A micro inverter, control method and storage medium

Abstract

The present application provides a micro inverter, a control method and a storage medium, which relate to the field of inverter technology, and include: a primary H-bridge circuit, a transformer, a secondary bridge arm circuit, a switch and a target controller, wherein the target controller is used to obtain a first phase shift control amount according to the grid voltage and the target output voltage, and drive and control a group of switch tubes according to the first phase shift control amount, so that the target output voltage is synchronized with the grid voltage; when it is determined that the target output voltage is synchronized with the grid voltage, the target controller is also used to obtain a second phase shift control amount according to the target output current, a preset reference current and a preset feedforward control amount, and drive and control a group of switch tubes according to the second phase shift control amount, so that the target output current of the micro inverter when it is connected to the grid is equal to the preset reference current. The technical solution of the present application is implemented to achieve the effect of effectively reducing the impact current at the moment of grid connection.

Description

Technical Field

[0001] The present application relates to the technical field of inverters, and in particular to a micro inverter, a control method and a storage medium. Background Art

[0002] With the growing global demand for renewable energy, photovoltaic power generation systems have been widely used. As a key component in photovoltaic power generation systems, photovoltaic micro-inverters are responsible for converting the direct current generated by photovoltaic modules into alternating current and transmitting it to the power grid. Compared with traditional string inverters, micro-inverters have the advantages of modular design, flexible installation, fault isolation and maximizing the output of each photovoltaic module. Therefore, they have been increasingly used in distributed photovoltaic power generation systems. However, micro-inverters are prone to generate large inrush currents during the grid-connected process. The instantaneous inrush current at the time of grid connection will cause large electrical stress on the inverter's devices, which may cause device damage and affect the reliability and life of the system. Therefore, how to reduce the instantaneous inrush current at the time of grid connection has become a technical problem that needs to be solved in this field. Summary of the invention

[0003] The purpose of the present application is to overcome the above-mentioned technical problems. The present application provides a micro inverter, a control method and a storage medium.

[0004] In the first aspect, the present application provides a micro inverter, including: a primary H-bridge circuit, a transformer, a secondary bridge arm circuit, a switch and a target controller, wherein the input end of the primary H-bridge circuit is electrically connected to the output end of the photovoltaic panel, the output end of the primary H-bridge circuit is electrically connected to the primary winding of the transformer, the input end of the secondary bridge arm circuit is electrically connected to the secondary winding of the transformer, and the output end of the secondary bridge arm circuit is connected to the power grid through the switch; the secondary bridge arm circuit includes a bidirectional switch bridge arm and a capacitor bridge arm, the two ends of the secondary winding of the transformer are electrically connected to the midpoint of the bidirectional switch bridge arm and the midpoint of the capacitor bridge arm respectively, the two ends of the bidirectional switch bridge arm are connected in parallel with the two ends of the capacitor bridge arm, and serve as the output end of the secondary bridge arm circuit; the target controller is electrically connected to each switch tube in a group of switch tubes, wherein a group of switches The tubes include each switch tube in the primary H-bridge circuit and each switch tube in the bidirectional switch bridge arm; the target controller is used to obtain a first phase-shift control amount according to the grid voltage and the target output voltage, and drive and control a group of switch tubes according to the first phase-shift control amount, so that the target output voltage is synchronized with the grid voltage, wherein the target output voltage is used to represent the output voltage of the micro-inverter; when it is determined that the target output voltage is synchronized with the grid voltage, the target controller is also used to obtain a second phase-shift control amount according to the target output current, a preset reference current and a preset feedforward control amount, and drive and control a group of switch tubes according to the second phase-shift control amount, so that the target output current of the micro-inverter when connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter.

[0005] By adopting the above technical solution, the primary H-bridge circuit cooperates with the transformer to achieve efficient and stable DC to AC conversion; the design of the bidirectional switch bridge arm and the capacitor bridge arm ensures the stable output of the secondary bridge arm circuit and reduces the current fluctuation at the moment of grid connection; the target controller synchronizes the target output voltage with the grid voltage through a precise phase shift control strategy, thereby reducing the impact current during the grid connection process; when the target output voltage is synchronized with the grid voltage, the target controller can also obtain the second phase shift control amount according to the target output current, the preset reference current and the preset feedforward control amount, and drive and control a group of switch tubes to ensure that the target output current of the micro inverter is equal to the preset reference current when it is grid-connected, thereby achieving precise current control and further reducing the impact of the impact current; that is, the target controller drives and controls a group of switch tubes through the second phase shift control amount to ensure that the target output current reaches or exceeds the preset current reference value, thereby improving the grid connection efficiency and stability and ensuring the stable operation of the system. The micro inverter in this technical solution can effectively reduce the impact current at the moment of grid connection, thereby improving the reliability and life of the system.

[0006] Optionally, the micro inverter further includes a first capacitor, wherein the first capacitor is connected in parallel to the input end of the primary H-bridge circuit; the primary H-bridge circuit includes a first MOS tube, a second MOS tube, a third MOS tube and a fourth MOS tube, wherein the drain of the first MOS tube is electrically connected to the drain of the third MOS tube and serves as one end of the input end of the primary H-bridge circuit, the source of the first MOS tube is electrically connected to the drain of the second MOS tube, the source of the third MOS tube is electrically connected to the drain of the fourth MOS tube, the source of the second MOS tube is electrically connected to the source of the fourth MOS tube and serves as the other end of the input end of the primary H-bridge circuit; the bidirectional switch bridge arm includes a fifth MOS tube, a sixth MOS tube, a seventh MOS tube and an eighth MOS tube, and the capacitor bridge arm includes a second capacitor and a third capacitor, wherein, The source of the fifth MOS tube is electrically connected to the source of the sixth MOS tube, the drain of the sixth MOS tube is electrically connected to the drain of the seventh MOS tube, the source of the seventh MOS tube is electrically connected to the source of the eighth MOS tube, the second capacitor and the third capacitor are connected in series between the drain of the fifth MOS tube and the drain of the eighth MOS tube, the drain of the fifth MOS tube and the drain of the eighth MOS tube serve as the output end of the secondary bridge arm circuit; the drain of the sixth MOS tube is electrically connected to one end of the secondary winding of the transformer through the leakage inductance, the connection point of the second capacitor and the third capacitor is electrically connected to the other end of the secondary winding of the transformer, and a group of switch tubes includes a first MOS tube, a second MOS tube, a third MOS tube, a fourth MOS tube, a fifth MOS tube, a sixth MOS tube, a seventh MOS tube and an eighth MOS tube.

[0007] By adopting the above technical solution, the first capacitor is connected in parallel with the input end of the primary H-bridge circuit to filter and smooth the input voltage, reduce voltage fluctuations, and improve the stability of the system; the primary H-bridge circuit is composed of four MOS tubes to form a standard H-bridge topology, which can realize the conversion from DC to AC; the bidirectional switch bridge arm is composed of four MOS tubes, which can realize bidirectional conduction and is suitable for the AC output of the secondary side of the transformer; the capacitor bridge arm is composed of two capacitors in series, which plays the role of filtering and energy storage, helps to smooth the output current and reduce the impact current.

[0008] Optionally, the target controller includes a PR controller and a PI controller, wherein the PR controller is used to generate a first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, and the target controller is used to adjust the inner phase shift angle and the outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm; the PI controller is used to generate a phase shift angle adjustment amount according to the difference between the target output current and a preset reference current, and the target controller superimposes the phase shift angle adjustment amount and the preset feedforward control amount to obtain a second phase shift control amount, wherein the preset feedforward control amount is a compensation phase shift angle pre-set according to system parameters.

