Control system and control method of micro-inverter

Abstract

The invention discloses a control system and a control method of a micro inverter, and belongs to the technical field of inverters. The control system of the micro-inverter comprises a power tracking control module which is used for outputting a grid-connected current reference value according to the photovoltaic voltage and the photovoltaic current of a photovoltaic module and the voltage of a power grid; the output current loop control module is connected with the output end of the power tracking control module and is used for outputting an inverter voltage reference value according to the grid-connected current reference value and the grid-connected current; the inverter voltage loop control module is connected with the output end of the output current loop control module and is used for outputting an inverter current reference value according to the inverter voltage reference value and the inverter output voltage; the inversion output voltage is the output voltage of the output end of the secondary side bridge arm; and the feed-forward modulation module is connected with the output end of the inverter voltage loop output module and is used for controlling the working states of the primary side bridge arm and the secondary side bridge arm according to the inverter current reference value. According to the embodiment of the invention, the operation reliability of the micro inverter can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a control system and a control method for a micro-inverter. Background Art

[0002] A micro photovoltaic grid-connected inverter (microinverter for short) is a modular power conversion unit based on independent photovoltaic modules. Its core function is to achieve maximum power point tracking (MPPT) of a single photovoltaic module. Compared with traditional centralized inverter systems, microinverter systems have the following advantages: 1) High reliability: Each photovoltaic panel is independently equipped with an MPPT controller and DC-AC converter, and a single point failure does not affect the overall operation of the system. 2) Improved safety: Directly connecting to the grid via AC cables can avoid the potential risks of high-voltage DC lines. 3) Flexible scalability: The modular architecture supports the combination of any number of photovoltaic panels and inverters, making it suitable for home and industrial distributed power generation scenarios.

[0003] However, the application of microinverters still faces challenges. Related technologies typically achieve grid synchronization by directly controlling the output current through a current loop. However, this control strategy relies on current feedback and suffers from insufficient dynamic response. When the grid voltage suddenly changes or the load rapidly changes, the system's response lags, resulting in large output current fluctuations. Furthermore, the system has poor resistance to changes in grid impedance, which directly affects the stability of the control loop and can cause oscillation or instability. Therefore, the operational reliability of microinverters in related technologies still needs to be improved. Summary of the Invention

[0004] The present invention provides a control system and a control method for a micro-inverter, so as to improve the operational reliability of the micro-inverter.

[0005] In a first aspect, an embodiment of the present invention provides a control system for a microinverter, the microinverter comprising: a primary bridge arm, a transformer, and a secondary bridge arm; the input end of the primary bridge arm is connected to a photovoltaic module, the output end of the primary bridge arm is connected to the primary side of the transformer, the secondary side of the transformer is connected to the input end of the secondary bridge arm, and the output end of the secondary bridge arm is connected to a power grid;

[0006] The control system of the micro-inverter includes:

[0007] A power tracking control module is used to output a grid-connected current reference value according to the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage;

[0008] an output current loop control module, connected to the output end of the power tracking control module, and configured to output an inverter voltage reference value according to the grid-connected current reference value and the grid-connected current; wherein the grid-connected current is the output current provided by the micro-inverter to the grid;

[0009] an inverter voltage loop control module, connected to the output end of the output current loop control module, and configured to output an inverter current reference value according to the inverter voltage reference value and the inverter output voltage; wherein the inverter output voltage is the output voltage of the output end of the secondary bridge arm;

[0010] A feedforward modulation module is connected to the output end of the inverter voltage loop output module and is used to control the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value.

[0011] Optionally, the control system of the micro-inverter further includes: an inverter current loop control module, connected between the output end of the inverter voltage loop control module and the feedforward modulation module, and configured to output a phase shift angle control value according to the inverter current reference value and the inverter output current; the feedforward modulation module is configured to control the working states of the primary bridge arm and the secondary bridge arm according to the phase shift angle control value; wherein the inverter output current is determined based on the resonant current of the secondary side of the transformer.

[0012] Optionally, the output current loop control module includes:

[0013] a first operator connected to the output terminal of the power tracking control module and inputting the grid-connected current, for calculating the difference between the grid-connected current reference value and the grid-connected current to obtain a first operation value;

[0014] a first controller, connected to the output end of the first operator, and configured to determine the inverter voltage reference value according to the first operation value;

[0015] A second operator is connected between the output end of the first controller and the output end of the output current loop control module, and inputs the grid voltage; the second operator is used to calculate the sum of the grid voltage and the inverter voltage reference value to obtain a second operation value; the inverter voltage loop control module is used to output the inverter current reference value based on the second operation value and the inverter output voltage.

[0016] Optionally, the inverter voltage loop control module includes:

[0017] a third operator connected to the output end of the output current loop control module and inputting the inverter output voltage; the third operator is used to calculate the difference between the output signal of the output current loop control module and the inverter output voltage to obtain a third operation value;

[0018] The second controller is connected between the output terminal of the third operator and the output terminal of the inverter voltage loop control module, and is used to determine the inverter current reference value according to the third operation value.

[0019] Optionally, the controlled object of the inverter voltage loop control module takes the grid-connected current as a negative disturbance term; the inverter voltage loop control module further includes:

[0020] A fourth operator is connected between the output end of the second controller and the output end of the inverter voltage loop control module, and inputs a feedforward amount; the fourth operator is used to calculate the sum of the feedforward amount and the inverter current reference value to obtain a fourth operation value; the feedforward modulation module is used to control the working state of the primary bridge arm and the secondary bridge arm according to the fourth operation value; wherein the feedforward amount is the grid-connected current or the grid-connected current reference value.

[0021] Optionally, the inverter current loop control module includes:

[0022] a fifth operator, connected to the output end of the inverter voltage loop control module, and configured to calculate a difference between an output signal of the inverter voltage loop control module and the inverter output current to obtain a fifth operation value;

[0023] The third controller is connected between the output end of the fifth operator and the output end of the inverter current loop control module, and is used to obtain the phase shift angle control value according to the fifth operation value.

[0024] Optionally, the power tracking control module includes:

[0025] a maximum power point tracking unit, configured to determine a given photovoltaic voltage value according to the photovoltaic voltage and the photovoltaic current;

[0026] a sixth operator connected to the output terminal of the maximum power point tracking unit and inputting the photovoltaic voltage; the sixth operator is used to calculate the difference between the given photovoltaic voltage value and the photovoltaic voltage to obtain a sixth operation value;

[0027] a fourth controller, connected to the output end of the sixth operator, and configured to determine a grid-connected current amplitude reference value according to the sixth operation value;

[0028] a phase-locked loop, connected to the power grid, and configured to obtain a grid voltage phase according to the power grid voltage;

[0029] a sine processing unit, connected to the output end of the phase-locked loop, and configured to calculate the sine value of the grid voltage phase;

[0030] The seventh operator is respectively connected to the output end of the sinusoidal processing unit, the output end of the fourth controller and the output end of the power tracking control module, and is used to calculate the product of the grid-connected current amplitude reference value and the sine value of the grid voltage phase to obtain the grid-connected current reference value.

