Control method of photovoltaic grid-connected inverter and photovoltaic grid-connected inverter

Abstract

The present application discloses a control method of a photovoltaic grid-connected inverter and a photovoltaic grid-connected inverter, and relates to the technical field of photovoltaic grid-connected inverters. The control method comprises: determining an AC output peak power reference value of a photovoltaic panel based on the output voltage of the photovoltaic panel and the output current of the photovoltaic panel. Determining the instantaneous phase of the grid based on the voltage of the grid. Determining the instantaneous value of the AC output power of a flyback switch conversion circuit based on the AC output peak power reference value and the instantaneous phase of the grid. Determining the switching cycle and conduction time of the flyback switch when the flyback switch conversion circuit operates in a discontinuous conduction mode based on the AC output power instantaneous value, and controlling the operation of the flyback switch based on the switching cycle and the conduction time. Controlling the operation of the H-bridge circuit based on the instantaneous phase of the grid so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the grid. The present application aims to reduce the circuit cost of a photovoltaic grid-connected inverter and reduce the operating loss of the circuit.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic grid-connected inverters, and in particular to a control method of a photovoltaic grid-connected inverter and a photovoltaic grid-connected inverter. Background Art

[0002] Photovoltaic grid-connected inverter is the core component of photovoltaic power generation system. Its main function is to convert the direct current generated by photovoltaic panels into alternating current compatible with the power grid and feed it into the public power grid safely and reliably. It not only undertakes the task of power conversion, but also ensures the stable operation of the system and optimizes energy output.

[0003] The photovoltaic grid-connected inverters commonly used in the market currently usually adopt a two-stage control system: the front-stage flyback switching power supply boost control system uses a flyback switching power supply to boost the low voltage of the photovoltaic panel to a DC high voltage, and the rear-stage AC inverter control system converts DC power into AC power and feeds it into the grid through an H-bridge inverter circuit. However, this two-stage control system has the disadvantages of more control loops, complex circuit structure, and low power generation efficiency. Summary of the invention

[0004] The main purpose of this application is to provide a control method for a photovoltaic grid-connected inverter, aiming to solve the problems of multiple control loops, complex circuit structure and low power generation efficiency when the existing photovoltaic grid-connected inverter is connected to the photovoltaic grid through a two-level control system.

[0005] To achieve the above-mentioned purpose, the control method of the photovoltaic grid-connected inverter proposed in the present application is applied to a photovoltaic power generation system, wherein the photovoltaic power generation system includes a photovoltaic panel and a power grid, the photovoltaic grid-connected inverter includes a flyback switch conversion circuit and an H-bridge circuit, the flyback switch conversion circuit includes a transformer and a flyback switch, the first end of the primary coil of the transformer is connected to the output end of the photovoltaic panel; the first end of the flyback switch is connected to the second end of the primary coil of the transformer, and the second end of the flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; the steps of the control method include: S1. determining an AC output peak power reference value of the photovoltaic panel based on the output voltage and the output current of the photovoltaic panel; S2. determining an instantaneous phase of the power grid based on the voltage of the power grid; S3, determining the instantaneous value of the AC output power of the flyback switch conversion circuit based on the AC output peak power reference value and the instantaneous phase of the power grid; S4, determining the switching cycle and on-time of the flyback switch when the flyback switch conversion circuit operates in a discontinuous conduction mode based on the instantaneous value of the AC output power, and controlling the operation of the flyback switch based on the switching cycle and the on-time; S5. Based on the instantaneous phase of the power grid, control the operation of the H-bridge circuit so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid.

[0006] In one embodiment, the step of determining that the flyback switch conversion circuit operates in a discontinuous conduction mode based on the instantaneous value of the AC output power, and the switching period and conduction time of the flyback switch comprises: Determine, based on the instantaneous value of the AC output power, the parameters of the transformer, the parameters of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid, the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode; Determining a switching period of the flyback switch based on a peak current value of the primary coil of the transformer, parameters of the transformer and an instantaneous value of the AC output power; The conduction time of the flyback switch is determined based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel.

[0007] In one embodiment, the parameters of the transformer include the inductance of the primary coil of the transformer and the ratio of the number of turns of the primary coil of the transformer to the number of turns of the secondary coil; the flyback switch is a MOS tube, and the parameters of the flyback switch include the equivalent output junction capacitance of the MOS tube; the step of determining the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode based on the instantaneous value of the AC output power, the parameters of the transformer, the parameters of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid comprises: Based on the instantaneous value of the AC output power, the inductance of the primary coil of the transformer, the ratio of the number of turns of the primary coil of the transformer to the number of turns of the secondary coil, the equivalent output junction capacitance of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid, a first calculation formula is introduced to determine the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode; The first calculation formula is:

[0008] in, The instantaneous value of the AC output power, The inductance value of the primary coil of the transformer, is the ratio of the number of turns of the primary coil to the number of turns of the secondary coil of the transformer, The peak current value of the primary coil of the transformer, is the equivalent output junction capacitance of the MOS tube, is the voltage of the grid, is the output voltage of the photovoltaic panel; The step of determining the switching period of the flyback switch based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the instantaneous value of the AC output power comprises: Based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the instantaneous value of the AC output power, a second calculation formula is introduced to determine the switching period of the MOS tube; The second calculation formula is:

[0009] in, The instantaneous value of the AC output power, The inductance value of the primary coil of the transformer, The peak current value of the primary coil of the transformer, The switching cycle of the MOS tube; The step of determining the on-time of the flyback switch based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel comprises: Based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel, a third calculation formula is introduced to determine the conduction time of the MOS tube; The third calculation formula is:

[0010] in, The conduction time of the MOS tube, The inductance value of the primary coil of the transformer, The peak current value of the primary coil of the transformer, is the output voltage of the photovoltaic panel.

[0011] In one embodiment, step S3 includes: Based on the AC output peak power reference value and the instantaneous phase of the power grid, a fourth calculation formula is introduced to determine the instantaneous value of the AC output power of the flyback switch conversion circuit; The fourth calculation formula is:

[0012] in, The instantaneous value of the AC output power, The AC output peak power reference value, The instantaneous phase of the grid, The conversion efficiency of the flyback switching conversion circuit.

