Energy storage type voltage sag compensation device

Abstract

This application relates to the fields of energy storage and power quality management, and particularly to an energy storage-type voltage sag compensation device, comprising: a power execution unit, wherein the controller is configured to: determine that a voltage sag has occurred in the power grid, control the bypass thyristor to conduct briefly and disconnect the main circuit switch; generate a compensation voltage command based on the voltage amplitude and rated voltage of the power grid; control the compensation converter to output the compensation voltage, and control the energy storage converter to switch from grid-connected current control mode to DC bus voltage support mode; after determining that the compensation is successful, continuously acquire the voltage amplitude of the power grid, and when the power grid voltage returns to normal, control the bypass thyristor to conduct briefly and close the main circuit switch; control the compensation converter to stop outputting the compensation voltage, and control the energy storage converter to switch from DC bus voltage support mode to grid-connected current control mode. This device coordinates the compensation activation and deactivation with the continuous power supply process to the load, improving the stability of the load-side voltage compensation process.

Description

Technical Field

[0001] This application belongs to the field of energy storage and power quality management technology, and particularly relates to energy storage type voltage sag compensation device. Background Technology

[0002] Sensitive load users such as semiconductor manufacturers, data centers, and precision chemical industries have extremely high requirements for voltage quality. Even a voltage dip of tens of milliseconds during power supply can cause production line shutdowns, equipment malfunctions, or process interruptions, resulting in significant economic losses. Dynamic voltage restorers (DVRs) are an effective means of addressing voltage dips, compensating for load-side voltage when grid voltage dips occur. Existing energy storage devices are mostly used in grid-connected charging and discharging, peak shaving and valley filling, or power support scenarios. Their main function is energy regulation, and they cannot provide timely support to the load during voltage dips.

[0003] While existing technologies have proposed combining energy storage with DVR functionality to enable energy storage devices to support load-side voltage during grid voltage anomalies, the compensation function needs to be rapidly activated and deactivated during voltage dips and grid voltage recovery. If the activation and deactivation of compensation are not properly coordinated with the continuous power supply to the load, problems such as load-side voltage fluctuations, switching shocks, or uneven compensation deactivation can easily occur, affecting the stable operation of sensitive loads during voltage dips and voltage recovery.

[0004] In summary, existing power supply equipment with energy storage functions suffers from poor stability and reliability in the load-side voltage compensation process during voltage dips and recovery due to insufficient coordination between compensation input / output and continuous load power supply. Summary of the Invention

[0005] This application provides an energy storage type voltage sag compensation device, which can solve the problem in the related art that existing power supply equipment with energy storage function has poor stability and reliability in the load-side voltage compensation process due to insufficient coordination between compensation input and output and the continuous power supply process of the load during the voltage sag and voltage recovery process of the power grid.

[0006] In a first aspect, embodiments of this application provide an energy storage type voltage sag compensation device, comprising: The power execution unit includes an energy storage unit, an energy storage converter, a compensation converter, an injection transformer, a composite switch, an energy storage switch, and a compensation switch. The composite switch includes a main circuit switch and a bypass thyristor. One side of the main circuit switch is connected to the grid side, and the other side is connected to the series winding of the injection transformer. The series winding of the injection transformer is connected to the load side, forming a main circuit. The bypass thyristor is connected in parallel on both sides of the main circuit switch, forming the composite switch. One side of the energy storage switch is connected to the AC side of the energy storage converter, and the other side is connected to the grid side. The DC side of the energy storage converter is connected to the DC bus. The energy storage unit is connected to the DC bus. The converter-side winding of the injection transformer is connected to one side of the compensation switch, and the other side of the compensation switch is connected to the AC side of the compensation converter. The DC side of the compensation converter is connected to the DC bus. The controller is configured as follows: Obtain the voltage amplitude on the grid side. If the voltage amplitude on the grid side is less than a voltage threshold, determine that a voltage sag has occurred on the grid. The voltage threshold is N times the rated voltage on the grid side, where N is less than 1. In the event of a voltage dip in the power grid, the bypass thyristor in the composite switch is briefly turned on, and the main switch in the composite switch is turned off during the period when the bypass thyristor is turned on; after the main switch is turned off, the bypass thyristor is turned off, and a first mode switching command is generated. The sag depth is determined based on the grid-side voltage amplitude and the grid-side rated voltage, and a compensation voltage command is generated based on the sag depth. The compensation switch is closed, and the compensation converter is controlled to output compensation voltage to the load side through the injection transformer according to the compensation voltage command; the energy storage converter is controlled to switch from grid-connected current control mode to DC bus voltage support mode according to the first mode switching command. The load-side voltage amplitude is obtained, and the compensation is determined to be successful based on the load-side voltage amplitude and the grid-side rated voltage. During the voltage sag compensation period, the main circuit switch is in the open state and the bypass thyristor is in the off state to isolate the grid side from the load side. After successful compensation, the voltage amplitude on the grid side is continuously acquired. If the voltage amplitude on the grid side is greater than the voltage threshold, it is determined that the grid voltage has returned to normal. When the grid voltage returns to normal, the bypass thyristor is briefly turned on, and the main circuit switch is closed during the period when the bypass thyristor is turned on; after the main circuit switch is closed, the bypass thyristor is turned off, and a second mode switching command and a shutdown command are generated. According to the shutdown command, the compensation converter is controlled to stop outputting the compensation voltage, and the compensation switch is controlled to open; according to the second mode switching command, the energy storage converter is controlled to switch from DC bus voltage support mode to grid-connected current control mode.