[0009] By adopting the above technical solution, the PR controller can accurately generate the first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, thereby effectively adjusting the inner phase shift angle and the outer phase shift angle to ensure that the target output voltage is synchronized with the grid voltage. This not only improves the grid-connected efficiency of the system, but also reduces the impact current during the grid-connected process, protects the inverter components from electrical stress damage, and extends the service life of the system. At the same time, the PI controller generates a phase shift angle adjustment amount according to the difference between the target output current and the preset reference current, and superimposes it with the preset feedforward control amount, further optimizing the second phase shift control amount, ensuring that the target output current of the micro inverter is stable at the preset reference current level when it is grid-connected, and enhancing the stability and reliability of the system. Through the joint control of the PR controller and the PI controller, the impact current at the moment of grid connection can be significantly reduced. The PR controller ensures that the output voltage is synchronized with the grid voltage, and the PI controller accurately controls the output current, thereby effectively reducing the impact current, protecting the internal components of the inverter, and extending the service life. Accurate voltage and current control improves the stability and reliability of the system. The dual guarantees of voltage synchronization and current control make the micro inverter more stable during the grid connection process, reduce voltage fluctuations and current mutations, and improve the overall performance of the system.

[0010] Optionally, the target controller also includes a grid-connected judgment module, which is used to obtain a first phase-shift control amount or a second phase-shift control amount, wherein, when it is determined that the target output voltage and the grid voltage meet a first preset condition, the grid-connected judgment module outputs the first phase-shift control amount, and instructs the target controller to control the inner phase-shift angle and the outer phase-shift angle according to the first phase-shift control amount, wherein the first preset condition includes that the target output voltage and the grid voltage do not meet the synchronization condition or the target output voltage and the grid voltage meet the synchronization condition for less than a preset time; when it is determined that the target output voltage and the grid voltage meet the second preset condition, the grid-connected judgment module outputs the second phase-shift control amount, and instructs the target controller to control the inner phase-shift angle and the outer phase-shift angle according to the second phase-shift control amount, wherein the second preset condition is used to indicate that the target output voltage and the grid voltage meet the synchronization condition or the time for which the target output voltage and the grid voltage meet the synchronization condition is greater than or equal to the preset time.

[0011] By adopting the above technical solution, the grid-connected judgment module obtains the first phase-shift control amount or the second phase-shift control amount to ensure that the grid-connected output process is more accurate and smooth. When the target output voltage is not completely synchronized with the grid voltage or the synchronization time is insufficient, the first phase-shift control amount is used for adjustment to avoid the impact current caused by premature grid connection. When the target output voltage and the grid voltage have reached the synchronization condition or meet the synchronization condition and last for a long enough time, the second phase-shift control amount is used to further optimize the grid-connected process, so that the target output current when the switch is closed is stable at the preset reference current level, thereby reducing the impact of the impact current on the device.

[0012] Optionally, the switch includes a first relay and a second relay, wherein the first output end of the secondary bridge arm circuit is connected to the live wire of the grid through the first relay, and the second output end of the secondary bridge arm circuit is connected to the neutral wire of the grid through the second relay.

[0013] By adopting the above technical solution, the setting of the first relay and the second relay ensures the reliable connection and disconnection between the secondary bridge arm circuit and the grid, realizes the precise control of the grid connection process, and avoids the large current shock at the moment of grid connection. Through the cooperation of the first relay and the second relay, the switch can be closed when the target output voltage is synchronized with the grid voltage, thereby achieving smooth grid connection and further reducing the impact of the impact of the impact current. This design not only improves the stability and safety of the system, but also extends the service life of the micro inverter and related components.

[0014] In a second aspect of the present application, a control method for a micro-inverter is also provided, which is applied to any of the micro-inverters mentioned above, and includes: obtaining a grid voltage and a target output voltage, wherein the target output voltage is used to represent the output voltage of the micro-inverter; obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling a group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage; when it is determined that the target output voltage is synchronized with the grid voltage, controlling the switch to close so that the micro-inverter is connected to the grid, and obtaining a second phase shift control amount according to the target output current, a preset reference current and a preset feedforward control amount, and driving and controlling a group of switch tubes according to the second phase shift control amount so that the target output current of the micro-inverter when connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter.

[0015] By adopting the above technical solution, the grid voltage and the target output voltage are obtained, and the target output voltage is ensured to be synchronized with the grid voltage, thereby avoiding the impact current caused by voltage asynchrony at the moment of grid connection, and improving the stability and reliability of the system. When it is determined that the target output voltage is synchronized with the grid voltage, the switch is controlled to close, so that the micro inverter is smoothly connected to the grid. At the same time, the second phase shift control amount is obtained according to the target output current, the preset reference current and the preset feedforward control amount, and the grid-connected output current is further accurately controlled to be equal to the preset reference current, so as to ensure the stability of the output current after grid connection, reduce the impact of current fluctuations on the grid, and extend the service life of the inverter and its related components.

[0016] Optionally, obtaining a grid voltage and a target output voltage includes: obtaining a first amplitude of the grid voltage, and obtaining a second amplitude of the target output voltage; obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling a group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, including: determining the amplitude difference between the grid voltage and the target output voltage; using a PR controller to generate a first phase shift control amount according to the amplitude difference, wherein the target controller includes a PR controller; adjusting an inner phase shift angle and an outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm.

[0017] By adopting the above technical solution, the first amplitude of the grid voltage and the second amplitude of the target output voltage are obtained, ensuring that the system can accurately measure and compare the two voltage values ​​before grid connection. The amplitude difference between the grid voltage and the target output voltage is determined so that the system can identify the difference between the two, thereby providing a basis for subsequent control. The PR controller is used to generate the first phase shift control amount according to the amplitude difference, which improves the response speed and accuracy of the control and ensures that the target output voltage quickly and accurately follows the grid voltage changes. Adjusting the inner phase shift angle and the outer phase shift angle synchronizes the target output voltage with the grid voltage, effectively reducing the instantaneous impact current of grid connection, reducing the electrical stress on the components in the inverter, and improving the reliability and life of the system.

[0018] Optionally, when it is determined that the target output voltage is synchronized with the grid voltage, a second phase-shift control quantity is obtained according to the target output current, a preset reference current and a preset feedforward control quantity, and a group of switching tubes are driven and controlled according to the second phase-shift control quantity, including: when it is determined that the target output voltage is synchronized with the grid voltage, determining the current difference between the target output current and the preset reference current; using a PI controller to generate a phase-shift angle adjustment quantity according to the current difference, wherein the target controller also includes a PI controller; superimposing the phase-shift angle adjustment quantity and the preset feedforward control quantity to obtain a second phase-shift control quantity, wherein the preset feedforward control quantity is a compensation phase-shift angle pre-set according to system parameters; and driving and controlling a group of switching tubes according to the second phase-shift control quantity.

[0019] By adopting the above technical solution, the current difference between the target output current and the preset reference current is determined, so that the current change in the grid-connected process can be monitored in real time to ensure the accuracy of current control; the PI controller is used to generate a phase shift angle adjustment amount according to the current difference, which can quickly respond and adjust the phase shift angle so that the target output current quickly approaches the preset reference current, thereby reducing the grid-connected impact current; the phase shift angle adjustment amount and the preset feedforward control amount are superimposed to obtain a second phase shift control amount, which further optimizes the control strategy and improves the dynamic response speed and stability of the system; a group of switching tubes are driven and controlled according to the second phase shift control amount to ensure a smooth current transition in the grid-connected process and avoid device damage and system instability caused by sudden changes.