[0013] In one embodiment, the step S1 comprises: Performing MPPT tracking based on the output voltage and output current of the photovoltaic panel to determine the output current setting value at the maximum power point of the photovoltaic panel; Determining a first current difference between the output current setting value and the output current of the photovoltaic panel based on the output current setting value and the output current of the photovoltaic panel; The first current difference is substituted into a PI controller for calculation to obtain an AC output peak power reference value of the photovoltaic panel.

[0014] In one embodiment, step S2 comprises: The voltage of the power grid is input into a phase-locked loop to obtain the instantaneous phase of the power grid.

[0015] In one embodiment, the H-bridge circuit includes a first IGBT tube, a second IGBT tube, a third IGBT tube and a fourth IGBT tube; the collector of the first IGBT tube and the collector of the second IGBT tube are connected to the first end of the secondary coil of the transformer; the emitter of the first IGBT tube and the collector of the third IGBT tube are connected to the first access point of the power grid; the emitter of the second IGBT tube and the collector of the fourth IGBT tube are connected to the second access point of the power grid; the emitter of the third IGBT tube and the emitter of the fourth IGBT tube are connected to the second end of the secondary coil of the transformer; the step S5 includes: A zero-crossing judgment is performed on the instantaneous phase of the power grid. If the voltage of the power grid is in a positive half cycle, the first IGBT tube and the fourth IGBT tube are controlled to be turned on, and the second IGBT tube and the third IGBT tube are controlled to be turned off. If the voltage of the power grid is in a negative half cycle, the second IGBT tube and the third IGBT tube are controlled to be turned on, and the first IGBT tube and the fourth IGBT tube are controlled to be turned off.

[0016] In one embodiment, the photovoltaic power generation system includes N photovoltaic panels, and the photovoltaic grid-connected inverter includes N flyback switch conversion circuits and H-bridge circuits; each flyback switch conversion circuit includes a transformer and a flyback switch; The first end of the primary coil of the Nth transformer is connected to the output end of the Nth photovoltaic panel; the first end of the Nth flyback switch is connected to the second end of the primary coil of the Nth transformer, and the second end of the Nth flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the Nth transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; The control method comprises: Determining an AC output peak power reference value of the Nth photovoltaic panel based on the output voltage of the Nth photovoltaic panel and the output current of the Nth photovoltaic panel; determining an instantaneous phase of the grid based on the voltage of the grid; Determining an instantaneous value of the AC output power of the Nth flyback switch conversion circuit based on the Nth AC output peak power reference value and the instantaneous phase of the power grid; Based on the instantaneous value of the Nth AC output power, determine the switching period and conduction time of the Nth flyback switch when the Nth flyback switch conversion circuit operates in a discontinuous conduction mode, and control the operation of the Nth flyback switch based on the Nth switching period and the Nth conduction time; Based on the instantaneous phase of the power grid, the operation of the H-bridge circuit is controlled so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the direction of the current of the power grid.

[0017] The present application also proposes a photovoltaic grid-connected inverter, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes a photovoltaic panel and a power grid. The photovoltaic grid-connected inverter includes a flyback switch conversion circuit and an H-bridge circuit. The flyback switch conversion circuit includes a transformer and a flyback switch. The first end of the primary coil of the transformer is connected to the output end of the photovoltaic panel; the first end of the flyback switch is connected to the second end of the primary coil of the transformer, and the second end of the flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; the photovoltaic grid-connected inverter also includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the control method of the photovoltaic grid-connected inverter as described above.

[0018] In one embodiment, the photovoltaic grid-connected inverter further includes an LCL filter, wherein two input ends of the LCL filter are respectively connected to two output ends of the H-bridge circuit, and two output ends of the LCL filter are respectively connected to two access points of the power grid.

[0019] The technical solution of the present application adopts a control method of a photovoltaic grid-connected inverter, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes a photovoltaic panel and a power grid, and the photovoltaic grid-connected inverter includes a flyback switch conversion circuit and an H-bridge circuit. The control method includes: step S1, based on the output voltage of the photovoltaic panel and the output current of the photovoltaic panel, determining the AC output peak power reference value of the photovoltaic panel. Step S2, based on the voltage of the power grid, determining the instantaneous phase of the power grid. Step S3, based on the AC output peak power reference value and the instantaneous phase of the power grid, determining the instantaneous value of the AC output power of the flyback switch conversion circuit. Step S4, based on the instantaneous value of the AC output power, determining the switching cycle and conduction time of the flyback switch when the flyback switch conversion circuit operates in a discontinuous conduction mode, and controlling the operation of the flyback switch based on the switching cycle and the conduction time. Step S5, based on the instantaneous phase of the power grid, controlling the operation of the H-bridge circuit so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid. In this way, the present application can directly convert the output voltage of the photovoltaic panel into an AC output through a flyback switch conversion circuit through a primary control, and the output closed-loop control can be achieved through a PI controller, thereby reducing the circuit cost. Moreover, the present application uses two voltage detection devices and one current detection device for sampling, and uses fewer detection devices, thereby reducing the circuit cost. At the same time, the H-bridge circuit of the present application is only used to control the direction of the output current, that is, the switch tube of the H-bridge circuit only needs to be used for low-frequency switching work following the voltage phase change of the power grid, and does not need to be used for high-frequency modulation, thereby eliminating the inverter switch loss, reducing the working loss of the switch, and improving the power generation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0021] Figure 1 A schematic diagram of the structure of an embodiment of a control method for a photovoltaic grid-connected inverter provided in the present application; Figure 2 An electronic circuit diagram of an embodiment of a photovoltaic grid-connected inverter provided in this application; Figure 3 A control logic diagram of an embodiment of a photovoltaic grid-connected inverter provided in this application; Figure 4 An electronic circuit diagram of another embodiment of the photovoltaic grid-connected inverter provided by the present application; Figure 5 A circuit diagram of an exemplary photovoltaic grid-connected inverter provided in this application; Figure 6 A control logic diagram of a boost control system of a front-stage flyback switching power supply of an exemplary photovoltaic grid-connected inverter provided in the present application; Figure 7 A control logic diagram of a rear-stage AC inverter control system of an exemplary photovoltaic grid-connected inverter provided in the present application; Figure 8 A schematic structural diagram of another embodiment of the photovoltaic grid-connected inverter provided in this application.

