight, and the higher the material requirements, so its cost is usually higher. The low-frequency pulsation that cannot be eliminated will cause the output waveform of the grid-connected inverter to contain a large number of low-order harmonics. These low-order harmonics cannot be filtered out by the filter. If this output voltage waveform is directly applied to the actual system, it will cause great pollution to the power grid and bring many harms to the electrical equipment.

[0004] Therefore, it is necessary to take certain measures to suppress the resulting waveform distortion. Summary of the invention

[0005] The present application provides a control method and control system for a photovoltaic grid-connected power generation system, which improves the suppression effect of low-frequency pulsation in the DC side, i.e., the DC power output by the photovoltaic panels, thereby suppressing the distortion of the output voltage waveform and reducing pollution to the power grid.

[0006] In a first aspect, the present application provides a control method for a photovoltaic grid-connected power generation system, which is applied to a control system of the photovoltaic grid-connected power generation system; the control system includes a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger; the photovoltaic grid-connected power generation system includes a photovoltaic panel, an inverter, and a power grid; the inverter includes a plurality of switch tubes and a plurality of inductors; the method includes:

[0007] The trigger generates a first output signal based on the high-level clock signal currently received by the set input terminal, wherein the output terminal of the trigger is at a high level and the reverse output terminal is at a low level in the first output signal;

[0008] The first selection switch determines the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal;

[0009] The maximum power point tracking unit determines the reference operating voltage of the photovoltaic panel at the maximum power point;

[0010] The calculation unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage;

[0011] The proportional-integral controller processes the first voltage to obtain a first current;

[0012] The coordinate transformation unit performs coordinate transformation on the first current and the preset second current to obtain a grid-connected current reference value;

[0013] The second selection switch tube determines the inductor current based on the voltage of the power grid in the stage of the current cycle, wherein the inductor current is one of multiple currents corresponding to multiple inductors;

[0014] The first multiplier performs product processing on the DC voltage output by the photovoltaic panel and the inductor current and then inputs the product into the integrator; the second multiplier performs product processing on the grid-connected current reference value and the voltage of the grid;

[0015] The comparator compares the output of the second multiplier and the output of the integrator, and generates a high level input signal for the reset input terminal of the trigger when the output of the integrator is greater than or equal to the output of the second multiplier;

[0016] The trigger generates a second output signal based on a high level input signal at a reset input terminal, wherein the inverting output terminal of the trigger is at a high level and the output terminal is at a low level in the second output signal;

[0017] The first selection switch determines the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

[0018] In a second aspect, the present application provides a control system for a photovoltaic grid-connected power generation system, the control system comprising a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger;

[0019] A trigger, for generating a first output signal based on a high-level clock signal currently received at a set input terminal, wherein the output terminal of the trigger is at a high level and the reverse output terminal is at a low level in the first output signal;

[0020] A first selection switch, used to determine a first control signal corresponding to each of a plurality of switch tubes at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, wherein the plurality of switch tubes are a plurality of switch tubes in an inverter in a photovoltaic power generation system;

[0021] A maximum power point tracking unit is used to determine the reference working voltage of the photovoltaic panel in the photovoltaic power generation system at the maximum power point; a calculation unit is used to calculate the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage; a proportional integral controller is used to process the first voltage to obtain a first current; a coordinate transformation unit is used to perform coordinate transformation on the first current and a preset second current to obtain a grid-connected current reference value;

[0022] A second selection switch tube is used to determine the inductor current based on the voltage of the power grid in the photovoltaic power generation system at the stage of the current cycle, wherein the inductor current is one of multiple currents corresponding to multiple inductors in the inverter;

[0023] The first multiplier is used to multiply the DC voltage output by the photovoltaic panel and the inductor current and then input the product into the integrator; the second multiplier is used to multiply the grid-connected current reference value and the voltage of the grid;

[0024] a comparator, used for comparing the output of the second multiplier and the output of the integrator, and generating a high level input signal for a reset input terminal of the trigger when the output of the integrator is greater than or equal to the output of the second multiplier;

[0025] The trigger is further used to generate a second output signal based on a high level input signal at the reset input terminal, wherein the inverting output terminal of the trigger is at a high level and the output terminal is at a low level in the second output signal;

[0026] The first selection switch is also used to determine the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

[0027] In a third aspect, the present application provides a photovoltaic power generation system; the photovoltaic power generation system includes a photovoltaic panel, a capacitor, an inverter, a filter, and a power grid; the inverter includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a first inductor, a second inductor, a first device, and a second device;

[0028] Two ends of the capacitor are connected to two ends of the photovoltaic panel; the other end of the first switch tube, the other end of the fourth switch tube, one end of the third switch tube, and one end of the sixth switch tube are all connected to one end of the capacitor; one end of the fifth switch tube and one end of the second switch tube are all connected to the other end of the capacitor;

[0029] One end of the second device is connected to the other end of the second inductor and the other end of the fifth switch tube, and the other end of the second device and the other end of the third switch tube are both connected to one end of the filter; one end of the first device is connected to the other end of the second switch tube and the other end of the first inductor, and the other end of the first device and the other end of the sixth switch tube are both connected to the other end of the filter; both ends of the filter are connected to the power grid.

