AC loop rapid discharge control system and control method of inverter

Abstract

The invention discloses a rapid discharge control system and control method for an AC loop of an inverter. The rapid discharge control system comprises an inverter side circuit module, a mains supply detection module, a control module and a discharge execution module, the inverter side circuit module is used for forming a detection and electric loop; the mains supply detection module is used for judging whether the AC power grid has mains supply; the control module is used for receiving detection signals of the mains supply detection module and outputting driving control signals; and the discharge execution module is used for receiving the drive control signal of the control module and controlling the conduction states of a switch tube Q3 and a switch tube Q4 in the full-bridge circuit to form a discharge loop of the AC side capacitor. The hardware cost is not increased, and the problem of cost increase and hardware transformation workload are avoided. Rapid discharge of AC side capacitor voltage is realized through software control, and the risk of electric shock of operators is fundamentally avoided. The control algorithm is simplified, the DSP operation load is reduced, misjudgment can be avoided, and the accuracy and reliability of discharge triggering are ensured. The method has a wide application scene.

Description

Technical Field

[0001] This invention relates to a fast discharge control system and method for the AC circuit of an inverter, belonging to the technical field of inverter control systems and methods. Background Technology

[0002] Active grid-connected inverters, as core equipment for power conversion, are widely used in photovoltaic grid-connected systems, energy storage systems, and other scenarios. Their function is to convert DC power into AC power that conforms to AC grid standards and achieve grid connection. In actual operation, when an anomaly occurs in the AC grid (such as power outage, voltage drop, frequency anomaly, etc.) causing the inverter to shut down, the energy storage components (mainly AC-side capacitors) on the AC side of the inverter will store a large amount of electrical energy, forming a high residual voltage.

[0003] In existing technologies, the release of residual voltage at the AC terminal after the inverter is disconnected from the grid relies solely on the natural energy dissipation of internal fixed resistors. This method has significant drawbacks: First, to achieve effective discharge, high-power resistors are required, which not only increases the hardware cost of the inverter but also generates additional conversion losses during normal operation, reducing energy utilization efficiency. Second, the natural discharge speed of the resistors is slow, causing the AC terminal network to remain energized for extended periods, increasing the risk of electric shock to operators during equipment maintenance and repair, posing a serious safety hazard.

[0004] Therefore, there is an urgent need to design an inverter AC circuit discharge scheme that requires no additional hardware, is low in cost, and has high discharge efficiency, in order to solve the problems of high cost and poor safety in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art. In view of the problems in the prior art, such as the reliance on additional resistors for discharging the residual AC terminal voltage after the active inverter is disconnected from the grid, the increased hardware costs, high conversion losses, and long discharge time, this invention proposes a fast discharge control system and method for the AC circuit of the inverter.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A fast discharge control system for the AC circuit of an inverter includes an inverter-side circuit module, a mains power detection module, a control module, and a discharge execution module. The inverter-side circuit module includes a full-bridge circuit composed of switching transistors Q1, Q2, Q3, and Q4, current sampling resistors R1 and R2, an LC low-pass filter circuit, and an AC-side capacitor. The LC low-pass filter circuit includes inductors L1 and L2. The AC-side capacitor is electrically connected to the LC low-pass filter circuit and the full-bridge circuit in sequence. The current sampling resistors R1 and R2 are connected in series in the loop between the full-bridge circuit and the LC low-pass filter circuit. The mains power detection module is the Ecap capture module built into the inverter. The Ecap capture module is used to capture the rising edge and falling edge signals of the mains voltage pulse to determine whether there is mains power in the AC grid. The control module is electrically connected to the mains power detection module and the discharge execution module. The control module has a built-in time counting unit and a logic judgment unit, which are used to receive the detection signal from the mains power detection module and output the drive control signal through the time counting unit and the logic judgment unit. The discharge execution module is electrically connected to the control module and the full-bridge circuit. The discharge execution module is used to receive the drive control signal from the control module and control the conduction state of the switching transistors Q3 and Q4 in the full-bridge circuit to form a discharge circuit for the AC side capacitor.

