A method for grid pre-charging control of an energy storage inverter and an energy storage inverter system

Abstract

The application relates to the technical field of energy storage inverters, and discloses an energy storage inverter power grid pre-charging control method and an energy storage inverter system. The pre-charging control method is applied to the energy storage inverter system, and the energy storage inverter system comprises a controller, a pre-charging relay, a first live wire relay, a second live wire relay, a zero line relay, a direct current bus capacitor and a voltage detection unit, and specifically comprises the following steps: S11: executing a self-checking program when the energy storage inverter system is powered on; after the self-checking program is completed, the voltage detection unit is used to collect the power grid side voltage and the voltage across the direct current bus capacitor in real time, and the power grid voltage effective value and the power grid voltage phase are calculated according to the collected power grid side voltage. According to the application, the contact adhesion detection is performed on the pre-charging relay, the live wire relay and the zero line relay before pre-charging starting, and the online resistance value of the pre-charging resistor is checked, so that the safety risk caused by the faults of key devices is eliminated.

Description

Technical Field

[0001] This invention relates to the technical field of energy storage inverters, and more specifically, to a grid pre-charging control method for an energy storage inverter and an energy storage inverter system. Background Technology

[0002] With the widespread application of energy storage inverters in residential and commercial energy storage scenarios, the pre-charge control of the DC bus capacitor before grid connection has become a key link in ensuring the safe operation of the system. At present, energy storage inverters generally adopt a current-limiting pre-charge scheme with a pre-charge resistor and a pre-charge relay. That is, the bus capacitor is first charged to near the grid voltage through the pre-charge circuit, and then the main circuit relay is closed to complete the grid connection. In the grid connection stage after the pre-charge is completed, a phase-locked loop is usually used to track the grid phase, and phase pre-synchronization and amplitude pre-synchronization control strategies are used to make the inverter output voltage consistent with the grid voltage in phase and amplitude before switching to grid connection. In addition, some schemes also introduce safety protection measures such as relay contact sticking detection to improve the reliability of the pre-charge and grid connection process.

[0003] However, the precharge control technology still has obvious shortcomings. On the one hand, the precharge process uses fixed precharge resistors and control parameters, which lacks the ability to adaptively adjust to grid fluctuations, capacitor tolerance and resistor temperature drift, and problems such as insufficient precharge or overcharge occur from time to time. At the same time, the system lacks a comprehensive self-check of the health status of the precharge relay, main relay and precharge resistor itself before precharge, and safety hazards are difficult to detect in time. On the other hand, the phase and amplitude regulation during the grid connection transition phase often uses fixed control parameters and fixed sampling frequency, which makes it difficult to adapt to sudden changes in grid frequency or phase fluctuations. This can easily lead to excessive instantaneous inrush current during grid connection, and the lack of fine control over relay switching timing further increases the risk of current surge. Summary of the Invention

[0004] The purpose of this invention is to provide a grid pre-charge control method for energy storage inverters and an energy storage inverter system. By performing contact adhesion detection on the pre-charge relay, live wire relay, and neutral wire relay before pre-charge starts, and performing online resistance value verification on the pre-charge resistor, the safety risks caused by the failure of key components are eliminated.

[0005] This invention is implemented as follows: a grid pre-charge control method for an energy storage inverter, applied to an energy storage inverter system. The energy storage inverter system includes a controller, a pre-charge relay, a first live wire relay, a second live wire relay, a neutral wire relay, a DC bus capacitor, and a voltage detection unit. Specifically, it includes the following steps: S11: The energy storage inverter system executes a self-test program upon power-up. After the self-test program is completed, the voltage detection unit collects the grid-side voltage and the voltage across the DC bus capacitor in real time. Based on the collected grid-side voltage, the effective value and phase of the grid voltage are calculated. At the same time, the system detects whether there is a DC power input to the energy storage inverter system. S12: When the controller detects that there is no DC power input to the energy storage inverter system, it sends a closing command to the pre-charge relay and the first live wire relay. The pre-charge relay and the first live wire relay execute the closing command, and the grid current flows into the DC bus capacitor through the first live wire relay, the pre-charge relay and the pre-charge resistor connected in series, to pre-charge the DC bus capacitor. S13: When the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition, and the controller starts the phase adjustment loop to adaptively adjust the phase adjustment step size according to the phase difference change rate. S14: After phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop according to the amplitude deviation, so that the output voltage amplitude of the energy storage inverter is close to the voltage amplitude of the grid side, and determines whether the energy storage inverter meets the grid connection conditions. S15: When the energy storage inverter is determined to meet the grid connection conditions, the controller performs the grid connection operation according to the timing control strategy. After the grid connection is completed, the controller records the pre-charge control parameters, phase adjustment parameters and amplitude adjustment parameters into the non-volatile memory for the next pre-charge control call.