[0030] Implementing this application has the following beneficial effects:

[0031] The control method and control system of the photovoltaic grid-connected power generation system provided by the present application include a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger; the photovoltaic grid-connected power generation system includes a photovoltaic panel, an inverter, and a power grid; the inverter includes a plurality of switch tubes and a plurality of inductors; a high-level clock signal can be sent to the set input terminal of the trigger at a preset frequency, and then the trigger generates a first output signal based on the high-level clock signal currently received at the set input terminal, wherein the first output signal The output end of the trigger is high level and the reverse output end is low level; then the first selection switch determines the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, and accordingly, each switch tube can be turned on or off based on the corresponding first control signal; and the maximum power point tracking unit determines the reference working voltage of the photovoltaic panel at the maximum power point; the operation unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain the first voltage; the proportional integral controller processes the first voltage to obtain the first current; the coordinate transformation unit processes the first current and the preset second current The coordinate transformation of the current is performed to obtain the grid-connected current reference value; the second selection switch tube determines the inductor current based on the voltage of the grid at the stage of the current cycle, wherein the inductor current is one of the multiple currents corresponding to the multiple inductors; then the first multiplier performs product processing on the DC voltage output by the photovoltaic panel and the inductor current and then inputs them into the integrator; the second multiplier performs product processing on the grid-connected current reference value and the voltage of the grid; then the comparator compares the output of the second multiplier and the output of the integrator, and when the output of the integrator is greater than or equal to the output of the second multiplier, a high-level input signal of the reset input terminal of the trigger is generated; then the trigger is based on the reset input terminal A high-level input signal generates a second output signal, wherein the reverse output end of the trigger in the second output signal is high and the output end is low; then the first selection switch determines the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal. Accordingly, each switch tube is turned on or off based on the corresponding second control signal. In the photovoltaic grid-connected power generation system, the direct current output of the photovoltaic panel needs to be converted into alternating current and fed to the power grid. Since the output direct current will have low-frequency pulsation, if it is not filtered out, the waveform of the final output alternating current will be distorted.

[0032] That is to say, through the above control method, with a single cycle as the granularity, the voltage of the power grid is used in the current cycle stage, such as the positive half-cycle stage or the negative half-cycle stage, and the clock signal received, firstly controls the conduction or closing of each switch tube in the inverter, and through the maximum power point tracking unit, adjusts the working point in real time according to the output voltage and current of the photovoltaic panel to ensure that the photovoltaic system always operates at the maximum power point, and can avoid working in the nonlinear region, which helps to reduce low-order harmonics; then the proportional-integral controller processes the voltage error, that is, the first voltage, and generates a corresponding current. Such a feedback mechanism ensures that the current waveform is smoother and reduces the generation of harmonics, and then the coordinate transformation unit converts the first current and the preset first current into a proportional-integral controller. The coordinate transformation of the two currents is carried out to avoid the generation of low-order harmonics caused by phase mismatch; then the trigger and comparator can be adjusted in real time according to the change of grid voltage or the output current. Under the action of the comparator, when the system finds that the current or voltage waveform in a certain state does not meet the expectations, if the output value of the integrator is greater than or equal to the output of the second multiplier (usually related to the grid voltage), a reset signal will be issued, and the trigger will adjust its output according to this signal, which helps to smooth the response of the system and can adjust the output of the inverter in real time, so that the photovoltaic current waveform is as close to the ideal sine wave as possible, suppressing low-order harmonics, thereby improving the quality of the grid-connected current and avoiding the impact of harmonics on the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A schematic diagram of a photovoltaic grid-connected power generation system provided in an embodiment of the present application;

[0035] Figure 2 A schematic diagram of a control system of a photovoltaic grid-connected power generation system provided in an embodiment of the present application;

[0036] Figure 3 A control schematic diagram of a photovoltaic grid-connected power generation system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] The terms "first", "second", "third" and "fourth" etc. in the specification, claims and drawings of the present application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0039] Reference to "embodiments" herein means that a particular feature, result, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0040] First, the relevant terms involved in this application are explained:

[0041] Maximum power point tracking (MPPT): It is a technology commonly used in wind turbines and photovoltaic solar systems. Its purpose is to obtain maximum power output under various circumstances.

[0042] Proportional-integral controller (PI): It uses proportional and integral regulation to achieve precise control of system output. Its principle can be roughly divided into (1) input signal processing: the PI regulator receives the actual value measured by the sensor and compares it with the set value to obtain a deviation signal; (2) proportional regulation: multiply the deviation signal by the proportional coefficient to obtain a proportional control signal; (3) integral regulation: integrate the deviation signal to obtain an integral control signal; (4) control signal synthesis: add the proportional control signal and the integral control signal to obtain the final control signal; (5) output signal processing: after appropriate conversion and amplification, the control signal is output to the actuator to achieve system control.

[0043] Trigger: This application mainly refers to the RS trigger， It includes the set input terminal (denoted as S), the reset input terminal (denoted as R), the output terminal (denoted as Q), the reverse output terminal (denoted as ).

[0044] First, the present application does not limit the types of the switch tube, the first device, and the second device. The embodiments of the present application are mainly explained by taking the switch tube as a triode and the first device and the second device as diodes as examples.

[0045] The photovoltaic grid-connected power generation system and the control system of the photovoltaic grid-connected power generation system of the present application will be described below with reference to the accompanying drawings.

[0046] See also Figure 1 , Figure 1 A schematic diagram of a photovoltaic grid-connected power generation system provided in an embodiment of the present application.

