Miniature photovoltaic grid-connected inverter and control method and controller thereof

Abstract

The invention discloses a miniature photovoltaic grid-connected inverter and a control method and a controller thereof. The method comprises the following steps: controlling a photovoltaic module to execute closed-loop boosting and output a first direct-current voltage to the input end of an inverter circuit; acquiring information of the power grid voltage, and when a difference value between an effective value of a preset reference voltage and the power grid voltage is smaller than a preset first difference value, controlling an inverter circuit to execute open-loop soft start by taking the power grid voltage as a reference; and under the condition that the voltage difference between the two ends of the relay is smaller than the preset relay voltage difference, the relay is controlled to start to execute the closing action based on the phase parameter of the power grid voltage, so that the relay completes the closing action under the condition that the power grid voltage is within the preset voltage interval, wherein the preset voltage interval comprises an interval in which the power grid voltage changes from a peak value to zero. The invention aims to improve the grid-connected safety of the micro photovoltaic grid-connected inverter.

Description

Technical Field

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

[0002] During the startup and grid-connection process of a micro-PV grid-connected inverter, when the relay is activated, the relay's activation time may fluctuate, making it difficult to accurately activate at the zero point of the grid voltage. If it is activated at a non-zero point, there will be a large voltage difference between the inverter output voltage and the grid voltage, and the resulting surge current can damage the relay. If the inverter is controlled to open-loop soft start before the relay is activated, the combined effect of the grid voltage and the inverter output voltage may cause the voltage on the BUS capacitor on the inverter input side to increase, causing the BUS capacitor to exceed the safe voltage range. Summary of the Invention

[0003] The main purpose of this application is to provide a micro photovoltaic grid-connected inverter and its control method and controller, aiming to improve the safety of the micro photovoltaic grid-connected inverter being connected to the grid.

[0004] To achieve the above objectives, the present application provides a control method for a micro photovoltaic grid-connected inverter. The micro photovoltaic grid-connected inverter comprises: a photovoltaic module, a bus capacitor, an inverter circuit, and a relay electrically connected in sequence, wherein the photovoltaic module is connected to an input terminal of the inverter circuit, the bus capacitor is connected in parallel to the input terminal of the inverter circuit, and the output terminal of the inverter circuit is connected to the power grid via the relay; wherein the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage; The micro photovoltaic grid-connected inverter control method includes: Step S100, controlling the photovoltaic module to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit; Step S200: When the voltage on the BUS capacitor reaches a preset first voltage, controlling the inverter circuit to perform an open-loop soft start based on a first reference voltage and output a first AC voltage to the first terminal of the relay; wherein the first reference voltage includes a preset reference voltage that changes in a positive correlation with time; Step S300, obtaining grid voltage information, and when the difference between the effective value of the preset reference voltage and the grid voltage is less than a preset first difference, controlling the inverter circuit to perform an open-loop soft start based on the grid voltage; and When the voltage difference across the relay is less than a preset relay voltage difference, the relay is controlled to start performing a closing action based on a phase parameter of the grid voltage, so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset voltage range includes: an interval in which the grid voltage changes from a peak value to zero.

[0005] Optionally, controlling the relay to start performing a closing action based on a phase parameter of the grid voltage so that the relay completes the closing action when the grid voltage is within a preset voltage range includes: Step S310: determining a phase parameter of the grid voltage based on the grid voltage information; Step S320: When the phase parameter is a preset phase parameter, control the relay to start performing a closing action so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset phase parameter includes: ±π / 2-2πf*t1; f is the frequency of the grid voltage, and t1 is the minimum closing time of the relay.

[0006] Optionally, controlling the relay to start performing a closing action based on the phase parameter of the grid voltage further includes: controlling the photovoltaic assembly to stop performing closed-loop boosting.

[0007] Optionally, controlling the relay to start a closing action based on the phase parameter of the grid voltage further includes: In the case of controlling the inverter circuit to perform open-loop soft start based on the grid voltage, a preset duty cycle corresponding to the current open-loop soft start performed by the inverter circuit is increased according to a preset duty cycle adjustment value.

