Control method for off-grid micro inverter, and related device

Abstract

The present application relates to the technical field of micro inverters, and relates to a control method for an off-grid micro inverter, and a related device. A specific embodiment of the method comprises: acquiring an output voltage given value, and an output voltage value corresponding to an output end of a voltage-doubling rectifier circuit, and determining the voltage difference between the output voltage given value and the output voltage value; determining an output current given value on the basis of the voltage difference, acquiring an induced-current value in the voltage-doubling rectifier circuit, and determining the current difference between the output current given value and the induced-current value; and on the basis of the current difference, determining a target switching frequency of each of a plurality of switch tubes in a micro inverter, and by means of the target switching frequency, controlling the micro inverter to convey to a load an output voltage meeting the output voltage given value. By means of the embodiment, an off-grid function of a micro inverter based on first-stage power conversion topology is realized, thereby improving the economy of power utilization of loads, and expanding application scenarios of the micro inverter.

Description

Control method and related equipment of off-grid micro-inverter

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on August 30, 2023, with application number 202311114723.X, entitled “Control Method and Related Equipment for Off-Grid Micro-Inverter,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field of micro-inverters, and in particular to a control method and related equipment for an off-grid micro-inverter. Background Art

[0004] A microinverter, as opposed to a traditional centralized inverter, generally refers to an inverter with a power of less than or equal to 1000 watts in a photovoltaic power generation system and module-level MPPT (Maximum Power Point Tracking). Its full name is micro photovoltaic inverter. The traditional photovoltaic inversion method is to connect all the DC power generated by photovoltaic cells under sunlight in series and parallel, and then use a centralized inverter to convert the DC power into AC power for connection to the grid. A microinverter performs inversion on each photovoltaic module. The advantage is that each photovoltaic module can be independently controlled by MPPT, which can significantly improve overall efficiency.

[0005] Microinverters connect to PV panels and the AC grid, converting the DC power from the panels into AC power for grid connection. To meet the demands of high-power PV panels, related technologies primarily employ a two-stage power conversion topology to improve the power and efficiency of microinverters. However, this still struggles to meet the demands of high-power PV panels. Furthermore, grid-connected microinverters often rely on grid power, resulting in poor economic efficiency and a limited range of applications.

[0006] Summary of the Invention

[0007] The embodiments of the present invention provide a control method and related equipment for an off-grid micro-inverter, which at least solve the problems in the related art that there is no control solution for realizing off-grid function for a micro-inverter with a one-stage power conversion topology, and that grid-connected micro-inverters have poor economy and narrow application scenarios.

[0008] To address the above-mentioned issues, one aspect of an embodiment of the present invention provides a control method for an off-grid micro-inverter. The micro-inverter is configured to deliver sinusoidal AC power to a load based on a circuit topology of primary power conversion. The circuit topology of the micro-inverter includes a resonant circuit, a winding transformer, and a voltage-doubling rectifier circuit. The resonant circuit is connected to the primary winding of the winding transformer, and the voltage-doubling rectifier circuit is connected to the secondary winding of the winding transformer. The method includes:

[0009] Obtaining an output voltage given value and an output voltage value corresponding to an output end of the voltage doubler rectifier circuit, and determining a voltage difference between the output voltage given value and the output voltage value;

[0010] Determine the output current given value according to the voltage difference, obtain the induced current value in the voltage doubler rectifier circuit, and determine the current difference between the output current given value and the induced current value;

[0011] The target switching frequency of multiple switching tubes in the micro-inverter is determined according to the current difference, and the micro-inverter is controlled by the target switching frequency to transmit an output voltage that meets a given output voltage value to the load.

[0012] In some embodiments, the step of determining the output current set value according to the voltage difference includes:

[0013] The controller performs proportional-integral control or proportional resonant control on the voltage difference to determine the output current set value corresponding to the micro-inverter; wherein, when the output current of the micro-inverter meets the output current set value, the output voltage of the micro-inverter meets the output voltage set value.

[0014] In some embodiments, the step of determining the target switching frequencies of the plurality of switches in the micro-inverter according to the current difference includes:

[0015] The controller performs proportional-integral control or proportional-resonance control on the current difference to determine a control signal;

[0016] The control signal is subjected to voltage-frequency conversion via a voltage-frequency converter to generate a drive signal. The drive signal is used to drive the on and off of multiple switching tubes in the micro-inverter, and the adjustment frequency of the drive signal is consistent with the target switching frequency of the multiple switching tubes.

[0017] In some embodiments, the method further includes an output gain control step, comprising:

[0018] Determine whether the target switching frequency is less than or equal to a preset switching frequency threshold; if so, determine that the switching frequency adjustment strategy is the target adjustment strategy; if not, determine that the phase shift angle adjustment strategy is the target adjustment strategy; wherein the switching frequency adjustment strategy is to adjust the switching frequencies of multiple switching tubes in the micro-inverter, and the phase shift angle adjustment strategy is to adjust the phase shift angles between the multiple switching tubes in the micro-inverter;

[0019] According to the target regulation strategy, multiple switch tubes are regulated to control the output gain of the micro inverter.