[0007] Preferably, both the switching transistors Q3 and Q4 are equipped with anti-parallel diodes. The anti-parallel diodes are used to form a complete discharge circuit with the switching transistors when the polarity of the AC side capacitor voltage changes. The current sampling resistors R1 and R2 are used to collect the circuit current signal and to consume the energy stored in the AC side capacitor during the discharge process.

[0008] Preferably, the control module is further connected to a flyback-side drive unit and an inverter-side drive unit; The flyback-side drive unit is used to control the PWM swirl state of the flyback circuit, and the inverter-side drive unit is used to control the PWM swirl state of the full-bridge circuit.

[0009] This invention also proposes a control method for a fast discharge control system of the AC circuit of an inverter, comprising the following steps: S1 Mains Power Detection and Judgment: The mains voltage signal is captured in real time by the capture module Ecap. If the capture module Ecap does not detect the rising edge of the mains voltage pulse during the continuous capture cycle, it is determined that the mains power is missing, and the control module sets the no mains voltage flag to 1. S2 Delay handling after mains power failure: When the mains power failure flag is 1, the control module starts the first counting cycle of the time counter unit, and simultaneously outputs control signals to the flyback-side drive unit and the inverter-side drive unit, disabling the flyback-side drive enable and the inverter-side drive enable, and prohibiting PWM ripple between the flyback side and the full-bridge circuit; S3 Performs subsequent operations according to different cases: Scenario A: If the capture module Ecap detects the rising edge of the mains voltage pulse again during the first counting cycle, the control module starts the second counting cycle of the time counting unit. During the second counting cycle, the flyback side and inverter side drive enable are kept off. After the second counting cycle ends, the control module first enables the inverter side drive and allows the full-bridge circuit PWM to ripple. After a waiting period, the flyback side drive enable is enabled and the flyback circuit PWM to ripple. The inverter resumes normal operation. The waiting period is 5~40ms. Scenario B: If no mains power is detected at the end of the first counting cycle, the control module sets the AC side start discharge flag to 1, starting the third counting cycle of the time counting unit; at the same time, it disables the flyback side drive enable, disables flyback circuit PWM swirl, enables the inverter side drive enable, allows full-bridge circuit PWM swirl, and controls the conduction state of switching transistors Q3 and Q4 through the discharge execution module to form a discharge loop for the AC side capacitor; S4 Discharge End and Fault Handling: After the third counting cycle ends, the control module sets the AC side start discharge flag to 0, disables flyback and inverter side drive enable, disconnects the inverter relay and reports a no mains power fault, and the inverter enters a fault state; when the Ecap module detects that the mains power has returned to normal, the inverter restarts and resumes operation.

[0010] Preferably, in step S3, during the discharge process of case B, when the AC-side capacitor voltage is positive, the discharge circuit path is as follows: sequentially passing through inductor L1 of the LC low-pass filter circuit, switch Q4, current sampling resistor R2, current sampling resistor R1, the anti-parallel diode of switch Q3, inductor L2, and the negative terminal of AC-side capacitor; when the AC-side capacitor voltage is negative, the discharge circuit path is as follows: sequentially passing through inductor L2, switch Q3, current sampling resistor R1, current sampling resistor R2, the anti-parallel diode of switch Q4, inductor L1, and the positive terminal of AC-side capacitor.

[0011] Preferably, in step S3, during the discharge process of case B, there is no need to detect the polarity of the AC side capacitor voltage in real time. By alternately turning on the switching transistors Q3 and Q4, the self-inductance of the inductor in the LC low-pass filter circuit is utilized to make the polarity of the AC side capacitor voltage automatically change with the conduction state of the switching transistors.

[0012] The beneficial effects of this invention are mainly reflected in: 1. Zero increase in hardware cost: The system is built entirely on the existing hardware circuit of the inverter, without the need for additional components such as resistors, capacitors, and sensors, or any modification to the circuit structure, thus avoiding hardware cost investment and installation and debugging workload.

[0013] 2. The AC side capacitor voltage is rapidly discharged through software control, and the residual voltage can be reduced to 0V in just 3ms, which greatly shortens the energized time of the AC network and fundamentally avoids the risk of electric shock to operators.