[0008] Optionally, the increasing a preset duty cycle corresponding to the current open-loop soft start of the inverter circuit according to a preset duty cycle adjustment value includes: Step S330: Based on the grid voltage information, if the grid voltage is greater than a preset grid voltage, obtaining a grid voltage difference between the two. Step S340: setting the preset duty cycle adjustment value based on the grid voltage difference, and increasing the preset duty cycle corresponding to the current open-loop soft start of the inverter circuit according to the preset duty cycle adjustment value; wherein the grid voltage difference is positively correlated with the preset duty cycle adjustment value.

[0009] Optionally, there are multiple photovoltaic modules. The controlling the photovoltaic assembly to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit includes: selecting one of the plurality of photovoltaic assemblies to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit.

[0010] Optionally, controlling the photovoltaic assembly to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit further includes: When the voltage on the BUS capacitor does not reach the preset first voltage within the preset first time period, the current photovoltaic component is controlled to stop performing closed-loop boosting, and one of the remaining photovoltaic components is controlled to perform closed-loop boosting.

[0011] Optionally, after controlling the relay to start performing the closing action so that the relay completes the closing action when the grid voltage is within a preset voltage range, the micro photovoltaic grid-connected inverter control method further includes: Step S400: When it is determined based on the grid voltage information that the phase of the grid voltage is 0 or π, or when it is determined that the voltage on the BUS capacitor is less than a preset second voltage, or when it is determined that the output current of the inverter circuit is greater than a preset first current, controlling the inverter circuit to stop performing open-loop soft starting; Step S500: After a preset second time period, control the micro photovoltaic grid-connected inverter to perform grid-connected operation.

[0012] The present application also proposes a controller, which includes a memory, a processor, and a micro photovoltaic grid-connected inverter control method as described in any one of the above items, which is stored in the memory and can be run on the processor.

[0013] The present application also proposes a micro photovoltaic grid-connected inverter, which includes a photovoltaic component, a BUS capacitor, an inverter circuit and a relay electrically connected in sequence, and a controller as described in claim 9; wherein the photovoltaic component is connected to the input end of the inverter circuit, the BUS capacitor is connected in parallel to the input end of the inverter circuit, and the output end of the inverter circuit is connected to the power grid via the relay; the controller is electrically connected to the relay, the photovoltaic component, the BUS capacitor and the inverter circuit respectively, and the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage.

[0014] The micro photovoltaic grid-connected inverter control method of the present application includes: controlling the photovoltaic component to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit; when the voltage on the BUS capacitor reaches a preset first voltage, controlling the inverter circuit to perform open-loop soft start based on a first reference voltage and output a first AC voltage to the first end of the relay; wherein the first reference voltage includes a preset reference voltage that changes in a positive correlation with time; obtaining grid voltage information, and when the difference between the effective value of the preset reference voltage and the grid voltage is less than the preset first difference, controlling the inverter circuit to perform open-loop soft start based on the grid voltage; and, when the voltage difference between the two ends of the relay is less than the preset relay voltage difference, controlling the relay to start a closing action based on the phase parameter of the grid voltage, so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset voltage range includes: an interval in which the grid voltage changes from a peak value to zero. With this arrangement, the influence of the grid voltage on the BUS capacitor gradually decreases during the closing process of the relay, and the voltage on the BUS capacitor will not continue to rise due to the effect of the grid voltage, thereby effectively improving the safety of the BUS capacitor and further improving the safety of the micro photovoltaic grid-connected inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0016] In order to more clearly illustrate the embodiments of the present application 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 This is a flow chart of an embodiment of a control method for a micro photovoltaic grid-connected inverter of the present application; Figure 2 This is a flow chart of another embodiment of the micro photovoltaic grid-connected inverter control method of the present application; Figure 3 This is a flow chart of another embodiment of the micro photovoltaic grid-connected inverter control method of the present application; Figure 4 This is a flow chart of another embodiment of the micro photovoltaic grid-connected inverter control method of the present application; Figure 5 This is a schematic diagram of a circuit module of an embodiment of a micro photovoltaic grid-connected inverter of the present application; Figure 6This is the timing diagram of the control relay closure of the micro photovoltaic grid-connected inverter in this application.

[0018] The purpose, features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0019] It should be understood that the specific embodiments described herein are merely used to explain the technical solutions of the present application and are not intended to limit the present application.

[0020] In order to better understand the technical solutions of this application, the following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] 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, etc. between the various components under a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly. It should be understood that although the various steps in the flowcharts in the embodiments of the present application are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and they can be executed in other orders.