[0047] like Figure 1 The photovoltaic grid-connected power generation system shown includes a photovoltaic panel (denoted as PV), a capacitor (denoted as C), an inverter, a filter, and a power grid. The inverter includes a plurality of switch tubes, a plurality of inductors, a first device (corresponding to Figure 1 The diode D1 in the second device (corresponding to Figure 1 The plurality of switch tubes include a first switch tube (corresponding to Figure 1 The transistor Q1 in the second switch tube (corresponding to Figure 1 The transistor Q2 in the middle), the third switch tube (corresponding to Figure 1 The transistor Q3 in the fourth switch tube (corresponding to Figure 1 The transistor Q4 in the middle), the fifth switch tube (corresponding to Figure 1 The transistor Q5 in the middle), the sixth switch tube (corresponding to Figure 1 The transistor Q6 in the embodiment); the plurality of inductors include a first inductor (corresponding to Figure 1 L1 in), the second inductor (corresponding to Figure 1 in L2).

[0048] Both ends of the capacitor C are connected to a photovoltaic panel (denoted as PV); one end of the first switch tube is connected to one end of the first inductor, and one end of the fourth switch tube is connected to one end of the second inductor; the other end of the first switch tube, the other end of the fourth switch tube, one end of the third switch tube, and one end of the sixth switch tube are all connected to one end of the capacitor; one end of the fifth switch tube and one end of the second switch tube are both connected to the other end of the capacitor; one end of the second device is connected to the other end of the second inductor and the other end of the fifth switch tube, and the other end of the second device and the other end of the third switch tube are both connected to one end of the filter; one end of the first device is connected to the other end of the second switch tube and the other end of the first inductor, and the other end of the first device and the other end of the sixth switch tube are both connected to the other end of the filter; both ends of the filter are connected to the power grid.

[0049] See also Figure 2 , Figure 2 A schematic diagram of a control system of a photovoltaic grid-connected power generation system provided in an embodiment of the present application.

[0050] Figure 2 The control system of the photovoltaic grid-connected power generation system shown includes a maximum power point tracking unit (denoted as MPPT), an operation unit, a proportional integral controller (denoted as PI), a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger.

[0051] The first selection switch includes a plurality of output terminals corresponding to the plurality of switch tubes, each output terminal is used to connect to each corresponding switch tube; the output terminal (i.e., Q terminal) and the reverse output terminal ( The reset input terminal (R terminal) of the trigger is connected to the output terminal of the comparator; the set input terminal (S terminal) of the trigger is used to receive a clock signal, such as from an external clock circuit, etc. The present application does not limit the source of the clock signal; the first input terminal of the comparator (i.e., corresponding to Figure 2 The “-” terminal of the comparator in the middle) is connected to the output terminal of the second multiplier; the second input terminal of the comparator (i.e., corresponding to Figure 2 The "+" end of the comparator in the middle) is connected to the output end of the integrator; the input end of the integrator is connected to the output end of the first multiplier; the inverting output end of the trigger is also connected to the integrator; the input end of the first multiplier is connected to the second selection switch.

[0052] A trigger is used to generate a first output signal based on a high-level clock signal currently received at a set input terminal, wherein the output terminal of the trigger is high level and the reverse output terminal is low level in the first output signal; a first selection switch is used to determine a first control signal corresponding to each of a plurality of switch tubes at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, wherein the plurality of switch tubes are a plurality of switch tubes in an inverter in a photovoltaic power generation system.

[0053] The maximum power point tracking unit is used to receive the voltage and current of the photovoltaic panel and determine the reference working voltage of the photovoltaic panel when it is at the maximum power point; then the calculation unit is used to calculate the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage; then the proportional integral controller is used to process the first voltage to obtain a first current; then the coordinate transformation unit is used to perform coordinate transformation on the first current and a preset second current to obtain a grid-connected current reference value.

[0054] The second selection switch is used to receive the current of the first inductor or the current of the second inductor in the photovoltaic grid-connected power generation system based on the voltage of the power grid in the photovoltaic power generation system at the stage of the current cycle, and determine it as the inductor current, wherein the inductor current is one of multiple currents corresponding to multiple inductors in the inverter; then the first multiplier is used to multiply the DC voltage output by the photovoltaic panel and the inductor current and then input them into the integrator.

[0055] And a second multiplier is used to receive the voltage of the power grid and the grid-connected current reference value, and multiply the grid-connected current reference value and the voltage of the power grid; then the comparator is used to compare the output of the second multiplier and the output of the integrator, and when the output of the integrator is greater than or equal to the output of the second multiplier, a high-level input signal is generated for the reset input terminal of the trigger.

[0056] The trigger is also used to generate a second output signal based on a high-level input signal at the reset input terminal, wherein the reverse output terminal of the trigger is at a high level and the output terminal is at a low level in the second output signal; then the first selection switch is also used to determine the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

[0057] In an optional embodiment, the plurality of switch tubes include a first switch tube group and a second switch tube group; the first switch tube group includes a first switch tube, a second switch tube, and a third switch tube; the second switch tube includes a fourth switch tube, a fifth switch tube, and a sixth switch tube; in terms of determining the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, when the voltage of the power grid is at the positive half cycle stage of the current cycle, the first selection switch is further used to determine, based on the first output signal, that the first control signal corresponding to the first switch tube and the second switch tube is a conduction signal, and is further used to determine that the first control signal corresponding to the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube is a shutdown signal. When the voltage of the power grid is at the negative half cycle stage of the current cycle, the first selection switch is further used to determine, based on the first output signal, that the first control signal corresponding to the fourth switch tube and the fifth switch tube is a conduction signal, and is further used to determine that the first control signal corresponding to the first switch tube, the second switch tube, the third switch tube, and the sixth switch tube is a shutdown signal.