[0007] The technical solutions described in this application embodiment have at least the following technical effects: The energy storage voltage sag compensation device provided in this application constructs a coordinated control system for energy storage operation, voltage sag identification, short-time transition of composite switches, load-side voltage compensation, and grid recovery and disconnection. When a voltage sag is detected in the grid, the controller briefly turns on the bypass thyristor and controls the main circuit switch to open during the bypass thyristor's conduction. After the main circuit switch is opened, the controller stops triggering the bypass thyristor to turn it off, isolating the grid side from the load side and preventing the sag voltage from continuing to propagate to the load side. Simultaneously, the controller closes the compensation switch, controlling the compensation converter to output compensation voltage to the load side via the injection transformer, and controls the energy storage converter to switch from grid-connected current control mode to DC bus voltage support mode, providing stable DC-side energy support for the compensation converter. After grid recovery, the controller can briefly trigger the bypass thyristor to turn on and close the main circuit switch. After the main circuit switch is closed, the controller stops triggering the bypass thyristor to turn it off, controls the compensation converter to stop outputting compensation voltage, and disconnects the compensation switch, allowing the energy storage converter to return to grid-connected current control mode. Through the above timing sequence, the bypass thyristor does not serve as a continuous conducting path during the voltage sag compensation period, but rather as a short-term transition branch during the opening and closing process of the main circuit switch. This ensures that the compensation input and output are coordinated with the continuous power supply process of the load, reducing the main circuit switching impact and load-side voltage fluctuations, and improving the stability and reliability of the load-side voltage compensation process.

[0008] Secondly, embodiments of this application provide a control method for an energy storage type voltage sag compensation device. The energy storage type voltage sag compensation device includes a power execution unit, which includes an energy storage unit, an energy storage converter, a compensation converter, an injection transformer, a composite switch, an energy storage switch, and a compensation switch. The method includes: Obtain the voltage amplitude on the grid side. If the voltage amplitude on the grid side is less than a voltage threshold, determine that a voltage sag has occurred on the grid. The voltage threshold is N times the rated voltage on the grid side, where N is less than 1. In the event of a voltage dip in the power grid, the bypass thyristor in the composite switch is briefly turned on, and the main switch in the composite switch is turned off during the period when the bypass thyristor is turned on; after the main switch is turned off, the bypass thyristor is turned off, and a first mode switching command is generated. The sag depth is determined based on the grid-side voltage amplitude and the grid-side rated voltage, and a compensation voltage command is generated based on the sag depth. The compensation switch is closed, and the compensation converter is controlled to output compensation voltage to the load side through the injection transformer according to the compensation voltage command; the energy storage converter is controlled to switch from grid-connected current control mode to DC bus voltage support mode according to the first mode switching command. The load-side voltage amplitude is obtained, and the compensation is determined to be successful based on the load-side voltage amplitude and the grid-side rated voltage. During the voltage sag compensation period, the main circuit switch is in the open state and the bypass thyristor is in the off state to isolate the grid side from the load side. After successful compensation, the voltage amplitude on the grid side is continuously acquired. If the voltage amplitude on the grid side is greater than the voltage threshold, it is determined that the grid voltage has returned to normal. When the grid voltage returns to normal, the bypass thyristor is briefly turned on, and the main circuit switch is closed during the period when the bypass thyristor is turned on; after the main circuit switch is closed, the bypass thyristor is turned off, and a second mode switching command and a shutdown command are generated. According to the shutdown command, the compensation converter is controlled to stop outputting the compensation voltage, and the compensation switch is controlled to open; according to the second mode switching command, the energy storage converter is controlled to switch from DC bus voltage support mode to grid-connected current control mode.

[0009] Thirdly, embodiments of this application provide an electronic device including means for performing the energy storage type voltage sag compensation device control method in the second aspect.

[0010] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the structure of an energy storage type voltage sag compensation device provided in an embodiment of this application; Figure 2 This is a schematic diagram of the power execution unit in an energy storage type voltage sag compensation device provided in an embodiment of this application; Figure 3 This is a flowchart of the controller in an energy storage voltage sag compensation device provided in an embodiment of this application. Detailed Implementation

[0013] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0014] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0015] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0016] In related technologies, the design focus of conventional energy storage devices is primarily on energy storage and bidirectional power regulation. Their core functions mainly include grid-connected charging and discharging control, active and reactive power regulation, and energy management. While conventional energy storage devices can provide energy support for power quality disturbances such as grid voltage dips and short-term drops, their output is typically used for grid-connected power regulation and is unlikely to directly and quickly maintain load-side voltage stability.

[0017] To mitigate the adverse effects of voltage sags on sensitive loads, existing technologies employ Dynamic Voltage Restorers (DVRs). DVRs inject compensating voltage into the lines when voltage sags occur, maintaining load-side voltage stability. However, traditional DVRs require separate configuration as independent devices, meaning they must be added as an extra compensation unit outside the existing power supply and distribution system. This leads to a more complex system structure, more dispersed equipment, and increased difficulty in engineering installation and system integration. Traditional DVRs typically do not participate in daily energy regulation under normal power supply conditions, only activating during abnormal conditions such as voltage sags. Therefore, they spend most of the time in standby or underutilized mode, resulting in low equipment utilization.

[0018] In practical engineering, to balance energy storage regulation and voltage sag compensation functions, some solutions combine energy storage systems with digital voltage regulators (DVRs). The energy storage system handles daily charging and discharging, while the DVR compensates for voltage sags, thus addressing both energy management and power quality control needs. However, these energy storage + DVR combinations typically require separate configurations for energy storage and DVR compensation devices, forming relatively independent functional units. Since each functional unit requires its own main circuit, control system, protection circuit, and installation space, the overall system often suffers from high investment costs, a large number of devices, complex structure, and a large footprint. In user-side applications with high requirements for construction costs, installation space, and system integration, these issues further limit the promotion and application of this type of solution.