[0020] Optionally, the preset feedforward control amount is calculated according to the following formula: F = 4 × f smax ×L lk ×I * o ×sinθ / (N×V in ), where F represents the preset feedforward control amount, f smax Indicates the maximum switching frequency of a group of switching tubes, L lk Represents the leakage inductance of the transformer, I * orepresents the preset reference current, θ represents the phase angle of the grid voltage, N represents the turns ratio between the primary and secondary sides of the transformer, V in Indicates the voltage of the photovoltaic panel.

[0021] By adopting the above technical solution, the preset feedforward control quantity can be accurately calculated, the impact of system parameter changes can be effectively compensated, the output current of the micro inverter during the grid connection process can be ensured to be stable, the instantaneous impact current of the grid connection can be reduced, and the reliability and service life of the system can be improved. Specifically, the solution improves the control accuracy and enhances the adaptability and stability of the system by introducing multiple parameters such as the maximum switching frequency, transformer leakage inductance, preset reference current, grid voltage phase angle, transformer turns ratio and photovoltaic panel voltage.

[0022] In a third aspect of the present application, an electronic device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, any of the above method steps is implemented.

[0023] In a fourth aspect of the present application, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores instructions, and when the instructions are executed, any of the above method steps is performed.

[0024] In summary, one or more technical solutions provided in this application have at least the following technical effects or advantages:

[0025] 1. It can effectively reduce the impact current at the moment of grid connection, so as to improve the reliability and life of the system;

[0026] 2. The PR controller ensures that the output voltage is synchronized with the grid voltage, while the PI controller accurately controls the output current, which can significantly reduce the instantaneous impact current of grid connection, making the micro inverter more stable during the grid connection process, reducing voltage fluctuations and current mutations, and improving the overall performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a framework diagram of a micro inverter provided in an embodiment of the present application;

[0028] Figure 2 is a circuit diagram of a micro inverter provided in an embodiment of the present application;

[0029] Figure 3 is a flow chart of a control method for a micro inverter provided in an embodiment of the present application;

[0030] Figure 4 It is a principle block diagram of a control method for a micro inverter provided in an embodiment of the present application;

[0031] Figure 5It is an overall flow chart of a micro-inverter grid-connected output control provided by an embodiment of the present application;

[0032] Figure 6 This is an example waveform diagram of the switch tube control provided in the embodiment of the present application.

[0033] Description of reference numerals:

[0034] C1-first capacitor, C2-second capacitor, C3-third capacitor, Q1-first MOS tube, Q2-second MOS tube, Q3-third MOS tube, Q4-fourth MOS tube, Q5-fifth MOS tube, Q6-sixth MOS tube, Q7-seventh MOS tube, Q8-eighth MOS tube, L lk -leakage inductance, T1-transformer, S1-first relay, S2-second relay. DETAILED DESCRIPTION

[0035] In order to enable technicians in this field to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments.

[0036] In the description of the embodiments of the present application, words such as "for example" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "for example" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "for example" or "for example" is intended to present related concepts in a specific way.

[0037] In the description of the embodiments of the present application, the term "plurality" means two or more. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. The terms "include", "comprise", "have" and their variations all mean "including but not limited to", unless otherwise specifically emphasized.

[0038] The following is combined with Figure 1-Figure 6 The embodiments of the present application are described in detail.

[0039] The present application provides a micro inverter, referring to Figure 1 , Figure 1It is a framework diagram of a micro inverter provided by an embodiment of the present application, including: a primary H-bridge circuit, a transformer, a secondary bridge arm circuit, a switch and a target controller, wherein the input end of the primary H-bridge circuit is electrically connected to the output end of the photovoltaic panel, the output end of the primary H-bridge circuit is electrically connected to the primary winding of the transformer, the input end of the secondary bridge arm circuit is electrically connected to the secondary winding of the transformer, and the output end of the secondary bridge arm circuit is connected to the power grid through the switch; the secondary bridge arm circuit includes a bidirectional switch bridge arm and a capacitor bridge arm, the two ends of the secondary winding of the transformer are electrically connected to the midpoint of the bidirectional switch bridge arm and the midpoint of the capacitor bridge arm respectively, the two ends of the bidirectional switch bridge arm are connected in parallel with the two ends of the capacitor bridge arm, and serve as the output end of the secondary bridge arm circuit; the target controller is electrically connected to each switch tube in a group of switch tubes, wherein a group The switch tubes include each switch tube in the primary H-bridge circuit and each switch tube in the bidirectional switch bridge arm; the target controller is used to obtain a first phase-shift control amount according to the grid voltage and the target output voltage, and drive and control a group of switch tubes according to the first phase-shift control amount, so that the target output voltage is synchronized with the grid voltage, wherein the target output voltage is used to represent the output voltage of the micro-inverter; when it is determined that the target output voltage is synchronized with the grid voltage, the target controller is also used to obtain a second phase-shift control amount according to the target output current, a preset reference current and a preset feedforward control amount, and drive and control a group of switch tubes according to the second phase-shift control amount, so that the target output current of the micro-inverter when connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter.

[0040] In the above embodiment, the primary H-bridge circuit cooperates with the transformer to realize efficient and stable DC to AC conversion; the design of the bidirectional switch bridge arm and the capacitor bridge arm ensures the stable output of the secondary bridge arm circuit and reduces the current fluctuation at the moment of grid connection; the target controller synchronizes the target output voltage with the grid voltage through a precise phase shift control strategy, thereby reducing the impact current during the grid connection process; when the target output voltage is synchronized with the grid voltage, the target controller can also obtain the second phase shift control amount according to the target output current, the preset reference current and the preset feedforward control amount, and drive and control a group of switch tubes to ensure that the target output current of the micro inverter is equal to the preset reference current when it is grid-connected, thereby realizing accurate current control and further reducing the impact of the impact current; that is, the target controller drives and controls a group of switch tubes through the second phase shift control amount to ensure that the target output current reaches or exceeds the preset current reference value, thereby improving the grid connection efficiency and stability and ensuring the stable operation of the system. The micro inverter in this embodiment can effectively reduce the impact current at the moment of grid connection, thereby achieving the effect of improving the reliability and life of the system. Through the precise phase shift control of the target controller, the output voltage and current of the micro inverter can be smoothly adjusted, thereby reducing the impact current at the moment of grid connection, reducing the electrical stress on the components in the inverter, and improving the reliability and life of the system. The target controller performs preliminary phase shift control according to the grid voltage and the target output voltage to achieve voltage synchronization; and then performs further phase shift control according to the target output current and the preset reference current to achieve current regulation. This control method can ensure that the output voltage and current of the micro inverter are synchronized and stable with the grid when it is connected to the grid.

[0041] The primary side H-bridge circuit is responsible for converting the direct current generated by the photovoltaic panel into alternating current, and transmitting it to the secondary side through the transformer; the transformer realizes electrical isolation and voltage conversion; the switch connects the output end of the secondary side bridge arm circuit and the power grid to control the grid connection process; the target controller is responsible for phase shift control according to the grid voltage and the target output voltage, the target output current and the preset reference current to achieve synchronization and regulation of the output voltage and current. This embodiment can perform synchronous control according to the grid voltage and the target output voltage through the target controller to ensure the stability and quality of the inverter output voltage; the design of the secondary side bridge arm circuit makes the inverter more flexible in output current regulation and can adapt to different load requirements. Through the precise control of the target controller, the output voltage of the inverter is synchronized with the grid voltage, and after synchronization, further current regulation is performed according to the target output current, thereby reducing the impact current at the moment of grid connection. Through precise phase shift control, the impact current generated by the inverter at the moment of grid connection is greatly reduced, protecting the components of the inverter and improving the reliability and life of the system. The target controller achieves precise control of the output voltage and current by adjusting the state of a group of switch tubes, especially by phase shift control to ensure the synchronization of the output voltage and the grid voltage, and to make the target output current close to the preset reference current when the grid is connected to the output. This micro inverter can effectively reduce the impact current at the moment of grid connection and improve the stability and reliability of the system. That is, this embodiment enables the micro inverter to better adapt to the grid conditions and enhance the overall stability of the system by accurately controlling the output voltage and current; reducing the impact current helps to protect the key components inside the inverter, such as the switch tube, to avoid damage due to excessive electrical stress, thereby extending the service life of the equipment; a more stable grid connection process means higher energy conversion efficiency, which helps to optimize the energy utilization of the entire photovoltaic power generation system.