[0022] During the startup and grid-connection process of a micro-PV grid-connected inverter, when the relay is activated, the relay's activation time may fluctuate, making it difficult to accurately activate at the zero point of the grid voltage. If it is activated at a non-zero point, there will be a large voltage difference between the inverter output voltage and the grid voltage, and the resulting surge current can damage the relay. If the inverter is controlled to open-loop soft start before the relay is activated, the combined effect of the grid voltage and the inverter output voltage may cause the voltage on the BUS capacitor on the inverter input side to increase, causing the BUS capacitor to exceed the safe voltage range.

[0023] To this end, the present application proposes a micro photovoltaic grid-connected inverter control method, wherein the micro photovoltaic grid-connected inverter includes: a photovoltaic component, a BUS capacitor, an inverter circuit and a relay electrically connected in sequence, the photovoltaic component is connected to the input end of the inverter circuit, the BUS capacitor is connected in parallel to the input end of the inverter circuit, and the output end of the inverter circuit is connected to the power grid via the relay; wherein the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage.

[0024] In this embodiment, reference Figure 5 , photovoltaic components can be implemented using photovoltaic panels and voltage conversion circuits connected to photovoltaic panels, such as BOOST boost circuits, or boost modes, etc. Photovoltaic panels can convert light energy into electrical energy and output it. The voltage conversion circuit is used to boost the voltage output by the photovoltaic panel under the control of the controller and then output it. The inverter circuit includes an inverter switching circuit and a filter circuit. The inverter switching circuit can be implemented using a full-bridge switching circuit, in which the switch tube can be implemented using IGBT tubes, MOS tubes and other devices. The filter circuit can be implemented using LC filter circuit architecture, LLC filter architecture, CLLC filter architecture, etc. Figure 5 During grid-connected operation, the micro-PV grid-connected inverter shown here inverts the voltage output by the PV panels and outputs it to the grid. Relays can be selected and configured by developers based on the requirement that the difference between the relay's maximum and minimum closing times is less than one-quarter of the grid voltage cycle. These maximum and minimum closing times are pre-set in the controller.

[0025] In this embodiment, the micro photovoltaic grid-connected inverter may be provided with a controller (not shown in the figure), which is integrated with a memory for storing the following method and a processor for executing the following method. The controller may be implemented using an MCU, a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), a PLC, a SOC (System on Chip), or the like.

[0026] refer to Figure 1 In one embodiment of the present application, the micro photovoltaic grid-connected inverter control method includes: Step S100, controlling the photovoltaic module to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit; Optionally, in one embodiment, there are multiple photovoltaic components; controlling the photovoltaic components to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit includes: selecting one of the multiple photovoltaic components to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit.

[0027] In this embodiment, it is understood that within the operating environment of the micro photovoltaic grid-connected inverter, the lighting conditions at different locations are different. Therefore, multiple photovoltaic modules may be provided to ensure lighting conditions at multiple locations and / or angles. The controller may select a photovoltaic module according to its number for the closed-loop boost process during the startup of the micro photovoltaic grid-connected inverter, or may select the module based on its current operating condition, such as its health, number of errors, or number of times it has been used during startup. When the controller controls the photovoltaic module to perform a closed-loop boost, the closed-loop reference value is the preset first voltage described below (set by R&D personnel based on requirements).

[0028] Furthermore, in one embodiment, controlling the photovoltaic component to perform closed-loop boost and output a first DC voltage to the input end of the inverter circuit also includes: when the voltage on the BUS capacitor does not reach a preset first voltage within a preset first time period, controlling the current photovoltaic component to stop performing closed-loop boost, and controlling one of the remaining photovoltaic components to perform closed-loop boost.

[0029] In this embodiment, it can be seen from the above embodiments that different photovoltaic modules have different lighting conditions due to their different installation positions and / or angles. The micro photovoltaic grid-connected inverter can also be provided with a voltage detection circuit for detecting the voltage on the BUS capacitor, such as a voltage detection circuit formed by a resistor voltage divider circuit, or a voltage detection chip. The controller can determine the voltage on the BUS capacitor through the voltage detection circuit, and if the voltage fails to reach the preset first voltage within a preset first time (set by the R&D personnel according to requirements, such as 5 minutes) after controlling the photovoltaic module to perform closed-loop boosting, then it will be determined that the lighting conditions of the current photovoltaic module are poor, and then the controller will control the current photovoltaic module to stop performing closed-loop boosting, and control one of the remaining photovoltaic modules to perform closed-loop boosting.