[0020] In some embodiments, the method further comprises:

[0021] Detect the maximum power value of the photovoltaic module corresponding to the micro inverter and receive the current input by the photovoltaic module.

[0022] In some embodiments, the working state of the multiple switch tubes is a soft switching working state.

[0023] In order to solve the above problems, one aspect of an embodiment of the present invention provides a micro inverter, including: a processor, and a memory for storing a program, the program including instructions, which, when executed by the processor, enable the processor to execute any of the above-mentioned control methods for an off-grid micro inverter.

[0024] In order to solve the above problems, one aspect of an embodiment of the present invention provides a non-transitory machine-readable medium storing computer instructions, where the computer instructions are used to enable a computer to execute any of the above-mentioned control methods for an off-grid micro-inverter.

[0025] The beneficial effects of the embodiments of the present invention are as follows: a micro-inverter that delivers sinusoidal AC power to a load based on a circuit topology of a first-stage power conversion circuit determines the voltage difference between the output voltage set value and the output voltage value by obtaining the output voltage set value and the output voltage value corresponding to the output end of the voltage-doubling rectifier circuit; determines the output current set value based on the voltage difference, obtains the induced current value in the voltage-doubling rectifier circuit, and determines the current difference between the output current set value and the induced current value; determines the target switching frequency of multiple switches in the micro-inverter based on the current difference, and controls the micro-inverter to deliver an output voltage that meets the output voltage set value to the load through the target switching frequency. This overcomes the problems in the related art that there is no control scheme for realizing off-grid functionality for micro-inverters with a first-stage power conversion topology, and that grid-connected micro-inverters have poor economic efficiency and a narrow range of applicable scenarios; and realizes off-grid functionality control for micro-inverters based on a first-stage power conversion topology, improves the economic efficiency of load power consumption, increases the efficiency and power of the micro-inverter, and expands the applicable scenarios of the micro-inverter.

[0026] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below so that other features, objects, and advantages of the invention are more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be derived from these drawings without inventive effort.

[0028] FIG1 is a flow chart of a control method for an off-grid micro-inverter according to an embodiment of the present invention.

[0029] FIG2 is a schematic diagram of the electrical topology of a micro-inverter with a one-stage power conversion topology according to an embodiment of the present invention.

[0030] FIG3 is a schematic structural diagram of the electronic device of this embodiment. DETAILED DESCRIPTION

[0031] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0032] Microinverters connect to photovoltaic panels and the AC grid. Their circuit topology is primarily a flyback circuit. The secondary side of the transformer converts the output current to AC through a folded circuit, thereby converting the DC power from the photovoltaic panel into AC for grid connection. This circuit topology is limited by the transformer core volume and switching frequency, making it difficult to increase power and resulting in low inverter efficiency. As the power of photovoltaic panels increases, the power and efficiency of microinverters must be increased. Related microinverters typically use a two-stage power conversion topology. However, with two-stage power conversion, the total efficiency of the microinverter is equal to the product of the two conversion efficiencies, making it difficult to exceed 96% efficiency. While related art uses a two-stage power conversion topology to improve the power and efficiency of microinverters, it still fails to meet the requirements of high-power photovoltaic panels. Furthermore, the microinverter's control process is complex and the cost is high. Currently, there is no control solution for microinverters with a one-stage power conversion topology to achieve off-grid functionality. Furthermore, grid-connected microinverters suffer from poor economic efficiency and limited applicability.

[0033] To solve the above problems, an embodiment of the present invention provides a control method for an off-grid micro-inverter. The control method for an off-grid micro-inverter is applied to a micro-inverter based on a one-stage power conversion topology. As shown in FIG1 , the control method for the micro-inverter includes:

[0034] Step S101 , obtaining a given output voltage value and an output voltage value corresponding to an output terminal of a voltage doubler rectifier circuit, and determining a voltage difference between the given output voltage value and the output voltage value.

[0035] Step S102 : determining an output current given value according to the voltage difference, obtaining an induced current value in the voltage doubler rectifier circuit, and determining a current difference between the output current given value and the induced current value.

[0036] Step S103 , determining a target switching frequency of a plurality of switches in the micro-inverter according to the current difference, and controlling the micro-inverter to transmit an output voltage meeting a given output voltage value to the load through the target switching frequency.

[0037] Among them, the micro inverter provided by an embodiment of the present invention is used to transmit sinusoidal AC power to the load based on a circuit topology of primary power conversion. The circuit topology of the micro inverter includes: a resonant circuit, a winding transformer and a voltage doubler rectifier circuit. The resonant circuit is connected to the primary winding of the winding transformer, and the voltage doubler rectifier circuit is connected to the secondary winding of the winding transformer.