[0058] In an optional embodiment, the multiple inductors include a first inductor and a second inductor; one end of the first switching tube is connected to one end of the first inductor, and one end of the fourth switching tube is connected to one end of the second inductor; when the voltage of the power grid is in the positive half-cycle stage of the current cycle, the inductor current is the current corresponding to the first inductor; when the voltage of the power grid is in the negative half-cycle stage of the current cycle, the inductor current is the current corresponding to the second inductor.

[0059] In an optional embodiment, in terms of determining the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal, when the voltage of the power grid is at the positive half cycle stage of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the first switch tube and the third switch tube are on signals, and determines that the second control signals corresponding to the second switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are off signals;

[0060] When the voltage of the power grid is in the negative half cycle of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the fourth switch tube and the sixth switch tube are on signals, and determines that the second control signals corresponding to the first switch tube, the second switch tube, the third switch tube, and the fifth switch tube are off signals.

[0061] In an optional embodiment, after generating the second output signal, the integrator is also used to receive notification information for the second output signal from the reverse output terminal of the trigger, and then the integrator is also used to clear the current integration result, so that when the set input terminal of the trigger receives a high-level clock signal again, the integrator starts integrating again to obtain the second control signal corresponding to each switch tube again.

[0062] It should be noted that Figure 2 The steps and principles executed by each structure in the control system shown are not limited to the above embodiments, and can also refer to the corresponding description of the method embodiment below, which will not be elaborated in detail here.

[0063] For ease of understanding, the following Figure 1 and Figure 2 For an example, see Figure 3 , Figure 3 A control schematic diagram of a photovoltaic grid-connected power generation system provided in an embodiment of the present application, and combined with Figure 3 The control method of the photovoltaic grid-connected power generation system of the present application is described in the embodiment. The control method is applied to the control system of the photovoltaic grid-connected power generation system in the above embodiment, which will not be described in detail here. The control method specifically includes but is not limited to steps S11-S22:

[0064] S11. The trigger generates a first output signal based on a high-level clock signal currently received at the set input terminal.

[0065] In an embodiment of the present application, the sending frequency of the clock signal can be set in advance; at the beginning, when the S end of the trigger receives the clock signal (generally a high level), the circuit in the photovoltaic grid-connected power generation system starts to operate and a cycle begins. At this time, the trigger generates a first output signal based on the currently received high-level clock signal, wherein the output end of the trigger in the first output signal is a high level and the reverse output end is a low level.

[0066] S12. The first selection switch determines a first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal.

[0067] Among them, the multiple switch tubes include a first switch tube group and a second switch tube group; the first switch tube group includes a first switch tube, a second switch tube, and a third switch tube; the second switch tube includes a fourth switch tube, a fifth switch tube, and a sixth switch tube. It should be noted that the cycle of the present application is similar to the transformation of a sine curve. In each cycle, a value greater than zero indicates the positive half-cycle stage of the cycle, and a value less than zero indicates the negative half-cycle stage of the cycle. Exemplary:

[0068] When the voltage of the power grid is in the positive half-cycle phase of the current cycle, the first selection switch determines, based on the first output signal, that the first control signals corresponding to the first switch tube and the second switch tube are on signals, and determines that the first control signals corresponding to the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are off signals, that is, at this time Q1 and Q2 are turned on, and Q3, Q4, Q5, and Q6 are turned off.

[0069] When the voltage of the power grid is in the negative half-cycle phase of the current cycle, the first selection switch determines, based on the first output signal, that the first control signals corresponding to the fourth switch tube and the fifth switch tube are on signals, and determines that the first control signals corresponding to the first switch tube, the second switch tube, the third switch tube, and the sixth switch tube are off signals, that is, at this time Q4 and Q5 are turned on, and Q1, Q2, Q3, and Q6 are turned off.

[0070] S13. The maximum power point tracking unit determines a reference operating voltage of the photovoltaic panel at the maximum power point.

[0071] S14, the calculation unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage.

[0072] S15. The proportional-integral controller processes the first voltage to obtain a first current.

[0073] S16. The coordinate transformation unit performs coordinate transformation on the first current and the preset second current to obtain a grid-connected current reference value.

[0074] At the same time, the maximum power point tracking unit receives the voltage u of the photovoltaic panel from the photovoltaic panel. PV and current i PV , and based on the voltage u PV and current i PV , determine the reference operating voltage u of the photovoltaic panel at the maximum power point dcref ; Then the calculation unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage; then the proportional integral controller processes the first voltage to obtain a first current i dref Then the coordinate transformation unit transforms the first current and the preset second current i qref Perform coordinate transformation to obtain the grid-connected current reference value i ref .

[0075] S17, the second selection switch tube determines the inductor current based on the voltage of the power grid in the stage of the current cycle.