[0006] Furthermore, in S11, the energy storage inverter system performs a self-test procedure upon power-up, including: The controller executes a self-test program to detect the initial state of the precharge relay, the first live wire relay, the second live wire relay, and the neutral wire relay. By sending test pulse signals to each relay and detecting the voltage change at both ends of the contacts, it determines whether each relay is in a normal open state and whether there is a contact sticking fault, and confirms that all relays are in an open state. After confirming that all relays are in the normal open state, the controller further performs online resistance detection on the pre-charge resistor connected in series with the pre-charge relay. It applies a detection voltage to the pre-charge resistor and measures the current flowing through it to calculate the actual resistance value. The actual resistance value is compared with the pre-stored nominal resistance value. If the deviation exceeds the preset resistance tolerance range, a pre-charge resistor abnormality alarm is issued and the pre-charge control process is terminated.

[0007] Furthermore, in S12, the grid current flows into the DC bus capacitor via the first live wire relay, the pre-charge relay, and the pre-charge resistor connected in series, pre-charging the DC bus capacitor, including: The controller first sends a closing command to the first live wire relay. After confirming that the first live wire relay has been successfully closed, it sends a closing command to the pre-charge relay, so that the grid current flows through the first live wire relay, the pre-charge relay and the pre-charge resistor in sequence and then enters the DC bus capacitor. After the pre-charge is started, the controller controls the second live wire relay and the neutral wire relay to remain in the open state. After pre-charging is initiated, the controller collects the voltage value across the DC bus capacitor in real time at the first sampling frequency and calculates the voltage rise rate. When the voltage rise rate is greater than the preset first rate threshold, the pre-charging current is reduced. When the voltage rise rate is less than the preset second rate threshold, an abnormal warning is issued. The controller dynamically adjusts the pre-charging control parameters according to the voltage rise rate.

[0008] Furthermore, in S13, if the energy storage inverter is determined to meet the pre-charge completion conditions, the controller initiates the phase adjustment loop, including: When the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition. The controller immediately starts the phase adjustment loop. The phase adjustment loop uses the grid-side voltage phase as a reference, tracks the grid phase in real time through a phase-locked loop, and generates a reference phase signal that is synchronized with the grid-side voltage phase. The controller adjusts the output voltage phase of the energy storage inverter according to the reference phase signal, so that the phase difference between the output voltage phase and the grid voltage phase gradually transitions from a first angle to a second angle. The second angle is smaller than the first angle and close to zero degrees. When the phase difference reaches the second angle, the controller locks the current phase adjustment result.

[0009] Furthermore, the controller adjusts the output voltage phase of the energy storage inverter according to the reference phase signal, so that the phase difference between the output voltage phase and the grid-side voltage phase gradually transitions from a first angle to a second angle, including: The controller uses the reference phase signal as a given target and successively adjusts the phase setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter so that the output voltage phase of the energy storage inverter gradually approaches the grid-side voltage phase from the current phase, and the phase difference gradually decreases from the first angle. During phase adjustment, the controller monitors the phase difference change rate in real time at the second sampling frequency and adaptively adjusts the phase adjustment step size according to the phase difference change rate to prevent phase overshoot. When the phase difference reaches the second angle and the absolute value of the phase difference change rate is less than the preset locking threshold, the controller locks the current phase adjustment result and freezes the integral term of the phase adjustment loop.

[0010] Furthermore, in S14, after phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop based on the amplitude deviation, including: After phase locking, the controller continuously collects the grid-side voltage amplitude and the energy storage inverter output voltage amplitude at the third sampling frequency. Fourier analysis is performed on the collected grid-side voltage and inverter output voltage to extract the fundamental component amplitude. The difference between the inverter output voltage amplitude and the grid-side voltage amplitude is calculated as the amplitude deviation. The controller uses the amplitude deviation as the input error signal of the amplitude adjustment loop. After proportional-integral operation, it generates an amplitude adjustment amount and adds it to the amplitude setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, so that the output voltage amplitude of the energy storage inverter gradually approaches the grid-side voltage amplitude until the amplitude deviation is less than the preset grid-connected amplitude threshold.

[0011] Furthermore, after proportional-integral calculation, an amplitude adjustment is generated and superimposed on the amplitude setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, including: The controller inputs the amplitude deviation into the proportional-integral control unit, which generates an amplitude adjustment amount after proportional-integral calculation. The amplitude adjustment amount is then superimposed on the current amplitude setpoint of the sinusoidal pulse width modulation wave. The updated amplitude setpoint is used to generate a drive signal to control the output voltage amplitude of the energy storage inverter, so as to continuously approximate the voltage amplitude on the grid side. During amplitude adjustment, the controller continuously monitors the phase difference and amplitude deviation between the output voltage of the energy storage inverter and the grid-side voltage. When the phase difference is less than the preset grid-connected phase threshold and the amplitude deviation is less than the preset grid-connected amplitude threshold, the controller determines that the energy storage inverter meets the grid-connection conditions and prepares to perform subsequent grid-connection operations.

[0012] Furthermore, in S15, the controller performs grid connection operations according to the timing control strategy, including: First, send a closing command to the second live wire relay to close the second live wire relay and connect the second live wire path to the grid-connected circuit; After a preset relay action delay time, the controller sends a disconnect command to the precharge relay, causing the precharge relay to disconnect and cut off the precharge circuit, thus completing the disconnection of the precharge circuit. Finally, the controller sends a closing command to the neutral line relay, causing the neutral line relay to close. This completes the grid connection between the energy storage inverter and the power grid, and the energy storage inverter enters normal operation.