[0038] Through the above-mentioned setting, the embodiment of the present invention calculates the voltage difference between the output voltage value and the output voltage set value through the controller, and then determines the output current set value; then, the target switching frequency of multiple switching tubes in the micro-inverter is determined based on the current difference between the output current set value and the induced current value, thereby controlling the micro-inverter to deliver an output voltage to the load while meeting the output voltage set value, thereby realizing the off-grid function of the micro-inverter based on the first-level power conversion topology, improving the economy of load electricity consumption, and expanding the applicable scenarios of the micro-inverter.

[0039] The output voltage value provided in the embodiment of the present invention refers to the actual voltage value output by the output terminal of the micro-inverter; the output voltage set value refers to the voltage value required when the load is operating normally, that is, the rated voltage value. Since the rated voltage value corresponding to the load operation has a certain floating range, the above-mentioned output voltage set value can be a range value, such as being set to 220V to 240V, and the above-mentioned output voltage set value can be any value between 220V and 240V, such as 220V, 230V, and 240V. The output current set value provided in the present invention refers to the current value when the load is operating normally, that is, the rated current value. Since the rated current value corresponding to the load operating normally also has a certain floating range, the above-mentioned output current set value can be a range value.

[0040] In some embodiments, the step of determining the output current set value based on the voltage difference includes: performing proportional-integral control or proportional resonant control on the voltage difference by a controller to determine the output current set value corresponding to the microinverter; wherein, when the output current of the microinverter satisfies the output current set value, the output voltage of the microinverter satisfies the output voltage set value.

[0041] The controllers provided by the embodiments of the present invention include a PI controller (proportional integral (PI) controller, a controller that combines proportional and integral regulation) and a PR controller (proportional resonant (PR) controller). Specifically, a PI controller is a linear controller that forms a control deviation based on a given value and an actual output value, and linearly combines the proportional (P) and integral (I) of the deviation to form a control variable to control the controlled object. PR controllers are primarily used in power electronic control and can track specific frequency signals without static error, thereby increasing the gain amplitude of the loop at a specific frequency point.

[0042] According to a specific embodiment of the present invention, an output voltage setpoint corresponding to a drive controller is obtained as a target voltage setpoint signal, and then an actual output voltage value corresponding to the output terminal of the voltage-doubling rectifier circuit is obtained. The actual output voltage value is used as a voltage sampling feedback signal. The voltage sampling feedback signal is compared with the target voltage setpoint signal to determine a voltage signal difference. The voltage signal difference is then regulated by a PI controller for PI control or a PR controller for PR control to form a voltage loop control signal. The voltage loop control signal indicates an output current setpoint value. That is, the output current in the circuit topology of the micro-inverter needs to be regulated to the output current setpoint value in order for the corresponding output voltage to be regulated to the output voltage setpoint value. Through the above arrangement, the voltage loop control signal formed using the voltage difference as data input determines the output current setpoint value, so that the current difference is subsequently determined using the output current setpoint value and the induced current, and then the current loop control signal is formed, forming a nested voltage-current dual-loop control signal, thereby controlling the micro-inverter to deliver an output voltage to the load while meeting the output voltage setpoint value.

[0043] In some embodiments, the step of determining the target switching frequency of multiple switching tubes in the micro-inverter based on the current difference includes: performing proportional-integral control or proportional resonant control on the current difference by a controller to determine a control signal; performing voltage-frequency conversion on the control signal by a voltage-frequency converter to generate a drive signal; wherein the drive signal is used to drive the conduction and shutdown of multiple switching tubes in the micro-inverter, and the adjustment frequency of the drive signal is consistent with the target switching frequency of the multiple switching tubes.

[0044] According to a specific implementation of an embodiment of the present invention, after determining the output current given value based on the voltage loop control signal determined by the voltage difference, the output current given value is used as the target current given signal of the drive controller, and then the induced current value in the secondary winding of the voltage doubler rectifier circuit is obtained, and the induced current value is used as the current sampling feedback signal for output current sampling. The current sampling feedback signal is compared with the target current given signal of the drive controller to determine the current signal difference, and the current signal difference is subjected to PI control adjustment by a PI controller or PR control adjustment by a PR controller to form a current loop control signal. The current loop control signal is then processed by a voltage-frequency converter to output a frequency-adjustable drive signal (the adjustment frequency of the drive signal is consistent with the target switching frequency corresponding to the switch tube). The drive signal is used to drive multiple switch tubes in the micro inverter to turn on and off according to the target switching frequency, thereby achieving the output voltage meeting the output voltage given value to the load.

[0045] Through the above settings, the output current set value is determined according to the voltage difference, and the current difference is then determined according to the output current set value and the induced current value. The controller is adjusted according to the current difference, and the target switching frequency corresponding to the switching tube is determined by voltage-frequency conversion processing. The micro-inverter is controlled to deliver an output voltage that meets the output voltage set value and an output current that meets the output current set value to the load, further improving the control effect and control rate of the off-grid control of the micro-inverter, and improving the safety and stability of the load's power consumption.