[0076] At the same time, the second selection switch tube determines the inductor current i based on the grid voltage in the current cycle phase. L , where the inductor current is one of the multiple currents corresponding to the multiple inductors, that is, the inductor current is i L1 、i L2 one of the first switch tubes; one end of the first inductor is connected to one end of the first switch tube, and one end of the fourth switch tube is connected to one end of the second inductor. When the voltage of the power grid is in the positive half cycle of the current cycle, the inductor current is the current corresponding to the first inductor; when the voltage of the power grid is in the negative half cycle of the current cycle, the inductor current is the current corresponding to the second inductor; since Q1 and Q2 are turned on and Q3, Q4, Q5, and Q6 are turned off at this time, that is, the voltage of the power grid is in the positive half cycle of the current cycle, the inductor current i L Just for i L1 .

[0077] S18, the first multiplier performs product processing on the DC voltage output by the photovoltaic panel and the inductor current, and then inputs the product into the integrator.

[0078] S19. The second multiplier performs product processing on the grid-connected current reference value and the voltage of the grid.

[0079] The first multiplier outputs a DC voltage u dc , inductor current i L After the product is processed, it is input into the integrator; and the second multiplier is used to calculate the grid-connected current reference value i ref , the voltage of the power grid u grid Perform product processing.

[0080] S20, the comparator compares the output of the second multiplier and the output of the integrator, and when the output of the integrator is greater than or equal to the output of the second multiplier, generates a high level input signal for the reset input terminal of the trigger.

[0081] The comparator compares the output of the second multiplier and the output of the integrator to obtain the input signal of the reset input terminal of the trigger, wherein when the output of the integrator is greater than or equal to the output of the second multiplier, the input signal of the reset input terminal is a high-level input signal, and when the output of the integrator is less than the output of the second multiplier, the input signal of the reset input terminal is a low-level input signal. The control equation in the control system satisfies Formula 1:

[0082]

[0083] Among them, u grid is the voltage of the grid; i ref is the grid-connected current reference value; u dc is the DC side voltage output by the photovoltaic panel; i L is the inductor current. When it is the positive half cycle, i L for i L1 ; When it is the negative half cycle phase, i L for i L1 ; T is the switching period.

[0084] S21. The trigger generates a second output signal based on a high level input signal at the reset input terminal.

[0085] When the output of the integrator is greater than or equal to the output of the second multiplier, the trigger generates a second output signal based on the high level input signal at the reset input terminal, wherein the inverting output terminal of the trigger is high level and the output terminal is low level in the second output signal.

[0086] S22. The first selection switch determines a second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

[0087] Exemplarily, when the voltage of the power grid is in the positive half-cycle phase of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the first switch tube and the third switch tube are on signals, and determines that the second control signals corresponding to the second switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are off signals. That is, at this time, the on and off conditions of the switch tubes are switched from Q1 and Q2 being on, Q3, Q4, Q5, and Q6 being off, to Q1 and Q3 being on, and Q2, Q4, Q5, and Q6 being off.

[0088] When the voltage of the power grid is in the negative half-cycle phase of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the fourth switch tube and the sixth switch tube are on signals, and determines that the second control signals corresponding to the first switch tube, the second switch tube, the third switch tube, and the fifth switch tube are off signals. That is, at this time, the on and off conditions of the switch tubes are switched from Q4 and Q5 being on, Q1, Q2, Q3, and Q6 being off, to Q4 and Q6 being on, and Q1, Q2, Q5, and Q6 being off.

[0089] Of course, when the output of the integrator is less than the output of the second multiplier, the trigger generates a third output signal based on the low-level input signal at the reset input terminal, wherein the third output signal is consistent with the first output signal at this time, and the output terminal of the trigger is still high level and the reverse output terminal is low level. Then the first selection switch determines the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the third output signal. The principle is similar to the principle of the first selection switch determining the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, and will not be repeated here.

[0090] Of course, if the trigger generates a second output signal, the integrator can also receive notification information for the second output signal from the trigger, and then the integrator clears the current integration result so that when the set input of the trigger receives a high-level clock signal again, the integrator starts integrating again to obtain the second control signal corresponding to each switch tube again.

[0091] That is to say, when the set input terminal of the trigger receives a high-level clock signal at the beginning, a cycle starts, and if the cycle starts from the positive half cycle, that is, the voltage of the power grid is in the positive half cycle stage at this time, and the output terminal of the trigger outputs a high level and the reverse output terminal outputs a low level, then the control switch tubes Q1 and Q2 are turned on, and Q3, Q4, Q5, and Q6 are turned off. At the same time, the second selection switch determines that the inductor current is the current corresponding to L1, and then the second multiplier, the first multiplier, the integrator, the comparator, etc. perform the corresponding steps in accordance with the principles of the above embodiments in sequence; if the output of the integrator is greater than or equal to the output of the second multiplier, the trigger is reset, the output terminal of the trigger outputs a low level, and the reverse output terminal outputs a high level. Accordingly, the control switch tubes Q1 and Q3 are turned on, Q2, Q4, Q5, and Q6 are turned off, and the integrator clears the current integration result until if in this In the positive half-cycle stage of the cycle, the S end of the trigger receives a high-level clock signal again, and the above steps S11-S22 are repeated. That is to say, the output end of the trigger outputs a high level, and the reverse output end outputs a low level. Accordingly, the switch tubes Q1 and Q2 are controlled to be turned on, and Q3, Q4, Q5, and Q6 are turned off, and the second selection switch determines that the inductor current is the current corresponding to L2, and the subsequent steps are performed in sequence. If the output of the integrator is greater than or equal to the output of the second multiplier, the trigger is reset, the output end of the trigger outputs a low level, and the reverse output end outputs a high level. Accordingly, the switch tubes Q1 and Q3 are controlled to be turned on, and Q2, Q4, Q5, and Q6 are turned off, and the integrator clears the current integration result again, until the S end of the trigger receives a high-level clock signal again in the positive half-cycle stage of the cycle, and the above steps S11-S22 are repeated.