[0019] To reduce costs and improve equipment reusability, existing technologies have proposed integrating energy storage and DVR functions into a single device. This allows the device to perform energy storage charging / discharging or power regulation under normal power supply conditions, and switch to voltage compensation mode when a voltage dip occurs in the grid to provide voltage support to the load side. However, during voltage dips and grid voltage recovery, the device needs to rapidly switch between different operating states, and the compensation function also needs to be quickly activated and deactivated. If the activation and deactivation of compensation are not properly coordinated with the continuous power supply process to the load, issues such as load-side voltage fluctuations, switching shocks, uneven compensation response, or unstable recovery can easily occur, thus affecting the stable operation of the load during voltage dips and voltage recovery.

[0020] Specifically, when the grid voltage is normal, the equipment is typically in normal energy storage operation. When the grid voltage experiences a voltage dip, the equipment needs to promptly enter voltage compensation mode to ensure that the load-side voltage remains within the allowable range. Once the grid voltage returns to normal, the equipment needs to smoothly exit compensation mode and resume normal operation. If there is a lack of effective coordination between the timing of compensation activation, deactivation, and continuous load power supply, it may lead to untimely compensation intervention, voltage spikes during deactivation, or electrical surges during state transitions, thereby reducing the stability and reliability of the voltage dip compensation process.

[0021] To address the aforementioned issues, this application provides an energy storage-type voltage sag compensation device. This device establishes a coordinated control system encompassing energy storage operation, voltage sag detection, short-term transition of the composite switch, load-side voltage compensation, and grid recovery / exit. When a voltage sag is detected in the grid, the controller briefly turns on the bypass thyristor and controls the main circuit switch to open during the bypass thyristor's conduction. After the main circuit switch opens, triggering the bypass thyristor stops, causing it to turn off and isolating the grid side from the load side, preventing the sag voltage from continuing to propagate to the load side. Simultaneously, the controller closes the compensation switch, controlling the compensation converter to output compensation voltage to the load side via the injection transformer, and switches the energy storage converter from grid-connected current control mode to DC bus voltage support mode, providing stable DC-side energy support for the compensation converter. After the grid is restored, the controller can briefly trigger the bypass thyristor to conduct and close the main circuit switch. After the main circuit switch is closed, it stops triggering the bypass thyristor, causing it to turn off, and controls the compensation converter to stop outputting compensation voltage and disconnect the compensation switch, so that the energy storage converter returns to the grid-connected current control mode. Through the above timing sequence, the bypass thyristor does not serve as a continuous conducting path during voltage sag compensation, but rather as a short-term transition branch during the opening and closing of the main circuit switch. This coordinates the compensation input and output with the continuous power supply process to the load, reduces the impact of main circuit switching and load-side voltage fluctuations, and improves the stability and reliability of the load-side voltage compensation process.

[0022] For example, please refer to Figure 1 The energy storage type voltage sag compensation device 100 may include a power execution unit 10 and a controller 20. (See also...) Figure 2The power execution unit 10 may include an energy storage unit 17, an energy storage converter 16, a compensation converter 15, an injection transformer 13, a composite switch, an energy storage switch 18, and a compensation switch 14. The injection transformer 13 includes a series winding 131 and a converter winding 132. The energy storage unit 17 can store electrical energy for peak-valley arbitrage, demand management, and to provide energy support for the compensation converter 15 during voltage sags. It can be a battery cluster (such as a lithium iron phosphate battery pack, a lithium titanate battery pack), a supercapacitor module, etc. The energy storage converter 16 can realize bidirectional energy conversion between the energy storage unit 17 and the grid. Under normal conditions, it operates in grid-connected current control mode for charging and discharging. During voltage sags, it switches to DC bus voltage support mode to stabilize the DC bus voltage. It can be a three-level NPC bidirectional converter, a three-phase two-level converter, a modular multilevel converter (MMC), etc. The compensation converter 15 can act as an AC voltage source during voltage sags to generate the required amplitude and phase compensation voltage. It can be a static synchronous compensator (STATCOM), a three-phase voltage source type PWM converter, etc. The injection transformer 13 can raise the low voltage (such as 800V) output by the compensation converter 15 to the grid level (such as 10kV) while providing electrical isolation. It can be a single-phase or three-phase oil-immersed transformer, a dry-type transformer, etc.

[0023] The composite switch includes a main circuit switch 11 and a bypass thyristor 12. The bypass thyristor 12 is connected in parallel across the main circuit switch 11 and is used to conduct briefly during the opening or closing of the main circuit switch 11, providing a transition current path for the operation of the main circuit switch 11. After the main circuit switch 11 completes the opening or closing, the controller 20 stops outputting trigger signals to the bypass thyristor 12, causing the bypass thyristor 12 to turn off when the branch current crosses zero.

[0024] The main circuit breaker 11 is normally closed, carrying the load current; during a voltage dip, it opens during the short-term conduction of the bypass thyristor 12. After the main circuit breaker 11 opens and the bypass thyristor 12 turns off, the grid side is isolated from the load side; it closes again after the grid is restored. The main circuit breaker 11 can be a permanent magnet vacuum circuit breaker, a mechanical switch, etc., and the bypass thyristor 12 can be an anti-parallel thyristor module.

[0025] The energy storage switch 18 can connect or isolate the energy storage converter 16 from the power grid for normal switching or fault protection. It can be an AC contactor, a molded case circuit breaker, etc. The energy storage switch 18 remains closed when the grid-side voltage is normal (i.e., normal energy storage mode) and when the grid-side voltage is sag (i.e., voltage sag compensation mode). When the energy storage converter 16 needs maintenance, the energy storage switch 18 can isolate the energy storage converter 16 from the AC side; when the energy storage converter 16 fails, the energy storage switch 18 can be used as an AC side disconnection method; when the system is powered on, connected to the grid, or disconnected, the energy storage switch 18 can participate in the control sequence.