[0031] Optionally, the control system of the micro-inverter further includes: a current processing module, configured to determine the inverter output current according to the resonant current of the secondary side of the transformer;

[0032] Wherein, the current processing module includes:

[0033] A sampling unit, comprising a current transformer and an integrating capacitor; the current transformer is used to sample the resonant current, and the integrating capacitor is connected between two ends of the secondary side of the current transformer;

[0034] An average current calculation unit is connected to both ends of the integrating capacitor and is used to calculate the inverter output current according to the capacitance value of the integrating capacitor, the voltage across the integrating capacitor and the switching frequency of the switching tube in the secondary bridge arm.

[0035] In a second aspect, an embodiment of the present invention further provides a micro-inverter control method, which is applied to the control system of the micro-inverter provided in any embodiment of the present invention; the micro-inverter control method includes:

[0036] The power tracking control module outputs a grid-connected current reference value based on the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage;

[0037] The output current loop control module outputs an inverter voltage reference value according to a grid-connected current reference value and a grid-connected current; wherein the grid-connected current is the output current provided by the micro-inverter to the grid;

[0038] The inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage; wherein the inverter output voltage is the output voltage of the output end of the secondary bridge arm;

[0039] The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value.

[0040] Optionally, the control system of the micro-inverter further includes an inverter current loop control module; after the inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage, the control method of the micro-inverter further includes:

[0041] The inverter current loop control module outputs a phase shift angle control value according to the inverter current reference value and the inverter output current;

[0042] The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value, including:

[0043] The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the phase shift angle control amount.

[0044] The microinverter control system provided by an embodiment of the present invention features multiple closed-loop control systems, effectively improving the control accuracy and stability of the inverter's operation. Specifically, a power tracking control module tracks the maximum power point of photovoltaic modules and, in combination with the grid voltage, generates reference quantities related to the outer loop control within the multiple closed-loop control system. A feedforward modulation module provides drive signals for the primary and secondary bridge arms of the inverter based on the outputs of the multiple closed-loop control systems. The multiple closed-loop control systems can specifically include: grid-connected current loop control based on the output current loop control module, and inverter voltage loop control based on the inverter voltage loop control module. Each loop is controlled in a hierarchical manner, with each link focusing on a different control objective, thereby improving the system's robustness and dynamic performance. The grid-connected current loop is responsible for overall power regulation and grid synchronization, while the inverter voltage loop stabilizes the output voltage, reduces the impact of voltage fluctuations on the current loop, improves immunity to grid impedance changes, suppresses grid impedance disturbances, and enhances control loop stability.

[0045] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 1 is a schematic structural diagram of a control system of a micro-inverter provided by an embodiment of the present invention;

[0048] Figure 2 This is a basic working principle diagram of a micro-inverter provided by an embodiment of the present invention;

[0049] Figure 3 is a structural diagram of a control system of another micro-inverter provided by an embodiment of the present invention;

[0050] Figure 4 This is a control block diagram of an output current loop control module provided by an embodiment of the present invention;

[0051] Figure 5 This is a control block diagram of another output current loop control module provided by an embodiment of the present invention;

[0052] Figure 6This is a control block diagram of an inverter voltage loop control module provided by an embodiment of the present invention;

[0053] Figure 7 This is a control block diagram of another inverter voltage loop control module provided by an embodiment of the present invention;

[0054] Figure 8 This is a control block diagram of an inverter current loop control module provided by an embodiment of the present invention;

[0055] Figure 9 This is a schematic structural diagram of a sampling unit provided by an embodiment of the present invention;

[0056] Figure 10 This is a control block diagram of a micro-inverter control system provided by an embodiment of the present invention;

[0057] Figure 11 This is a structural diagram of a control system of another micro-inverter provided by an embodiment of the present invention;

[0058] Figure 12 This is a structural diagram of a control system of another micro-inverter provided by an embodiment of the present invention;

[0059] Figure 13 This is a control block diagram of another micro-inverter control system provided by an embodiment of the present invention;

[0060] Figure 14 This is a structural diagram of a control system of another micro-inverter provided by an embodiment of the present invention;

[0061] Figure 15 This is a structural diagram of a control system of another micro-inverter provided by an embodiment of the present invention;

[0062] Figure 16 1 is a flow chart of a control method for a micro-inverter provided by an embodiment of the present invention;

[0063] Figure 17 is a flow chart of another micro-inverter control method provided by an embodiment of the present invention;

[0064] Figure 18 This is a diagram of system simulation results under a steady-state full-load condition provided by an embodiment of the present invention;

[0065] Figure 19 This is a diagram showing the simulation results of a system transient response under a sudden change in grid voltage provided by an embodiment of the present invention;

[0066] Figure 20 This is a simulation result diagram of a system dynamic response under a condition of simulated light intensity change provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0067] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0068] It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and the accompanying drawings are used to distinguish similar items and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, such that the embodiments of the present invention described herein can be implemented in sequences other than those illustrated or described herein. Furthermore, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0069] An embodiment of the present invention provides a control system for a micro-inverter, which can improve the operational reliability of the micro-inverter. Figure 1 This is a schematic diagram of the structure of a control system of a micro-inverter provided by an embodiment of the present invention. Figure 1 The micro-inverter includes: a primary bridge arm, a transformer T and a secondary bridge arm. The input end of the primary bridge arm is connected to the photovoltaic module PV, the output end of the primary bridge arm is connected to the primary side of the transformer T, the secondary side of the transformer T is connected to the input end of the secondary bridge arm, and the output end of the secondary bridge arm is connected to the grid G. Exemplarily, the micro-inverter can be a single-stage micro-inverter. The micro-inverter can specifically be a DAB (Dual ActiveBridge) type micro-inverter, which has the following advantages: 1) Single-stage power conversion: low-voltage DC to AC conversion can be achieved without additional components; 2) Device simplification: the secondary half-bridge structure reduces the number of power devices; 3) High transformer utilization: soft switching is achieved through phase-shift control to reduce switching losses.

[0070] Specifically, the primary bridge arm may include four switching tubes Q1-Q4, and the gates of these four switching tubes are sequentially input with drive signals S1-S4; the transformer T may be a high-frequency transformer with a turns ratio of 1:n; the secondary bridge arm may include four switching tubes Q5-Q8, and the gates of these four switching tubes are sequentially input with drive signals S5-S8. The input end of the primary bridge arm 10 may also be connected to a decoupling capacitor C bus The secondary winding of the transformer T can be connected to a resonant inductor, which can be an independently set inductor or a Figure 1 The leakage inductance L of the transformer T k constitute, Figure 1According to the characteristics of transformer T, the excitation inductance L of transformer T is also equivalently drawn. m The micro-inverter may further include a first capacitor C1 and a second capacitor C2, which together with the secondary bridge arm 30 form a half-bridge structure of the secondary side.