[0022] Description of Figure Numbers:

[0023] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0024] 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 only 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.

[0025] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0026] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0027] The common photovoltaic grid-connected inverters on the market usually adopt a two-stage control system: the front-stage flyback switching power supply boost control system uses a flyback switching power supply to boost the low voltage of the photovoltaic panel to a DC high voltage, and the rear-stage AC inverter control system converts DC power into AC power through an H-bridge inverter circuit and feeds it into the grid.

[0028] See also Figure 5 , Figure 6 and Figure 7 , Figure 5 A circuit diagram of an exemplary photovoltaic grid-connected inverter provided in this application, Figure 6 The control logic diagram of a front-stage flyback switching power supply boost control system of an exemplary photovoltaic grid-connected inverter provided in the present application is as follows: Figure 7 A control logic diagram of a post-stage AC inverter control system of an exemplary photovoltaic grid-connected inverter provided in the present application. In the pre-stage flyback switch power supply boost control system of the exemplary photovoltaic grid-connected inverter, the output voltage Vpv and output current Ipv of the photovoltaic panel are sampled for MPPT tracking, the maximum power point output current setting value Ipv_ref of the photovoltaic panel is calculated, and the difference (Gi1) between the current setting value Ipv_ref and the output current Ipv of the photovoltaic panel is calculated, and substituted into the first PI controller to calculate the duty cycle of the first switch signal (PWM1) of the flyback switch power supply switch tube, and then the operation of the flyback switch power supply is closed-loop controlled to boost the photovoltaic low voltage to the DC bus voltage Vbus_meas. In the post-stage AC inverter control system, the DC bus voltage Vbus_meas, the grid voltage Vo and the AC output current Ifd are sampled. Calculate the difference (Gv1) between the DC bus voltage Vbus_meas and the DC bus voltage setting value Vbus_Ref given by the circuit design, substitute it into the second PI controller, and calculate the inverter output AC current peak setting value Inv_I_Ref. Substitute the grid voltage Vo into the phase-locked loop (PLL) to calculate the current grid phase θ, and obtain the AC current peak reference value Inv_I_Ref given by the circuit design and The product of, calculates the difference (Gi2) between the AC output current Ifdbk and the product, substitutes it into the third PI controller, calculates the duty cycle of the second switch signal (PWM2) of the switch tube of the inverter H-bridge, and closes the loop to control the operation of the inverter H-bridge, thereby achieving the goal of controlling the grid-connected power. However, the two-stage control system has many control loops. In this exemplary photovoltaic grid-connected inverter, three voltage detection devices and two current detection devices are required for sampling, and three PI controllers are required for control. The circuit uses many electronic devices, the circuit structure is relatively complex, and the switch tube of the H-bridge needs to be used to convert DC power into AC power. The high-frequency switching loss during the inverter modulation process is large, resulting in low power generation efficiency.

[0029] The present application provides a control method for a photovoltaic grid-connected inverter.

[0030] See also Figure 1 , Figure 2 and Figure 3 , Figure 1 This is a schematic flow chart of an embodiment of a control method for a photovoltaic grid-connected inverter provided in the present application. Figure 2This is an electronic circuit diagram of an embodiment of a photovoltaic grid-connected inverter provided in this application. Figure 3 A control logic diagram of an embodiment of a photovoltaic grid-connected inverter provided in the present application. In an embodiment of the present application, the control method of the photovoltaic grid-connected inverter is applied to a photovoltaic power generation system, the photovoltaic power generation system includes a photovoltaic panel PV and a power grid, the photovoltaic grid-connected inverter includes a flyback switch conversion circuit 01 and an H-bridge circuit 02, the flyback switch conversion circuit 01 includes a transformer T1 and a flyback switch Q1, the first end of the primary coil of the transformer T1 is connected to the output end of the photovoltaic panel PV; the first end of the flyback switch Q1 is connected to the second end of the primary coil of the transformer T1, and the second end of the flyback switch Q1 is grounded; the two input ends of the H-bridge circuit 02 are respectively connected to the two ends of the secondary coil of the transformer T1, and the two output ends of the H-bridge circuit 02 are respectively connected to the two access points of the power grid; the steps of the control method include steps S1 to S5: Step S1, determining an AC output peak power reference value of the photovoltaic panel PV based on an output voltage of the photovoltaic panel PV and an output current of the photovoltaic panel PV.

[0031] In this embodiment, the output voltage and output current of the photovoltaic panel PV can be monitored, and the maximum power point tracking (MPPT) algorithm can be used to dynamically adjust the working point of the photovoltaic panel PV to obtain the highest DC power output. At the highest DC power output working point, the PI controller can be used to calculate the equivalent AC peak power reference value of the photovoltaic panel PV.

[0032] Step S2, determining the instantaneous phase of the power grid based on the voltage of the power grid.

[0033] In this embodiment, a phase-locked loop (PLL) technology or other synchronization mechanisms may be used to accurately measure the instantaneous phase angle of the grid voltage.

[0034] Step S3, determining the instantaneous value of the AC output power of the flyback switch conversion circuit 01 based on the AC output peak power reference value and the instantaneous phase of the power grid.

[0035] In this embodiment, the instantaneous value of the AC output power of the flyback switch conversion circuit 01 is determined based on the AC peak power reference value equivalent to the photovoltaic panel PV and the instantaneous phase of the power grid. While ensuring a larger output of the flyback switch conversion circuit 01, the power output can be adjusted in combination with the instantaneous phase of the power grid, so that the output power meets the requirements of the power grid at every moment.

[0036] Step S4, based on the instantaneous value of the AC output power, determining the switching cycle and on-time of the flyback switch Q1 when the flyback switch conversion circuit 01 operates in the discontinuous conduction mode, and controlling the operation of the flyback switch Q1 based on the switching cycle and on-time.