[0042] When the inverter is connected to the grid, if the output current is too small, the grid connection process may be unstable and may even cause fluctuations in the grid. Setting a minimum grid-connected output current reference value can ensure that the inverter can provide sufficient current when connected to the grid, thereby maintaining the stable operation of the grid. If the output current of the inverter is too small when connected to the grid, a large impact current may be generated at the moment of grid connection, which will not only damage the inverter itself, but also affect other devices in the grid. By setting the minimum grid-connected output current reference value, this situation can be effectively avoided. In actual applications, the above-mentioned preset reference current can be set by software. The preset reference current at the time of just connecting to the grid may be small, such as 0.1A, and then gradually increase the preset reference current after connecting to the grid, such as 2A, or 3A, or others.

[0043] In an optional embodiment, if Figure 2As shown, the micro inverter further includes a first capacitor C1, wherein the first capacitor C1 is connected in parallel with the input end of the primary H-bridge circuit; the primary H-bridge circuit includes a first MOS transistor Q1, a second MOS transistor Q2, a third MOS transistor Q3 and a fourth MOS transistor Q4, wherein the drain of the first MOS transistor Q1 is electrically connected to the drain of the third MOS transistor Q3 and serves as one end of the input end of the primary H-bridge circuit, the source of the first MOS transistor Q1 is electrically connected to the drain of the second MOS transistor Q2, the source of the third MOS transistor Q3 is electrically connected to the drain of the fourth MOS transistor Q4, the source of the second MOS transistor Q2 is electrically connected to the source of the fourth MOS transistor Q4 and serves as the other end of the input end of the primary H-bridge circuit; the bidirectional switch bridge The arm includes a fifth MOS tube Q5, a sixth MOS tube Q6, a seventh MOS tube Q7 and an eighth MOS tube Q8, and the capacitor bridge arm includes a second capacitor C2 and a third capacitor C3, wherein the source of the fifth MOS tube Q5 is electrically connected to the source of the sixth MOS tube Q6, the drain of the sixth MOS tube Q6 is electrically connected to the drain of the seventh MOS tube Q7, the source of the seventh MOS tube Q7 is electrically connected to the source of the eighth MOS tube Q8, the second capacitor C2 and the third capacitor C3 are connected in series between the drain of the fifth MOS tube Q5 and the drain of the eighth MOS tube Q8, and the drain of the fifth MOS tube Q5 and the drain of the eighth MOS tube Q8 serve as the output end of the secondary bridge arm circuit; the drain of the sixth MOS tube Q6 is electrically connected to the drain of the seventh MOS tube Q7 through the leakage inductance L lk The second MOS transistor Q1 is electrically connected to one end of the secondary winding of the transformer T1, the connection point between the second capacitor C2 and the third capacitor C3 is electrically connected to the other end of the secondary winding of the transformer T1, and a group of switch transistors includes a first MOS transistor Q1, a second MOS transistor Q2, a third MOS transistor Q3, a fourth MOS transistor Q4, a fifth MOS transistor Q5, a sixth MOS transistor Q6, a seventh MOS transistor Q7 and an eighth MOS transistor Q8.

[0044] In the above embodiment, the first capacitor C1 is connected in parallel with the input end of the primary H-bridge circuit to filter and smooth the input voltage, reduce voltage fluctuations, and improve system stability; the primary H-bridge circuit is composed of four MOS tubes, forming a standard H-bridge topology, which can realize the conversion from DC to AC; the bidirectional switch bridge arm is composed of four MOS tubes, which can realize bidirectional conduction and is suitable for the AC output of the secondary side of the transformer; the capacitor bridge arm is composed of two capacitors in series, which plays the role of filtering and energy storage, helps to smooth the output current and reduce the impact current. It should be noted that Figure 2 The target controller is not shown in the figure, and the target controller is connected to each MOS tube.

[0045] Traditional micro inverters are prone to generate large surge currents at the moment of grid connection due to the output voltage being out of sync with the grid voltage or improper output current control. This will not only increase system losses, but may also damage the internal components of the inverter and reduce the stability and service life of the entire system. Figure 2 : is a schematic diagram of the circuit of the micro-inverter of this embodiment, the input end of the micro-inverter is connected to the photovoltaic panel, and the output end is connected to the grid. The first capacitor C1 is connected in parallel with the input end of the primary H-bridge circuit, which can stabilize the input voltage, reduce voltage fluctuations, and thus reduce the impact current at the moment of grid connection. The four MOS tubes in the primary H-bridge circuit form a full-bridge structure, which can efficiently perform DC-AC conversion and ensure the quality of the output voltage waveform. The design of the bidirectional switch bridge arm and the capacitor bridge arm enables the secondary bridge arm circuit to achieve efficient energy transmission and voltage conversion on the secondary side of the transformer, further improving the stability and reliability of the system. A group of switch tubes are precisely driven and controlled by the target controller to ensure that the target output voltage is synchronized with the grid voltage, thereby reducing the electrical stress at the moment of grid connection and protecting the devices in the inverter from damage. This embodiment achieves the synchronization of the output voltage and the grid voltage by precisely controlling the switching state of the MOS tube, and controls the consistency of the grid-connected output current with the preset value, which can significantly reduce the impact current at the moment of grid connection, protect the internal components of the inverter, and extend the service life.

[0046] In an optional embodiment, the target controller includes a PR controller and a PI controller, wherein the PR controller is used to generate a first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, and the target controller is used to adjust the inner phase shift angle and the outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm; the PI controller is used to generate a phase shift angle adjustment amount according to the difference between the target output current and the preset reference current, and the target controller superimposes the phase shift angle adjustment amount and the preset feedforward control amount to obtain a second phase shift control amount, wherein the preset feedforward control amount is a compensation phase shift angle pre-set according to system parameters.

[0047] In the above embodiment, the PR controller can accurately generate the first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, thereby effectively adjusting the inner phase shift angle and the outer phase shift angle to ensure that the target output voltage is synchronized with the grid voltage. This not only improves the grid-connected efficiency of the system, but also reduces the impact current during the grid-connected process, protects the components of the inverter from electrical stress damage, and prolongs the service life of the system. At the same time, the PI controller generates a phase shift angle adjustment amount according to the difference between the target output current and the preset reference current, and superimposes it with the preset feedforward control amount, further optimizing the second phase shift control amount, ensuring that the target output current of the micro inverter is stable at the preset reference current level when it is grid-connected, and enhancing the stability and reliability of the system. Through the joint control of the PR controller and the PI controller, the impact current at the moment of grid connection can be significantly reduced. The PR controller ensures that the output voltage is synchronized with the grid voltage, and the PI controller accurately controls the output current, thereby effectively reducing the impact current, protecting the internal components of the inverter, and prolonging the service life. Accurate voltage and current control improves the stability and reliability of the system. The dual guarantees of voltage synchronization and current control make the micro inverter more stable during the grid connection process, reduce voltage fluctuations and current mutations, and improve the overall performance of the system.