[0092] In short, since the clock signal is sent at a preset frequency, the S terminal of the trigger can receive multiple high-level clock signals in the positive half-cycle phase of a cycle. When the high-level clock signal is received for the first time, the switch tubes Q1 and Q2 are controlled to be turned on, and Q3, Q4, Q5, and Q6 are turned off. Then, the integrator continuously integrates based on the above principle until the output of the integrator is greater than or equal to the output of the second multiplier (it can also be understood that the left side of the above formula (1) is greater than or equal to the right side). The trigger is reset, and accordingly, the switch tubes Q1 and Q3 are controlled to be turned on. , Q2, Q4, Q5, and Q6 are turned off; then when receiving a high-level clock signal for the second time, the switch tubes Q1 and Q2 are turned on, and Q3, Q4, Q5, and Q6 are turned off, and then the integration is continued until the switch tubes Q1 and Q3 are turned on, and Q2, Q4, Q5, and Q6 are turned off. Similarly, when receiving a high-level clock signal for the third, fourth, ... Nth time in the positive half-cycle stage of a cycle, the principle is the same as above, and finally in the positive half-cycle stage of a cycle, Q4, Q5, and Q6 are always turned off, Q1 is always turned on, and Q2 and Q3 are turned on alternately.

[0093] Furthermore, similarly, when receiving from the positive half cycle of a cycle to the negative half cycle of a cycle, the S terminal of the trigger can still receive multiple high-level clock signals. When the high-level clock signal is received for the first time, the switch tubes Q4 and Q5 are controlled to be turned on, and Q1, Q2, Q3, and Q6 are turned off. Then, the integrator continuously integrates based on the above principle until the output of the integrator is greater than or equal to the output of the second multiplier (it can also be understood that the left side of the above formula (1) is greater than or equal to the right side), and the trigger is reset. Accordingly, the switch tubes Q4 and Q6 are controlled to be turned on. , Q1, Q2, Q3, and Q5 are turned off; then when receiving a high-level clock signal for the second time, the switch tubes Q4 and Q5 are turned on, and Q1, Q2, Q3, and Q6 are turned off, and then the integration is continued until the switch tubes Q4 and Q6 are turned on, and Q1, Q2, Q3, and Q5 are turned off. Similarly, when receiving a high-level clock signal for the third, fourth, and Nth time in the negative half-cycle stage of a cycle, the principle is the same as above, and finally in the negative half-cycle stage of a cycle, Q1, Q2, and Q3 are always turned off, Q4 is always turned on, and Q5 and Q6 are turned on alternately.

[0094] Furthermore, when entering the positive half cycle stage of the next cycle, the same logic is repeated here, and single-cycle control is achieved, which has a better effect on suppressing low-order harmonics.

[0095] The control method and control system of the photovoltaic grid-connected power generation system provided by the present application include a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger; the photovoltaic grid-connected power generation system includes a photovoltaic panel, an inverter, and a power grid; the inverter includes a plurality of switch tubes and a plurality of inductors; a high-level clock signal can be sent to the set input terminal of the trigger at a preset frequency, and then the trigger generates a first output signal based on the high-level clock signal currently received at the set input terminal, wherein the first output signal The output end of the trigger is high level and the reverse output end is low level; then the first selection switch determines the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, and accordingly, each switch tube can be turned on or off based on the corresponding first control signal; and the maximum power point tracking unit determines the reference working voltage of the photovoltaic panel at the maximum power point; the operation unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain the first voltage; the proportional integral controller processes the first voltage to obtain the first current; the coordinate transformation unit processes the first current and the preset second current The coordinate transformation of the current is performed to obtain the grid-connected current reference value; the second selection switch tube determines the inductor current based on the voltage of the grid at the stage of the current cycle, wherein the inductor current is one of the multiple currents corresponding to the multiple inductors; then the first multiplier performs product processing on the DC voltage output by the photovoltaic panel and the inductor current and then inputs them into the integrator; the second multiplier performs product processing on the grid-connected current reference value and the voltage of the grid; then the comparator compares the output of the second multiplier and the output of the integrator, and when the output of the integrator is greater than or equal to the output of the second multiplier, a high-level input signal of the reset input terminal of the trigger is generated; then the trigger is based on the reset input terminal A high-level input signal generates a second output signal, wherein the reverse output end of the trigger in the second output signal is high and the output end is low; then the first selection switch determines the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal. Accordingly, each switch tube is turned on or off based on the corresponding second control signal. In the photovoltaic grid-connected power generation system, the direct current output of the photovoltaic panel needs to be converted into alternating current and fed to the power grid. Since the output direct current will have low-frequency pulsation, if it is not filtered out, the waveform of the final output alternating current will be distorted.