[0037] It should be noted that when the flyback switch conversion circuit 01 operates in the discontinuous conduction mode (DCM), a simpler control strategy is allowed to be used, and no complex compensation network is required to stabilize the loop. In the discontinuous conduction mode, energy transfer is completed by relying on the control of the switching cycle. In this way, this embodiment has only one level of control, and the switching cycle and conduction time of the flyback switch Q1 can also be calculated to control the operation of the flyback switch Q1.

[0038] Step S5, based on the instantaneous phase of the power grid, control the operation of the H-bridge circuit 02 so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid.

[0039] It should be noted that the photovoltaic grid-connected inverter may include voltage detection devices Vpv_SEN, Vo_SEN and current detection device Ipv_SEN. The output voltage of the photovoltaic panel PV is detected by the voltage detection device Vpv_SEN, the voltage of the grid is detected by the voltage detection device Vo_SEN, and the output current of the photovoltaic panel PV is detected by the current detection device Ipv_SEN.

[0040] It should be noted that the photovoltaic grid-connected inverter may also include a first capacitor C1 and a second capacitor C2, wherein one end of the first capacitor C1 and one end of the second capacitor C2 are connected to the first end of the primary coil of the transformer T1, the other end of the first capacitor C1 is grounded, and the other end of the second capacitor C2 is connected to the second end of the primary coil of the transformer T1. The first capacitor C1 is used to filter the output voltage of the photovoltaic panel PV, and the second capacitor C2 is used to absorb the switching spike pulse of the flyback switch conversion circuit 01 during the switching process. The photovoltaic grid-connected inverter may also include a third capacitor C3, a fourth capacitor C4 and a first diode D1, wherein one end of the third capacitor C3 and the positive electrode of the first diode D1 are connected to the first end of the secondary coil of the transformer T1, the negative electrode of the first diode D1 and one end of the fourth capacitor C4 are connected to the first input end of the H-bridge circuit 02, and the other end of the third capacitor C3, the other end of the fourth capacitor C4, and the second end of the secondary coil of the transformer T1 are connected to the second input end of the H-bridge circuit 02. The third capacitor C3 and the fourth capacitor C4 are used for energy storage and filtering, and the first diode D1 is used for rectification.

[0041] It should be noted that, in this embodiment, the output voltage Vpv and the output current Ipv of the photovoltaic panel PV can be obtained by sampling, and the MPPT tracking calculation can be performed to obtain the AC output peak power reference value Ipv_ref of the photovoltaic panel PV, and the difference (Gi) between the AC output peak power reference value Ipv_ref and the output current Ipv of the photovoltaic panel PV is calculated and substituted into the PI controller to obtain the AC peak power reference value P_ref. The sampled voltage Vo of the power grid can be substituted into the phase-locked loop (PLL) to calculate the instantaneous phase θ of the power grid. The AC peak power reference value P_ref can be multiplied by to obtain the AC output power instantaneous value P(t) of the flyback switch conversion circuit 01. Based on the AC output power instantaneous value P(t), the formula is calculated according to the working characteristics of the flyback switch conversion circuit 01 working in the discontinuous conduction mode to obtain the switching cycle and conduction time of the flyback switch Q1, so as to output the flyback switch control signal to close the loop and control the operation of the flyback switch Q1. At the same time, the instantaneous phase of the power grid can be used to judge the zero point of the power grid voltage, and the H-bridge control signal is output according to the judgment result to control the power frequency switching of the switch of the H-bridge circuit 02 to ensure that the output current is consistent with the current direction of the power grid. In this way, this embodiment realizes photovoltaic grid connection. Compared with the prior art, this embodiment has only one level of control, and directly converts the output voltage of the photovoltaic panel PV into an AC output through the flyback switch conversion circuit 01, that is, this embodiment can realize output closed-loop control through a PI controller, which reduces the circuit cost. Moreover, this embodiment only needs to use two voltage detection devices and one current detection device, reducing the use of sampling detection devices and reducing the circuit cost. At the same time, the H-bridge circuit 02 of this embodiment is only used to control the direction of the output current, that is, the switch tube of the H-bridge circuit 02 only needs to be used to follow the voltage phase change of the power grid for low-frequency switching work, and does not need to be used for high-frequency modulation, eliminating the inverter switch loss, reducing the working loss of the switch, and improving the power generation efficiency.

[0042] The present application adopts a control method of a photovoltaic grid-connected inverter, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes a photovoltaic panel PV and a power grid. The photovoltaic grid-connected inverter includes a flyback switch conversion circuit 01 and an H-bridge circuit 02. The control method includes: step S1, based on the output voltage of the photovoltaic panel PV and the output current of the photovoltaic panel PV, determine the AC output peak power reference value of the photovoltaic panel PV. Step S2, based on the voltage of the power grid, determine the instantaneous phase of the power grid. Step S3, based on the AC output peak power reference value and the instantaneous phase of the power grid, determine the instantaneous value of the AC output power of the flyback switch conversion circuit 01. Step S4, based on the instantaneous value of the AC output power, determine the switching cycle and conduction time of the flyback switch Q1 when the flyback switch conversion circuit 01 operates in a discontinuous conduction mode, and control the operation of the flyback switch Q1 based on the switching cycle and the conduction time. Step S5, based on the instantaneous phase of the power grid, control the operation of the H-bridge circuit 02 so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid. Thus, compared with the prior art, the present application has only one level of control, and directly converts the output voltage of the photovoltaic panel PV into an AC output through the flyback switch conversion circuit 01, and the output closed-loop control can be achieved through a PI controller, thereby reducing the circuit cost. Moreover, the present application only needs to use two voltage detection devices and one current detection device, thereby reducing the use of sampling detection devices and reducing the circuit cost. At the same time, the H-bridge circuit 02 of the present application is only used to control the direction of the output current, that is, the switch tube of the H-bridge circuit 02 only needs to be used for low-frequency switching following the voltage phase change of the power grid, and does not need to be used for high-frequency modulation, thereby eliminating the inverter switch loss, reducing the working loss of the switch, and improving the power generation efficiency.