[0026] The compensation switch 14 can connect or isolate the compensation converter 15 from the primary side of the injection transformer 13. It is disconnected under normal conditions to reduce no-load losses and closed during temporary sags. It can be an AC contactor or a solid-state relay.

[0027] The controller 20 can monitor the grid voltage in real time, perform voltage sag detection, control the timing of the composite switch / energy storage switch 18 / compensation switch 14, switch the mode of the energy storage converter 16, control the start and stop of the compensation converter 15, perform voltage closed-loop regulation, and handle communication protocol processing and data processing. It can be a combination board of FPGA (such as Xilinx Artix-7) and DSP (such as TI TMS320F28388), industrial-grade PLC control system, etc.

[0028] The controller 20 is connected to the energy storage converter 16, the compensation converter 15, the composite switch, the energy storage switch 18, and the compensation switch 14, respectively. Specifically, the output terminal of the energy storage converter control signal (such as the first mode switching command, the second mode switching command, and control parameters) of the controller 20 is connected to the control signal input terminal of the energy storage converter 16, and the state feedback output terminal of the energy storage converter 16 is connected to the state acquisition input terminal of the controller 20; the output terminal of the compensation converter control signal (such as the compensation voltage command and the start / stop command) of the controller 20 is connected to the control signal input terminal of the compensation converter 15, and the state feedback output terminal of the compensation converter 15 is connected to the state acquisition input terminal of the controller 20; the trigger signal output terminal of the controller 20 is connected to the drive circuit input terminal of the bypass thyristor 12, and the output terminal of the drive circuit is connected to the bypass thyristor 12. The gate trigger terminal of thyristor 12 is connected; the output terminal of the main circuit switch control signal (such as closing command, opening command) of controller 20 is connected to the actuator input terminal of main circuit switch 11, and the auxiliary contact output terminal of main circuit switch 11 is connected to the status acquisition input terminal of controller 20; the output terminal of the energy storage switch control signal of controller 20 is connected to the actuator input terminal of energy storage switch 18, and the auxiliary contact output terminal of energy storage switch 18 is connected to the status acquisition input terminal of controller 20; the output terminal of the compensation switch control signal of controller 20 is connected to the actuator input terminal of compensation switch 14, and the auxiliary contact output terminal of compensation switch 14 is connected to the status acquisition input terminal of controller 20.

[0029] One side of the main circuit switch 11 is connected to the grid side, and the other side is connected to the series winding 131 of the injection transformer 13. The series winding 131 of the injection transformer 13 is connected to the load side, forming the main circuit. Under normal voltage conditions, current flows from the grid side through the main circuit switch 11 to the load side. The bypass thyristor 12 is connected in parallel on both sides of the main circuit switch 11, forming a composite switch. It is used for short-term transitional conduction during the opening or closing process of the main circuit switch 11, and is turned off after the main circuit switch 11 completes its operation, thereby achieving main circuit switching and isolation from the grid side. Energy storage switch One side of 18 is connected to the AC side of the energy storage converter 16, and the other side is connected to the grid side; the DC side of the energy storage converter 16 is connected to the DC bus; the energy storage unit 17 is connected to the DC bus, or the energy storage unit 17 is connected to the bidirectional DC / DC converter, and the bidirectional DC / DC converter is connected to the DC bus; the energy storage unit 17 and the energy storage converter 16 constitute the main body of energy storage. When the voltage is normal, it is a standard energy storage PCS structure; when the voltage drops, it switches from the grid-connected current control mode to the DC bus voltage support mode to provide an energy source for the compensation converter 15.

[0030] The converter-side winding 132 of the injection transformer 13 is connected to one side of the compensation switch 14, and the other side of the compensation switch 14 is connected to the AC side of the compensation converter 15. The DC side of the compensation converter 15 is connected to the DC bus. The compensation converter 15 and the injection transformer 13 constitute the main body of the DVR function. The compensation voltage output by the compensation converter 15 is injected in series in the main circuit through the injection transformer 13, so that the load-side voltage is restored to close to the rated value.

[0031] The energy storage converter 16 and the compensation converter 15 are independent power conversion units. They are energy-coupled through a DC bus, rather than using the same converter for multiplexing between grid-connected and series compensation operation. When the grid voltage is normal, the energy storage converter 16 operates in grid-connected current control mode to perform charging and discharging control between the energy storage unit and the grid; the compensation converter 15 is in standby or hot standby state.

[0032] When a voltage dip occurs in the power grid, the bypass thyristor 12 is briefly turned on and disconnected in conjunction with the main switch 11. After the main switch 11 is disconnected, the bypass thyristor 12 is turned off, isolating the power grid side from the load side. The compensation switch 14 is closed, and the compensation converter 15 operates as an AC voltage source according to the compensation voltage command, and outputs the compensation voltage to the load side through the injection transformer 13. The energy storage converter 16 switches to DC bus voltage support mode to stabilize the DC bus voltage and provide DC side energy support to the compensation converter 15.

[0033] The energy storage converter 16 mainly undertakes the energy support function between the energy storage unit and the DC bus, the compensation converter 15 mainly undertakes the load-side voltage compensation function, and the composite switch mainly undertakes the main circuit switching and transition conduction function during the compensation input and output process. The three are coordinated in time by the controller 20, which can reduce the switching impact and load-side voltage fluctuation caused by the lack of coordination between the compensation input, compensation output and the continuous power supply process of the load.

[0034] To better understand the energy storage voltage sag compensation device provided in the embodiments of this application, the specific execution process of the energy storage voltage sag compensation device provided in the embodiments of this application will be described by way of example below.