[0046] The target switching frequency provided in this embodiment of the present invention corresponds to the frequency at which multiple switching transistors in a micro-inverter with a single-stage power conversion topology are turned on and off. The specific value of this frequency changes dynamically. Specifically, the target switching frequency changes dynamically in response to both the voltage difference and the current difference.

[0047] In some embodiments, the above method further includes an output gain control step, including: determining whether the target switching frequency is less than or equal to a preset switching frequency threshold; if so, determining the switching frequency adjustment strategy as the target adjustment strategy; if not, determining the phase shift angle adjustment strategy as the target adjustment strategy; wherein the switching frequency adjustment strategy is to adjust the switching frequency of multiple switching tubes in the microinverter, and the phase shift angle adjustment strategy is to adjust the phase shift angle between the multiple switching tubes in the microinverter; according to the target adjustment strategy, the multiple switching tubes are adjusted to control the output gain of the microinverter.

[0048] The target switching frequency mentioned in the determination step is the switching frequency corresponding to the multiple switches in the microinverter, determined based on the current difference. The preset switching frequency threshold is the upper limit of the switching frequency for the switch, determined based on the switch model and operating conditions, while ensuring stable performance.

[0049] The above steps specifically disclose the steps of determining a target adjustment strategy based on the switching frequency to control the output gain of the micro-inverter. When the target switching frequency is less than or equal to the preset switching frequency threshold, the switching frequency of the switch tube is negatively correlated with the output gain. Increasing the switching frequency can reduce the output gain. Therefore, the target adjustment strategy is determined to be the switching frequency adjustment strategy, that is, the output gain is controlled by adjusting the switching frequencies corresponding to multiple switch tubes in the micro-inverter. When the target switching frequency is large, that is, the target switching frequency is greater than the preset switching frequency threshold, since the actual switching frequency of the switch tube has been adjusted to the maximum (adjusted to the preset switching frequency threshold), the output gain can no longer be reduced by increasing the switching frequency. At this time, the target adjustment strategy can be determined to be the phase shift angle adjustment strategy, that is, the output gain is controlled by adjusting the phase shift angles corresponding to multiple switch tubes in the micro-inverter. The embodiment of the present invention thus realizes output gain control over a wide voltage range for a micro-inverter with a one-stage power conversion topology, expanding the applicable scenarios of micro-inverters with a one-stage power conversion topology.

[0050] According to a specific implementation of an embodiment of the present invention, when the above-mentioned target adjustment strategy is a switching frequency adjustment strategy (i.e., output gain control is achieved by adjusting the switching frequency of multiple switching tubes in the micro-inverter), a load current value is obtained, and the load current value is used as the output current set value. The output current set value is processed by taking the absolute value and serving as the target set signal of the drive controller. At the same time, the induced current value in the secondary winding of the voltage doubler rectifier circuit is obtained, and after the absolute value and filtering processing, it is used as the feedback signal of the output current sampling. The feedback signal of the output current sampling is compared with the target set signal of the drive controller to determine the signal difference. The signal difference is PI-regulated by a PI regulator to form a current loop control signal. The current loop control signal is then processed by a voltage-frequency converter to output a frequency-adjustable drive signal to adjust the switching frequency of the multiple switching tubes in the micro-inverter, thereby controlling the output gain of the micro-inverter and improving the power and efficiency of the micro-inverter. Among them, after the above difference is adjusted by the PI regulator, the switching frequency corresponding to the switching tube is finally output. Among them, when the target given signal corresponding to the output current given value is greater than the feedback signal corresponding to the induced current value, that is, the signal difference is positive, the output switching frequency decreases; when the target non-given signal corresponding to the output current given value is less than the feedback signal corresponding to the induced current value, that is, the signal difference is negative, the output switching frequency increases.