[0043] See also Figure 2 and Figure 3 In one embodiment of the present application, the step of determining the switching cycle and conduction time of the flyback switch Q1 based on the instantaneous value of the AC output power to determine whether the flyback switch conversion circuit 01 operates in the discontinuous conduction mode includes steps S41 to S43: Step S41, based on the instantaneous value of the AC output power, the parameters of the transformer T1, the parameters of the flyback switch Q1, the output voltage of the photovoltaic panel PV and the voltage of the grid, determine the peak current value of the primary coil of the transformer T1 when the flyback switch conversion circuit 01 operates in the discontinuous conduction mode.

[0044] Step S42 , determining the switching period of the flyback switch Q1 based on the peak current value of the primary coil of the transformer T1 , the parameters of the transformer T1 , and the instantaneous value of the AC output power.

[0045] Step S43 , determining the on-time of the flyback switch Q1 based on the peak current value of the primary coil of the transformer T1 , the parameters of the transformer T1 , and the output voltage of the photovoltaic panel PV.

[0046] In one possible implementation, see Figure 2 The parameters of the transformer T1 include the inductance of the primary coil of the transformer T1 and the turns ratio of the primary coil of the transformer T1 to the secondary coil. The flyback switch Q1 is a MOS tube, and the parameters of the flyback switch Q1 include the equivalent output junction capacitance of the MOS tube. The step S41 includes step S411: Step S411, based on the instantaneous value of the AC output power, the inductance of the primary coil of the transformer T1, the ratio of the number of turns of the primary coil of the transformer T1 to the number of turns of the secondary coil, the equivalent output junction capacitance of the flyback switch Q1, the output voltage of the photovoltaic panel PV and the voltage of the grid, introduce the first calculation formula to determine the peak current value of the primary coil of the transformer T1 when the flyback switch conversion circuit 01 operates in the discontinuous conduction mode.

[0047] The first calculation formula is:

[0048] in, Instantaneous value of AC output power, The inductance of the primary coil of transformer T1, is the ratio of the number of turns of the primary coil of transformer T1 to the number of turns of the secondary coil, The peak current value of the primary coil of transformer T1, is the equivalent output junction capacitance of the MOS tube, which can be specifically the total capacitance between the drain and source of the MOS tube, is the voltage of the grid, is the output voltage of the photovoltaic panel PV.

[0049] It should be noted that the instantaneous value of AC output power is

[0050] Among them, the frequency = 1 / , and the switching cycle By the conduction time , Demagnetization time With oscillation time The composition is as follows: , ,

[0051] The step S42 includes step S421: Step S421, based on the peak current value of the primary coil of the transformer T1, the parameters of the transformer T1 and the instantaneous value of the AC output power, a second calculation formula is introduced to determine the switching period of the MOS tube; The second calculation formula is:

[0052] in, Instantaneous value of AC output power, The inductance of the primary coil of transformer T1, The peak current value of the primary coil of transformer T1, The switching cycle of the MOS tube.

[0053] The step S43 comprises step S431: Step S431, based on the peak current value of the primary coil of the transformer T1, the parameters of the transformer T1 and the output voltage of the photovoltaic panel PV, a third calculation formula is introduced to determine the conduction time of the MOS tube; The third calculation formula is:

[0054] in, The conduction time of the MOS tube, The inductance of the primary coil of transformer T1, The peak current value of the primary coil of transformer T1, is the output voltage of the photovoltaic panel.

[0055] Thus, through the working characteristics of the flyback switch conversion circuit 01 working in the DCM mode, according to the first calculation formula, the second calculation formula and the third calculation formula, the peak current value of the primary coil of the transformer T1 can be obtained. , and then the switching cycle of the MOS tube is obtained With on-time , the output of the flyback switch conversion circuit 01 can be closed-loop controlled.

[0056] See also Figure 2 and Figure 3 In one embodiment of the present application, step S3 includes step S31: Step S31, based on the AC output peak power reference value and the instantaneous phase of the power grid, a fourth calculation formula is introduced to determine the instantaneous value of the AC output power of the flyback switch conversion circuit 01; The fourth calculation formula is:

[0057] in, Instantaneous value of AC output power, AC output peak power reference value, The instantaneous phase of the grid, Conversion efficiency of the flyback switching conversion circuit 01.

[0058] In this embodiment, the instantaneous value of the AC output power of the flyback switch conversion circuit 01 can be calculated by the fourth calculation formula, and then the flyback switch Q1 control signal can be obtained by formula calculation.

[0059] See also Figure 2 and Figure 3 In one embodiment of the present application, step S1 includes steps S11 to S13: Step S11 , performing MPPT tracking (Maximum Power Point Tracking) based on the output voltage and the output current of the photovoltaic panel PV to determine an output current setting value Ipv_ref at the maximum power point of the photovoltaic panel PV.

[0060] It should be noted that the output characteristics of the photovoltaic panel PV are nonlinear and will change according to environmental conditions (such as light intensity and temperature). In this embodiment, the MPPT algorithm determines the maximum power point of the photovoltaic panel PV by monitoring the output voltage and output current of the photovoltaic panel PV, and sets the output current set value Ipv_ref at this point, so that the photovoltaic panel PV operates at this operating point.

[0061] Step S12, based on the output current setting value Ipv_ref and the output current Ipv of the photovoltaic panel PV, determining a first current difference between the output current setting value and the output current of the photovoltaic panel PV.

[0062] It should be noted that the difference between the output current setting value Ipv_ref and the actually measured output current Ipv of the photovoltaic panel PV reflects the degree of deviation between the current operating point and the maximum power point.

[0063] Step S13, substituting the first current difference into a PI (proportional integral) controller for calculation to obtain an AC output peak power reference value of the photovoltaic panel PV.

[0064] It should be noted that the PI controller is a feedback control mechanism that makes adjustments based on the proportional and integral parts of the error (here, the current difference). Specifically, the proportional part is directly proportional to the current error. If there is a large immediate error, the proportional part will produce a large adjustment. The integral part takes into account the time accumulation of all past errors, which helps to eliminate static errors and ensure the stability of control. In this way, this embodiment can obtain the corresponding AC output peak power reference value when the photovoltaic panel PV is maintained near the maximum power point through the calculation of the PI controller.

[0065] See also Figure 2 and Figure 3 In one embodiment of the present application, step S2 includes step S21: Step S21, inputting the voltage of the power grid into a phase-locked loop to obtain the instantaneous phase of the power grid.