[0048] This embodiment introduces a PR controller to generate a first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, and adjusts the inner phase shift angle and the outer phase shift angle so that the target output voltage is accurately synchronized with the grid voltage; this helps to ensure the quality of electric energy and safe grid connection, and improve the stability and reliability of the system. The PI controller generates a phase shift angle adjustment amount according to the difference between the target output current and the preset reference current, and superimposes it with the preset feedforward control amount to obtain a second phase shift control amount; this control method can more accurately adjust the output current and reduce the influence of system parameter changes, external interference and other factors on the current regulation accuracy. By introducing a PR controller and a PI controller, combined with the adjustment of the inner phase shift angle and the outer phase shift angle, and the compensation of the preset feedforward control amount, the problems of insufficient voltage synchronization accuracy, insufficient current regulation accuracy and complex phase shift control in the prior art are solved. By combining the advantages of the PR controller and the PI controller, a simple and effective phase shift control method is provided, which does not require complex algorithms and calculations, reduces the complexity and cost of the system, and improves the performance and stability of the system.

[0049] In an optional embodiment, the target controller also includes a grid-connected judgment module, which is used to obtain a first phase-shift control amount or a second phase-shift control amount, wherein, when it is determined that the target output voltage and the grid voltage meet a first preset condition, the grid-connected judgment module outputs the first phase-shift control amount, and instructs the target controller to control the inner phase-shift angle and the outer phase-shift angle according to the first phase-shift control amount, wherein the first preset condition includes that the target output voltage and the grid voltage do not meet the synchronization condition or the target output voltage and the grid voltage meet the synchronization condition for less than a preset time; when it is determined that the target output voltage and the grid voltage meet the second preset condition, the grid-connected judgment module outputs the second phase-shift control amount, and instructs the target controller to control the inner phase-shift angle and the outer phase-shift angle according to the second phase-shift control amount, wherein the second preset condition is used to indicate that the target output voltage and the grid voltage meet the synchronization condition or the time for which the target output voltage and the grid voltage meet the synchronization condition is greater than or equal to the preset time.

[0050] In the above embodiment, the grid-connected judgment module obtains the first phase-shift control amount or the second phase-shift control amount to ensure that the grid-connected output process is more accurate and smooth. When the target output voltage is not completely synchronized with the grid voltage or the synchronization time is insufficient, the first phase-shift control amount is used for adjustment to avoid the impact current caused by premature grid connection. When the target output voltage and the grid voltage have reached the synchronization condition or meet the synchronization condition and last for a long enough time, the second phase-shift control amount is used to further optimize the grid-connected process, so that the target output current when the switch is closed is stable at the preset reference current level, thereby reducing the impact of the impact current on the device.

[0051] The first preset condition may be that the target output voltage and the grid voltage have not yet satisfied the synchronization condition. Optionally, the first preset condition may also be that the time during which the target output voltage and the grid voltage satisfy the synchronization condition is less than a preset time. The second preset condition may be that the target output voltage and the grid voltage have satisfied the synchronization condition. Alternatively, the second preset condition may also be that the time during which the target output voltage and the grid voltage satisfy the synchronization condition is greater than or equal to a preset time.

[0052] By introducing a grid connection judgment module and setting a first preset condition and a second preset condition according to the synchronization of the target output voltage and the grid voltage, this embodiment can more accurately judge the timing of grid connection. When the target output voltage and the grid voltage do not meet the synchronization condition or meet the condition but the duration is insufficient, the system will continue to use the first phase shift control amount for adjustment; when the synchronization condition is met and the duration is sufficient, the system will switch to the second phase shift control amount to achieve more refined current regulation. Target control can automatically adjust the control strategy according to the synchronization of the grid voltage and the target output voltage without manual intervention or complex control logic. This reduces the complexity and cost of the system and improves the response speed and efficiency of the system. The grid connection judgment module dynamically selects a suitable control strategy based on the first preset condition and the second preset condition. When the output voltage is not synchronized with the grid voltage or the synchronization time is insufficient, voltage synchronization control is performed first; when the synchronization condition is met and the duration is sufficient, it switches to current control. This dynamic switching mechanism ensures the smoothness and stability of the grid connection process.

[0053] In an optional embodiment, if Figure 2 As shown, the switch includes a first relay S1 and a second relay S2, wherein the first output end of the secondary bridge arm circuit is connected to the live wire of the grid through the first relay S1, and the second output end of the secondary bridge arm circuit is connected to the neutral wire of the grid through the second relay S2.

[0054] In the above embodiment, the setting of the first relay S1 and the second relay S2 ensures the reliable connection and disconnection between the secondary bridge arm circuit and the power grid, realizes the precise control of the grid connection process, and avoids the large current impact at the moment of grid connection. Through the cooperation of the first relay S1 and the second relay S2, the switch can be closed when the target output voltage is synchronized with the grid voltage, thereby achieving smooth grid connection and further reducing the impact of the impact current. This design not only improves the stability and safety of the system, but also prolongs the service life of the micro inverter and related components.

[0055] By using the first relay S1 and the second relay S2 as switches, a reliable connection between the secondary bridge arm circuit of the micro inverter and the live and neutral wires of the grid is achieved. The relay has stable electrical performance and mechanical life, which can ensure a good connection state during long-term use, thereby improving the reliability of the connection between the micro inverter and the grid. By controlling the on and off of the relay, the micro inverter can be easily connected and disconnected from the grid. This increases the flexibility and adaptability of the micro inverter in specific application scenarios, such as disconnecting from the grid when necessary to achieve island operation, or reconnecting after the grid returns to normal. The dual relay design ensures that the connection and disconnection operations of the secondary bridge arm circuit and the grid are safer during grid connection and disconnection.

[0056] The present application also provides a micro-inverter control method, which is applied to the micro-inverter of any of the above embodiments. Figure 3 : is a flow chart of a control method of a micro inverter provided in an embodiment of the present application, the process includes:

[0057] Step S301, obtaining a grid voltage and a target output voltage, wherein the target output voltage is used to represent an output voltage of a micro inverter;

[0058] Step S302, obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling a group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage;

[0059] Step S303, when it is determined that the target output voltage is synchronized with the grid voltage, the switch is controlled to close so that the micro-inverter is connected to the grid, and a second phase-shift control amount is obtained according to the target output current, the preset reference current and the preset feedforward control amount, and a group of switch tubes are driven and controlled according to the second phase-shift control amount so that the target output current of the micro-inverter when connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter.

[0060] Through the above steps, the grid voltage and the target output voltage are obtained to ensure that the target output voltage is synchronized with the grid voltage, thereby avoiding the impact current caused by voltage asynchrony at the moment of grid connection, and improving the stability and reliability of the system. When it is determined that the target output voltage is synchronized with the grid voltage, the switch is controlled to close so that the micro inverter is smoothly connected to the grid. At the same time, the second phase shift control amount is obtained according to the target output current, the preset reference current and the preset feedforward control amount, and the grid-connected output current is further accurately controlled to be equal to the preset reference current, ensuring the stability of the output current after grid connection, reducing the impact of current fluctuations on the grid, and extending the service life of the inverter and its related components.

[0061] This embodiment obtains the grid voltage and the target output voltage, calculates the first phase-shift control amount, and drives and controls a group of switch tubes according to the control amount to ensure that the target output voltage is synchronized with the grid voltage; this process ensures voltage synchronization before grid connection and reduces the risk of impact current. After determining that the target output voltage is synchronized with the grid voltage, the switch is controlled to close, and at the same time, the second phase-shift control amount is calculated according to the target output current, the preset reference current and the preset feedforward control amount, and a group of switch tubes are driven and controlled according to the control amount to ensure that the grid-connected output current is equal to the preset reference current; this process ensures current control after grid connection and improves the stability and performance of the system.