[0096] It can be seen that through the above control method, with a single cycle as the granularity, the voltage of the power grid in the current cycle stage, such as the positive half-cycle stage or the negative half-cycle stage and the received clock signal, first control the conduction or shutdown of each switch tube in the inverter, and through the maximum power point tracking unit, adjust the working point in real time according to the output voltage and current of the photovoltaic panel to ensure that the photovoltaic system always operates at the maximum power point and can avoid working in the nonlinear region, which helps to reduce low-order harmonics; then the proportional-integral controller processes the voltage error, that is, the first voltage, and generates a corresponding current. Such a feedback mechanism ensures that the current waveform is smoother and reduces the generation of harmonics. Then the coordinate transformation unit transforms the first current and the preset second current to avoid the generation of phase mismatch. The trigger and comparator can then be adjusted in real time according to the change of grid voltage or the output current. Under the action of the comparator, when the system finds that the current or voltage waveform in a certain state does not meet expectations, if the output value of the integrator is greater than or equal to the output of the second multiplier (usually related to the grid voltage), a reset signal will be issued. The trigger adjusts its output according to this signal, and then allows each switch to be alternately turned on in the positive half-cycle or negative half-cycle of a single cycle, and adjusts the output of the inverter in real time to ensure that the left side of the above formula (1) is less than or equal to the right side, so that the photovoltaic current waveform is as close to the ideal sine wave as possible, suppressing low-order harmonics, thereby improving the quality of the grid-connected current and avoiding the impact of harmonics on the power system.

[0097] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described order of actions, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0098] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0099] In the several embodiments provided in the present application, it should be understood that the disclosed device can be implemented in other ways. For example, the device embodiments described above are only schematic, such as the division of units, which is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or units can be electrical or other forms.

[0100] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0101] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit may be implemented in the form of hardware or in the form of a software program module.

[0102] If the integrated unit is implemented in the form of a software program module and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of each embodiment method of the present application. The aforementioned memory includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, disk or optical disk and other media that can store program codes.

[0103] A person skilled in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable memory, and the memory can include: a flash drive, a read-only memory (English: Read-Only Memory, abbreviated as: ROM), a random access memory (English: Random Access Memory, abbreviated as: RAM), a magnetic disk or an optical disk, etc.

[0104] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A control method for a photovoltaic grid-connected power generation system, characterized in that: A control system applied to a photovoltaic grid-connected power generation system; the control system comprises a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger; The photovoltaic grid-connected power generation system includes a photovoltaic panel, an inverter, and a power grid; the inverter includes a plurality of switch tubes and a plurality of inductors; the method includes: The trigger generates a first output signal based on a high-level clock signal currently received at the set input terminal, wherein the output terminal of the trigger is at a high level and the reverse output terminal is at a low level in the first output signal; The first selection switch determines a first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal; The maximum power point tracking unit determines a reference operating voltage of the photovoltaic panel at the maximum power point; The computing unit calculates the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage; The proportional-integral controller processes the first voltage to obtain a first current; The coordinate transformation unit performs coordinate transformation on the first current and the preset second current to obtain a grid-connected current reference value; The second selection switch tube determines the inductor current based on the stage of the voltage of the power grid in the current cycle, wherein the inductor current is one of the multiple currents corresponding to the multiple inductors; The first multiplier performs product processing on the DC voltage output by the photovoltaic panel and the inductor current and then inputs the product into the integrator; The second multiplier performs product processing on the grid-connected current reference value and the voltage of the grid; The comparator compares the output of the second multiplier and the output of the integrator, and generates a high level input signal for the reset input terminal of the trigger when the output of the integrator is greater than or equal to the output of the second multiplier; The trigger generates a second output signal based on the high level input signal of the reset input terminal, wherein the inverting output terminal of the trigger is at a high level and the output terminal is at a low level in the second output signal; The first selection switch determines a second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

2. The method according to claim 1, characterized in that The plurality of switch tubes include a first switch tube group and a second switch tube group; the first switch tube group includes a first switch tube, a second switch tube, and a third switch tube; the second switch tube includes a fourth switch tube, a fifth switch tube, and a sixth switch tube; The first selection switch determines a first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, including: When the voltage of the power grid is in the positive half cycle of the current cycle, the first selection switch determines, based on the first output signal, that the first control signals corresponding to the first switch tube and the second switch tube are on signals, and determines that the first control signals corresponding to the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are off signals; When the voltage of the power grid is in the negative half cycle of the current cycle, the first selection switch determines, based on the first output signal, that the first control signals corresponding to the fourth switch tube and the fifth switch tube are on signals, and determines that the first control signals corresponding to the first switch tube, the second switch tube, the third switch tube, and the sixth switch tube are off signals.

3. The method according to claim 2, characterized in that The multiple inductors include a first inductor and a second inductor; one end of the first switch tube is connected to one end of the first inductor, and one end of the fourth switch tube is connected to one end of the second inductor; When the voltage of the power grid is in the positive half cycle phase of the current cycle, the inductor current is the current corresponding to the first inductor; When the voltage of the power grid is in the negative half cycle stage of the current cycle, the inductor current is the current corresponding to the second inductor.