[0030] Step S200: When the voltage on the BUS capacitor reaches a preset first voltage, controlling the inverter circuit to perform an open-loop soft start based on a first reference voltage and output a first AC voltage to the first terminal of the relay; wherein the first reference voltage includes a preset reference voltage that changes in a positive correlation with time; Step S300, obtaining grid voltage information, and when the difference between the effective value of the preset reference voltage and the grid voltage is less than a preset first difference, controlling the inverter circuit to perform an open-loop soft start based on the grid voltage; and When the voltage difference across the relay is less than a preset relay voltage difference, the relay is controlled to start performing a closing action based on a phase parameter of the grid voltage, so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset voltage range includes: an interval in which the grid voltage changes from a peak value to zero.

[0031] In this embodiment, if the controller determines, based on the voltage detection process described in the above embodiment, that the voltage on the BUS capacitor has reached a preset first voltage, it determines that a soft start can be initiated. It then controls the inverter circuit to perform an open-loop soft start based on the first reference voltage and output a first AC voltage to the first terminal of the relay. During the open-loop soft start process, the controller can control the inverter circuit to operate according to a corresponding duty cycle based on a reference voltage-duty cycle mapping table pre-stored by the developer and the current first reference voltage, so that the first AC voltage output by the inverter circuit approaches the first reference voltage. The first reference voltage comprises a preset reference voltage that changes in a positive correlation with time. Specifically, the preset reference voltage increases as the open-loop soft start duration increases, thereby gradually increasing the first AC voltage output by the inverter circuit to the first terminal of the relay. This ensures that when the relay subsequently closes, the relay is not subjected to a large current surge due to an excessive voltage difference across the relay, effectively ensuring the safety and reliability of the relay.

[0032] The micro photovoltaic grid-connected inverter may also be equipped with a grid voltage detection circuit, such as a grid voltage detection module, electrically connected to the controller and the grid. The controller can determine grid voltage information, such as voltage value, phase, and peak value, based on the feedback from the grid voltage detection circuit. When the difference between the effective value of the preset reference voltage and the grid voltage is less than a preset first difference, the inverter circuit is controlled to perform an open-loop soft start based on the grid voltage, further reducing the voltage difference across the relay. Furthermore, when the voltage difference across the relay is less than a preset relay voltage difference (set by the developer), the relay is controlled to initiate a closing action based on the grid voltage phase parameter, ensuring that the relay closes when the grid voltage is within a preset voltage range. The preset voltage range includes the period from the peak value of the grid voltage to zero.

[0033] Specifically, refer to Figure 2In one embodiment, controlling the relay to start a closing action based on the phase parameter of the grid voltage so that the relay completes the closing action when the grid voltage is within a preset voltage range includes: Step S310: determining a phase parameter of the grid voltage based on the grid voltage information; Step S320: When the phase parameter is a preset phase parameter, control the relay to start performing a closing action so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset phase parameter includes: ±π / 2-2πf*t1; f is the frequency of the grid voltage, and t1 is the minimum closing time of the relay.

[0034] In this embodiment, reference Figure 2 、 Figure 5 and Figure 6 From the above, we can see that the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage. Therefore, the controller only needs to determine the time point to start controlling the relay to perform the closing action based on the minimum closing time of the relay. The phase of the grid voltage corresponding to this time point is: ±π / 2-2πf*t1. In other words, refer to Figure 6 It can be seen that Figure 6 The horizontal axis represents time T. When the grid voltage reaches the above phase, the control relay begins to close. Regardless of the controller's current closing duration, the corresponding grid voltage will decrease over time. With this configuration, the influence of the grid voltage on the BUS capacitor gradually decreases during the relay's closing process. The voltage on the BUS capacitor will not continue to rise due to the grid voltage, effectively improving the safety of the BUS capacitor and, in turn, the safety of the micro-PV grid-connected inverter.