[0051] In some embodiments, if the sinusoidal wave period of the output current is the positive half period of the sinusoidal wave, then in the process of adjusting the switching frequency to control the output gain: when the first switch tube and the fourth switch tube in the resonant circuit are turned on, the current input by the photovoltaic component forms a first conduction current loop in the resonant circuit, and generates an induced current in the voltage doubler rectifier circuit, controlling the fifth switch tube and the sixth switch tube to be turned on, and the induced current flows through the second capacitor in the capacitor bridge arm to form a first induced current loop; wherein, the current input by the photovoltaic component in the first conduction current loop passes through the MOS tube of the first switch tube, the LLC circuit, the MOS tube of the fourth switch tube, and the first capacitor in sequence; the induced current in the first induced current loop passes through the MOS tube of the sixth switch tube, the parasitic diode of the fifth switch tube, and the second capacitor in sequence. When the first and fourth switching tubes in the resonant circuit are turned off, the resonant cavity current in the resonant circuit feeds the first capacitor on the DC side bus, controlling the third and second switching tubes to be turned on to form a second conduction current loop, and forming an induced current in the voltage doubler rectifier circuit. The seventh and eighth switching tubes are controlled to be turned on, and the induced current flows through the third capacitor in the capacitor bridge arm to form a second induced current loop; wherein, the resonant cavity current in the second conduction current loop passes through the parasitic diode of the third switching tube, the first capacitor, the parasitic diode of the second switching tube, and the LLC circuit in sequence; and the induced current in the second induced current loop passes through the third capacitor, the MOS tube of the eighth switching tube, and the parasitic diode of the seventh switching tube in sequence. When the resonant cavity current is zero, the photovoltaic component inputs current into the resonant circuit through the first capacitor on the DC side bus to form a third conduction current loop, and generates an induced current in the voltage doubler rectifier circuit. The induced current flows through the third capacitor in the capacitor bridge arm to form a third induced current loop; wherein, the current input by the photovoltaic component in the third conduction current loop passes through the MOS tube of the third switch tube, the LLC circuit, the MOS tube of the second switch tube, and the first capacitor in sequence, and the induced current in the third induced current loop passes through the third capacitor, the MOS tube of the eighth switch tube, and the parasitic diode of the seventh switch tube in sequence. When the third and second switching tubes in the resonant circuit are turned off, the resonant cavity current in the resonant circuit feeds the first capacitor on the DC side bus, controlling the first and fourth switching tubes to be turned on to form a fourth conduction current loop, and generating an induced current in the voltage doubler rectifier circuit. The fifth and sixth switching tubes are controlled to be turned on, and the induced current flows through the second capacitor in the capacitor bridge arm to form a fourth induced current loop; wherein, the current in the fourth conduction current loop passes through the parasitic diode of the fourth switching tube, the LLC circuit, the parasitic diode of the first switching tube, and the first capacitor in sequence, and the induced current in the fourth induced current loop passes through the MOS tube of the sixth switching tube, the parasitic diode of the fifth switching tube, and the second capacitor in sequence.If the sine wave period of the output current is the negative half-period of the sine wave, then in the process of adjusting the switching frequency to control the output gain: when the first and fourth switching tubes in the resonant circuit are turned on, the current input by the photovoltaic module forms a fifth conduction current loop in the resonant circuit, and generates an induced current in the voltage doubler rectifier circuit, which controls the seventh and eighth switching tubes to be turned on, and the induced current flows through the third capacitor in the capacitor bridge arm to form a fifth induced current loop; wherein, the current input by the photovoltaic module in the fifth conduction current loop passes through the MOS tube of the first switching tube, the LLC circuit, the MOS tube of the fourth switching tube, and the first capacitor in sequence; and the induced current in the fifth induced current loop passes through the MOS tube of the seventh switching tube, the parasitic diode of the eighth switching tube, and the third capacitor in sequence. When the first and fourth switching tubes in the resonant circuit are turned off, the resonant cavity current in the resonant circuit feeds the first capacitor on the DC bus, controlling the third and second switching tubes to be turned on to form a sixth conduction current loop, and generating an induced current in the voltage doubler rectifier circuit. The fifth and sixth switching tubes are controlled to be turned on, and the induced current flows through the second capacitor in the capacitor bridge arm to form a sixth induced current loop. The resonant cavity current in the sixth conduction current loop sequentially passes through the parasitic diode of the second switching tube, the LLC circuit, the parasitic diode of the third switching tube, and the first capacitor. The induced current in the sixth induced current loop sequentially passes through the second capacitor, the MOS tube of the fifth switching tube, and the parasitic diode of the sixth switching tube. When the resonant cavity current is zero, the current input by the photovoltaic module forms a seventh conduction current loop in the resonant circuit and generates an induced current in the voltage-doubling rectifier circuit. The induced current flows through the second capacitor of the capacitor bridge arm to form a seventh induced current loop. In the seventh conduction current loop, the current input by the photovoltaic module passes through the MOS tube of the third switch tube, the LLC circuit, the MOS tube of the second switch tube, and the first capacitor in sequence. The induced current in the seventh induced current loop passes through the second capacitor, the MOS tube of the fifth switch tube, and the parasitic diode of the sixth switch tube in sequence. When the third and second switching tubes in the resonant circuit are turned off, the resonant cavity current in the resonant circuit feeds the first capacitor on the DC side bus, controlling the first and fourth switching tubes to be turned on to form an eighth conduction current loop, and generating an induced current in the voltage doubler rectifier circuit. The seventh and eighth switching tubes are controlled to be turned on, and the induced current flows through the third capacitor of the capacitor bridge arm to form an eighth induced current loop; wherein, the current in the eighth conduction current loop passes through the parasitic diode of the fourth switching tube, the LLC circuit, the parasitic diode of the first switching tube, and the first capacitor in sequence, and the induced current in the eighth induced current loop passes through the MOS tube of the seventh switching tube, the parasitic diode of the eighth switching tube, and the third capacitor in sequence.