[0014] 3. The automatic switching of capacitor voltage polarity is achieved by utilizing the self-inductance of the inductor. The software does not need to detect the polarity in real time, which simplifies the control algorithm and reduces the computational load of the DSP. At the same time, multiple time counting units (time1, time2, time3) are used to avoid misjudgment and ensure the accuracy and reliability of discharge triggering.

[0015] 4. This system and method are applicable to all types of active grid-connected inverters, without the need for customized adjustments based on inverter power and model, and have a wide range of application scenarios. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of a fast discharge control system for the AC circuit of an inverter according to the present invention.

[0017] Figure 2 This is a schematic diagram of the discharge circuit electrical path when the AC side capacitor voltage is positive in the AC circuit fast discharge control system of an inverter according to the present invention.

[0018] Figure 3 This is a schematic diagram of the discharge circuit electrical path when the AC side capacitor voltage is negative in the AC circuit fast discharge control system of an inverter according to the present invention.

[0019] Figure 4 This is a flowchart illustrating a fast discharge control method for the AC circuit of an inverter according to the present invention.

[0020] Figure 5 This is an experimental diagram showing the accelerated discharge effect of the AC side capacitor in the AC circuit fast discharge control method of an inverter according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0023] This invention provides a fast discharge control system for the AC circuit of an inverter, such as... Figures 1 to 3 As shown, it includes an inverter-side circuit module, a mains power detection module, a control module, and a discharge execution module; each module works together to realize the functions of mains power detection, discharge triggering, and energy dissipation.

[0024] The hardware circuitry is as follows Figures 1 to 3 As shown, the inverter-side circuit module includes a full-bridge circuit composed of switching transistors Q1, Q2, Q3, and Q4, current sampling resistors R1 and R2, an LC low-pass filter circuit, and an AC-side capacitor. The LC low-pass filter circuit includes inductors L1 and L2. The AC-side capacitor is electrically connected to the LC low-pass filter circuit and the full-bridge circuit in sequence. The current sampling resistors R1 and R2 are connected in series in the loop between the full-bridge circuit and the LC low-pass filter circuit.

[0025] As the hardware foundation of the discharge system, this module is the core circuit for energy conversion and discharge, including: Full-bridge circuit: Composed of switching transistors Q1, Q2, Q3, and Q4 (Q3 and Q4 are key discharge actuators), used to control the current flow and form a stable energy discharge channel during the discharge phase.

[0026] Current sampling resistors R1 and R2 are connected in series between the full-bridge circuit and the LC low-pass filter circuit. On the one hand, they collect the loop current signal in real time and feed it back to the control module. On the other hand, they consume the energy stored in the AC side capacitor through the Joule effect during the discharge process.

[0027] LC low-pass filter circuit: includes inductors L1 and L2 and filter capacitors, used to filter out high-frequency interference signals from the inverter output, ensuring grid-connected power quality, and at the same time, assisting the capacitor voltage polarity conversion through the self-inductance of the inductor during the discharge phase.

[0028] AC side capacitors: used to store electrical energy during inverter operation, and are the main source of residual voltage after grid disconnection. The voltage across their terminals needs to be quickly reduced to a safe value through a discharge system.

[0029] like Figures 1 to 3 The diagram shown is a circuit diagram of the inverter-side circuit module. The full-bridge circuit, LC low-pass filter circuit, AC-side capacitor, etc., are components of existing technology. Figures 1 to 3The circuit structure can reveal its principle, which belongs to the conventional circuit construction technology in this field, and will not be elaborated here.

[0030] In this case, the mains power detection module is the Ecap capture module built into the inverter. The Ecap capture module is used to capture the rising edge and falling edge signals of the mains voltage pulse to determine whether there is mains power in the AC grid.

[0031] An enhanced capture (Ecap) module based on the inverter's internal digital signal processor (DSP) is used. This module has high-frequency signal capture capability and can detect the periodic changes in the mains voltage in real time. The mains voltage is a sinusoidal alternating current with a fixed zero-crossing point (rising edge from negative to positive, falling edge from positive to negative). The Ecap module determines whether the mains voltage is normal by capturing the rising edge signal of the voltage. If the Ecap module does not detect the rising edge signal continuously, it can be determined that the mains voltage is missing, providing a basis for subsequent discharge triggering.