[0013] Compared with the prior art, the grid pre-charge control method and energy storage inverter system provided by the present invention have the following advantages: 1. By performing contact adhesion detection on the pre-charge relay, live wire relay, and neutral wire relay before pre-charge starts, and performing online resistance value verification on the pre-charge resistor, the safety risks caused by the failure of key components are eliminated; during the pre-charge process, the pre-charge current is dynamically adjusted according to the real-time voltage rise rate of the DC bus capacitor, so that the pre-charge duration and the pre-charge end voltage can adapt to grid fluctuations and device parameter deviations; during the grid connection transition phase, the phase adjustment loop adaptively adjusts the adjustment step size according to the phase difference change rate, and the amplitude adjustment loop extracts the fundamental amplitude through Fourier analysis and uses proportional-integral control to achieve fine adjustment, effectively suppressing the current surge at the moment of grid connection; 2. By sequentially closing the second live wire relay, opening the pre-charge relay, and closing the neutral wire relay, along with setting the relay action delay time, the electrical safety of each path during grid connection switching is ensured. The pre-charge control parameters, phase adjustment parameters, and amplitude adjustment parameters are recorded in non-volatile memory after grid connection is completed for subsequent pre-charge control calls, enabling the system to have self-optimization capabilities based on historical operating data. Furthermore, the pre-charge resistance online detection unit and the pre-charge current adjustment unit based on the power switch tube integrated in the pre-charge module enable closed-loop adjustment of the pre-charge current.

[0014] An energy storage inverter system for grid pre-charge control is provided, for executing the above-described pre-charge control method, wherein the energy storage inverter system comprises: The grid interface module is used to connect to the AC grid, receive grid-side voltage and current, and feed AC power output from the inverter. The DC bus module, including the DC bus capacitor, is used to smooth DC power to provide a stable operating voltage for the inverter unit. An inverter unit, connected between the DC bus module and the grid interface module, is used to convert DC power into AC power and adjust the phase and amplitude of the output voltage according to the control signal. The pre-charge module includes a pre-charge relay and a pre-charge resistor connected in series with it, and is connected in parallel with the output terminal of the inverter unit. It is used to pre-charge the DC bus capacitor with grid power before grid connection. The first live wire relay, the second live wire relay, and the neutral wire relay are respectively connected to the live wire and neutral wire paths corresponding to the inverter unit and the power grid interface module, and are used to control the on / off state of each path. A voltage detection unit is connected to the power grid interface module and the DC bus module, and is used to collect the power grid side voltage and the voltage across the DC bus capacitor. A current detection unit is connected to the output terminal of the inverter unit and is used to collect the output current; The controller is electrically connected to each relay, the voltage detection unit, and the current detection unit, respectively, and is used to perform grid pre-charge control of the energy storage inverter; A non-volatile memory, connected to the controller, is used to store pre-charge control parameters, phase adjustment parameters, amplitude adjustment parameters, and grid connection event records; The human-machine interface is connected to the controller and is used to display the pre-charging progress, grid connection status and operating parameters in real time, and to receive user control commands.