[0052] According to a specific implementation of an embodiment of the present invention, when the above-mentioned target adjustment strategy is a phase shift angle adjustment strategy (i.e., output gain control is achieved by adjusting the phase shift angles of multiple switching tubes in the micro-inverter), the output current corresponding to the output end of the voltage doubler rectifier circuit is obtained, and the output current is used as the output current given value; and the sine wave period corresponding to the output current at the output end of the voltage doubler rectifier circuit and the switching frequency of the multiple switching tubes in the micro-inverter within the sine wave period are determined; the mapping relationship between the output voltage gain and the phase shift angle is obtained, and according to the mapping relationship, the sine wave period and the switching frequency, the phase shift angle between the switching tubes of the first bridge arm and the second bridge arm in the resonant circuit is adjusted to adjust the duty cycle of the multiple switching tubes in the voltage doubler rectifier circuit and achieve control of the output gain of the micro-inverter. Among them, the phase shift angle adjustment strategy provided by the embodiment of the present invention is: output gain control is performed by adjusting the phase shift angles corresponding to the multiple switching tubes in the micro-inverter.

[0053] When the target switching frequency is high—that is, the target switching frequency of multiple switches determined based on the current difference is greater than a preset switching frequency threshold—the target switching frequency has already been adjusted to its maximum, and increasing the switching frequency can no longer reduce the output gain. In this case, the target adjustment strategy can be determined to further reduce the output gain by adjusting the phase shift angles corresponding to the multiple switches in the microinverter. This enables output gain control over a wide voltage range for microinverters with a one-stage power conversion topology, expanding the application scenarios of microinverters with this topology.

[0054] In some embodiments, the method further includes: detecting a maximum power value of a photovoltaic module corresponding to the micro-inverter, and receiving a current input by the photovoltaic module.

[0055] According to an embodiment of the present invention, an MPPT (Maximum Power Point Tracking) controller may be used to detect the maximum power value of a photovoltaic module, and then receive the current input by the photovoltaic module when the photovoltaic module meets the maximum power value.

[0056] In some of the embodiments, the smaller one between the output current set value determined based on MPPT and the current set value generated based on the actual output voltage value corresponding to the voltage doubler rectifier current output terminal can be taken as the actual load current loop set value, which can ensure that in off-grid mode, the device will not be unable to carry the load due to overpower operation and the photovoltaic components will not be able to carry the load.

[0057] In some embodiments, the operating state of the plurality of switch tubes is a soft switching operating state.

[0058] In the micro-inverter with a one-stage power conversion topology provided by the embodiment of the present invention, multiple switching tubes can operate in a soft switching state, thereby reducing switching losses and thereby increasing the power generation capacity of the micro-inverter.

[0059] In some embodiments, the turns ratio between the primary winding and the secondary winding in the winding transformer is determined by actual operating conditions such as the power and quantity of the photovoltaic modules and the grid voltage.

[0060] Among them, the micro-inverter provided by an embodiment of the present invention is used to transmit sinusoidal AC power to the load based on a circuit topology of primary power conversion. Figure 2 shows a circuit topology schematic diagram of the micro-inverter in an embodiment of the present invention. As shown in Figure 2, the circuit topology of the above-mentioned micro-inverter includes: a resonant circuit, a winding transformer and a voltage doubler rectifier circuit. The resonant circuit is connected to the primary winding of the winding transformer, and the voltage doubler rectifier circuit is connected to the secondary winding of the winding transformer.

[0061] Specifically, the resonant circuit is connected to the primary winding of the winding transformer, and the input end of the resonant circuit is connected to the photovoltaic module for receiving the current input by the photovoltaic module; the voltage doubler rectifier circuit includes a switch bridge arm and a capacitor bridge arm connected in parallel, and the voltage doubler rectifier circuit is connected to the secondary winding of the winding transformer, and is used to generate an induced current through the secondary winding. The induced current flows through the capacitor in the capacitor bridge arm to form an induced current loop and achieve a multiple voltage boost; wherein, the output end of the voltage doubler rectifier circuit is used to deliver a sinusoidal output current to the load.

[0062] In some embodiments, as shown in FIG2 , when the resonant circuit is a full-bridge resonant circuit, it includes: a first bridge arm, a second bridge arm, and an LLC circuit; wherein the first bridge arm and the second bridge arm are connected in parallel, the first bridge arm includes a first switch transistor Q1 and a second switch transistor Q2 connected in series, and the second bridge arm includes a third switch transistor Q3 and a fourth switch transistor Q4 connected in series; the LLC circuit includes a leakage inductor Lr, an excitation inductor Lm, and a resonant capacitor Cr connected in series, wherein the excitation inductor Lm also represents the primary winding of the winding transformer. One end of the LLC circuit is connected to the midpoint of the first bridge arm, and the other end of the LLC circuit is connected to the midpoint of the second bridge arm.