[0066] It should be noted that there is a voltage-controlled oscillator (VCO) inside the phase-locked loop (PLL), and its output frequency is controlled by the phase difference between the input signal and the feedback signal. When the phase-locked loop is locked, it means that the output frequency of the VCO has been adjusted to the same frequency as the input grid voltage signal, and the phase difference between the two is maintained at a constant value. In this way, according to the working characteristics of the phase-locked loop, the voltage of the input grid can be input to obtain the instantaneous phase information of the grid voltage.

[0067] See also Figure 2 and Figure 3 In one embodiment of the present application, the H-bridge circuit 02 includes a first IGBT tube IG1, a second IGBT tube IG2, a third IGBT tube IG3 and a fourth IGBT tube IG4; the collector of the first IGBT tube IG1 and the collector of the second IGBT tube IG2 are connected to the first end of the secondary coil of the transformer T1; the emitter of the first IGBT tube IG1 and the collector of the third IGBT tube IG3 are connected to the first access point of the power grid; the emitter of the second IGBT tube IG2 and the collector of the fourth IGBT tube IG4 are connected to the second access point of the power grid; the emitter of the third IGBT tube IG3 and the emitter of the fourth IGBT tube IG4 are connected to the second end of the secondary coil of the transformer T1; the step S5 includes step S51: Step S51, performing zero-crossing judgment on the instantaneous phase of the power grid. If the voltage of the power grid is in the positive half cycle, the first IGBT tube IG1 and the fourth IGBT tube IG4 are controlled to be turned on, and the second IGBT tube IG2 and the third IGBT tube IG3 are controlled to be turned off. If the voltage of the power grid is in the negative half cycle, the second IGBT tube IG2 and the third IGBT tube IG3 are controlled to be turned on, and the first IGBT tube IG1 and the fourth IGBT tube IG4 are controlled to be turned off.

[0068] In this embodiment, an IGBT tube is used in the secondary coil of the transformer T1 to set the output of the H-bridge circuit 02 to follow the voltage cycle change of the power grid, and control the output voltage polarity to be synchronized with the power grid. The IGBT tube is suitable for processing high voltage and large current, while providing lower conduction loss and improving power generation efficiency.

[0069] Specifically, if the voltage of the power grid is in the positive half cycle, the first IGBT tube IG1 and the fourth IGBT tube IG4 are controlled to be turned on, and the second IGBT tube IG2 and the third IGBT tube IG3 are controlled to be turned off. The current can reach the first access point of the power grid from the first end of the secondary coil of the transformer T1 through the first IGBT tube IG1, and then return from the second access point of the power grid, and flow to the second end of the secondary coil of the transformer T1 through the fourth IGBT tube IG4. At this time, the current direction is the same as the voltage direction of the power grid. If the voltage of the power grid is in the negative half cycle, the second IGBT tube IG2 and the third IGBT tube IG3 are controlled to be turned on, and the first IGBT tube IG1 and the fourth IGBT tube IG4 are controlled to be turned off, and the current path is changed. The current flows through the first end of the secondary coil of the transformer T1, reaches the second access point of the power grid through the second IGBT tube IG2, and then returns from the first access point of the power grid, and returns to the second end of the secondary coil of the transformer T1 through the third IGBT tube IG3. At this time, the current direction is the same as the voltage direction of the power grid. In this embodiment, the IGBT tube is not used for high-frequency switching for inverter modulation, which eliminates the switching loss of inverter modulation and improves the power generation efficiency of photovoltaic grid connection.

[0070] See also Figure 4 In one embodiment of the present application, the photovoltaic power generation system includes N photovoltaic panels PV, and the photovoltaic grid-connected inverter includes N flyback switch conversion circuits 01 and H-bridge circuits 02; each flyback switch conversion circuit 01 includes a transformer T1 and a flyback switch Q1; The first end of the primary coil of the Nth transformer T1 is connected to the output end of the Nth photovoltaic panel PV; the first end of the Nth flyback switch Q1 is connected to the second end of the primary coil of the Nth transformer T1, and the second end of the Nth flyback switch Q1 is grounded; the two input ends of the H-bridge circuit 02 are respectively connected to the two ends of the secondary coil of the Nth transformer T1, and the two output ends of the H-bridge circuit 02 are respectively connected to the two access points of the power grid; Control methods include: Determine an AC output peak power reference value of the Nth photovoltaic panel PV based on an output voltage of the Nth photovoltaic panel PV and an output current of the Nth photovoltaic panel PV; Based on the voltage of the grid, determining the instantaneous phase of the grid; Determine the instantaneous value of the AC output power of the Nth flyback switch conversion circuit 01 based on the Nth AC output peak power reference value and the instantaneous phase of the power grid; Based on the instantaneous value of the Nth AC output power, determine the switching cycle and conduction time of the Nth flyback switch Q1 when the Nth flyback switch conversion circuit 01 operates in the discontinuous conduction mode, and control the operation of the Nth flyback switch Q1 based on the Nth switching cycle and the Nth conduction time; Based on the instantaneous phase of the power grid, the operation of the H-bridge circuit 02 is controlled so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid.

[0071] In this embodiment, the photovoltaic grid-connected inverter includes N flyback switch conversion circuits 01 and an H-bridge circuit 02, wherein the N flyback switch conversion circuits 01 share an H-bridge circuit 02 to ensure that the direction of the output current of the photovoltaic grid-connected inverter is the same as the direction of the current of the power grid. Wherein, N is a positive integer greater than or equal to 2.