[0032] The control module is electrically connected to the mains power detection module and the discharge execution module. The control module has a built-in time counting unit and a logic judgment unit, which are used to receive the detection signal from the mains power detection module and output the drive control signal through the time counting unit and the logic judgment unit.

[0033] The control module serves as a signal receiver and processor: it receives the mains power detection signal from the Ecap module and the current feedback signal from the current sampling resistor, and performs logic analysis; the time counting module has three built-in time counting modules for the first counting cycle, the second counting cycle, and the third counting cycle, which are used to realize the mains power shortage delay judgment, mains power recovery buffer, and discharge duration control.

[0034] Drive control: Based on the logic judgment result, output high and low level signals to the discharge execution module to control the on / off state of the circuit and the working state of the switching transistor.

[0035] The discharge execution module is electrically connected to the control module and the full-bridge circuit. The discharge execution module is used to receive the drive control signal from the control module and control the conduction state of the switching transistors Q3 and Q4 in the full-bridge circuit to form a discharge circuit for the AC side capacitor.

[0036] It is electrically connected to the control module and the full-bridge circuit to receive the drive signal from the control module, precisely control the turn-on and turn-off timing of the Q3 and Q4 switching transistors, and form a complete discharge circuit under different capacitor voltage polarities to ensure stable energy discharge.

[0037] In one specific embodiment, both switching transistors Q3 and Q4 are equipped with anti-parallel diodes. The anti-parallel diodes are used to form a complete discharge circuit with the switching transistors when the polarity of the AC side capacitor voltage changes. The current sampling resistors R1 and R2 are used to collect the circuit current signal and to consume the energy stored in the AC side capacitor during the discharge process.

[0038] This design satisfies the switching requirements of the discharge circuit electrical path when the AC side capacitor voltage is positive or negative, while also meeting the compatibility requirements of electrical signals and energy consumption.

[0039] In one specific embodiment, the control module is further connected to a flyback-side drive unit and an inverter-side drive unit; the flyback-side drive unit is used to control the PWM swirl state of the flyback circuit, and the inverter-side drive unit is used to control the PWM swirl state of the full-bridge circuit.

[0040] The control module outputs signals to the flyback-side drive unit and the inverter-side drive unit, disabling both the flyback-side drive enable and the inverter-side drive enable, thus preventing PWM ripple from the flyback circuit and the full-bridge circuit, putting the circuit in a low-power standby state. This maintains a low-power state during the control process.

[0041] like Figure 4 As shown, a control method for a fast discharge control system of the AC circuit of an inverter is described, with the following specific steps: S1 Mains Power Detection and Judgment: The mains voltage signal is captured in real time by the capture module Ecap. If the capture module Ecap does not detect the rising edge of the mains voltage pulse during the continuous capture cycle, it is determined that the mains power is missing, and the control module sets the no mains voltage flag to 1.

[0042] The control module drives the mains power detection module (Ecap module) to capture the mains voltage signal in real time. Since the mains power is a periodic zero-crossing AC signal, the Ecap module is set to rising edge capture mode. If the Ecap module does not detect the rising edge of the AC mains voltage pulse for 40ms, it indicates that the AC mains has been disconnected. The control module sets the no mains voltage flag to 1 and triggers the subsequent delay processing procedure. If a rising edge signal is detected within 40ms, the mains power is considered normal, and the system maintains the inverter's normal operating state.

[0043] S2 Delay processing after mains power failure: When the mains power failure flag is 1, the control module starts the first counting cycle of the time counting unit, and at the same time outputs control signals to the flyback side drive unit and the inverter side drive unit, disables the flyback side drive enable and the inverter side drive enable, and prohibits PWM wagging between the flyback side and the full bridge circuit.