[0062] Through voltage synchronization control, the target output voltage before grid connection is ensured to be synchronized with the grid voltage, reducing the impact current at the moment of grid connection. This not only protects the internal components of the inverter, but also improves the stability and reliability of the system. Through precise voltage and current control, the accuracy of the grid connection process is ensured. The dual guarantee of voltage synchronization and current control makes the system more stable during the grid connection process, reduces voltage fluctuations and current mutations, and improves the overall performance of the system. This control strategy improves the response speed and control accuracy of the system, allowing the system to maintain high performance under various working conditions.

[0063] In an optional embodiment, a grid voltage and a target output voltage are obtained, including: obtaining a first amplitude of the grid voltage, and obtaining a second amplitude of the target output voltage; obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling a group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, including: determining the amplitude difference between the grid voltage and the target output voltage; using a PR controller to generate a first phase shift control amount according to the amplitude difference, wherein the target controller includes a PR controller; adjusting an inner phase shift angle and an outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm.

[0064] In the above embodiment, the first amplitude of the grid voltage and the second amplitude of the target output voltage are obtained, ensuring that the system can accurately measure and compare the two voltage values ​​before grid connection. The amplitude difference between the grid voltage and the target output voltage is determined so that the system can identify the difference between the two, thereby providing a basis for subsequent control. The PR controller is used to generate the first phase shift control amount according to the amplitude difference, which improves the response speed and accuracy of the control and ensures that the target output voltage quickly and accurately follows the grid voltage changes. The inner phase shift angle and the outer phase shift angle are adjusted so that the target output voltage is synchronized with the grid voltage, which effectively reduces the impact current at the moment of grid connection, reduces the electrical stress on the components in the inverter, and improves the reliability and life of the system.

[0065] By obtaining the first amplitude of the grid voltage and the second amplitude of the target output voltage, the amplitude difference is calculated, and the first phase shift control amount is generated by the PR controller, and the inner phase shift angle and the outer phase shift angle are adjusted to ensure that the target output voltage is synchronized with the amplitude of the grid voltage. This process ensures the voltage amplitude synchronization before grid connection and reduces the risk of impact current. The PR controller generates the first phase shift control amount according to the amplitude difference, and adjusts the inner phase shift angle and the outer phase shift angle according to the control amount to ensure that the target output voltage is synchronized with the amplitude and phase of the grid voltage. The use of the PR controller improves the control accuracy and ensures the accuracy of voltage synchronization. Through amplitude synchronization control, the amplitude of the target output voltage before grid connection is synchronized with the amplitude of the grid voltage, reducing the impact current at the moment of grid connection. This not only protects the internal components of the inverter, but also improves the stability and reliability of the system. The use of the PR controller improves the control accuracy of the system. The first phase shift control amount is generated by the amplitude difference, and the inner phase shift angle and the outer phase shift angle are adjusted to ensure the precise synchronization of the voltage amplitude and phase. This high-precision control strategy improves the system's response speed and control accuracy, allowing the system to maintain high performance under various operating conditions.

[0066] In an optional embodiment, when it is determined that the target output voltage is synchronized with the grid voltage, a second phase shift control quantity is obtained according to the target output current, a preset reference current and a preset feedforward control quantity, and a group of switch tubes are driven and controlled according to the second phase shift control quantity, including: when it is determined that the target output voltage is synchronized with the grid voltage, the current difference between the target output current and the preset reference current is determined; a phase shift angle adjustment quantity is generated according to the current difference by a PI controller, wherein the target controller also includes a PI controller; the phase shift angle adjustment quantity and the preset feedforward control quantity are superimposed to obtain a second phase shift control quantity, wherein the preset feedforward control quantity is a compensation phase shift angle pre-set according to system parameters; and a group of switch tubes are driven and controlled according to the second phase shift control quantity.

[0067] In the above embodiment, the current difference between the target output current and the preset reference current is determined, so that the current change in the grid-connected process can be monitored in real time to ensure the accuracy of current control; the PI controller is used to generate a phase shift angle adjustment amount according to the current difference, which can quickly respond and adjust the phase shift angle so that the target output current quickly approaches the preset reference current, thereby reducing the grid-connected impact current; the phase shift angle adjustment amount and the preset feedforward control amount are superimposed to obtain a second phase shift control amount, which further optimizes the control strategy and improves the dynamic response speed and stability of the system; a group of switching tubes are driven and controlled according to the second phase shift control amount to ensure a smooth current transition in the grid-connected process and avoid device damage and system instability caused by sudden changes.

[0068] By using the PI controller to generate the phase shift angle adjustment amount according to the current difference, and combining the preset feedforward control amount for compensation, the method can adjust the drive control of the switch tube more quickly, thereby achieving a fast response to the grid-connected output current. This improves the dynamic performance of the current control, so that the micro inverter can recover the stable state more quickly when the load changes suddenly or the grid voltage fluctuates. The PI controller reduces the current difference by continuously adjusting the phase shift angle adjustment amount, thereby achieving precise control of the grid-connected output current. At the same time, the addition of the preset feedforward control amount further improves the accuracy of the current control, so that the grid-connected output current can track the preset reference current more accurately. The introduction of the preset feedforward control amount takes into account the impact of system parameter changes on current control, and offsets these impacts by compensating the phase shift angle. This enhances the robustness of the system, so that the micro inverter can still maintain stable current control performance when the system parameters change. The use of the PI controller ensures a fast response to current changes and improves the dynamic performance of the system. This enables the system to quickly adjust the output current and maintain stable operation of the system when facing load changes or other disturbances. More precise current control and higher dynamic response capabilities improve the energy transmission efficiency of the system. It reduces energy loss, improves the overall performance of the photovoltaic power generation system, and optimizes energy utilization.

[0069] In an optional embodiment, the preset feedforward control amount is calculated according to the following formula: F=4×f smax ×L lk ×I * o ×sinθ / (N×V in ), where F represents the preset feedforward control amount, f smax Indicates the maximum switching frequency of a group of switching tubes, L lk Represents the leakage inductance of the transformer, I * o represents the preset reference current, θ represents the phase angle of the grid voltage, N represents the turns ratio between the primary and secondary sides of the transformer, V in Indicates the voltage of the photovoltaic panel.

[0070] In the above embodiment, the preset feedforward control quantity can be accurately calculated, the influence of the system parameter change can be effectively compensated, the output current of the micro inverter during the grid connection process can be ensured to be stable, the instantaneous impact current of the grid connection can be reduced, and the reliability and service life of the system can be improved. Specifically, the scheme introduces multiple parameters such as the maximum switching frequency, transformer leakage inductance, preset reference current, grid voltage phase angle, transformer turns ratio and photovoltaic panel voltage, among which V in It indicates the voltage input from the photovoltaic panel to the inverter, which improves the control accuracy and enhances the adaptability and stability of the system.

[0071] When the micro inverter is connected to the grid, its system parameters (such as the leakage inductance of the transformer, the voltage of the photovoltaic panel, etc.) may change, and these changes will affect the accuracy and stability of the current control. By setting the feedforward control amount, the phase shift amount can be prevented from suddenly changing, thereby causing a sudden change in the grid-connected current. The current control method in the prior art often ignores these parameter changes, resulting in a decrease in control performance. The above formula in this embodiment takes into account multiple system parameters such as the leakage inductance of the transformer, the preset reference current, the phase angle of the grid voltage, the turns ratio of the primary side to the secondary side of the transformer, and the voltage of the photovoltaic panel, so that the feedforward control amount can more accurately reflect the impact of system parameter changes on current control, thereby improving the accuracy of feedforward compensation. Through the precise calculation of the feedforward control amount, the output current is highly consistent with the preset reference current. The multiple parameters in the formula take into account the key characteristics of the system, making the feedforward control more accurate, reducing current fluctuations, and improving the stability and performance of the system. The introduction of feedforward control improves the dynamic response capability of the system. By adjusting the control amount in advance, the system can quickly respond to current changes, reduce control lag, and ensure the stable operation of the system.