[0035] In addition, it can be understood that in one embodiment of the present application, the control of the relay to start the closing action based on the phase parameter of the grid voltage also includes: controlling the photovoltaic module to stop performing closed-loop boosting. In this embodiment, it can be seen from the above content that during the process of the relay performing the closing action, the grid voltage will also affect the BUS capacitor. In this case, the controller can also control the photovoltaic module to stop performing closed-loop boosting after controlling the relay to perform the closing action. Furthermore, when the grid phase is ±π / 2, the photovoltaic module can be controlled to stop performing closed-loop boosting, so that the inverter circuit consumes the electrical energy in the BUS capacitor to reduce the voltage value in the BUS capacitor during the open-loop soft start. Through the above setting, it is possible to further improve the situation where the BUS capacitor voltage is too high due to the grid voltage while the relay performs the closing action, and even make the BUS capacitor voltage in a decreasing state, thereby further improving the safety of the BUS capacitor operation.

[0036] It's important to understand that, in practice, grid voltages often contain harmonics. Therefore, when the relay closes, the grid voltage may rebound. In other words, while the grid voltage decreases from its peak value toward zero during the relay closing process, the presence of harmonics may cause the grid voltage to rise again, thereby increasing the voltage on the bus capacitor.

[0037] To this end, in one embodiment of the present application, controlling the relay to start performing a closing action based on the phase parameter of the grid voltage further includes: In the case of controlling the inverter circuit to perform open-loop soft start based on the grid voltage, a preset duty cycle corresponding to the current open-loop soft start performed by the inverter circuit is increased according to a preset duty cycle adjustment value.

[0038] In this embodiment, based on the above content, a reference voltage-duty cycle mapping table is set up inside the controller by the R&D personnel. Therefore, after the controller determines the preset duty cycle corresponding to the current grid voltage based on the grid voltage and the above mapping table, it will increase the preset duty cycle adjustment value on the current preset duty cycle. In this way, the actual voltage output by the inverter circuit can be made larger, and because the actual voltage output by the inverter circuit is larger, the energy in the BUS capacitor of the previous stage will also be transferred to the grid through the inverter circuit, that is, the voltage of the current BUS capacitor will further decrease, thereby in disguise making it so that when harmonics appear in the grid voltage, the grid voltage increase caused by the harmonics will not completely cause the voltage of the BUS capacitor to be increased, effectively ensuring the safety of the BUS capacitor.

[0039] Optionally, in one embodiment, the preset duty cycle adjustment value may be preset as a fixed value by a developer and stored in the controller.

[0040] Optionally, in another embodiment, the preset duty cycle adjustment value may also be adaptively changed according to the current grid voltage. Figure 3 , the step of increasing the preset duty cycle corresponding to the current open-loop soft start of the inverter circuit according to the preset duty cycle adjustment value includes: Step S330: Based on the grid voltage information, if the grid voltage is greater than a preset grid voltage, obtaining a grid voltage difference between the two. Step S340: setting the preset duty cycle adjustment value based on the grid voltage difference, and increasing the preset duty cycle corresponding to the current open-loop soft start of the inverter circuit according to the preset duty cycle adjustment value; wherein the grid voltage difference is positively correlated with the preset duty cycle adjustment value.

[0041] In this embodiment, if the controller determines, based on the grid voltage information acquired by the grid voltage acquisition circuit, that the current actual grid voltage is greater than a preset grid voltage, it determines that harmonics are present in the current actual grid voltage. The preset grid voltage is the theoretical value of the grid voltage at the current phase. The controller then determines the grid voltage difference between the actual grid voltage and the preset grid voltage, i.e., the value of the grid voltage increase caused by the current grid voltage harmonics. The controller then sets a corresponding preset duty cycle adjustment value based on the grid voltage difference. For example, the controller may pre-store a mapping table between grid voltage difference and preset duty cycle adjustment value. This mapping table can be preset by R&D personnel based on specific needs. In this mapping table, the preset duty cycle adjustment value tends to increase with increasing grid voltage difference. The controller can determine the final preset duty cycle adjustment value based on the current grid voltage difference and the mapping table. In another example, R&D personnel can also set a grid voltage difference-preset duty cycle adjustment value transfer function in the controller so that the controller determines the final preset duty cycle adjustment value based on the transfer function and the grid voltage difference. The transfer function still meets the setting requirement that the grid voltage difference is positively correlated with the preset duty cycle adjustment value.

[0042] Thus, through the above setting, when the relay performs the closing action, the controller will also match the appropriate preset duty cycle adjustment value according to the harmonic conditions of the current grid voltage, thereby further improving the safety of the BUS capacitor operation.