[0044] Delay processing after mains power loss (time1 counting stage: when the "no mains voltage flag" is 1, the control module starts the time1 counting unit (counting period 60ms). The core purpose of this stage is to avoid accidental discharge caused by short-term fluctuations in mains power (such as momentary power outage).

[0045] The control module outputs signals to the flyback-side drive unit and the inverter-side drive unit, disables the flyback-side drive enable and the inverter-side drive enable, and prohibits PWM wagging of the flyback circuit and the full-bridge circuit, so that the circuit is in a low-power standby state.

[0046] During the time1 counting period, the Ecap module continuously monitors the mains power signal and handles it in two ways depending on whether the mains power has been restored. S3 performs subsequent operations based on the following case: (mains power restored / discharge started).

[0047] Scenario A: If the capture module Ecap detects the rising edge of the mains voltage pulse again during the first counting cycle, the control module starts the second counting cycle of the time counting unit. During the second counting cycle, the flyback side and inverter side drive enable are kept off. After the second counting cycle ends, the control module first enables the inverter side drive and allows the full-bridge circuit PWM to ripple. After a waiting period, the flyback side drive enable is enabled and the flyback circuit PWM to ripple. The inverter resumes normal operation. The waiting period is 5~40ms.

[0048] When mains power is restored (time2 counting phase), if the Ecap module detects a rising edge of the mains voltage again during the time1 counting period (mains power restored to normal), the control module starts the time2 counting unit (counting period 300ms): During the time2 counting period, the flyback and inverter side drive enable remain off to prevent current surges caused by instantaneous circuit startup and protect the components.

[0049] After time2 countdown ends, the control module enables the drive in the order of "inverter side first, then flyback side": first enable the inverter side drive to allow the full-bridge circuit PWM to ripple; after an interval of 20ms, enable the flyback side drive to allow the flyback circuit PWM to ripple, ensuring that the inverter smoothly transitions to normal operation.

[0050] Case B: If no mains power is detected at the end of the first counting cycle, the control module sets the AC side start discharge flag to 1 and starts the third counting cycle of the time counting unit; at the same time, it turns off the flyback side drive enable, disables the flyback circuit PWM swirl, turns on the inverter side drive enable, allows the full-bridge circuit PWM swirl, and controls the conduction state of switch Q3 and switch Q4 through the discharge execution module to form a discharge circuit for the AC side capacitor.

[0051] If the mains power is continuously absent (time3 counting and discharge phase), and time1 counting ends (no mains power detected for a cumulative 100ms), the control module determines that the mains power has been absent for a long time, sets the "accelerated AC side start discharge flag" to 1, starts the time3 counting unit (counting period 10ms), and formally triggers the fast discharge logic.

[0052] The control module disables flyback-side drive enable and prohibits flyback circuit PWM swirl, while enabling inverter-side drive enable and allowing full-bridge circuit PWM swirl.

[0053] The discharge execution module receives the control signal and controls the Q3 and Q4 switches to conduct alternately in a fixed sequence: the conduction frequency is 1kHz (period is 1ms), Q4 is turned on and Q3 is turned off in the first 0.5ms, and Q3 is turned on and Q4 is turned off in the last 0.5ms.

[0054] Discharge circuit formation: Based on the different polarities of the AC side capacitor voltage, two types of discharge circuits are formed (such as...). Figure 2 , Figure 3 (as shown) When the capacitor voltage is positive: L1 → Q4 (conducting) → R2 → R1 → Q3 anti-parallel diode (forward conducting) → L2 → negative terminal of AC side capacitor, energy is consumed through the internal resistance of Q4, R1, and R2.

[0055] When the capacitor voltage is negative: L2 → Q3 (conducting) → R1 → R2 → Q4 anti-parallel diode (forward conducting) → L1 → positive terminal of AC side capacitor, energy is consumed through the internal resistance of Q3, R1, and R2.

[0056] In one specific embodiment, due to the self-inductance of the inductor in the LC low-pass filter circuit, the induced electromotive force generated by the inductor each time Q3 and Q4 alternately conduct will cause the polarity of the capacitor voltage to automatically reverse. Therefore, the software does not need to detect the polarity separately, simplifying the control logic. S4 Discharge End and Fault Handling: After the third counting cycle ends, the control module sets the accelerated AC side discharge start flag to 0, disables the flyback side and inverter side drive enable, disconnects the inverter relay and reports a no-mains-power fault, and the inverter enters a fault state; when the Ecap module detects that the mains power has returned to normal, the inverter restarts and resumes operation.