[0035] Please see Figure 1 and Figure 2 This application provides an energy storage type voltage sag compensation device 100, comprising: The power execution unit 10 includes an energy storage switch 18, an energy storage unit 17, an energy storage converter 16, a compensation converter 15, a compensation switch 14, an injection transformer 13, and a composite switch. The composite switch includes a main circuit switch 11 and a bypass thyristor 12. One side of the main circuit switch 11 is connected to the grid side, and the other side is connected to the series winding 131 of the injection transformer 13. The series winding 131 of the injection transformer 13 is connected to the load side, forming the main circuit. The bypass thyristor 12 is connected in parallel on both sides of the main circuit switch 11, forming the composite switch. One side of the energy storage switch 18 is connected to the AC side of the energy storage converter 16, and the other side is connected to the grid side. The DC side of the energy storage converter 16 is connected to the DC bus, and the energy storage unit 17 is connected to the DC bus. The converter-side winding 132 of the injection transformer 13 is connected to one side of the compensation switch 14, and the other side of the compensation switch 14 is connected to the AC side of the compensation converter 15. The DC side of the compensation converter 15 is connected to the DC bus.

[0036] Controller 20 is configured to perform the following steps: S100: Obtain the voltage amplitude on the grid side. If the voltage amplitude on the grid side is less than the voltage threshold, determine that a voltage sag has occurred on the grid. The voltage threshold is N times the rated voltage on the grid side, where N is less than 1.

[0037] For example, the controller can acquire grid-side voltage signals in real time using voltage sensors or voltage transformers (PTs). The sampling frequency can be high enough to ensure rapid detection of short-term voltage dips, such as updating every millisecond or every few milliseconds. The acquired grid-side voltage signals can be filtered and processed to eliminate high-frequency noise and grid transient effects.

[0038] The controller can use instantaneous amplitude calculation methods to calculate the amplitude of the acquired voltage signal, such as the root mean square (RMS) calculation method. ,in, Indicates the voltage amplitude on the grid side. The voltage waveform is sampled from the power grid, where T is one complete power grid cycle (e.g., 20ms for 50Hz). Real-time RMS values ​​can be achieved using a sliding window or a digital filter.

[0039] The voltage threshold can be set through the controller's parameter configuration module. The voltage threshold can be... Where N < 1, such as , This indicates the rated voltage on the grid side, which can be determined based on the grid level to which it is connected. For example, if the application scenario is low-voltage user-side energy storage, and the grid level is 380V / 400V, then... It is 380V or 400V; the application scenario is medium-voltage user-side energy storage, and the grid level is 10kV / 20kV. It is 10kV or 20kV.

[0040] The controller will measure the voltage amplitude on the grid side. With voltage threshold If a comparison is made, This can be used to determine if a voltage dip has occurred in the power grid; if This allows the system to determine that the grid voltage is in a normal state. The determination result can be output as a flag signal to trigger subsequent compensation actions. This determination can be implemented as a logic judgment module within the controller, which facilitates timely compensation even when the response speed is less than the duration of the voltage dip.

[0041] This step enables real-time and accurate monitoring of the grid-side voltage status, timely identification of voltage sag events, and provides reliable triggering conditions for timely response to subsequent compensation measures. This ensures that the energy storage device can activate the voltage sag compensation function the instant a voltage sag occurs, effectively maintaining load-side voltage stability and power supply reliability.

[0042] In one possible implementation, in step S100, the acquisition of the grid-side voltage amplitude is configured as follows: S110: Obtain the three-phase voltage signal from the grid side, and calculate the current grid phase based on the three-phase voltage signal from the grid side using a phase-locked loop.

[0043] For example, the controller acquires the three-phase voltage signal from the grid side through a voltage sensor or voltage transformer. , , .right , , Perform a Clarke transform to convert it into voltage components in a two-phase stationary coordinate system. , .

[0044] When the phase-locked loop (PLL) starts, the controller can provide an initial value for the phase angle. After the phase-locked loop (PLL) has stabilized, the controller can read the phase angle output from the previous control cycle. , which serves as the input angle for the current period's Park transform. The controller can then... ,right , Perform a dq transformation to convert it into voltage components in a rotating coordinate system. , and will The error signal is input to the phase-locked loop (PLL) regulator. The PLL regulator adjusts the phase deviation through proportional-integral (PI) control to obtain an estimated grid angular frequency. The controller performs an integral operation on the estimated grid angular frequency to obtain the current grid phase angle. .

[0045] S120, based on the current grid phase, perform coordinate transformation on the three-phase voltage signal on the grid side to obtain the d-axis voltage component and the q-axis voltage component. The d-axis voltage component and the q-axis voltage component are voltage components in the dq coordinate system.

[0046] For example, the formulas for calculating the d-axis voltage component and the q-axis voltage component are as follows: ,Right now , .

[0047] S130, calculate the voltage amplitude on the grid side based on the d-axis voltage component and the q-axis voltage component.

[0048] For example, the formula for calculating the voltage amplitude on the grid side is as follows: .

[0049] Since the three-phase voltage itself is an alternating quantity that changes with time, it is inconvenient to directly compare instantaneous values. After dq transformation, the voltage signal becomes an approximate DC quantity or a slow variable, which improves the accuracy of voltage detection and anti-interference ability, and provides a reliable basis for subsequent voltage sag judgment and compensation control.

[0050] S200: In the event of a voltage dip in the power grid, the bypass thyristor in the composite switch is briefly turned on, and the main switch in the composite switch is turned off during the period when the bypass thyristor is turned on; after the main switch is turned off, the bypass thyristor is turned off, and a first mode switching command is generated.