[0043] refer to Figure 4 and Figure 5In one embodiment of the present application, after controlling the relay to start performing the closing action so that the relay completes the closing action when the grid voltage is within the preset voltage range, the micro photovoltaic grid-connected inverter control method further includes: Step S400: When it is determined based on the grid voltage information that the phase of the grid voltage is 0 or π, or when it is determined that the voltage on the BUS capacitor is less than a preset second voltage, or when it is determined that the output current of the inverter circuit is greater than a preset first current, controlling the inverter circuit to stop performing open-loop soft starting; Step S500: After a preset second time period, control the micro photovoltaic grid-connected inverter to perform grid-connected operation.

[0044] In this embodiment, after the controller determines the maximum closing time after the relay closing action begins based on an internal timer, it confirms that the current relay has completed the closing action. At this point, the controller confirms that the current micro photovoltaic grid-connected inverter has completed the startup process. Subsequently, based on the grid voltage information acquired by the grid voltage acquisition circuit, if the grid voltage phase is determined to be 0 or π, or if the voltage on the BUS capacitor is less than a preset second voltage, or if the output current of the inverter circuit is greater than a preset first current, the controller controls the inverter circuit to stop performing open-loop soft starting, thereby preparing for subsequent grid connection. After controlling the inverter circuit to stop performing the switch soft starting action, after a preset second time (predetermined by R&D personnel and stored in the controller, for example, 8 ms), the micro photovoltaic grid-connected inverter is controlled to perform grid connection, thereby inverting the output voltage of the photovoltaic module according to the grid connection requirements and then feeding it back to the grid. For example, based on the above embodiment, multiple photovoltaic modules are controlled to start outputting simultaneously to increase the amount of electrical energy output to the grid. This process can refer to the relevant processes in the prior art and will not be described in detail here.

[0045] The present application also proposes a controller, which includes a memory, a processor, and a micro photovoltaic grid-connected inverter control method as described in any one of the above items, which is stored in the memory and can be run on the processor.

[0046] It is worth noting that since the controller of the present application includes the above-mentioned micro photovoltaic grid-connected inverter control method, the controller of the present application also includes all embodiments of the above-mentioned micro photovoltaic grid-connected inverter control method and the effects brought about by each embodiment, which will not be repeated here.

[0047] The present application also proposes a micro photovoltaic grid-connected inverter, comprising a photovoltaic assembly, a BUS capacitor, an inverter circuit and a relay electrically connected in sequence, and the controller as described above; wherein the photovoltaic assembly is connected to the input end of the inverter circuit, the BUS capacitor is connected in parallel to the input end of the inverter circuit, and the output end of the inverter circuit is connected to the power grid via the relay; the controller is electrically connected to the relay, the photovoltaic assembly, the BUS capacitor and the inverter circuit respectively, and the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage.

[0048] It is worth noting that, since the micro photovoltaic grid-connected inverter of the present application includes the above-mentioned controller, the micro photovoltaic grid-connected inverter of the present application also includes all embodiments of the above-mentioned controller and the effects brought about by each embodiment, which will not be repeated here.

[0049] The above description is only part of the embodiments of the present application and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A micro photovoltaic grid-connected inverter control method, characterized in that: The micro photovoltaic grid-connected inverter comprises: a photovoltaic module, a BUS capacitor, an inverter circuit, and a relay electrically connected in sequence, wherein the photovoltaic module is connected to the input end of the inverter circuit, the BUS capacitor is connected in parallel to the input end of the inverter circuit, and the output end of the inverter circuit is connected to the power grid via the relay; wherein the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the power grid voltage; The micro photovoltaic grid-connected inverter control method includes: Step S100, controlling the photovoltaic module to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit; Step S200: When the voltage on the BUS capacitor reaches a preset first voltage, controlling the inverter circuit to perform an open-loop soft start based on a first reference voltage and output a first AC voltage to the first terminal of the relay; wherein the first reference voltage includes a preset reference voltage that changes in a positive correlation with time; Step S300, obtaining grid voltage information, and when the difference between the effective value of the preset reference voltage and the grid voltage is less than a preset first difference, controlling the inverter circuit to perform an open-loop soft start based on the grid voltage; and When the voltage difference across the relay is less than a preset relay voltage difference, the relay is controlled to start performing a closing action based on a phase parameter of the grid voltage, so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset voltage range includes: an interval in which the grid voltage changes from a peak value to zero.