[0057] After time3 counting ends (10ms discharge complete), the control module sets the accelerated AC side discharge start flag to 0, outputs a signal to disable the flyback and inverter side drive enable, and simultaneously disconnects the relay connecting the inverter to the AC grid to prevent accidental grid connection when mains power is restored. The control module reports a no-mains-power fault signal to the inverter's main control system, and the inverter enters a fault standby state; once the Ecap module detects that the mains power has returned to normal (voltage and frequency meet grid connection standards), the inverter resumes normal operation through a restart process.

[0058] like Figure 5 The figure shows the effect of the accelerated discharge experiment on the AC side capacitor. As can be seen from the figure, after the mains power is cut off, the device determines that there is no mains power within 100ms. At this time, the accelerated discharge logic is not triggered, and the AC voltage discharge curve is flat. Subsequently, the accelerated discharge logic is triggered, and switches Q3 and Q4 are alternately turned on, causing the AC voltage to discharge rapidly. Within approximately 3ms, the AC side capacitor voltage can be reduced to 0V, avoiding the safety hazard to operators caused by high voltage on the AC side capacitor when the mains power is cut off.

[0059] In addition, due to the self-inductance of the inductor in the discharge circuit, the polarity of the capacitor voltage changes once every time the Q3 and Q4 switches are switched on alternately. Therefore, the software does not need to determine the polarity of the capacitor voltage in real time, which reduces the complexity of software control and makes the software control lightweight and effective.

[0060] As described above, the hardware cost is zero: the system is built entirely on the existing hardware circuitry of the inverter, requiring no additional resistors, capacitors, sensors, or other components, and no modification to the circuit structure, thus avoiding hardware cost investment and installation / debugging workload. Software control enables rapid discharge of the AC-side capacitor voltage, reducing the residual voltage to 0V in just 3ms, significantly shortening the AC-side network energization time and fundamentally eliminating the risk of electric shock to operators. The self-inductance of the inductor enables automatic polarity switching of the capacitor voltage, eliminating the need for real-time polarity detection in the software, simplifying the control algorithm, reducing the DSP's computational load, and using multiple time counting units (time1, time2, time3) to avoid misjudgments and ensure the accuracy and reliability of discharge triggering. This system and method are applicable to various active grid-connected inverters, requiring no customization based on inverter power or model, and have broad application scenarios.

[0061] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0062] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A fast discharge control system for the AC circuit of an inverter, characterized in that: It includes an inverter-side circuit module, a mains power detection module, a control module, and a discharge execution module; The inverter-side circuit module includes a full-bridge circuit composed of switching transistors Q1, Q2, Q3, and Q4, current sampling resistors R1 and R2, an LC low-pass filter circuit, and an AC-side capacitor. The LC low-pass filter circuit includes inductors L1 and L2. The AC-side capacitor is electrically connected to the LC low-pass filter circuit and the full-bridge circuit in sequence. The current sampling resistors R1 and R2 are connected in series in the loop between the full-bridge circuit and the LC low-pass filter circuit. The mains power detection module is the Ecap capture module built into the inverter. The Ecap capture module is used to capture the rising edge and falling edge signals of the mains voltage pulse to determine whether there is mains power in the AC grid. The control module is electrically connected to the mains power detection module and the discharge execution module. The control module has a built-in time counting unit and a logic judgment unit, which are used to receive the detection signal from the mains power detection module and output the drive control signal through the time counting unit and the logic judgment unit. The discharge execution module is electrically connected to the control module and the full-bridge circuit. The discharge execution module is used to receive the drive control signal from the control module and control the conduction state of the switching transistors Q3 and Q4 in the full-bridge circuit to form a discharge circuit for the AC side capacitor.