[0071] In the micro-inverter, the photovoltaic module PV on the input side is connected to the decoupling capacitor C bus To balance power fluctuations, the first capacitor C1 and the second capacitor C2 on the secondary side divide the voltage and filter out high-frequency harmonics. By adjusting the primary voltage duty cycle (i.e., the inner phase shift angle D1, specifically the angle between the drive signal S1 and the drive signal S4) and the phase difference (i.e., the outer phase shift angle D2, specifically the angle between the fundamental wave of the primary voltage and the fundamental wave of the secondary voltage of the high-frequency transformer), the leakage inductance L is controlled. k The current on the resonant current i r ) to achieve power transmission. Specifically, the basic working principle of DAB type micro inverter is as follows Figure 2 As shown, the full bridge circuit of the primary bridge arm can generate {+V pv ,0,-V pv}3 levels, converted to the secondary side voltage (ie nv p ) is a square wave with variable duty cycle, V pv is the photovoltaic voltage of the photovoltaic module; the half-bridge circuit on the secondary side can generate {+|v g | / 2,-|v g | / 2} 2 levels, secondary voltage (i.e. v s ) is a quasi-square wave with a fixed duty cycle of 0.5, v g The leakage inductance L of transformer T can be adjusted by controlling the duty cycle of the primary voltage and the phase of the primary and secondary voltages. k The resonant current i r , thus achieving a given power transmission.

[0072] The control system based on the micro-inverter can realize the above control. The control system of the micro-inverter is described in detail below.

[0073] Continue to see Figure 1 The control system of the micro-inverter includes: a power tracking control module 10, an output current loop control module 21, an inverter voltage loop control module 22 and a feedforward modulation module 30.

[0074] The power tracking control module 10 can obtain the photovoltaic voltage V of the photovoltaic module PV. pv and photovoltaic current I pv , and obtain the grid voltage v g ; The power tracking control module 10 is used to follow the photovoltaic voltage V pv , photovoltaic current I pv and grid voltage v gOutput grid-connected current reference value i g_ref The output current loop control module 21 is connected to the output end of the power tracking control module 10 and inputs the grid-connected current i g , grid-connected current i g The micro-inverter provides output current to the grid G; the output current loop control module 21 is used to control the output current of the micro-inverter according to the grid current reference value i g_ref and grid-connected current i g Output inverter voltage reference value v inv_ref The inverter voltage loop control module 22 is connected to the output end of the output current loop control module 21 and inputs the inverter output voltage v inv , inverter output voltage v inv is the output voltage of the output end of the secondary bridge arm, that is, the voltage difference between the upper end of the switch tube Q5 and the lower end of the switch tube Q8. The inverter voltage loop control module 22 is used to control the inverter voltage reference value v inv_ref and inverter output voltage v inv Output inverter current reference value i inv_ref The feedforward modulation module 30 is connected to the output end of the inverter voltage loop output module 22, and is used to modulate the inverter current reference value i inv_ref Control the working status of the primary bridge arm and the secondary bridge arm.

[0075] It is understandable that the electrical signals obtained / inputted in the various embodiments of the present invention are derived from the micro-inverter and the related circuit topology connected thereto, such as the photovoltaic voltage V pv , photovoltaic current I pv , grid voltage v g , grid-connected current i g and inverter output voltage v inv Etc., can be obtained by electrical signal acquisition devices set at corresponding positions in the circuit topology, such as using current acquisition devices such as current transformers to sample current and using voltage acquisition devices such as voltmeters to sample voltage, which will not be repeated below.

[0076] For example, the power tracking control module 10 can perform maximum power point tracking (MPPT) on the photovoltaic module PV to obtain a given photovoltaic voltage value, and calculate the photovoltaic voltage value according to the difference between the given photovoltaic voltage value and the actual photovoltaic voltage V pv The difference between the two generates the grid current amplitude reference value I m_ref And the power tracking control module 10 can be based on the grid voltage v g Analyze the grid voltage phase and combine it with the grid current amplitude reference value I m_ref The grid current reference value i is obtained by combining the grid voltage phase g_ref , used to guide the control process of the output current loop control module 21.

[0077] The output current loop control module 21 can also be called a grid-connected current loop control module, which is used to control the output current loop according to the grid-connected current reference value i g_ref The actual grid current i g The difference between the output current loop control module 21 generates the control reference of the subsequent control module, for example, the inverter voltage reference value v inv_ref , used to guide the control process of the inverter voltage loop control module 22. Among them, the output current loop control module 21 adjusts the error to achieve the grid-connected current i g Reference value of grid-connected current i g_ref Steady-state tracking is performed to complete power dispatch and grid synchronization.

[0078] The inverter voltage loop control module 22 is used to control the inverter voltage reference value v inv_ref The actual inverter output voltage v inv The difference between the two generates the control reference of the inverter voltage loop control module 22 and the subsequent control module, for example, generates the inverter current reference value i inv_ref , used to guide the control process of the feedforward modulation module 30. By adjusting the error through the inverter voltage loop control module 22, the AC side voltage of the micro-inverter can be stabilized and the fluctuation caused by the change of the grid impedance can be suppressed.

[0079] One of the output terminals of the feedforward modulation module 30 can be connected to the primary bridge arm to provide the required driving signal to each switch tube of the primary bridge arm, that is, to provide S 1-4 , to control the working state of the primary bridge arm; and the other output end of the feedforward modulation module 30 can be connected to the secondary bridge arm, for providing the required drive signal to each switch tube of the secondary bridge arm, ie, providing S 5-8 , to control the working state of the secondary bridge arm; this can achieve a given power transmission. Among them, the working state of the primary bridge arm includes the on-off state of each switch tube in the primary bridge arm. By controlling the on-off of each switch tube in the primary bridge arm, it is possible to control whether the primary bridge arm performs inversion conversion on the voltage provided by the photovoltaic module PV, and control the voltage polarity output by the primary bridge arm to the transformer T; the working state of the secondary bridge arm includes the on-off state of each switch tube in the secondary bridge arm. By controlling the on-off of each switch tube in the secondary bridge arm, the resonant current i r For example, the feedforward modulation module 30 can be based on the reference signal (for example, the inverter current reference value i) obtained after error processing by the front-stage control module to which it is connected. inv_ref ), combined with the photovoltaic voltage V pv , grid voltage v g and grid-connected current reference value i g_refDetermine the inner phase shift angle D1 and the outer phase shift angle D2, then control the working state of the primary bridge arm based on the inner phase shift angle D1, and control the working state of the secondary bridge arm based on the outer phase shift angle D2. 1-8 Both are high-frequency PWM (Pulse Width Modulation) drive signals with the same switching frequency.

[0080] The control system of the micro-inverter provided by the embodiment of the present invention provides a control system with multiple closed-loop control, which can effectively improve the control accuracy and stability of the inverter operation process. Specifically, based on the power tracking control module 10, the maximum power point tracking of the photovoltaic module PV can be achieved, and combined with the grid voltage v g Reference quantities related to the outer loop control in the multiple closed-loop control are obtained, and the feedforward modulation module 30 can provide drive signals for the primary and secondary bridge arms of the inverter based on the output results of the multiple closed-loop control. The multiple closed-loop control can specifically include: grid-connected current loop control based on the output current loop control module 21 and inverter voltage loop control based on the inverter voltage loop control module 22. Each loop is controlled in a hierarchical manner, and each link focuses on different control objectives, thereby improving the robustness and dynamic performance of the system. Among them, the grid-connected current loop is responsible for overall power regulation and grid synchronization, while the inverter voltage loop can stabilize the output voltage, reduce the impact of voltage fluctuations on the current loop, improve resistance to grid impedance changes, suppress grid impedance disturbances, and improve control loop stability.

[0081] The above embodiment provides a dual-loop control architecture including a grid-connected current loop and an inverter voltage loop, but is not intended to limit the present invention. In other embodiments, optionally, see Figure 3 An inverter current loop control module 23 may also be provided in the control system of the micro-inverter to provide inverter current loop control, thereby forming a three-loop control architecture.