[0072] It should be noted that the above-described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application will be described in detail below in conjunction with specific embodiments.

[0073] The embodiment of the present application provides a micro-inverter grid-connected output control method, which effectively reduces the instantaneous impact current of grid connection by optimizing the control strategy, avoids damage to devices, and thus improves the reliability of the inverter and the overall performance of the system. Figure 4 This is a principle block diagram of a control method for a micro inverter provided in an embodiment of the present application. The embodiment of the present application is described in detail below.

[0074] The circuit of micro inverter is as follows Figure 2 As shown in the figure, the circuit mainly controls the internal and external phase shift angles and operating frequencies of the primary H-bridge and the secondary half-bridge circuit (corresponding to the aforementioned bidirectional switch bridge arm) to realize output grid-connected control. Among them, the internal phase shift angle refers to the phase shift angle between the two bridge arms inside the primary H-bridge, and the external phase shift angle refers to the phase shift angle between the primary H-bridge and the secondary half-bridge. The operating frequency refers to the switching frequency of all switch tubes Q1 to Q8.

[0075] The inner phase shift angle is denoted as Φ, and the outer phase shift angle is denoted as δ.

[0076] Overall work control strategy such as Figure 4 As shown in the figure, before starting work, it has been confirmed that the photovoltaic panel has sufficient power generation to support grid-connected operation. First, the PLL phase-locked loop samples the grid voltage Vg to obtain the grid phase angle θ and the grid amplitude A, as well as the positive and negative half-cycle marks p and n. The feedforward control term Φ FF(corresponding to F in the previous formula) is determined by the actual circuit parameters, including f smax Maximum switching frequency, L lk Transformer leakage inductance, I * o Set the output current amplitude (corresponding to the preset reference current), V in is the input photovoltaic panel voltage.

[0077] Output voltage pre-matching working mode:

[0078] like Figure 4 As shown, the difference between the voltage Vo on the second capacitor C2 and the third capacitor C3 (corresponding to the aforementioned target output voltage, also referred to as the secondary capacitor voltage) and the grid voltage Vg is obtained, and the first phase shift control amount Φ1 is calculated after passing through the PR controller.

[0079] Get the grid-connected output current value io (select sampling on the grid side after the switch) and compare it with the minimum grid-connected output current reference value i * o The difference is calculated by the PI controller to output the phase shift correction value ∆Φ, and the feedforward control term Φ is superimposed. FF , and obtain the second phase shift control amount Φ2.

[0080] Superimposed feedforward control term Φ FF =4×f smax ×L lk ×I * o ×sinθ / (N×V in ), where N is the turns ratio of the primary to the secondary side of the transformer.

[0081] After the grid-connected judgment module, the actual phase-shift control value Φ is finally output, and a driving signal is generated to control Q1~Q8 to achieve seamless grid connection.

[0082] Grid connection judgment module: If the relay is not closed, due to the output current i o If the minimum grid-connected output current reference value cannot be reached, the second phase-shift control quantity Φ2 cannot follow the feedforward control item, and Φ2 outputs the saturated maximum value, such as 0.5, or other values. The secondary capacitor voltage is fed back by the PR controller to output the first phase-shift control quantity Φ1. Due to the control error, the secondary capacitor voltage can basically follow the grid voltage.

[0083] When the relay is closed, the secondary output capacitor voltage is equal to the grid voltage. At this time, there is no need to adjust the first phase shift control amount Φ1, and the output control is taken over by the second phase shift control amount Φ2.

[0084] When performing phase shift and frequency conversion control, Figure 4 The internal phase shift Φ, external phase shift δ and frequency f ins , generally δ=0.25Φ, before the relay is closed Φ=Φ1, after the relay is closed Φ=Φ2, and the frequency of the switch tube f s =(1-1.25*Φ)*f smax .

[0085] Figure 5 This is an overall flow chart of a micro-inverter grid-connected output control provided by an embodiment of the present application, including:

[0086] S501, obtaining the voltage amplitude, frequency and phase of the mains power Vg through a phase-locked loop;

[0087] S502, entering an output voltage pre-matching working mode, so that the output voltage of the micro inverter tracks the mains voltage;

[0088] S503, controlling the output relay switch to close, and making the micro inverter enter the grid-connected working mode.

[0089] Figure 6 This is an example of the waveform of the switch tube control provided by the embodiment of the present application. In the figure, Φ is the inner phase shift angle, Φ=Φ1 before the relay is closed, Φ=Φ2 after the relay is closed, δ is the outer phase shift angle, generally δ=0.25Φ. In the figure, Vab corresponds to Figure 2 The voltage between AB, Vcd corresponds to Figure 2 The voltage between CD.

[0090] Through the embodiments of the present application, the problem of inrush current in the micro-inverter at the moment of outputting the grid is solved, and the relays and components are effectively protected from damage.

[0091] Through the description of the above implementation methods, those skilled in the art can clearly understand that the method according to the above embodiment can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in each embodiment of the present application.

[0092] The present application also provides a computer-readable storage medium, in which instructions are stored. When the instructions are executed, any one of the method steps described above is executed.

[0093] In an exemplary embodiment, the computer-readable storage medium may include, but is not limited to, various media that can store computer programs, such as a USB flash drive, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk.

[0094] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0095] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are only schematic, such as the division of units, which is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some service interfaces, and the indirect coupling or communication connection of devices or units can be electrical or other forms.

[0096] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0097] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0098] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the various embodiments of the present application. The aforementioned memory includes: various media that can store program codes, such as USB flash drives, mobile hard drives, magnetic disks or optical disks.

[0099] The above is only an exemplary embodiment of the present disclosure and cannot be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the disclosure of the specification and practice, those skilled in the art will easily think of other embodiments of the present disclosure.

[0100] This application is intended to cover any modifications, uses or adaptations of the present disclosure, which follow the general principles of the present disclosure and include common knowledge or customary technical means in the technical field not recorded in the present disclosure.

Claims

1. A micro inverter, characterized in that: include: The primary side H-bridge circuit, transformer, secondary side bridge arm circuit, switch and target controller, among which, The input end of the primary H-bridge circuit is electrically connected to the output end of the photovoltaic panel, the output end of the primary H-bridge circuit is electrically connected to the primary winding of the transformer, the input end of the secondary bridge arm circuit is electrically connected to the secondary winding of the transformer, and the output end of the secondary bridge arm circuit is connected to the power grid through the switch; The secondary bridge arm circuit comprises a bidirectional switch bridge arm and a capacitor bridge arm, the two ends of the secondary winding of the transformer are electrically connected to the midpoint of the bidirectional switch bridge arm and the midpoint of the capacitor bridge arm respectively, the two ends of the bidirectional switch bridge arm are connected in parallel with the two ends of the capacitor bridge arm, and serve as the output ends of the secondary bridge arm circuit; The target controller is electrically connected to each switch tube in a group of switch tubes, wherein the group of switch tubes includes each switch tube in the primary H-bridge circuit and each switch tube in the bidirectional switch bridge arm; The target controller is used to obtain a first phase shift control amount according to the grid voltage and the target output voltage, and drive and control the group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the target output voltage is used to represent the output voltage of the micro inverter; In the case where it is determined that the target output voltage is synchronized with the grid voltage, the target controller is further used to obtain a second phase shift control amount according to the target output current, the preset reference current and the preset feedforward control amount, and drive and control the group of switch tubes according to the second phase shift control amount, so that the target output current of the micro-inverter when it is connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter; The target controller further includes a grid-connected judgment module, and the grid-connected judgment module is used to obtain the first phase-shifted control amount or the second phase-shifted control amount, wherein: When it is determined that the target output voltage and the grid voltage meet a first preset condition, the grid connection judgment module outputs the first phase shift control amount, and instructs the target controller to control the inner phase shift angle and the outer phase shift angle according to the first phase shift control amount, wherein the first preset condition includes that the target output voltage and the grid voltage do not meet a synchronization condition or the target output voltage and the grid voltage meet the synchronization condition for less than a preset time; When it is determined that the target output voltage and the grid voltage satisfy a second preset condition, the grid connection judgment module outputs the second phase shift control amount, and instructs the target controller to control the inner phase shift angle and the outer phase shift angle according to the second phase shift control amount, wherein the second preset condition is used to indicate that the target output voltage and the grid voltage satisfy a synchronization condition or the duration for which the target output voltage and the grid voltage satisfy the synchronization condition is greater than or equal to the preset duration.