[0063] In some embodiments, as shown in FIG2 , the switching arm in the voltage-doubling rectifier circuit includes an upper switching arm and a lower switching arm, wherein the upper switching arm includes a fifth switching transistor Q5 and a sixth switching transistor Q6 connected in series and arranged in a mirrored manner, and the lower switching arm includes a seventh switching transistor Q7 and an eighth switching transistor Q8 connected in series and arranged in a mirrored manner. The capacitor arm in the voltage-doubling rectifier circuit includes a second capacitor C2 and a third capacitor C3 connected in series; one end of the secondary winding is connected to the midpoint of the switching arm, and the other end of the secondary winding is connected to the midpoint of the capacitor arm. A filter inductor Lg is provided at the output end of the voltage-doubling rectifier circuit. The filter inductor Lg can be provided on one side of the output end of the voltage-doubling rectifier circuit, or on both sides of the output end of the voltage-doubling rectifier circuit. Furthermore, the filter inductor can be provided at the output end of the voltage-doubling rectifier circuit in the form of a common-mode inductor. In the embodiment of the present invention, the capacitor in the capacitor bridge arm provided in the voltage doubler rectifier circuit and the filter inductor provided at the output end of the voltage doubler rectifier circuit form an LC high-frequency filter circuit, thereby achieving a filtering processing effect on the output current.

[0064] The micro-inverter applied based on the embodiment of the present invention realizes a circuit topology based on primary power conversion to transmit sinusoidal AC power to the AC grid, thereby effectively improving the efficiency and power of the micro-inverter.

[0065] The control method for the off-grid micro-inverter provided in an embodiment of the present invention is a micro-inverter that transmits sinusoidal AC power to a load based on a circuit topology of a first-stage power conversion. The method determines the voltage difference between the output voltage set value and the output voltage value by obtaining the output voltage set value and the output voltage value corresponding to the output terminal of the voltage-doubling rectifier circuit; determines the output current set value based on the voltage difference, obtains the induced current value in the voltage-doubling rectifier circuit, and determines the current difference between the output current set value and the induced current value; determines the target switching frequency of multiple switches in the micro-inverter based on the current difference, and controls the micro-inverter to transmit an output voltage that meets the output voltage set value to the load using the target switching frequency. This method overcomes the problems in the related art of the lack of a control solution for realizing off-grid functionality for micro-inverters with a first-stage power conversion topology, and the problems of poor economic efficiency and narrow application scenarios for grid-connected micro-inverters. The method realizes off-grid functionality control for a micro-inverter based on a first-stage power conversion topology, improves the economic efficiency of load power consumption, increases the efficiency and power of the micro-inverter, and expands the application scenarios of the micro-inverter.

[0066] An embodiment of the present invention further provides a micro-inverter, comprising: at least one processor; and a memory communicatively connected to the at least one processor. The memory stores a computer program executable by the at least one processor, and when executed by the at least one processor, the computer program causes an electronic device to perform the method of an embodiment of the present invention.

[0067] An embodiment of the present invention further provides a non-transitory machine-readable medium storing a computer program, wherein the computer program, when executed by a processor of a computer, is used to cause the computer to perform the method of the embodiment of the present invention.

[0068] An embodiment of the present invention further provides a computer program product, including a computer program, wherein when the computer program is executed by a processor of a computer, it is used to enable the computer to perform the method of the embodiment of the present invention.

[0069] With reference to Figure 3, the structural block diagram of the electronic device that can be used as the server or client of an embodiment of the present invention will now be described, which is an example of a hardware device that can be applied to various aspects of the present invention. The electronic device is intended to represent various forms of digital electronic computer equipment, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present invention described and / or required herein.

[0070] As shown in Figure 3, the electronic device includes a computing unit 301, which can perform various appropriate actions and processes according to a computer program stored in a read-only memory (ROM) 302 or a computer program loaded from a storage unit 308 into a random access memory (RAM) 303. Various programs and data required for the operation of the electronic device can also be stored in the RAM 303. The computing unit 301, ROM 302, and RAM 303 are connected to each other via a bus 304. An input / output (I / O) interface 305 is also connected to the bus 304.

[0071] Multiple components within the electronic device are connected to the I / O interface 305, including an input unit 306, an output unit 307, a storage unit 308, and a communication unit 309. The input unit 306 can be any type of device capable of inputting information into the electronic device. The input unit 306 can receive input numeric or character information and generate key signal inputs related to user settings and / or function control of the electronic device. The output unit 307 can be any type of device capable of presenting information and may include, but is not limited to, a display, a speaker, a video / audio output terminal, a vibrator, and / or a printer. The storage unit 308 may include, but is not limited to, a magnetic disk or an optical disk. The communication unit 309 allows the electronic device to exchange information / data with other devices via a computer network such as the Internet and / or various telecommunication networks, and may include, but is not limited to, a modem, a network card, an infrared communication device, a wireless communication transceiver, and / or a chipset, such as a Bluetooth device, a WiFi device, a WiMax device, a cellular communication device, and / or the like.