[0082] For details, see Figure 3 The inverter current loop control module 23 is connected between the output end of the inverter voltage loop control module 22 and the feedforward modulation module 30, and inputs the inverter output current i inv ; Inverter output current i inv According to the resonant current i of the secondary side of transformer T r The inverter current loop control module 23 is used to determine the inverter current reference value i inv_ref and inverter output current i inv Output the phase shift angle control value D. Accordingly, the feedforward modulation module 30 is used to control the working state of the primary bridge arm and the secondary bridge arm according to the phase shift angle control value D.

[0083] Exemplarily, the inverter current loop control module 23 is used to control the inverter current reference value i inv_refThe actual inverter output current i inv The difference between the output and the output is used to generate the control reference of the inverter current loop control module 23, for example, to generate the phase shift angle control value D, which is used to guide the control process of the feedforward modulation module 30. The inverter current loop control module 23 adjusts the error, which can quickly track the inverter current reference value i inv_ref , realize high-frequency current tracking, suppress high-frequency harmonics and achieve dynamic response, solve the problem of weak suppression ability of single closed-loop / dual closed-loop on high-frequency harmonics, and improve control accuracy.

[0084] In summary, this embodiment provides a three-loop control structure of a grid-connected current outer loop + an inverter voltage intermediate loop + an inverter current inner loop. The three-loop control uses hierarchical control, with each link focusing on different control objectives, thereby improving the robustness and dynamic performance of the system. Specifically, the outer loop (grid-connected current loop) is responsible for overall power regulation and grid synchronization, the intermediate loop (inverter voltage loop) can stabilize the output voltage and reduce the impact of voltage fluctuations on the current loop, while the inner loop (inverter current loop) quickly responds to current changes and suppresses high-frequency interference. This hierarchical structure allows each loop to be optimized for different frequency bands. The outer loop processes low-frequency changes, the inner loop processes high-frequency disturbances, and the intermediate loop plays a connecting role between the two, thereby improving the overall control accuracy and stability.

[0085] The overall architecture of the control system is described in the above embodiments. The structure and operation of each control module are described in detail below. It is understood that, with the exception of the explanation of the inverter current loop control module 23, the explanation of other control modules, such as the explanation of the output current loop control module 21 and the inverter voltage loop control module 22, is applicable to both the dual-loop architecture and the triple-loop architecture.

[0086] Figure 4 This is a control block diagram of an output current loop control module provided by an embodiment of the present invention. Figure 4 In one embodiment, the output current loop control module 21 optionally includes: a first operator cal1 and a first controller ctr1. The first operator cal1 can be connected to the output terminal of the power tracking control module to input the grid current reference value i g_ref , and the first operator cal1 also inputs the grid current i g The first operator cal1 is, for example, a subtractor for calculating the difference between the two input signals of the output current loop control module 21, ie, calculating the grid current reference value i g_ref The grid-connected current i g The difference between the two is the first operation value e outer , specific, e outer =i g_ref -i gThe first controller ctr1 is a core control component in the output current loop control module 21 and is connected between the output end of the first operator cal1 and the output end of the output current loop control module 21. The first controller ctr1 is used to generate a first operation value e according to the first operation value e. outer Determine the inverter voltage reference value v inv_ref That is, the control target of the output current loop control module 21 is to adjust the error through the first controller ctr1 to achieve the grid-connected current i g Reference value of grid-connected current i g_ref The steady-state tracking is completed to complete the power dispatch and grid synchronization. In this way, after closed-loop control, the actual grid-connected current i g Able to track the grid current reference value i without static error g_ref , to achieve maximum power transmission of photovoltaic panels; and, grid-connected current i g Tracking grid current reference value i g_ref The grid voltage phase θ in is realized to achieve the same phase as the grid voltage.

[0087] Taking the mathematical model of the CL filter controlled object at the output end of the micro-inverter as an example, the mathematical model of the controlled object of the output current loop control module 21 (referred to as the first controlled object 51) can be represented by the 1 / sL link, where L is, for example, the grid-side inductance of the inverter. The control link between the output current loop control module 21 and the first controlled object 51 can be represented by the first equivalent transfer function G close (s) indicates that, for example, it may include the inverter voltage loop control and other links, which will not be explained here. The first equivalent transfer function G close (s) According to the inverter voltage reference value v inv_ref After processing, a first voltage signal u is provided L To the first controlled object 51, and then processed by the first controlled object 51 to obtain the grid-connected current i g , forming the overall control block diagram of the grid-connected current loop.

[0088] It is understandable that for any controller, the difference between the controller's output and input may not be the same physical quantity, but rather the output is related to the signal connected to the subsequent stage. For example, the subsequent stage of the first controller Ctr1 is the inverter voltage loop control module, whose output is the voltage reference. The relationship between the inverter voltage and the grid-connected current can be discovered by establishing a mathematical model at the output end. The output of the first controller Ctr1 represents the "±" relationship of the front-end error signal (i.e., the magnitude relationship between the actual input signal and the reference signal). Therefore, according to the corresponding mathematical model, the inverter voltage control process of the subsequent stage can be adjusted to make the grid-connected current track its reference signal (for example, if the output of the first controller Ctr1 is positive, it is considered that the reference is greater than the actual, and a closed-loop increase in the grid-connected current is required. In this case, adjusting the inverter voltage can increase the grid-connected current, thereby effectively tracking the reference signal).

[0089] Figure 5 This is a control block diagram of another output current loop control module provided by an embodiment of the present invention. Figure 5 On the basis of the above embodiment, the output current loop control module 21 may optionally further include: a second operator cal2. The second operator cal2 is connected between the output terminal of the first controller ctr1 and the output terminal of the output current loop control module 21, and inputs the grid voltage v g The second operator cal2 is, for example, an adder for calculating the grid voltage v g and the inverter voltage reference value v inv_ref The sum of the two gets the second operation value v comp ; specific, v comp =v inv_ref +v. Correspondingly, the first equivalent transfer function G close (s) According to the second operation value v comp After processing, it provides the inverter output voltage v inv To the first controlled object 51; wherein the inverter voltage loop control module 22 is used to control the inverter voltage loop according to the second operation value v comp With the inverter output voltage v inv Output inverter current reference value i inv_ref .

[0090] This embodiment can be applied to the controlled objects of the output current loop control module 21, that is, the first controlled object 51 includes the grid voltage v g This is the case of a negative disturbance term. For example, before the 1 / sL link, it also includes the grid voltage v g is the calculation process of negative disturbance term, the inverter output voltage v inv With the grid voltage v g The difference is the first voltage signal u L Then, due to the CL filter controlled object mathematical model at the output end of the micro-inverter, the grid voltage v g is a negative disturbance term (i.e. the processing in the first controlled object 51 is to subtract the grid voltage v g ), so feedforward is performed in the control loop, and the grid voltage v is added to the grid current loop or before the inverter voltage loop. g As a positive disturbance term, it can offset the negative disturbance term in the first controlled object 51, compensate for the grid voltage drop, and thus better control the grid current i g , and also simplifies the derivation of the closed-loop transfer function, making the design of the related controller less complicated.