4. The method according to claim 2 or 3, characterized in that: The first selection switch determines the second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal, including: When the voltage of the power grid is in the positive half cycle of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the first switch tube and the third switch tube are on signals, and determines that the second control signals corresponding to the second switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are off signals; When the voltage of the power grid is in the negative half cycle of the current cycle, the first selection switch determines, based on the second output signal, that the second control signals corresponding to the fourth switch tube and the sixth switch tube are on signals, and determines that the second control signals corresponding to the first switch tube, the second switch tube, the third switch tube, and the fifth switch tube are off signals.

5. The method according to any one of claims 1 to 3, characterized in that: After generating the second output signal, the method further comprises: The integrator clears the current integration result, so that when the set input terminal of the trigger receives a high-level clock signal again, the integrator starts integrating again to obtain the second control signal corresponding to each switch tube again.

6. The method according to claim 2 or 3, characterized in that: The photovoltaic grid-connected power generation system further includes a capacitor and a filter; the inverter further includes a first device and a second device; the two ends of the capacitor are connected to the two ends of the photovoltaic panel; the other end of the first switch tube, the other end of the fourth switch tube, one end of the third switch tube, and one end of the sixth switch tube are all connected to one end of the capacitor; one end of the fifth switch tube and one end of the second switch tube are all connected to the other end of the capacitor; One end of the second device is connected to the other end of the second inductor and the other end of the fifth switch tube, and the other end of the second device and the other end of the third switch tube are both connected to one end of the filter; one end of the first device is connected to the other end of the second switch tube and the other end of the first inductor, and the other end of the first device and the other end of the sixth switch tube are both connected to the other end of the filter; and both ends of the filter are connected to the power grid.

7. The method according to any one of claims 1 to 3, characterized in that: The first selection switch comprises a plurality of output terminals corresponding to the plurality of switch tubes, each output terminal being connected to each corresponding switch tube; The output terminal and the reverse output terminal of the trigger are both connected to the input terminal of the first selection switch; the reset input terminal of the trigger is connected to the output terminal of the comparator; The first input terminal of the comparator is connected to the output terminal of the second multiplier; the second input terminal of the comparator is connected to the output terminal of the integrator; the input terminal of the integrator is connected to the output terminal of the first multiplier; An input terminal of the first multiplier is connected to the second selection switch.

8. A control system for a photovoltaic grid-connected power generation system, characterized in that: The control system includes a maximum power point tracking unit, an operation unit, a proportional integral controller, a coordinate transformation unit, a first selection switch, a second selection switch, a first multiplier, a second multiplier, an integrator, a comparator, and a trigger; The trigger is used to generate a first output signal based on a high-level clock signal currently received by the set input terminal, wherein the output terminal of the trigger is at a high level and the reverse output terminal is at a low level in the first output signal; The first selection switch is used to determine a first control signal corresponding to each of a plurality of switch tubes at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, wherein the plurality of switch tubes are a plurality of switch tubes in an inverter of a photovoltaic power generation system; The maximum power point tracking unit is used to determine the reference operating voltage of the photovoltaic panel in the photovoltaic power generation system at the maximum power point; The computing unit is used to calculate the difference between the reference working voltage and the DC voltage output by the photovoltaic panel to obtain a first voltage; The proportional-integral controller is used to process the first voltage to obtain the first current; The coordinate transformation unit is used to perform coordinate transformation on the first current and the preset second current to obtain a grid-connected current reference value; The second selection switch tube is used to determine the inductor current based on the voltage of the power grid in the photovoltaic power generation system at the stage of the current cycle, wherein the inductor current is one of multiple currents corresponding to multiple inductors in the inverter; The first multiplier is used to perform product processing on the DC voltage output by the photovoltaic panel and the inductor current and then input the product into the integrator; The second multiplier is used to perform product processing on the grid-connected current reference value and the voltage of the grid; The comparator is used to compare the output of the second multiplier and the output of the integrator, and when the output of the integrator is greater than or equal to the output of the second multiplier, generate a high level input signal for the reset input terminal of the trigger; The trigger is further used to generate a second output signal based on the high level input signal of the reset input terminal, wherein the inverting output terminal of the trigger is at a high level and the output terminal is at a low level in the second output signal; The first selection switch is further used to determine a second control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the second output signal.

9. The control system according to claim 8, characterized in that: The plurality of switch tubes include a first switch tube group and a second switch tube group; the first switch tube group includes a first switch tube, a second switch tube, and a third switch tube; the second switch tube includes a fourth switch tube, a fifth switch tube, and a sixth switch tube; In terms of the first selection switch determining the first control signal corresponding to each switch tube at the stage of the current cycle based on the voltage of the power grid at the stage of the current cycle and the first output signal, When the voltage of the power grid is in the positive half cycle of the current cycle, the first selection switch is further used to determine, based on the first output signal, that the first control signal corresponding to the first switch tube and the second switch tube is a conduction signal, and is also used to determine that the first control signal corresponding to the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube is a shutdown signal; When the voltage of the power grid is in the negative half cycle of the current cycle, the first selection switch is also used to determine, based on the first output signal, that the first control signal corresponding to the fourth switch tube and the fifth switch tube is a conduction signal, and is also used to determine that the first control signal corresponding to the first switch tube, the second switch tube, the third switch tube, and the sixth switch tube is a shutdown signal.

10. The control system according to claim 8 or 9, characterized in that: After generating the second output signal, the integrator is also used to clear the current integration result, so that when the set input of the trigger receives a high-level clock signal again, the integrator starts integrating again to obtain the second control signal corresponding to each switch tube again.

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