2. The micro photovoltaic grid-connected inverter control method according to claim 1, characterized in that: The controlling the relay to start performing the closing action based on the phase parameter of the grid voltage so that the relay completes the closing action when the grid voltage is within a preset voltage range includes: Step S310: determining a phase parameter of the grid voltage based on the grid voltage information; Step S320: When the phase parameter is a preset phase parameter, control the relay to start performing a closing action so that the relay completes the closing action when the grid voltage is within a preset voltage range; wherein the preset phase parameter includes: ±π / 2-2πf*t1; f is the frequency of the grid voltage, and t1 is the minimum closing time of the relay.

3. The micro photovoltaic grid-connected inverter control method according to claim 1, wherein: The controlling the relay to start performing a closing action based on the phase parameter of the grid voltage further includes: controlling the photovoltaic assembly to stop performing closed-loop boosting.

4. The micro photovoltaic grid-connected inverter control method according to claim 1, wherein: The controlling the relay to start performing the closing action based on the phase parameter of the grid voltage further includes: In the case of controlling the inverter circuit to perform open-loop soft start based on the grid voltage, a preset duty cycle corresponding to the current open-loop soft start performed by the inverter circuit is increased according to a preset duty cycle adjustment value.

5. The micro photovoltaic grid-connected inverter control method according to claim 4, characterized in that: The step of increasing the preset duty cycle corresponding to the open-loop soft start of the inverter circuit according to the preset duty cycle adjustment value includes: Step S330: Based on the grid voltage information, if the grid voltage is greater than a preset grid voltage, obtaining a grid voltage difference between the two. Step S340: setting the preset duty cycle adjustment value based on the grid voltage difference, and increasing the preset duty cycle corresponding to the current open-loop soft start of the inverter circuit according to the preset duty cycle adjustment value; wherein the grid voltage difference is positively correlated with the preset duty cycle adjustment value.

6. The micro photovoltaic grid-connected inverter control method according to any one of claims 1 to 5, characterized in that: There are multiple photovoltaic modules; The controlling the photovoltaic assembly to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit includes: selecting one of the plurality of photovoltaic assemblies to perform closed-loop boosting and output a first DC voltage to the input end of the inverter circuit.

7. The micro photovoltaic grid-connected inverter control method according to claim 6, characterized in that: The step of controlling the photovoltaic assembly to perform closed-loop boosting and outputting a first DC voltage to the input end of the inverter circuit further includes: When the voltage on the BUS capacitor does not reach the preset first voltage within the preset first time period, the current photovoltaic component is controlled to stop performing closed-loop boosting, and one of the remaining photovoltaic components is controlled to perform closed-loop boosting.

8. The micro photovoltaic grid-connected inverter control method according to any one of claims 1 to 5, characterized in that: After controlling the relay to start performing the closing action so that the relay completes the closing action when the grid voltage is within the preset voltage range, the micro photovoltaic grid-connected inverter control method further includes: Step S400: When it is determined based on the grid voltage information that the phase of the grid voltage is 0 or π, or when it is determined that the voltage on the BUS capacitor is less than a preset second voltage, or when it is determined that the output current of the inverter circuit is greater than a preset first current, controlling the inverter circuit to stop performing open-loop soft starting; Step S500: After a preset second time period, control the micro photovoltaic grid-connected inverter to perform grid-connected operation.

9. A controller, characterized in that: The controller includes a memory, a processor, and a micro photovoltaic grid-connected inverter control method according to any one of claims 1 to 8, which is stored in the memory and can be run on the processor.

10. A micro photovoltaic grid-connected inverter, characterized in that: The micro photovoltaic grid-connected inverter includes a photovoltaic component, a BUS capacitor, an inverter circuit and a relay electrically connected in sequence, and a controller as described in claim 9; wherein, the photovoltaic component is connected to the input end of the inverter circuit, the BUS capacitor is connected in parallel with the input end of the inverter circuit, and the output end of the inverter circuit is connected to the power grid via the relay; the controller is electrically connected to the relay, the photovoltaic component, the BUS capacitor and the inverter circuit respectively, and the difference between the maximum closing time and the minimum closing time of the relay is less than one-quarter of the cycle time of the grid voltage.

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