[0072] In this embodiment, the output voltage Vpv1 of the photovoltaic panel PV1 and the output current Ipv1 of the photovoltaic panel PV can be obtained by sampling, and the MPPT tracking calculation can be performed to obtain the AC output peak power reference value Ipv_ref1 of the photovoltaic panel PV, and the difference between the AC output peak power reference value Ipv_ref1 and the output current Ipv1 of the photovoltaic panel PV is calculated and substituted into the PI controller to obtain the AC peak power reference value P_ref1. The sampled voltage Vo of the power grid can be substituted into the phase-locked loop (PLL) to calculate the instantaneous phase θ of the power grid. The AC peak power reference value P_ref1 can be multiplied by to obtain the AC output power instantaneous value P1(t) of the first flyback switch conversion circuit 01. Based on the AC output power instantaneous value P1(t), a formula is calculated according to the working characteristics of the first flyback switch conversion circuit 01 working in the discontinuous conduction mode to obtain the switching period of the first flyback switch Q1. 1 and on-time 1, and the operation of the first flyback switch Q1 is controlled in a closed loop. By analogy, the instantaneous value PN (t) of the AC output power of the Nth flyback switch conversion circuit 01 can be obtained, and then the switching period of the Nth flyback switch Q1 can be obtained. N and on-time N, to control the operation of the Nth flyback switch Q1 in a closed loop. At the same time, the instantaneous phase of the power grid can be used to judge the zero-crossing point of the power grid voltage to control the power frequency switching of the switch of the shared H-bridge circuit 02 to ensure that the output current is consistent with the current direction of the power grid. In this way, this embodiment realizes photovoltaic grid connection. Compared with the prior art, this embodiment can directly convert the output voltage of the photovoltaic panel PV into an AC output through N flyback switch conversion circuits 01, and each flyback switch conversion circuit 01 can realize output closed-loop control through a PI controller, thereby reducing the circuit cost. Moreover, this embodiment only needs to use N+1 voltage detection devices and N current detection devices, which can reduce the use of sampling detection devices and reduce the circuit cost. At the same time, the H-bridge circuit 02 of this embodiment is only used to control the direction of the output current, and the switch tube of the H-bridge circuit 02 only needs to be used for low-frequency switching work following the voltage phase change of the power grid, and does not need to be used for high-frequency modulation, thereby eliminating the inverter switch loss, reducing the working loss of the switch, and improving the power generation efficiency.

[0073] See also Figure 8 The present application also provides a photovoltaic grid-connected inverter, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes a photovoltaic panel PV and a power grid. The photovoltaic grid-connected inverter includes a flyback switch conversion circuit 01 and an H-bridge circuit 02. The flyback switch conversion circuit 01 includes a transformer T1 and a flyback switch Q1. The first end of the primary coil of the transformer T1 is connected to the output end of the photovoltaic panel PV; the first end of the flyback switch Q1 is connected to the second end of the primary coil of the transformer T1, and the second end of the flyback switch Q1 is grounded; the two inputs of the H-bridge circuit 02 are ... The two ends are respectively connected to the two ends of the secondary coil of the transformer T1, and the two output ends of the H-bridge circuit 02 are respectively connected to the two access points of the power grid; the photovoltaic grid-connected inverter also includes: a memory 04, a processor 05, and a computer program stored in the memory 04 and executable on the processor 05, the computer program is configured to implement the control method of the photovoltaic grid-connected inverter in the above embodiment, and can solve the technical problems of the existing photovoltaic grid-connected inverter having more control loops, complex circuit structure, and low power generation efficiency when the photovoltaic grid-connected inverter is connected to the photovoltaic grid through a two-level control system. Compared with the prior art, the beneficial effects of the photovoltaic grid-connected inverter provided in the present application are the same as the beneficial effects of the control method of the photovoltaic grid-connected inverter provided in the above embodiment, and the other technical features in the photovoltaic grid-connected inverter are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0074] See also Figure 2 In one embodiment of the present application, the photovoltaic grid-connected inverter also includes an LCL filter 03, two input ends of the LCL filter 03 are respectively connected to two output ends of the H-bridge circuit 02, and two output ends of the LCL filter 03 are respectively connected to two access points of the power grid.

[0075] In this embodiment, the LCL filter 03 may include a first common mode inductor M1, a second common mode inductor 02 and a fifth capacitor C5. In this way, the output end of the H-bridge circuit 02 of this embodiment uses the LCL filter 03 composed of the first common mode inductor M1, the second common mode inductor 02 and the fifth capacitor C5 to couple with the power grid, which can improve the grid connection quality.

[0076] The above description is only an exemplary embodiment of the present application and does not limit the patent scope of the present application. All equivalent structural changes made by using the contents of the present application specification and drawings under the technical concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A control method for a photovoltaic grid-connected inverter, characterized in that: Applied to a photovoltaic power generation system, the photovoltaic power generation system includes a photovoltaic panel and a power grid, the photovoltaic grid-connected inverter includes a flyback switch conversion circuit and an H-bridge circuit, the flyback switch conversion circuit includes a transformer and a flyback switch, the first end of the primary coil of the transformer is connected to the output end of the photovoltaic panel; the first end of the flyback switch is connected to the second end of the primary coil of the transformer, and the second end of the flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; The steps of the control method include: S1. determining an AC output peak power reference value of the photovoltaic panel based on the output voltage and the output current of the photovoltaic panel; S2. determining an instantaneous phase of the power grid based on the voltage of the power grid; S3, determining an instantaneous value of the AC output power of the flyback switch conversion circuit based on the AC output peak power reference value and the instantaneous phase of the power grid; S4, determining the switching cycle and on-time of the flyback switch when the flyback switch conversion circuit operates in a discontinuous conduction mode based on the instantaneous value of the AC output power, and controlling the operation of the flyback switch based on the switching cycle and the on-time; S5. Based on the instantaneous phase of the power grid, control the operation of the H-bridge circuit so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the current direction of the power grid.

2. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The step of determining, based on the instantaneous value of the AC output power, that the flyback switch conversion circuit operates in a discontinuous conduction mode and the switching period and conduction time of the flyback switch comprises: Determine, based on the instantaneous value of the AC output power, the parameters of the transformer, the parameters of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid, the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode; Determining a switching period of the flyback switch based on a peak current value of the primary coil of the transformer, parameters of the transformer and an instantaneous value of the AC output power; The conduction time of the flyback switch is determined based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel.