[0091] Figure 6 This is a control block diagram of an inverter voltage loop control module provided by an embodiment of the present invention. Figure 6In one embodiment, the inverter voltage loop control module 22 optionally includes: a third operator cal3 and a second controller ctr2. The third operator cal3 is connected to the output end of the output current loop control module 21 and inputs the inverter output voltage v inv The third operator cal3 is, for example, a subtractor for calculating the difference between the two input signals of the inverter voltage loop control module 22, that is, for calculating the output signal of the output current loop control module 21 (eg, the inverter voltage reference value v inv_ref Or the second operation value v comp ) and inverter output voltage v inv The difference is the third operation value e mid ; For example, e mid =v comp -v inv The second controller ctr2 is a core control component in the inverter voltage loop control module 22, connected between the output end of the third operator cal3 and the output end of the inverter voltage loop control module 22; the second controller ctr2 is used to generate a voltage signal according to the third operation value e mid Determine the inverter current reference value i inv_ref That is, the control goal of the inverter voltage loop control module 22 is to adjust the error through the second controller ctr2, stabilize the AC side voltage of the micro-inverter, and suppress the fluctuation caused by the change of the grid impedance.

[0092] Still taking the mathematical model of the CL filter controlled object at the output end of the micro-inverter as an example, the mathematical model of the controlled object of the inverter voltage loop control module 22 (referred to as the second controlled object 52) ​​can be represented by the 1 / sC link, where C is, for example, the grid-side filter capacitor of the inverter. The control link between the inverter voltage loop control module 22 and the second controlled object 52 can be represented by a second equivalent transfer function G2(s), which can include, for example, feedforward modulation and other links, which will not be explained here. The second equivalent transfer function G2(s) is based on the inverter current reference value i inv_ref After processing, a first current signal i is provided. C To the second controlled object 52, and then processed by the second controlled object 52 to obtain the inverter output voltage v inv , forming the overall control block diagram of the inverter voltage loop. It can be understood that the equivalent transfer function of the overall control block diagram of the inverter voltage loop is the first equivalent transfer function G close (s).

[0093] Figure 7 This is a control block diagram of another inverter voltage loop control module provided by an embodiment of the present invention, see Figure 7Based on the above embodiment, the inverter voltage loop control module 22 may optionally further include a fourth operator cal4. The fourth operator cal4 is connected between the output terminal of the second controller ctr2 and the output terminal of the inverter voltage loop control module 22, and inputs the feedforward quantity i f The fourth operator cal4 is, for example, an adder, used to calculate the feedforward quantity i f and the inverter current reference value i inv_ref The sum of the fourth operation value i is obtained sum Among them, the feedforward quantity i f is the grid-connected current i g Or grid-connected current reference value i g_ref For example, sum =i inv_ref +i. Accordingly, the second equivalent transfer function G2(s) is calculated based on the fourth operation value i sum After processing, it provides the inverter output current i inv To the second controlled object 52; wherein the feedforward modulation module 30 can be used according to the fourth operation value i sum Control the working status of the primary bridge arm and the secondary bridge arm.

[0094] This embodiment is applicable to the controlled object of the inverter voltage loop control module 22, that is, the second controlled object 52 also includes the grid-connected current i g This is the case of a negative disturbance term. For example, before the 1 / sC link, it also includes the grid current i g The calculation process of the negative disturbance term, the inverter output current i inv and grid-connected current i g The difference is the first current signal i C Then, due to the CL filter controlled object mathematical model at the output end of the micro-inverter, the grid current i g It is a negative disturbance term, so feedforward is performed in the control loop, and the feedforward amount i is added in the inverter voltage loop or before the inverter current loop / feedforward modulation. f As a positive disturbance term, it can offset the negative disturbance term in the second controlled object 52 to achieve dynamic compensation, thereby better controlling the inverter output voltage v inv , and simplifies the derivation of the closed-loop transfer function, making the design of the related controller less complicated.

[0095] In one embodiment, the grid-connected current i obtained by actual sampling can be used. g As the feedforward quantity i f , to improve the dynamic response speed; or, in another embodiment, the grid current reference value i g_ref As the feedforward quantity i f , in order to optimize the steady-state tracking accuracy. The above two types of feedforward if Both are connected to the grid current i g The relevant feedforward amount can be selected according to the actual control requirements.

[0096] Figure 8 This is a control block diagram of an inverter current loop control module provided by an embodiment of the present invention. Figure 8 In one embodiment, the inverter current loop control module 23 optionally includes: a fifth operator cal5 and a third controller ctr3. The fifth operator cal5 is connected to the output end of the inverter voltage loop control module 22 and inputs the inverter output current i inv The fifth operator cal5 is, for example, a subtractor for calculating the difference between the two input signals of the inverter current loop control module 23, for example, calculating the output signal of the inverter voltage loop control module 22 (for example, the inverter current reference value i inv_ref or the fourth operation value i sum ) and the inverter output current i inv The difference is the fifth operation value e inner ; For example, e inner =i sum -i inv The third controller ctr3 is a core control component in the inverter current loop control module 23, connected between the output end of the fifth operator cal5 and the output end of the inverter current loop control module 23; the third controller ctr3 is used to control the inverter current loop control module 23 according to the fifth operation value e inner The phase-shift angle control value D is obtained. In other words, the control objectives of the inverter current loop control module 23 are: to adjust the error through the third controller ctr3, quickly track the current command, suppress high-frequency harmonics, and achieve dynamic response. The phase-shift angle control value D output by the inverter current loop control module 23 is provided to the feedforward modulation module 30, and the phase-shift controller generates drive signals S1-S4 and S5-S8 for each switch tube in the primary and secondary bridge arms of the microinverter, and provides them to the microinverter topology 54. Specifically, the drive signals S1-S4 are sequentially provided to the switches Q1-Q4, and the drive signals S5-S8 are sequentially provided to the switches Q5-Q8. It can be understood that the equivalent transfer function of the overall control block diagram of the inverter current loop can be used as the second equivalent transfer function G2(s).

[0097] It can be understood that the phase-shift angle control variable D includes control variables for the inner phase-shift angle D1 and the outer phase-shift angle D2. In dual-loop control, the output of the inverter voltage loop, along with the feedforward variable, is provided as input current to the feedforward modulation module 30. In triple-loop control, the output control variable of the third controller ctr3 is provided to the feedforward modulation module 30. Based on the output of the multiple closed-loop control and the calculated relationship between the inner and outer phase shifts, the feedforward modulation module 30 calculates the required inner and outer phase-shift angles D1 and D2, and then generates the drive signals for the switches in the primary and secondary bridge arms of the microinverter.

[0098] Based on the above embodiments, optionally, the controllers in any control module, such as the first controller Ctr1, the second controller Ctr2, and the third controller Ctr3, all adhere to the basic principle of closed-loop control controllers, namely, based on a feedback mechanism, accurately controlling the controlled object by comparing the deviation between the actual output and the desired output and adjusting the control signal accordingly. Specifically, the controller can receive a deviation signal processed by its front-end arithmetic unit and then, based on the deviation signal and the system model, employ a corresponding control algorithm to calculate the control signal. The control algorithm may include proportional control, integral control, differential control, or a combination thereof, or other control algorithms, depending on the selected controller type. The control signal processed by the controller is output to the actuator, which adjusts and controls the controlled object accordingly to reduce or eliminate the deviation and bring the actual output closer to the desired output. During the closed-loop control process, the actual output is continuously monitored and compared with the desired output. The control signal is continuously adjusted based on the deviation signal, forming a continuous monitoring and adjustment cycle. Among them, in multiple closed-loop control, the control signal output by the outer control loop can be used as the desired signal of the inner control loop, until the control signal output by the innermost loop acts on the circuit topology, thereby realizing multiple closed-loop control.