[0015] Specifically, the pre-charge module includes a pre-charge relay drive unit, a pre-charge resistance online detection unit, and a pre-charge current adjustment unit; The precharge relay driving unit includes a driving circuit and a status feedback circuit. The driving circuit drives the precharge relay to operate according to the controller command. The status feedback circuit detects the voltage difference of the relay contacts and feeds it back to the controller to confirm the operation status. The pre-charge resistance online detection unit includes a detection voltage application circuit and a detection current measurement circuit, which are used to apply a detection voltage to the pre-charge resistance and measure the current under the control of the controller. The controller calculates the actual resistance value based on the detection voltage and current and compares it with the nominal resistance value to realize the monitoring of the pre-charge resistance. The precharge current regulation unit includes a power switch transistor connected in series with the precharge relay and the precharge resistor, as well as a sampling resistor and an amplification circuit connected in series in the precharge circuit. The power switch adjusts its duty cycle under the control of the controller's pulse width modulation signal to control the pre-charge current. The amplifier circuit amplifies the voltage across the sampling resistor and outputs it to the controller. The controller calculates the instantaneous value of the pre-charge current based on this and reduces the duty cycle to limit the peak value of the pre-charge current when it exceeds the preset maximum allowable value. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a grid pre-charging control method for an energy storage inverter and a structural diagram of an energy storage inverter system proposed in this invention. Figure 2 This is a schematic diagram of a grid pre-charging control method for an energy storage inverter and a structural diagram of an energy storage inverter system proposed in this invention. Figure 3 This is a schematic diagram of a grid pre-charging control method for an energy storage inverter and a structural diagram of an energy storage inverter system proposed in this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0019] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0020] Reference Figure 1-2 As shown, this embodiment of the invention provides a grid pre-charge control method for an energy storage inverter, applied to an energy storage inverter system. The energy storage inverter system includes a controller, a pre-charge relay, a first live wire relay, a second live wire relay, a neutral wire relay, a DC bus capacitor, and a voltage detection unit. Specifically, it includes the following steps: S11: The energy storage inverter system performs a self-test procedure upon power-up to confirm that the initial state of each relay is normal and the pre-charge resistor is healthy, eliminating potential safety hazards caused by device failures at the source. After the self-test procedure is completed, the voltage detection unit collects the grid-side voltage and the voltage across the DC bus capacitor in real time, and calculates the effective value and phase of the grid voltage based on the collected grid-side voltage to provide a reference for subsequent phase synchronization. At the same time, it detects whether there is a DC power input in the energy storage inverter system to determine the type of pre-charge energy source. In this embodiment, the energy storage inverter system executes a self-test procedure upon power-up. Specifically, the controller executes a self-test procedure to detect the initial state of the pre-charge relay, the first live wire relay, the second live wire relay, and the neutral wire relay. By sending test pulse signals to each relay and detecting voltage changes across the contacts, the controller determines whether each relay is in a normal open state and whether there is a contact sticking fault. It confirms that all relays are in an open state to avoid overcurrent faults caused by abnormal conduction of the main circuit due to contact sticking during pre-charge. After confirming that all relays are in a normal open state, the controller further performs online resistance detection on the pre-charge resistor connected in series with the pre-charge relay. It applies a detection voltage to the pre-charge resistor and measures the current flowing through it to calculate the actual resistance value. The actual resistance value is compared with the pre-stored nominal resistance value. If the deviation exceeds the preset resistance tolerance range, a pre-charge resistor abnormality alarm is issued and the pre-charge control process is terminated to ensure the effectiveness and consistency of subsequent current-limited charging and avoid pre-charge time deviation or pre-charge overcurrent caused by resistance value drift. S12: When the controller detects that there is no DC power input to the energy storage inverter system, it sends a closing command to the pre-charge relay and the first live wire relay. The pre-charge relay and the first live wire relay execute the closing command. The grid current flows into the DC bus capacitor through the first live wire relay, the pre-charge relay and the pre-charge resistor connected in series, to pre-charge the DC bus capacitor, so as to raise the voltage of the bus capacitor to close to the peak voltage of the grid voltage and avoid the generation of surge current when directly connected to the grid. In this embodiment, the grid current flows into the DC bus capacitor via the first live wire relay, the pre-charge relay, and the pre-charge resistor connected in series, to pre-charge the DC bus capacitor. Specifically, the controller first sends a closing command to the first live wire relay. After confirming that the first live wire relay has successfully closed, it sends a closing command to the pre-charge relay, so that the grid current flows sequentially through the first live wire relay, the pre-charge relay, and the pre-charge resistor before entering the DC bus capacitor. After pre-charging starts, the controller controls the second live wire relay and the neutral wire relay to remain open to prevent current shunting or incorrect grid connection caused by the conduction of non-target circuits during pre-charging. After pre-charging starts, the controller collects the voltage value across the DC bus capacitor in real time at a first sampling frequency and calculates the voltage rise rate. When the voltage rise rate is greater than a preset first rate threshold, the pre-charge current is reduced. When the voltage rise rate is less than a preset second rate threshold, an abnormal warning is issued. The controller dynamically adjusts the pre-charge control parameters according to the voltage rise rate to achieve adaptive closed-loop regulation of the pre-charge current, overcoming the problem of poor pre-charge consistency under grid fluctuations and device tolerance conditions in the fixed resistor scheme. S13: When the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition. The controller starts the phase adjustment loop and adaptively adjusts the phase adjustment step size according to the phase difference change rate so that the inverter output voltage phase smoothly approaches the grid voltage phase, avoiding overshoot or slow convergence when the fixed step size adjustment occurs during phase change. In this embodiment, when the energy storage inverter is determined to meet the pre-charge completion condition, the controller starts the phase adjustment loop. Specifically, when the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition. The controller immediately starts the phase adjustment loop. The phase adjustment loop uses the grid-side voltage phase as a reference, tracks the grid phase in real time through a phase-locked loop, and generates a reference phase signal synchronized with the grid-side voltage phase. This reference phase signal serves as the target setpoint for phase adjustment. The controller adjusts the output voltage phase of the energy storage inverter according to the reference phase signal, so that the phase difference between the output voltage phase and the grid-side voltage phase gradually transitions from a first angle to a second angle. The second angle is smaller than the first angle and close to zero degrees. When the phase difference reaches the second angle, the controller locks the current phase adjustment result, providing a prerequisite for phase stability for subsequent amplitude adjustment. Specifically, the formula for the phase adaptive adjustment algorithm is as follows:

[0021] Lock conditions: ; Where, θ inv (k+1) represents the inverter output voltage phase for the next cycle; θ inv (k) represents the phase of the inverter output voltage in the current cycle; θ grid The phase of the grid-side voltage; Δθ base Adjust the step size based on the baseline; α is the adaptive adjustment coefficient; The rate of change of phase difference; θ2 is the lock-in phase threshold; ε is the threshold for locking the rate of change; In this embodiment, the controller adjusts the output voltage phase of the energy storage inverter according to the reference phase signal, so that the phase difference between the output voltage phase and the grid voltage phase gradually transitions from a first angle to a second angle. Specifically, the controller uses the reference phase signal as a given target and successively adjusts the phase setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, so that the output voltage phase of the energy storage inverter gradually approaches the grid voltage phase from the current phase, and the phase difference gradually decreases from the first angle, so as to achieve progressive pre-synchronization of the phase. During the phase adjustment process, the controller monitors the phase difference change rate in real time at a second sampling frequency, and adaptively adjusts the phase adjustment step size according to the phase difference change rate to prevent phase overshoot. When the phase difference reaches the second angle and the absolute value of the phase difference change rate is less than the preset locking threshold, the controller locks the current phase adjustment result and freezes the integral term of the phase adjustment loop to avoid phase overshoot caused by integral accumulation effect and ensure the stability of the locked state. S14: After phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop according to the amplitude deviation, so that the output voltage amplitude of the energy storage inverter is close to the voltage amplitude of the grid side, and determines whether the energy storage inverter meets the grid connection conditions, so as to ensure the matching of the inverter output voltage and the grid voltage in amplitude at the moment of grid connection, and further suppress the closing inrush current. In this embodiment, after phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop based on the amplitude deviation. Specifically, after phase locking, the controller continuously collects the grid-side voltage amplitude and the output voltage amplitude of the energy storage inverter at a third sampling frequency. Fourier analysis is performed on the collected grid-side voltage and inverter output voltage to extract the fundamental component amplitude. The difference between the inverter output voltage amplitude and the grid-side voltage amplitude is calculated as the amplitude deviation. Fourier analysis is used to eliminate the interference of harmonic components on amplitude detection, thereby improving the accuracy of amplitude adjustment. The controller uses the amplitude deviation as the input error signal of the amplitude adjustment loop. After proportional-integral operation, the amplitude adjustment amount is generated and superimposed on the amplitude setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, so that the output voltage amplitude of the energy storage inverter gradually approaches the grid-side voltage amplitude until the amplitude deviation is less than the preset grid-connected amplitude threshold, thereby completing the amplitude pre-synchronization preparation before grid connection. In this embodiment, the amplitude adjustment amount is generated after proportional-integral (PI) operation and superimposed on the amplitude setpoint of the sinusoidal pulse width modulation (PWM) wave of the energy storage inverter. Specifically, the controller inputs the amplitude deviation into the PI control unit, generates the amplitude adjustment amount after PI operation, and superimposes the amplitude adjustment amount on the current amplitude setpoint of the sinusoidal PWM wave. The updated amplitude setpoint is used to generate a drive signal to control the output voltage amplitude of the energy storage inverter, so as to continuously approximate the grid-side voltage amplitude and ensure the balance between the speed of amplitude adjustment and steady-state accuracy. During the amplitude adjustment process, the controller continuously monitors the phase difference and amplitude deviation between the output voltage of the energy storage inverter and the grid-side voltage. When the phase difference is less than the preset grid-connected phase threshold and the amplitude deviation is less than the preset grid-connected amplitude threshold, the controller determines that the energy storage inverter meets the grid-connection conditions and prepares to execute subsequent grid-connection operations to ensure that the phase and amplitude are within the qualified synchronization window at the time of grid connection. Specifically, the formula for the amplitude adaptive adjustment algorithm includes: When θ grid → Grid connection phase threshold and V grid →V inv ; ; e v (k)=V grid (k)-V inv (k); Grid connection determination criteria: ; Where: V ref (k+1) The amplitude setpoint of the SPWM wave in the next cycle, i.e. the target output voltage amplitude of the inverter; V ref (k) is the amplitude setpoint of the SPWM wave in the current period; ev (k) represents the amplitude deviation in the kth period, which is the difference between the voltage amplitude on the grid side and the voltage amplitude of the inverter output. V grid (k) represents the voltage amplitude on the grid side during the kth period, which is the fundamental amplitude extracted by Fourier analysis; V inv (k) is the output voltage amplitude of the inverter in the kth cycle, that is, the fundamental amplitude extracted by Fourier analysis; K p This is the proportionality coefficient; K i The integral coefficient; θ th This is the grid-connected phase threshold; V th This is the threshold value for grid connection amplitude. S15: When the energy storage inverter is determined to meet the grid connection conditions, the controller performs the grid connection operation according to the timing control strategy. After the grid connection is completed, the controller records the pre-charge control parameters, phase adjustment parameters and amplitude adjustment parameters into the non-volatile memory for the next pre-charge control call. This enables the system to continuously optimize the control parameters of each link based on historical operating data, and achieve a long-term steady improvement in pre-charge performance.

[0022] In this embodiment, the controller executes the grid connection operation according to a timing control strategy, specifically including: first, sending a closing command to the second live wire relay to close the second live wire relay, connecting the second live wire path into the grid connection circuit to establish a second live wire path to realize a bidirectional current channel between the inverter and the grid; after a preset relay action delay time, the controller sends a disconnect command to the precharge relay to disconnect the precharge relay to cut off the precharge circuit, completing the removal of the precharge circuit to avoid the precharge resistor carrying the operating current for a long time after grid connection, causing additional losses and temperature rise; finally, the controller sends a closing command to the neutral wire relay to close the neutral wire relay, thus completing the grid connection between the energy storage inverter and the grid, and the energy storage inverter enters the normal operation state, ensuring the safe isolation of the actions of each relay during the grid connection switching process.