3. The control method of the photovoltaic grid-connected inverter according to claim 2, characterized in that: The parameters of the transformer include the inductance of the primary coil of the transformer and the ratio of the number of turns of the primary coil of the transformer to the number of turns of the secondary coil; the flyback switch is a MOS tube, and the parameters of the flyback switch include the equivalent output junction capacitance of the MOS tube; the step of determining the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode based on the instantaneous value of the AC output power, the parameters of the transformer, the parameters of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid comprises: Based on the instantaneous value of the AC output power, the inductance of the primary coil of the transformer, the ratio of the number of turns of the primary coil of the transformer to the number of turns of the secondary coil, the equivalent output junction capacitance of the flyback switch, the output voltage of the photovoltaic panel and the voltage of the grid, a first calculation formula is introduced to determine the peak current value of the primary coil of the transformer when the flyback switch conversion circuit operates in a discontinuous conduction mode; The first calculation formula is: in, The instantaneous value of the AC output power, The inductance value of the primary coil of the transformer, is the ratio of the number of turns of the primary coil to the number of turns of the secondary coil of the transformer, The peak current value of the primary coil of the transformer, is the equivalent output junction capacitance of the MOS tube, is the voltage of the grid, is the output voltage of the photovoltaic panel; The step of determining the switching period of the flyback switch based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the instantaneous value of the AC output power comprises: Based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the instantaneous value of the AC output power, a second calculation formula is introduced to determine the switching period of the MOS tube; The second calculation formula is: in, The instantaneous value of the AC output power, The inductance value of the primary coil of the transformer, The peak current value of the primary coil of the transformer, The switching cycle of the MOS tube; The step of determining the on-time of the flyback switch based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel comprises: Based on the peak current value of the primary coil of the transformer, the parameters of the transformer and the output voltage of the photovoltaic panel, a third calculation formula is introduced to determine the conduction time of the MOS tube; The third calculation formula is: in, The conduction time of the MOS tube, The inductance value of the primary coil of the transformer, The peak current value of the primary coil of the transformer, is the output voltage of the photovoltaic panel.

4. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The step S3 comprises: Based on the AC output peak power reference value and the instantaneous phase of the power grid, a fourth calculation formula is introduced to determine the instantaneous value of the AC output power of the flyback switch conversion circuit; The fourth calculation formula is: in, The instantaneous value of the AC output power, The AC output peak power reference value, The instantaneous phase of the grid, The conversion efficiency of the flyback switching conversion circuit.

5. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The step S1 comprises: Performing MPPT tracking based on the output voltage and the output current of the photovoltaic panel to determine the output current setting value at the maximum power point of the photovoltaic panel; Determining a first current difference between the output current setting value and the output current of the photovoltaic panel based on the output current setting value and the output current of the photovoltaic panel; The first current difference is substituted into a PI controller for calculation to obtain an AC output peak power reference value of the photovoltaic panel.

6. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The step S2 comprises: The voltage of the power grid is input into a phase-locked loop to obtain the instantaneous phase of the power grid.

7. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The H-bridge circuit includes a first IGBT tube, a second IGBT tube, a third IGBT tube and a fourth IGBT tube; the collector of the first IGBT tube and the collector of the second IGBT tube are connected to the first end of the secondary coil of the transformer; the emitter of the first IGBT tube and the collector of the third IGBT tube are connected to the first access point of the power grid; the emitter of the second IGBT tube and the collector of the fourth IGBT tube are connected to the second access point of the power grid; The emitter of the third IGBT tube and the emitter of the fourth IGBT tube are connected to the second end of the secondary coil of the transformer; the step S5 comprises: A zero-crossing judgment is performed on the instantaneous phase of the power grid. If the voltage of the power grid is in a positive half cycle, the first IGBT tube and the fourth IGBT tube are controlled to be turned on, and the second IGBT tube and the third IGBT tube are controlled to be turned off. If the voltage of the power grid is in a negative half cycle, the second IGBT tube and the third IGBT tube are controlled to be turned on, and the first IGBT tube and the fourth IGBT tube are controlled to be turned off.

8. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The photovoltaic power generation system includes N photovoltaic panels, and the photovoltaic grid-connected inverter includes N flyback switch conversion circuits and H-bridge circuits; each flyback switch conversion circuit includes a transformer and a flyback switch; The first end of the primary coil of the Nth transformer is connected to the output end of the Nth photovoltaic panel; the first end of the Nth flyback switch is connected to the second end of the primary coil of the Nth transformer, and the second end of the Nth flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the Nth transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; The control method comprises: Determining an AC output peak power reference value of the Nth photovoltaic panel based on the output voltage of the Nth photovoltaic panel and the output current of the Nth photovoltaic panel; determining an instantaneous phase of the grid based on the voltage of the grid; Determining an instantaneous value of the AC output power of the Nth flyback switch conversion circuit based on the Nth AC output peak power reference value and the instantaneous phase of the power grid; Based on the instantaneous value of the Nth AC output power, determine the switching period and conduction time of the Nth flyback switch when the Nth flyback switch conversion circuit operates in a discontinuous conduction mode, and control the operation of the Nth flyback switch based on the Nth switching period and the Nth conduction time; Based on the instantaneous phase of the power grid, the operation of the H-bridge circuit is controlled so that the direction of the output current of the photovoltaic grid-connected inverter is the same as the direction of the current of the power grid.

9. A photovoltaic grid-connected inverter, characterized in that: The photovoltaic grid-connected inverter is applied to a photovoltaic power generation system, the photovoltaic power generation system includes a photovoltaic panel and a power grid, the photovoltaic grid-connected inverter includes a flyback switch conversion circuit and an H-bridge circuit, the flyback switch conversion circuit includes a transformer and a flyback switch, the first end of the primary coil of the transformer is connected to the output end of the photovoltaic panel; the first end of the flyback switch is connected to the second end of the primary coil of the transformer, and the second end of the flyback switch is grounded; the two input ends of the H-bridge circuit are respectively connected to the two ends of the secondary coil of the transformer, and the two output ends of the H-bridge circuit are respectively connected to the two access points of the power grid; The photovoltaic grid-connected inverter further includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the control method of the photovoltaic grid-connected inverter according to any one of claims 1 to 8.

10. The photovoltaic grid-connected inverter according to claim 9, characterized in that: The photovoltaic grid-connected inverter further includes an LCL filter, wherein two input ends of the LCL filter are respectively connected to two output ends of the H-bridge circuit, and two output ends of the LCL filter are respectively connected to two access points of the power grid.

Images