[0099] Exemplarily, the output current loop control module 21, the inverter voltage loop control module 22, and the inverter current loop control module 23 all include: a proportional integral (PI) controller, a proportional resonant (PR) controller, a quasi-proportional resonant (QPR) controller, and a sliding mode controller. Different controllers correspond to different control algorithms, which can be selected according to actual control requirements. Specifically, the proportional integral control algorithm adopted by the proportional integral controller is a control algorithm based on a proportional coefficient and an integral coefficient. The proportional control is used to linearly amplify the current error signal to produce a preliminary control effect. The integral control eliminates the steady-state error by accumulating the error signal. By adjusting the proportional coefficient and the integral coefficient, the response speed and steady-state accuracy can be balanced. The proportional resonant control algorithm adopted by the proportional resonant controller is a control algorithm based on a proportional coefficient and a resonant coefficient. At the target tracking frequency, the controller gain tends to infinity, which can achieve zero-static error tracking of a specific frequency signal. It is suitable for occasions where it is necessary to accurately track a sinusoidal reference signal or suppress specific frequency harmonics. The quasi-proportional resonant controller uses a quasi-proportional resonant control algorithm. This algorithm takes resonant frequency offset into account, introducing a damping factor to broaden the resonant bandwidth and enhance adaptability to frequency drift. The sliding mode controller uses a nonlinear control strategy whose core concept is to design a specific "sliding mode surface" to force the system state to be attracted to it within a finite time and maintain stable motion on the sliding mode surface. The control parameters include sliding mode surface parameters and sliding mode control parameters.

[0100] On this basis, any of the first controller ctr1, the second controller ctr2, and the third controller ctr3 can adopt any of the above controllers. In the above embodiments, the first controller ctr1 adopts a PR controller, the second controller ctr2 adopts a PI controller, and the third controller ctr3 adopts a PI controller, but this is not intended to limit the present invention.

[0101] Continue to see Figure 3 On the basis of the above embodiments, optionally, the control system of the micro-inverter further includes: a current processing module 40. The current processing module 40 is used to adjust the resonant current i of the secondary side of the transformer T according to the current i of the secondary side of the transformer T. r Determine the inverter output current i inv .

[0102] For example, the inverter output current i inv The leakage inductance L k The resonant current i r Specifically, the current processing module 40 may include: a sampling unit and an average current calculation unit. Figure 9 , the sampling unit may include a current transformer CT and an integrating capacitor C sThe current transformer CT is connected to the secondary side of the transformer T to sample the resonant current i r , integrating capacitor C s The average current calculation unit is connected to the sampling unit, which can be connected to the integration capacitor C s The average current calculation unit is used to calculate the average current according to the integration capacitor C s The capacitance value, integral capacitance C s The voltage across the two ends u s The inverter output current i is calculated based on the switching frequency of the switch tube in the secondary bridge arm inv The function of the current processing module 40 is to convert the sampled high-frequency current into the average output current of the bridge arm required by the inner loop feedback signal; the basic principle is as follows: during the opening time of the secondary bridge arm, by measuring the resonant cavity inductor current (i.e., the resonant current i r ) of the integrated charge, combined with the switching frequency (denoted as f sw ) information, the average output current of the bridge arm (denoted as I avg ), its expression is: I avg =Δu s ·C s ·f sw , where: Δu s The integral capacitor voltage change is used to reflect the charge (denoted as Q, Q = Δu s ·C s ). The calculated bridge arm output average current I avg Feedback to multiple closed-loop control systems as inverter output current i inv .

[0103] In summary, the expanded block diagram of the dual-loop control architecture can be found in Figure 10 , Figure 10 In the figure, the upper part represents the mathematical model of the control system, and the lower part represents the mathematical model of the controlled object. Figure 11 and Figure 12 The structure diagrams of two dual-loop architecture control systems are provided in Figure 11 and Figure 12 The difference is: Figure 11 China-Israel grid-connected current i g As a feedforward control, Figure 12 Reference value of grid-connected current i g_ref It is controlled as a feedforward quantity. It can be understood that Figure 11 and Figure 12 In the figure, the second operator cal2 and the third operator cal3 are combined into an eighth operator cal8 with three inputs for display.

[0104] The expanded block diagram of the three-loop control architecture can be found in Figure 13 , Figure 13 In the figure, the upper part represents the mathematical model of the control system, and the lower part represents the mathematical model of the controlled object. Figure 14 and Figure 15 The structure diagrams of two three-ring architecture control systems are provided in Figure 14 and Figure 15 The difference is: Figure 14 China-Israel grid-connected current i g As a feedforward control, Figure 15 Reference value of grid-connected current i g_ref It is controlled as a feedforward quantity. It can be understood that Figure 14 and Figure 15 In the figure, the second operator cal2 and the third operator cal3 are combined into an eighth operator cal8 with three inputs for display, and the fourth operator cal4 and the fifth operator cal5 are combined into a ninth operator cal9 with three inputs for display.

[0105] Based on the above embodiments, the power tracking control module 10 can optionally be configured to control the photovoltaic voltage V pv and photovoltaic current I pv Obtain the grid-connected current amplitude reference value I m_ref , and according to the grid voltage v g Obtain the grid voltage phase θ and calculate the grid current amplitude reference value I m_ref and the grid voltage phase θ to determine the grid-connected current reference value i g_ref , exemplary, i g_ref =I m_ref *sinθ.

[0106] See also Figure 11 Specifically, the power tracking control module 10 includes: a maximum power point tracking unit 11, a sixth operator cal6, a fourth controller ctr4, a phase-locked loop 61, a sine processing unit 62 and a seventh operator cal7. The maximum power point tracking unit 11 is used to track the photovoltaic voltage V pv and photovoltaic current I pv Determine the photovoltaic voltage set value V pv_ref The sixth operator cal6 is connected to the output terminal of the maximum power point tracking unit 11 and inputs the photovoltaic voltage V pv The sixth operator cal6 can be a subtractor for calculating the photovoltaic voltage given value V pv_ref and photovoltaic voltage V pv The fourth controller ctr4 is connected to the output terminal of the sixth operator cal6, and the fourth controller ctr4 is used to determine the grid current amplitude reference value I according to the sixth operation value m_refThe phase-locked loop 61 is connected to the grid G ​​and is used to g Get the grid voltage phase θ, for example, the grid voltage v g Phase-locked to obtain the grid voltage phase θ; the sine processing unit 62 is connected to the output end of the phase-locked loop 61, and the sine processing unit 62 is used to calculate the sine value sinθ of the grid voltage phase θ; the seventh operator cal7 is respectively connected to the output end of the sine processing unit 62, the output end of the fourth controller ctr4 and the output end of the power tracking control module 10; the seventh operator cal7 can be a multiplier for calculating the grid current amplitude reference value I m_ref The product of the sine value sinθ of the grid voltage phase θ is used to obtain the grid-connected current reference value i g_ref .