[0051] For example, the controller continuously monitors the flag signal generated in the previous step, and when the flag signal indicates that the voltage amplitude on the grid side is lower than the voltage threshold, it initiates the composite switch control process.

[0052] During normal grid-connected operation, the main circuit breaker is closed, and the bypass thyristor is in the off state. During sag triggering, the controller can check the status of the main circuit breaker through the auxiliary contact of the main circuit breaker to confirm that the switching conditions are met (such as the main circuit breaker being closed and the bypass thyristor not being turned on), which is conducive to the safety of the switching action and prevents short circuits or voltage surges. The auxiliary contact is a status feedback contact installed on the switch body.

[0053] The controller can send trigger pulses to the bypass thyristor to turn it on and establish a transitional current-carrying branch. The pulse width and trigger timing can be designed according to the thyristor characteristics and system voltage synchronization requirements. At the instant the bypass thyristor turns on or after a short delay, the controller sends a trip command to the actuator of the main circuit breaker. The actuator drives the main circuit breaker to open, achieving a smooth disconnection of the main circuit current and avoiding short circuits or transient impacts. After confirming the main circuit breaker is open via its auxiliary contacts, the controller stops sending trigger pulses to the bypass thyristor, and the bypass thyristor turns off. At this point, the main circuit breaker is open, the bypass thyristor is off, and the grid side is isolated from the load side.

[0054] While completing the composite switching action, the controller can generate a first mode switching command to notify the energy storage converter to switch from the grid-connected current control mode to the DC bus voltage support mode in order to adapt to the voltage sag compensation requirements.

[0055] This step enables the bypass thyristor to conduct briefly to form a transition current-carrying branch when a voltage dip occurs in the power grid. Subsequently, the main circuit breaker is opened, and the bypass thyristor is turned off after the main circuit breaker is opened. This avoids the arcing, inrush current, or voltage oscillation caused by the direct load disconnection of the main circuit breaker, and allows the main circuit to smoothly transition from the normal power supply state to the compensated operation state.

[0056] In one possible implementation, step S200, controlling the bypass thyristor in the composite switch to be briefly turned on, and controlling the main switch in the composite switch to be turned off during the period the bypass thyristor is turned on, is configured as follows: S210 generates a trigger signal when a voltage dip occurs in the power grid and outputs the trigger signal to the drive circuit of the bypass thyristor. The drive circuit applies a trigger pulse to the bypass thyristor according to the trigger signal, so that the bypass thyristor switches from the off state to the on state.

[0057] For example, if the main circuit breaker is directly opened / closed, it may cause problems such as current interruption leading to transient impact, system voltage drop or oscillation, and control loss of synchronization of the energy storage converter / compensation converter. A bypass thyristor connected in parallel with the main circuit breaker can be added to provide a transition current branch for a short time during the opening process of the main circuit breaker. After the main circuit breaker completes the opening, the triggering of the bypass thyristor is stopped and it is turned off, thereby avoiding the bypass thyristor from being continuously turned on during the voltage sag compensation period.

[0058] The controller acquires the flag signal in real time. When the flag signal indicates that the grid voltage has dropped, the controller enters the composite switch control process: the controller generates the corresponding trigger signal according to the flag signal and immediately outputs the trigger signal to the drive circuit of the bypass thyristor.

[0059] After receiving the trigger signal, the drive circuit isolates, shapes, and amplifies the signal to form a trigger pulse that meets the gate triggering conditions of the bypass thyristor. This trigger pulse is then applied between the gate and cathode of the bypass thyristor, causing it to switch from the off state to the on state, thus establishing a bypass conduction loop. The drive circuit can be a pulse transformer isolated drive circuit, an optocoupler isolated drive circuit, or a dedicated thyristor gate drive circuit, etc.

[0060] The controller can set the trigger pulse duration, such as 10ms. This means that from the moment of triggering, the drive circuit continuously outputs trigger pulses to the bypass thyristor. Once the main circuit breaker has opened or the trigger pulse duration has reached the preset time, the controller cancels the trigger signal, and the drive circuit stops outputting trigger pulses. The trigger pulse duration provides a buffer time for current transfer before the main circuit breaker has opened.

[0061] This step enables the bypass thyristor to be turned on in a timely manner, allowing the main circuit current to be smoothly transferred to the bypass branch before the main circuit switch is opened, and to exit the bypass branch conduction state after the main circuit switch is opened. This avoids a series of problems caused by the direct disconnection of the main circuit switch, and improves the smoothness of the circuit switching process and the stability of the system operation.

[0062] After the bypass thyristor is turned on (S220), a tripping command is generated and sent to the actuator of the main circuit breaker. The actuator then drives the main circuit breaker from a closed state to an open state according to the tripping command.

[0063] For example, the controller can acquire the branch current of the bypass thyristor through a current sensor, current transformer, or Hall current detection element, and filter and calculate the amplitude of the branch current. When the branch current is greater than the preset conduction current threshold, or when the main circuit current has been successfully transferred to the branch of the bypass thyristor and continues for a preset duration, the controller can determine that the bypass thyristor has been turned on and the bypass loop has been established.

[0064] After confirming the bypass thyristor is conducting, the controller can generate a tripping command and send it to the actuator of the main circuit breaker. The actuator can be an electromagnetic operating mechanism, an electric operating mechanism, a spring-powered operating mechanism, or a solid-state drive mechanism. Upon receiving the tripping command, the actuator drives the main circuit breaker to perform a disconnection action, changing the main circuit breaker from its closed state to its open state, thereby cutting off the main circuit.

[0065] After the controller outputs the tripping command, it can confirm whether the main circuit breaker has completed the tripping action through the auxiliary contacts. When the controller detects that the main circuit breaker status has changed from closed to open, it can determine that the main circuit breaker has successfully tripped.