[0023] This technical solution eliminates safety risks caused by key component failures by performing contact adhesion detection on the pre-charge relay, live wire relay, and neutral wire relay before pre-charge starts and by performing online resistance value verification on the pre-charge resistor. During pre-charge, the pre-charge current is dynamically adjusted according to the real-time voltage rise rate of the DC bus capacitor, so that the pre-charge duration and pre-charge termination voltage can adapt to grid fluctuations and device parameter deviations. During the grid connection transition phase, the phase adjustment loop adaptively adjusts the adjustment step size according to the phase difference change rate, and the amplitude adjustment loop extracts the fundamental amplitude through Fourier analysis and uses proportional-integral control to achieve fine adjustment, effectively suppressing the current surge at the moment of grid connection.

[0024] Reference Figure 3 As shown, an energy storage inverter system for grid pre-charge control is used to execute the above-mentioned pre-charge control method. The energy storage inverter system includes: The grid interface module is used to connect to the AC grid, receive grid-side voltage and current, and feed AC power output from the inverter. The DC bus module, including the DC bus capacitor, is used to smooth DC power to provide a stable operating voltage for the inverter unit. The inverter unit is connected between the DC bus module and the grid interface module. It is used to convert DC power into AC power and adjust the phase and amplitude of the output voltage according to the control signal. The pre-charge module, including a pre-charge relay and a pre-charge resistor connected in series with it, is connected in parallel with the output of the inverter unit and is used to pre-charge the DC bus capacitor with grid power before grid connection. The first live wire relay, the second live wire relay, and the neutral wire relay are respectively connected to the live wire and neutral wire paths corresponding to the inverter unit and the grid interface module, and are used to control the on / off state of each path. The voltage detection unit is connected to the grid interface module and the DC bus module to collect the grid-side voltage and the voltage across the DC bus capacitor. The current detection unit is connected to the output terminal of the inverter unit and is used to collect the output current. The controller is electrically connected to each relay, voltage detection unit, and current detection unit, and is used to perform grid pre-charge control of the energy storage inverter. Non-volatile memory, connected to the controller, is used to store pre-charge control parameters, phase adjustment parameters, amplitude adjustment parameters, and grid connection event records; The human-machine interface connects to the controller and is used to display the pre-charging progress, grid connection status and operating parameters in real time, and to receive user control commands.

[0025] Specifically, the precharge module includes a precharge relay drive unit, a precharge resistance online detection unit, and a precharge current adjustment unit; The precharge relay drive unit includes a drive circuit and a status feedback circuit. The drive circuit drives the precharge relay to operate according to the controller command. The status feedback circuit detects the voltage difference between the relay contacts and feeds it back to the controller to confirm the operation status. The pre-charge resistance online detection unit includes a detection voltage application circuit and a detection current measurement circuit. It is used to apply a detection voltage to the pre-charge resistance and measure the current under the control of the controller. The controller calculates the actual resistance value based on the detection voltage and current and compares it with the nominal resistance value to realize the monitoring of the pre-charge resistance. The precharge current regulation unit includes a power switch transistor connected in series with a precharge relay and a precharge resistor, as well as a sampling resistor and an amplifier circuit connected in series in the precharge circuit. The power switching transistor adjusts its duty cycle under the control of the controller's pulse width modulation signal to control the pre-charge current. The amplifier circuit amplifies the voltage across the sampling resistor and outputs it to the controller. The controller calculates the instantaneous value of the pre-charge current based on this and reduces the duty cycle to limit the peak value of the pre-charge current when it exceeds the preset maximum allowable value. The energy storage inverter system ensures electrical safety of each path during grid connection switching by sequentially closing the second live wire relay, opening the pre-charge relay, and closing the neutral wire relay, along with setting the relay action delay time. The pre-charge control parameters, phase adjustment parameters, and amplitude adjustment parameters are recorded in non-volatile memory after grid connection is completed for subsequent pre-charge control calls, enabling the system to have self-optimization capabilities based on historical operating data. Furthermore, the pre-charge resistance online detection unit and the pre-charge current adjustment unit based on the power switch tube integrated in the pre-charge module enable closed-loop adjustment of the pre-charge current.