2. The micro inverter according to claim 1, characterized in that: The micro-inverter further includes a first capacitor, wherein the first capacitor is connected in parallel with an input end of the primary H-bridge circuit; The primary H-bridge circuit comprises a first MOS tube, a second MOS tube, a third MOS tube and a fourth MOS tube, wherein the drain of the first MOS tube is electrically connected to the drain of the third MOS tube and serves as one end of the input end of the primary H-bridge circuit, the source of the first MOS tube is electrically connected to the drain of the second MOS tube, the source of the third MOS tube is electrically connected to the drain of the fourth MOS tube, the source of the second MOS tube is electrically connected to the source of the fourth MOS tube and serves as the other end of the input end of the primary H-bridge circuit; The bidirectional switch bridge arm includes a fifth MOS tube, a sixth MOS tube, a seventh MOS tube and an eighth MOS tube, and the capacitor bridge arm includes a second capacitor and a third capacitor, wherein the source of the fifth MOS tube is electrically connected to the source of the sixth MOS tube, the drain of the sixth MOS tube is electrically connected to the drain of the seventh MOS tube, the source of the seventh MOS tube is electrically connected to the source of the eighth MOS tube, the second capacitor and the third capacitor are connected in series between the drain of the fifth MOS tube and the drain of the eighth MOS tube, and the drain of the fifth MOS tube and the drain of the eighth MOS tube serve as the output end of the secondary bridge arm circuit; The drain of the sixth MOS tube is electrically connected to one end of the secondary winding of the transformer through a leakage inductance, the connection point between the second capacitor and the third capacitor is electrically connected to the other end of the secondary winding of the transformer, and the group of switch tubes includes the first MOS tube, the second MOS tube, the third MOS tube, the fourth MOS tube, the fifth MOS tube, the sixth MOS tube, the seventh MOS tube and the eighth MOS tube.

3. The micro inverter according to claim 1, characterized in that: The target controller includes a PR controller and a PI controller, wherein: The PR controller is used to generate the first phase shift control amount according to the voltage difference between the grid voltage and the target output voltage, and the target controller is used to adjust the inner phase shift angle and the outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm; The PI controller is used to generate a phase shift angle adjustment amount according to the difference between the target output current and the preset reference current. The target controller superimposes the phase shift angle adjustment amount and the preset feedforward control amount to obtain the second phase shift control amount, wherein the preset feedforward control amount is a compensation phase shift angle pre-set according to system parameters.

4. The micro inverter according to claim 1, characterized in that: The switch includes a first relay and a second relay, wherein the first output end of the secondary bridge arm circuit is connected to the live wire of the power grid through the first relay, and the second output end of the secondary bridge arm circuit is connected to the neutral wire of the power grid through the second relay.

5. A control method for a micro inverter, characterized in that: The micro inverter according to any one of claims 1 to 4 comprises: Acquire a grid voltage and a target output voltage, wherein the target output voltage is used to represent the output voltage of the micro inverter; Obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling the group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage; When it is determined that the target output voltage is synchronized with the grid voltage, the switch is controlled to be closed so that the micro-inverter is connected to the grid, and a second phase shift control amount is obtained according to the target output current, the preset reference current and the preset feedforward control amount, and the group of switch tubes are driven and controlled according to the second phase shift control amount so that the target output current of the micro-inverter when connected to the grid is equal to the preset reference current, wherein the target output current is used to represent the grid-connected output current of the micro-inverter; Wherein, obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling the group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, comprises: when it is determined that the target output voltage and the grid voltage meet the first preset condition, the grid connection judgment module outputs the first phase shift control amount, and instructs the target controller to control the inner phase shift angle and the outer phase shift angle according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage; When it is determined that the target output voltage is synchronized with the grid voltage, the switch is controlled to be closed so that the micro-inverter is connected to the grid, and a second phase shift control amount is obtained according to the target output current, a preset reference current and a preset feedforward control amount, and a group of switch tubes are driven and controlled according to the second phase shift control amount so that the target output current of the micro-inverter when it is connected to the grid is equal to the preset reference current, including: when it is determined that the target output voltage and the grid voltage meet the second preset condition, the switch is controlled to be closed so that the micro-inverter is connected to the grid, and the grid connection judgment module outputs the second phase shift control amount, and instructs the target controller to control the inner phase shift angle and the outer phase shift angle according to the second phase shift control amount, and a group of switch tubes are driven and controlled according to the second phase shift control amount so that the target output current of the micro-inverter when it is connected to the grid is equal to the preset reference current.

6. The control method of the micro inverter according to claim 5, characterized in that: Acquiring a grid voltage and a target output voltage, including: acquiring a first amplitude of the grid voltage, and acquiring a second amplitude of the target output voltage; Obtaining a first phase shift control amount according to the grid voltage and the target output voltage, and driving and controlling the group of switch tubes according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, including: Determining a difference between the grid voltage and the target output voltage; generating a first phase shift control amount according to the amplitude difference using a PR controller, wherein the target controller includes the PR controller; The inner phase shift angle and the outer phase shift angle are adjusted according to the first phase shift control amount so that the target output voltage is synchronized with the grid voltage, wherein the inner phase shift angle is used to represent the phase shift angle between the two bridge arms inside the primary H-bridge circuit, and the outer phase shift angle is used to represent the phase shift angle between the primary H-bridge circuit and the bidirectional switch bridge arm.

7. The control method of the micro inverter according to claim 6, characterized in that: When it is determined that the target output voltage is synchronized with the grid voltage, a second phase shift control amount is obtained according to the target output current, a preset reference current and a preset feedforward control amount, and the group of switch tubes are driven and controlled according to the second phase shift control amount, including: In the case where it is determined that the target output voltage is synchronized with the grid voltage, determining a current difference between the target output current and the preset reference current; Using a PI controller to generate a phase shift angle adjustment amount according to the current difference, wherein the target controller also includes the PI controller; The second phase shift control amount is obtained by superimposing the phase shift angle adjustment amount and the preset feedforward control amount, wherein the preset feedforward control amount is a compensation phase shift angle preset according to system parameters; The group of switch tubes are driven and controlled according to the second phase shift control amount.

8. The control method of the micro inverter according to claim 7, characterized in that: The preset feedforward control amount is calculated according to the following formula: F=4×f smax ×L lk ×I * o ×sinθ / (N×V in ), Wherein, F represents the preset feedforward control amount, f smax Indicates the maximum switching frequency of the switch tube group, L lk represents the leakage inductance of the transformer, I * o represents the preset reference current, θ represents the phase angle of the grid voltage, N represents the turns ratio between the primary and secondary sides of the transformer, V in Represents the voltage of the photovoltaic panel.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores instructions, and when the instructions are executed, the method according to any one of claims 5 to 8 is performed.

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