[0066] S230 stops outputting trigger signals to the drive circuit of the bypass thyristor after the main circuit switch changes from the closed state to the open state, so as to turn off the bypass thyristor.

[0067] It is understandable that the controller can confirm through the auxiliary contacts of the main circuit breaker that the main circuit breaker has completed its tripping action, then stop sending trigger signals to the drive circuit of the bypass thyristor, and detect whether the branch current of the bypass thyristor has crossed zero. If the branch current crosses zero, the controller can determine that the bypass thyristor has switched from the conducting state to the turning-off state. After the bypass thyristor is turned off, both the main circuit breaker and the bypass thyristor are in the open state during the voltage sag compensation period, thereby isolating the grid side from the load side and preventing the voltage sag on the grid side from continuing to be transmitted to the load side.

[0068] This step enables the main circuit switch to be driven to open in an orderly manner after the bypass thyristor is turned on, achieving a smooth switching of current from the main circuit to the bypass circuit, and providing stable circuit switching conditions for the subsequent voltage compensation process.

[0069] S300 determines the sag depth based on the grid-side voltage amplitude and the grid-side rated voltage, and generates a compensation voltage command based on the sag depth.

[0070] For example, the controller can calculate the voltage sag depth based on the relationship between the grid voltage and the rated voltage. The sag depth can be expressed in absolute form. Alternatively, relative depth can be used. ,in, is the absolute value of the descent depth, and D is the percentage of the descent depth.

[0071] The compensation voltage can be proportional to the depth of the sag, and the controller can adjust the voltage based on the sag depth. Calculate the compensation voltage, i.e. ,in, For the compensation voltage, K is the compensation coefficient, which can be determined according to the system design or dynamic adjustment strategy to ensure that the compensation is both sufficient and not excessive. The compensation voltage command generated by the controller includes the compensation voltage.

[0072] This step enables the accurate calculation of the voltage sag depth based on the actual voltage drop in the power grid, and generates a matching compensation voltage command to achieve adaptive control of the compensation voltage.

[0073] In one possible implementation, in step S300, a compensation voltage command is generated based on the sag depth and configured as follows: S310, if the sag depth is less than the depth threshold, generate a compensation voltage command corresponding to the in-phase compensation based on the grid-side rated voltage and grid-side voltage amplitude.

[0074] For example, the controller can compare the descent depth D with a preset depth threshold. (e.g., 0.3) Compare, if It can be determined that the current voltage sag is a shallow sag, and the in-phase compensation control process is initiated.

[0075] The reason for setting the depth threshold to 0.3 is that when the voltage sag depth is less than 30%, the voltage drop on the grid side is not severe, and the phase of the grid side voltage is basically stable. Therefore, only the voltage amplitude needs to be compensated to restore the load-side voltage. Thus, in-phase compensation can achieve stable and reliable voltage recovery without introducing additional phase disturbances, and the control implementation is simple. However, when the voltage sag depth is greater than or equal to 30%, the voltage distortion on the grid side is significant, and in-phase compensation alone is insufficient to meet the recovery requirements. Therefore, by adjusting the amplitude and phase of the compensation voltage, full voltage compensation (i.e., complete compensation) is achieved, thereby ensuring the recovery of the load-side voltage.

[0076] The controller can calculate the difference between the rated voltage on the grid side and the voltage amplitude on the grid side, which is the compensation voltage. The current power grid phase can be... The output phase of the compensation voltage is determined. This ensures that the compensation voltage is in phase with the grid voltage.

[0077] The controller can adjust the output phase of the compensation voltage. and compensation voltage The components are combined to generate the compensation voltage command corresponding to in-phase compensation, wherein the compensation voltage command may include... and .

[0078] Optionally, in step S310, a compensation voltage command corresponding to the in-phase compensation is generated based on the grid-side rated voltage and the grid-side voltage amplitude, and configured as follows: S311, calculate the compensation voltage based on the grid-side rated voltage and grid-side voltage amplitude.

[0079] For example, the goal of in-phase compensation is to restore the load-side voltage amplitude to its rated value while maintaining the compensation voltage in phase with the grid residual voltage. Therefore, the target load voltage phasor is: The residual voltage phasor of the power grid is .

[0080] The controller can calculate the compensation voltage phasor based on the in-phase compensation target, i.e. Since the target load voltage phasor and the grid residual voltage phasor are in phase, the compensation voltage is... .

[0081] S312 generates a compensation voltage command based on the compensation voltage and the current grid phase.

[0082] For example, since the target load voltage phasor and the grid residual voltage phasor are in phase, the output phase of the compensation voltage is in phase with the current grid phase, i.e. .

[0083] The controller can be based on and This generates an instantaneous reference value for the compensation voltage in the three-phase coordinate system, i.e. , , It can provide instantaneous reference values ​​for three phases. , , Amplitude limiting is applied to ensure that the compensation voltage does not exceed the converter's allowable output range.

[0084] The controller can , , Convert it to a reference voltage component suitable for modulation, such as the Clarke transform, and then convert it to a voltage component in a two-phase stationary coordinate system. , , or dq transform, will , , Voltage components converted to a rotating coordinate system , .

[0085] The controller can generate a PWM modulation reference signal based on the reference voltage component, such as by calculating the duty cycle of each phase switch using space vector PWM or sinusoidal PWM algorithms. The controller can then use the PWM duty cycle signal as a compensation voltage command.

[0086] These steps generate a synchronous compensation voltage command based on the current grid phase, ensuring that the output compensation voltage is synchronously superimposed with the grid voltage. This effectively increases the load-side voltage amplitude without introducing additional phase deviation, ensuring a smooth voltage recovery process, simple control, and rapid response, thereby improving the system's compensation accuracy and operational stability.