[0107] Specifically, the grid current amplitude reference value I m_ref , grid voltage phase θ and given reactive phase angle can be calculated to obtain the grid current reference value i g_ref The reactive phase angle refers to the phase angle offset used to adjust the grid current phase to achieve reactive power control during the generation of the grid current reference signal. It can be given through an external interface or communication command. The reactive phase angle defaults to 0 radians, that is, the system operates under unity power factor control, so I can be used directly. m_ref *sinθ to get the grid-connected current reference value i g_ref .

[0108] In this embodiment, the photovoltaic voltage given value V obtained by MPPT tracking pv_ref The actual photovoltaic voltage V pv The difference reflects the deviation between the current working point of the photovoltaic cell and the maximum power point, as well as the direction and size required to adjust the working point of the photovoltaic module PV. Therefore, the output of this difference after being processed by the fourth controller ctr4 is used as a reference signal for the amplitude of the grid-connected current. By adjusting the amplitude of the grid-connected current, the photovoltaic cell can always operate at the maximum power point, thereby achieving maximum power output. The working principle of the fourth controller ctr4 can also refer to the relevant explanation of the controller in any control module mentioned above, and will not be repeated here. Exemplarily, the fourth controller ctr4 can be one of a proportional integral (PI) controller, a proportional resonant (PR) controller, a quasi-proportional resonant (QPR) controller and a sliding mode controller. The PI controller is given here as an example, but it is not intended to limit the present invention.

[0109] In summary, the embodiment of the present invention provides a three-ring control architecture, the core control architecture of which is as follows:

[0110] 1) Grid-connected current outer loop: The grid voltage phase is tracked through a phase-locked loop (PLL). Based on the error signal between the grid-connected current reference value and the actual grid-connected current, an inverter voltage reference value is generated as the intermediate loop voltage command for power scheduling and grid synchronization.

[0111] 2) Inverter voltage intermediate loop: Based on the compensation superposition of the inverter voltage reference value and the grid voltage (i.e., the grid voltage is fed forward to the voltage reference compensation term), combined with the error signal with the actual inverter output voltage, the inverter current reference value is generated as the inner loop current instruction, which is used to stabilize the AC side voltage of the microinverter and suppress grid impedance disturbances.

[0112] 3) Inverter current inner loop: Based on the superposition of the inverter current reference value and the feedforward amount, combined with the error signal of the actual inverter output current (specifically, it can be the average current signal of the bridge arm output obtained based on the high-frequency resonant current), a phase shift angle control amount is generated as the control amount signal required by the modulation part, so that the feedforward modulation module generates a PWM drive signal to achieve high-frequency current tracking and harmonic suppression.

[0113] On this basis, the inverter current loop can be removed to form a dual-loop control architecture. The output of the middle loop can be modulated in conjunction with the feedforward variable to simplify the control loop complexity and achieve a simpler structure. For example, a dual-loop control architecture can be used in applications where precision requirements are low and cost control and simplified control loops are required. Otherwise, a three-loop control architecture can be used.

[0114] An embodiment of the present invention further provides a control method for a micro-inverter, which can be applied to the control system of the micro-inverter provided by any embodiment of the present invention and has corresponding beneficial effects. Figure 16 This is a flow chart of a control method for a micro-inverter provided by an embodiment of the present invention. Figure 16 , the control method of the micro-inverter includes:

[0115] S110 , the power tracking control module outputs a grid-connected current reference value according to the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage.

[0116] S120 , the output current loop control module outputs an inverter voltage reference value according to the grid-connected current reference value and the grid-connected current.

[0117] The grid-connected current is the output current provided by the micro-inverter to the grid.

[0118] S130 , the inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage.

[0119] The inverter output voltage is the output voltage of the output end of the secondary bridge arm.

[0120] S140 , the feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value.

[0121] This embodiment provides a control method for a control system with a dual-loop control architecture, wherein the grid-connected current loop is responsible for overall power regulation and grid synchronization, and the inverter voltage loop can stabilize the output voltage, reduce the impact of voltage fluctuations on the current loop, improve resistance to grid impedance changes, suppress grid impedance disturbances, and improve control loop stability.

[0122] Based on the above embodiments, the control system of the micro-inverter optionally further includes an inverter current loop control module. Then, after the inverter voltage loop control module outputs an inverter current reference value based on the inverter voltage reference value and the inverter output voltage, the control method of the micro-inverter further includes: the inverter current loop control module outputting a phase shift angle control value based on the inverter current reference value and the inverter output current. Accordingly, the feedforward modulation module controls the operating states of the primary and secondary bridge arms based on the inverter current reference value, including: the feedforward modulation module controlling the operating states of the primary and secondary bridge arms based on the phase shift angle control value.

[0123] Specifically, Figure 17 This is a flow chart of a control method for a micro-inverter provided by an embodiment of the present invention. Figure 17 , the control method of the micro-inverter includes:

[0124] S210 , the power tracking control module outputs a grid-connected current reference value according to the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage.

[0125] S220 , the output current loop control module outputs an inverter voltage reference value according to the grid-connected current reference value and the grid-connected current.

[0126] S230 , the inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage.

[0127] S240. The inverter current loop control module outputs a phase shift angle control value according to the inverter current reference value and the inverter output current.

[0128] S250 , the feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the phase shift angle control amount.

[0129] This embodiment provides a control method for a control system with a three-loop control architecture. The outer loop (grid-connected current loop) is responsible for overall power regulation and grid synchronization. The middle loop (inverter voltage loop) stabilizes the output voltage and reduces the impact of voltage fluctuations on the current loop. The inner loop (inverter current loop) quickly responds to current changes and suppresses high-frequency interference. This layered structure allows each loop to be optimized for different frequency bands. The outer loop handles low-frequency variations, the inner loop handles high-frequency disturbances, and the middle loop acts as a bridge between the two, thereby improving overall control accuracy and stability.

[0130] To verify the feasibility and correctness of this solution, the inventors built a DAB micro-inverter circuit for three-loop control simulation verification. Quasi-proportional resonant controllers were used in all three control loops to adjust the error signal. The simulation circuit parameters are shown in Table 1.

[0131] Table 1

[0132]

[0133] To verify the system performance under steady-state full load (500W) conditions, Figure 18 Given the grid voltage v under rated power operating conditions g , grid-connected current i g and resonant current i r The simulation results show that: when the system is in steady state operation, there is no grid-connected current i g and the resonant current i r In the event of a sudden change, power transmission is stable. And the grid-connected current i g Strictly track the grid voltage v g The phase is highly sinusoidal, with a total harmonic distortion (THD) of 2.1%, which meets the IEEE international standard requirement of THD below 5%, verifying the three-loop control's ability to suppress harmonics.

[0134] Figure 19 This is a diagram showing the simulation results of a system transient response under a sudden change in grid voltage provided by an embodiment of the present invention. Figure 19 In order to evaluate the robustness of the system under grid disturbance, the grid voltage is set to jump from 240V (RMS) to 280V (RMS) at time t1 and return to its original value at time t2. The simulation results show that after the grid voltage suddenly changes, the grid current i g and the resonant current i r There is basically no overshoot and no significant oscillation, indicating that under the action of the inverter voltage loop, the loop gain fluctuation caused by the change of grid impedance is effectively offset.