[0026] In this embodiment, the entire operation process can be automated by computer control. In each operation stage, sensors can be set up to provide signal feedback and ensure that the steps are performed sequentially. These are all conventional knowledge of current automation control, and will not be elaborated on in this embodiment.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A grid pre-charge control method for an energy storage inverter, characterized in that, This technology is applied to energy storage inverter systems, which include a controller, a pre-charge relay, a first live wire relay, a second live wire relay, a neutral wire relay, a DC bus capacitor, and a voltage detection unit. Specifically, it includes the following steps: S11: The energy storage inverter system executes a self-test program upon power-up. After the self-test program is completed, the voltage detection unit collects the grid-side voltage and the voltage across the DC bus capacitor in real time. Based on the collected grid-side voltage, the effective value and phase of the grid voltage are calculated. At the same time, the system detects whether there is a DC power input to the energy storage inverter system. S12: When the controller detects that there is no DC power input to the energy storage inverter system, it sends a closing command to the pre-charge relay and the first live wire relay. The pre-charge relay and the first live wire relay execute the closing command, and the grid current flows into the DC bus capacitor through the first live wire relay, the pre-charge relay and the pre-charge resistor connected in series, to pre-charge the DC bus capacitor. S13: When the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition, and the controller starts the phase adjustment loop to adaptively adjust the phase adjustment step size according to the phase difference change rate. S14: After phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop according to the amplitude deviation, so that the output voltage amplitude of the energy storage inverter is close to the voltage amplitude of the grid side, and determines whether the energy storage inverter meets the grid connection conditions. S15: When the energy storage inverter is determined to meet the grid connection conditions, the controller performs the grid connection operation according to the timing control strategy. After the grid connection is completed, the controller records the pre-charge control parameters, phase adjustment parameters and amplitude adjustment parameters into the non-volatile memory for the next pre-charge control call.

2. The grid pre-charge control method for an energy storage inverter as described in claim 1, characterized in that, In S11, the energy storage inverter system performs a self-test procedure upon power-up, including: The controller executes a self-test program to detect the initial state of the precharge relay, the first live wire relay, the second live wire relay, and the neutral wire relay. By sending test pulse signals to each relay and detecting the voltage change at both ends of the contacts, it determines whether each relay is in a normal open state and whether there is a contact sticking fault, and confirms that all relays are in an open state. After confirming that all relays are in the normal open state, the controller further performs online resistance detection on the pre-charge resistor connected in series with the pre-charge relay. It applies a detection voltage to the pre-charge resistor and measures the current flowing through it to calculate the actual resistance value. The actual resistance value is compared with the pre-stored nominal resistance value. If the deviation exceeds the preset resistance tolerance range, a pre-charge resistor abnormality alarm is issued and the pre-charge control process is terminated.

3. The grid pre-charge control method for an energy storage inverter as described in claim 2, characterized in that, In S12, the grid current flows into the DC bus capacitor through the first live wire relay, the pre-charge relay, and the pre-charge resistor connected in series, pre-charging the DC bus capacitor, including: The controller first sends a closing command to the first live wire relay. After confirming that the first live wire relay has been successfully closed, it sends a closing command to the pre-charge relay, so that the grid current flows through the first live wire relay, the pre-charge relay and the pre-charge resistor in sequence and then enters the DC bus capacitor. After the pre-charge is started, the controller controls the second live wire relay and the neutral wire relay to remain in the open state. After pre-charging is initiated, the controller collects the voltage value across the DC bus capacitor in real time at the first sampling frequency and calculates the voltage rise rate. When the voltage rise rate is greater than the preset first rate threshold, the pre-charging current is reduced. When the voltage rise rate is less than the preset second rate threshold, an abnormal warning is issued. The controller dynamically adjusts the pre-charging control parameters according to the voltage rise rate.

4. The grid pre-charge control method for an energy storage inverter as described in claim 3, characterized in that, In S13, it is determined that the energy storage inverter meets the pre-charge completion conditions, and the controller starts the phase adjustment loop, including: When the controller determines that the voltage across the DC bus capacitor reaches the preset pre-charge completion voltage threshold, it determines that the energy storage inverter meets the pre-charge completion condition. The controller immediately starts the phase adjustment loop. The phase adjustment loop uses the grid-side voltage phase as a reference, tracks the grid phase in real time through a phase-locked loop, and generates a reference phase signal that is synchronized with the grid-side voltage phase. The controller adjusts the output voltage phase of the energy storage inverter according to the reference phase signal, so that the phase difference between the output voltage phase and the grid voltage phase gradually transitions from a first angle to a second angle. The second angle is smaller than the first angle and close to zero degrees. When the phase difference reaches the second angle, the controller locks the current phase adjustment result.

5. The grid pre-charge control method for an energy storage inverter as described in claim 4, characterized in that, The controller adjusts the output voltage phase of the energy storage inverter based on the reference phase signal, so that the phase difference between the output voltage phase and the grid-side voltage phase gradually transitions from a first angle to a second angle, including: The controller uses the reference phase signal as a given target and successively adjusts the phase setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter so that the output voltage phase of the energy storage inverter gradually approaches the grid-side voltage phase from the current phase, and the phase difference gradually decreases from the first angle. During phase adjustment, the controller monitors the phase difference change rate in real time at the second sampling frequency and adaptively adjusts the phase adjustment step size according to the phase difference change rate to prevent phase overshoot. When the phase difference reaches the second angle and the absolute value of the phase difference change rate is less than the preset locking threshold, the controller locks the current phase adjustment result and freezes the integral term of the phase adjustment loop.