2. The AC circuit fast discharge control system for an inverter according to claim 1, characterized in that: Both the switching transistors Q3 and Q4 are equipped with anti-parallel diodes. These anti-parallel diodes are used to form a complete discharge circuit with the switching transistors when the polarity of the AC-side capacitor voltage changes. The current sampling resistors R1 and R2 are used to collect the circuit current signal and to consume the energy stored in the AC-side capacitor during the discharge process.

3. The AC circuit fast discharge control system for an inverter according to claim 1, characterized in that: The control module is also connected to a flyback-side drive unit and an inverter-side drive unit. The flyback-side drive unit is used to control the PWM swirl state of the flyback circuit, and the inverter-side drive unit is used to control the PWM swirl state of the full-bridge circuit.

4. A control method for a fast discharge control system of an inverter's AC circuit according to any one of claims 1 to 3, wherein the control module is further connected to a flyback-side drive unit and an inverter-side drive unit; The flyback-side drive unit is used to control the PWM swirl state of the flyback circuit, and the inverter-side drive unit is used to control the PWM swirl state of the full-bridge circuit. Includes the following steps: S1 Mains Power Detection and Judgment: The mains voltage signal is captured in real time by the capture module Ecap. If the capture module Ecap does not detect the rising edge of the mains voltage pulse during the continuous capture cycle, it is determined that the mains power is missing, and the control module sets the no mains voltage flag to 1. S2 Delay handling after mains power failure: When the mains power failure flag is 1, the control module starts the first counting cycle of the time counter unit, and simultaneously outputs control signals to the flyback-side drive unit and the inverter-side drive unit, disabling the flyback-side drive enable and the inverter-side drive enable, and prohibiting PWM ripple between the flyback side and the full-bridge circuit; S3 Performs subsequent operations according to different cases: Scenario A: If the capture module Ecap detects the rising edge of the mains voltage pulse again during the first counting cycle, the control module starts the second counting cycle of the time counting unit. During the second counting cycle, the flyback side and inverter side drive enable are kept off. After the second counting cycle ends, the control module first enables the inverter side drive and allows the full-bridge circuit PWM to ripple. After a waiting period, the flyback side drive enable is enabled and the flyback circuit PWM to ripple. The inverter resumes normal operation. The waiting period is 5~40ms. Scenario B: If no mains power is detected at the end of the first counting cycle, the control module sets the AC side start discharge flag to 1, starting the third counting cycle of the time counting unit; at the same time, it disables the flyback side drive enable, disables flyback circuit PWM swirl, enables the inverter side drive enable, allows full-bridge circuit PWM swirl, and controls the conduction state of switching transistors Q3 and Q4 through the discharge execution module to form a discharge loop for the AC side capacitor; S4 Discharge End and Fault Handling: After the third counting cycle ends, the control module sets the AC side start discharge flag to 0, disables flyback and inverter side drive enable, disconnects the inverter relay and reports a no mains power fault, and the inverter enters a fault state; when the Ecap module detects that the mains power has returned to normal, the inverter restarts and resumes operation.

5. The control method for a fast discharge control system of an inverter's AC circuit according to claim 4, characterized in that: In step S3, during the discharge process of case B, when the AC-side capacitor voltage is positive, the discharge circuit path is as follows: sequentially passing through inductor L1 of the LC low-pass filter circuit, switch Q4, current sampling resistor R2, current sampling resistor R1, the anti-parallel diode of switch Q3, inductor L2, and the negative terminal of AC-side capacitor; when the AC-side capacitor voltage is negative, the discharge circuit path is as follows: sequentially passing through inductor L2, switch Q3, current sampling resistor R1, current sampling resistor R2, the anti-parallel diode of switch Q4, inductor L1, and the positive terminal of AC-side capacitor.

6. The control method for a fast discharge control system of an inverter's AC circuit according to claim 4, characterized in that: In step S3, during the discharge process of case B, there is no need to detect the polarity of the AC side capacitor voltage in real time. By alternately turning on the switching transistors Q3 and Q4, the self-inductance of the inductor in the LC low-pass filter circuit is utilized to make the polarity of the AC side capacitor voltage automatically change with the on state of the switching transistors.

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