[0072] The computing unit 301 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the computing unit 301 include, but are not limited to, a CPU, a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units that run machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 301 performs the various methods and processes described above. For example, in some embodiments, the method embodiments of the present invention may be implemented as a computer program, which is tangibly contained in a machine-readable medium, such as a storage unit 308. In some embodiments, part or all of the computer program may be loaded and / or installed on an electronic device via a ROM 302 and / or a communication unit 309. In some embodiments, the computing unit 301 may be configured to perform the above-described method in any other appropriate manner (e.g., by means of firmware).

[0073] The computer programs for implementing the methods of the embodiments of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the computer programs are executed by the processor or controller, the functions / operations specified in the flowcharts and / or block diagrams are implemented. The computer programs may be executed entirely on the machine, partially on the machine, as a stand-alone software package, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0074] In the context of an embodiment of the present invention, a machine-readable medium can be a tangible medium that can contain or store a program for use by an instruction execution system, device or equipment or used in combination with an instruction execution system, device or equipment. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable signal medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium can include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0075] It should be noted that the term "including" and its variations used in the embodiments of the present invention are open-ended, i.e., "including but not limited to." The term "based on" means "based at least in part on." The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; and the term "some embodiments" means "at least some embodiments." The modifications of "one" and "a plurality of" mentioned in the embodiments of the present invention are illustrative and non-restrictive. Those skilled in the art should understand that, unless the context clearly indicates otherwise, they should be understood as "one or more."

[0076] The various steps described in the method implementation scheme provided in the embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method implementation scheme may include additional steps and / or omit the steps shown. The scope of protection of the present invention is not limited in this respect.

[0077] The term "embodiment" in this specification refers to specific features, structures, or characteristics described in conjunction with the embodiment that can be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments are referenced to each other. In particular, for the embodiments of the device, equipment, and system, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts are referred to the partial description of the method embodiment.

[0078] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A control method for an off-grid micro-inverter, characterized in that: The micro-inverter is used to deliver sinusoidal AC power to a load based on a circuit topology of primary power conversion. The circuit topology of the micro-inverter includes: a resonant circuit, a winding transformer and a voltage doubler rectifier circuit. The resonant circuit is connected to a primary winding of the winding transformer, and the voltage doubler rectifier circuit is connected to a secondary winding of the winding transformer. The method includes: Obtaining an output voltage given value and an output voltage value corresponding to an output end of the voltage doubler rectifier circuit, and determining a voltage difference between the output voltage given value and the output voltage value; Determine an output current given value according to the voltage difference, obtain an induced current value in the voltage doubler rectifier circuit, and determine a current difference between the output current given value and the induced current value; The target switching frequency of multiple switch tubes in the micro inverter is determined according to the current difference, and the micro inverter is controlled by the target switching frequency to transmit an output voltage that meets the given output voltage value to the load.

2. The control method according to claim 1, characterized in that: The step of determining the output current given value according to the voltage difference comprises: The voltage difference is subjected to proportional-integral control processing or proportional-resonance control processing by a controller to determine an output current given value corresponding to the micro-inverter; wherein, when the output current of the micro-inverter satisfies the output current given value, the output voltage of the micro-inverter satisfies the output voltage given value.

3. The control method according to claim 1, characterized in that: The step of determining the target switching frequency of a plurality of switch tubes in the micro inverter according to the current difference comprises: Performing proportional-integral control or proportional-resonance control on the current difference by a controller to determine a control signal; The control signal is subjected to voltage-frequency conversion processing via a voltage-frequency converter to generate a drive signal; wherein the drive signal is used to drive the conduction and shutdown of multiple switch tubes in the micro inverter, and the adjustment frequency of the drive signal is consistent with the target switching frequency of the multiple switch tubes.

4. The control method according to claim 1, characterized in that: The method further comprises an output gain control step, comprising: Determine whether the target switching frequency is less than or equal to a preset switching frequency threshold, and if so, determine that the switching frequency adjustment strategy is the target adjustment strategy; if not, determine that the phase shift angle adjustment strategy is the target adjustment strategy; wherein the switching frequency adjustment strategy is to adjust the switching frequencies of multiple switching tubes in the micro-inverter, and the phase shift angle adjustment strategy is to adjust the phase shift angles between multiple switching tubes in the micro-inverter; According to the target adjustment strategy, the multiple switch tubes are adjusted to control the output gain of the micro inverter.

5. The control method according to claim 1, characterized in that: The method further comprises: The maximum power value of the photovoltaic component corresponding to the micro-inverter is detected, and the current input by the photovoltaic component is received.

6. The control method according to claim 1, characterized in that: The working state of the multiple switch tubes is a soft switching working state.

7. A micro inverter, comprising: A processor, and a memory storing a program, wherein the program comprises instructions, which, when executed by the processor, cause the processor to perform the method according to any one of claims 1 to 6.

8. A non-transitory machine-readable medium storing computer instructions, characterized in that: The computer instructions are used to make a computer execute the method according to any one of claims 1-6.

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