6. The grid pre-charge control method for an energy storage inverter as described in claim 5, characterized in that, In S14, after phase locking, the controller calculates the amplitude deviation and adjusts the output voltage amplitude of the energy storage inverter through the amplitude adjustment loop based on the amplitude deviation, including: After phase locking, the controller continuously collects the grid-side voltage amplitude and the energy storage inverter output voltage amplitude at the third sampling frequency. Fourier analysis is performed on the collected grid-side voltage and inverter output voltage to extract the fundamental component amplitude. The difference between the inverter output voltage amplitude and the grid-side voltage amplitude is calculated as the amplitude deviation. The controller uses the amplitude deviation as the input error signal of the amplitude adjustment loop. After proportional-integral operation, it generates an amplitude adjustment amount and adds it to the amplitude setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, so that the output voltage amplitude of the energy storage inverter gradually approaches the grid-side voltage amplitude until the amplitude deviation is less than the preset grid-connected amplitude threshold.

7. The grid pre-charge control method for an energy storage inverter as described in claim 6, characterized in that, The amplitude adjustment is generated after proportional-integral operation and superimposed on the amplitude setpoint of the sinusoidal pulse width modulation wave of the energy storage inverter, including: The controller inputs the amplitude deviation into the proportional-integral control unit, which generates an amplitude adjustment amount after proportional-integral calculation. The amplitude adjustment amount is then superimposed on the current amplitude setpoint of the sinusoidal pulse width modulation wave. The updated amplitude setpoint is used to generate a drive signal to control the output voltage amplitude of the energy storage inverter, so as to continuously approximate the voltage amplitude on the grid side. During amplitude adjustment, the controller continuously monitors the phase difference and amplitude deviation between the output voltage of the energy storage inverter and the grid-side voltage. When the phase difference is less than the preset grid-connected phase threshold and the amplitude deviation is less than the preset grid-connected amplitude threshold, the controller determines that the energy storage inverter meets the grid-connection conditions and prepares to perform subsequent grid-connection operations.

8. The grid pre-charge control method for an energy storage inverter as described in claim 7, characterized in that, In S15, the controller performs grid connection operations according to the timing control strategy, including: First, send a closing command to the second live wire relay to close the second live wire relay and connect the second live wire path to the grid-connected circuit; After a preset relay action delay time, the controller sends a disconnect command to the precharge relay, causing the precharge relay to disconnect and cut off the precharge circuit, thus completing the disconnection of the precharge circuit. Finally, the controller sends a closing command to the neutral line relay, causing the neutral line relay to close. This completes the grid connection between the energy storage inverter and the power grid, and the energy storage inverter enters normal operation.

9. An energy storage inverter system with grid pre-charge control, characterized in that, For executing the pre-charge control method according to any one of claims 1-8, the energy storage inverter system comprises: The grid interface module is used to connect to the AC grid, receive grid-side voltage and current, and feed AC power output from the inverter. The DC bus module, including the DC bus capacitor, is used to smooth DC power to provide a stable operating voltage for the inverter unit. An inverter unit, connected between the DC bus module and the grid interface module, is used to convert DC power into AC power and adjust the phase and amplitude of the output voltage according to the control signal. The pre-charge module includes a pre-charge relay and a pre-charge resistor connected in series with it, and is connected in parallel with the output terminal of the inverter unit. It is used to pre-charge the DC bus capacitor with grid power before grid connection. The first live wire relay, the second live wire relay, and the neutral wire relay are respectively connected to the live wire and neutral wire paths corresponding to the inverter unit and the power grid interface module, and are used to control the on / off state of each path. A voltage detection unit is connected to the power grid interface module and the DC bus module, and is used to collect the power grid side voltage and the voltage across the DC bus capacitor. A current detection unit is connected to the output terminal of the inverter unit and is used to collect the output current; The controller is electrically connected to each relay, the voltage detection unit, and the current detection unit, respectively, and is used to perform grid pre-charge control of the energy storage inverter; A non-volatile memory, connected to the controller, is used to store pre-charge control parameters, phase adjustment parameters, amplitude adjustment parameters, and grid connection event records; The human-machine interface is connected to the controller and is used to display the pre-charging progress, grid connection status and operating parameters in real time, and to receive user control commands.

10. The energy storage inverter system with grid pre-charge control as described in claim 9, characterized in that, The pre-charge module includes a pre-charge relay drive unit, a pre-charge resistance online detection unit, and a pre-charge current adjustment unit; The precharge relay driving unit includes a driving circuit and a status feedback circuit. The driving circuit drives the precharge relay to operate according to the controller command. The status feedback circuit detects the voltage difference of the relay contacts and feeds it back to the controller to confirm the operation status. The pre-charge resistance online detection unit includes a detection voltage application circuit and a detection current measurement circuit, which are used to apply a detection voltage to the pre-charge resistance and measure the current under the control of the controller. The controller calculates the actual resistance value based on the detection voltage and current and compares it with the nominal resistance value to realize the monitoring of the pre-charge resistance. The precharge current regulation unit includes a power switch transistor connected in series with the precharge relay and the precharge resistor, as well as a sampling resistor and an amplification circuit connected in series in the precharge circuit. The power switch adjusts its duty cycle under the control of the controller's pulse width modulation signal to control the pre-charge current. The amplifier circuit amplifies the voltage across the sampling resistor and outputs it to the controller. The controller calculates the instantaneous value of the pre-charge current based on this and reduces the duty cycle to limit the peak value of the pre-charge current when it exceeds the preset maximum allowable value.

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