[0135] Figure 20This is a simulation result diagram of the system dynamic response under a condition of simulating light intensity changes provided by an embodiment of the present invention. Figure 20 To simulate the effect of sudden change in light intensity in the actual environment, the photovoltaic panel is shaded at time t3 (shown as a sudden drop in power), and the light intensity suddenly increases at time t4 (shown as a sudden increase in power). The simulation results show that: the grid current i g and the resonant current i r It drops smoothly at time t3 (response time <5ms) and rises rapidly at time t4 without any step mutation, indicating that the DAB microinverter has good transient performance under three-loop control.

[0136] In summary, the DAB micro-inverter achieves a balance between steady-state accuracy and dynamic performance through hierarchical regulation under the three-loop control (grid-connected current outer loop + inverter voltage middle loop + inverter current inner loop) architecture proposed in the embodiment of the present invention.

[0137] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0138] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A control system for a micro-inverter, characterized in that: The micro-inverter includes: a primary bridge arm, a transformer, and a secondary bridge arm; the input end of the primary bridge arm is connected to the photovoltaic module, the output end of the primary bridge arm is connected to the primary side of the transformer, the secondary side of the transformer is connected to the input end of the secondary bridge arm, and the output end of the secondary bridge arm is connected to the power grid; The control system of the micro-inverter includes: A power tracking control module is used to output a grid-connected current reference value according to the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage; an output current loop control module, connected to the output end of the power tracking control module, and configured to output an inverter voltage reference value according to the grid-connected current reference value and the grid-connected current; wherein the grid-connected current is the output current provided by the micro-inverter to the grid; an inverter voltage loop control module, connected to the output end of the output current loop control module, and configured to output an inverter current reference value according to the inverter voltage reference value and the inverter output voltage; wherein the inverter output voltage is the output voltage of the output end of the secondary bridge arm; A feedforward modulation module is connected to the output end of the inverter voltage loop output module and is used to control the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value.

2. The micro-inverter control system according to claim 1, characterized in that: Also includes: An inverter current loop control module is connected between the output end of the inverter voltage loop control module and the feedforward modulation module, and is used to output a phase shift angle control amount according to the inverter current reference value and the inverter output current; the feedforward modulation module is used to control the working states of the primary bridge arm and the secondary bridge arm according to the phase shift angle control amount; wherein the inverter output current is determined according to the resonant current of the secondary side of the transformer.

3. The micro-inverter control system according to claim 1 or 2, characterized in that: The output current loop control module includes: a first operator connected to the output terminal of the power tracking control module and inputting the grid-connected current, for calculating the difference between the grid-connected current reference value and the grid-connected current to obtain a first operation value; a first controller, connected to the output end of the first operator, and configured to determine the inverter voltage reference value according to the first operation value; A second operator is connected between the output end of the first controller and the output end of the output current loop control module, and inputs the grid voltage; the second operator is used to calculate the sum of the grid voltage and the inverter voltage reference value to obtain a second operation value; the inverter voltage loop control module is used to output the inverter current reference value based on the second operation value and the inverter output voltage.

4. The micro-inverter control system according to claim 1 or 2, characterized in that: The inverter voltage loop control module includes: a third operator connected to the output end of the output current loop control module and inputting the inverter output voltage; the third operator is used to calculate the difference between the output signal of the output current loop control module and the inverter output voltage to obtain a third operation value; The second controller is connected between the output terminal of the third operator and the output terminal of the inverter voltage loop control module, and is used to determine the inverter current reference value according to the third operation value.

5. The micro-inverter control system according to claim 4, characterized in that: The inverter voltage loop control module also includes: A fourth operator is connected between the output end of the second controller and the output end of the inverter voltage loop control module, and inputs a feedforward amount; the fourth operator is used to calculate the sum of the feedforward amount and the inverter current reference value to obtain a fourth operation value; the feedforward modulation module is used to control the working state of the primary bridge arm and the secondary bridge arm according to the fourth operation value; wherein the feedforward amount is the grid-connected current or the grid-connected current reference value.

6. The micro-inverter control system according to claim 2, characterized in that: The inverter current loop control module includes: a fifth operator, connected to the output end of the inverter voltage loop control module, and configured to calculate a difference between an output signal of the inverter voltage loop control module and the inverter output current to obtain a fifth operation value; The third controller is connected between the output end of the fifth operator and the output end of the inverter current loop control module, and is used to obtain the phase shift angle control value according to the fifth operation value.

7. The micro-inverter control system according to claim 1 or 2, characterized in that: The power tracking control module includes: a maximum power point tracking unit, configured to determine a given photovoltaic voltage value according to the photovoltaic voltage and the photovoltaic current; a sixth operator connected to the output terminal of the maximum power point tracking unit and inputting the photovoltaic voltage; the sixth operator is used to calculate the difference between the given photovoltaic voltage value and the photovoltaic voltage to obtain a sixth operation value; a fourth controller, connected to the output end of the sixth operator, and configured to determine a grid-connected current amplitude reference value according to the sixth operation value; a phase-locked loop, connected to the power grid, and configured to obtain a grid voltage phase according to the power grid voltage; a sine processing unit, connected to the output end of the phase-locked loop, and configured to calculate the sine value of the grid voltage phase; The seventh operator is respectively connected to the output end of the sinusoidal processing unit, the output end of the fourth controller and the output end of the power tracking control module, and is used to calculate the product of the grid-connected current amplitude reference value and the sine value of the grid voltage phase to obtain the grid-connected current reference value.

8. The micro-inverter control system according to claim 2, characterized in that: Also includes: a current processing module, configured to determine the inverter output current according to the resonant current of the secondary side of the transformer; Wherein, the current processing module includes: A sampling unit, comprising a current transformer and an integrating capacitor; the current transformer is used to sample the resonant current, and the integrating capacitor is connected between two ends of the secondary side of the current transformer; An average current calculation unit is connected to both ends of the integrating capacitor and is used to calculate the inverter output current according to the capacitance value of the integrating capacitor, the voltage across the integrating capacitor and the switching frequency of the switching tube in the secondary bridge arm.

9. A control method for a micro-inverter, characterized in that: A control system for a micro-inverter according to any one of claims 1 to 8; wherein the control method for the micro-inverter comprises: The power tracking control module outputs a grid-connected current reference value based on the photovoltaic voltage and photovoltaic current of the photovoltaic module and the grid voltage; The output current loop control module outputs an inverter voltage reference value according to a grid-connected current reference value and a grid-connected current; wherein the grid-connected current is the output current provided by the micro-inverter to the grid; The inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage; wherein the inverter output voltage is the output voltage of the output end of the secondary bridge arm; The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value.

10. The micro-inverter control method according to claim 9, characterized in that: The control system of the micro-inverter further includes an inverter current loop control module; after the inverter voltage loop control module outputs an inverter current reference value according to the inverter voltage reference value and the inverter output voltage, the control method of the micro-inverter further includes: The inverter current loop control module outputs a phase shift angle control value according to the inverter current reference value and the inverter output current; The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the inverter current reference value, including: The feedforward modulation module controls the working states of the primary bridge arm and the secondary bridge arm according to the phase shift angle control amount.

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