[0087] S320: If the sag depth is greater than or equal to the depth threshold, generate a compensation voltage command corresponding to full compensation based on the grid voltage amplitude and the current grid phase.

[0088] For example, if The controller can determine that the current situation is a deep voltage sag and enter the full compensation control process. It can calculate the difference between the grid-side rated voltage and the grid-side voltage amplitude, which is the compensation voltage, or determine the compensation voltage amplitude based on vector relationships, so that the load-side voltage reaches the rated value after compensation.

[0089] The controller can determine the output phase of the compensation voltage based on the current grid phase. This ensures that the compensation voltage and the grid-side voltage, when vector-superimposed, form a load-side voltage of rated amplitude. The controller will adjust the output phase of the compensation voltage. and compensation voltage By combining these parameters, a compensation voltage command corresponding to full compensation is generated, wherein the compensation voltage command may include... and .

[0090] When dealing with shallow voltage sags, a simple in-phase compensation method is used, while when dealing with deep voltage sags, a more powerful full compensation method is used. This approach can reduce control complexity and improve system stability and adaptability while ensuring the compensation effect, thereby achieving efficient response to voltage sags of different degrees.

[0091] Optionally, S320, based on the grid-side voltage amplitude and the current grid phase, generates a compensation voltage command corresponding to full compensation, configured as follows: S321, obtain the grid-side voltage and the corresponding grid phase before the voltage sag, and calculate the voltage phasor before the voltage sag based on the grid-side voltage and the grid phase before the voltage sag.

[0092] For example, the controller repeatedly executes the amplitude and phase calculation process of steps S110 to S130 in each sampling period, and stores the calculated grid voltage amplitude and corresponding grid phase in real time. A circular buffer or register queue can be used to continuously update and store the voltage amplitude and phase in the most recent sampling periods.

[0093] The controller can read the grid voltage amplitude and corresponding grid phase at the moment before the sag trigger from the cyclic buffer or register queue.

[0094] The goal of full compensation is to restore the load-side voltage to its pre-sag state, i.e., to restore both amplitude and phase simultaneously. Therefore, the target load voltage phasor (i.e., the pre-sag voltage phasor) is: ,in, This indicates the grid voltage before the temporary sag. The previous grid phase was temporarily downgraded.

[0095] S322, calculate the residual voltage phasor of the power grid based on the voltage amplitude on the grid side and the current grid phase.

[0096] For example, similar to step S311, the residual voltage phasor of the power grid is .

[0097] S323 calculates the compensation voltage based on the phasor of the voltage before the voltage dip and the phasor of the residual voltage of the grid through the phasor difference relationship.

[0098] For example, the controller can calculate the compensation voltage phasor based on the goal of full compensation, i.e. Because the phase difference between the voltage phasor before the voltage dip and the residual voltage phasor of the grid is different, the compensation voltage cannot be directly calculated using the amplitude difference. Instead, the compensation voltage can be calculated based on the phasor difference, i.e. .

[0099] S324. Calculate the compensation voltage phase based on the grid-side voltage before the voltage sag, the grid-side voltage phase before the voltage sag, the grid-side voltage amplitude, and the current grid phase.

[0100] For example, the real and imaginary parts of the compensation voltage phasor are respectively , The controller can calculate the phase of the compensation voltage based on the real and imaginary parts of the compensation voltage phasor, i.e. .

[0101] S325 generates a compensation voltage command based on the compensation voltage and the compensation voltage phase.

[0102] For example, the implementation process of this step is the same as the generation process of the compensation voltage command in step S312, and will not be described again here.

[0103] These steps enable a more accurate recovery of the actual voltage vector state of the load-side voltage, reducing voltage distortion or power fluctuations caused by phase deviations, improving the accuracy of voltage recovery and dynamic response performance, and enhancing the stability and compensation effect of the system under complex voltage sag conditions.

[0104] S400 controls the compensation switch to close and, according to the compensation voltage command, controls the compensation converter to output compensation voltage to the load side through the injection transformer; and, according to the first mode switching command, controls the energy storage converter to switch from grid-connected current control mode to DC bus voltage support mode.

[0105] For example, while the main circuit breaker is open, the controller can simultaneously start the compensation converter: during periods of normal grid voltage, the compensation converter is in hot standby mode, its control power supply and power drive power supply remain powered on, the DC side is pre-charged to the allowable operating voltage through the DC bus, and the PWM modulation module is in a locked state. When the controller determines that a voltage dip has occurred in the grid, the controller can release the PWM lockout of the compensation converter according to the compensation voltage command and control the compensation converter to output the compensation voltage according to the compensation voltage command. The process of putting the compensation converter into operation can be executed in parallel with the process of turning on the bypass thyristor of the composite switch and opening the main circuit breaker. The opening of the main circuit breaker is used to achieve main circuit isolation and maintain the compensation state, but is not the sole prerequisite for the compensation converter to start establishing the compensation voltage.

[0106] The controller sends a compensation voltage command to the compensation converter and a closing command to the actuator of the compensation switch. The actuator drives the compensation switch to close, enabling the output of the compensation converter to be connected to the injection transformer and the main circuit. The enabled PWM module of the compensation converter generates a corresponding PWM waveform based on the compensation voltage command and injects it into the load side through the injection transformer to form the compensation voltage. During the compensation process, the controller continuously samples the load-side and grid-side voltages and adjusts the compensation voltage in real time based on feedback, achieving closed-loop dynamic compensation.

[0107] After the compensating converter is put into operation and the DC bus starts supplying power to the compensating branch, the controller responds to the first mode switching command, latches the current internal control state of the energy storage converter, including the integral term of the PQ control loop, the switch status and the DC bus voltage information in the grid-connected current control mode, to ensure smooth control during the mode switching process; and switches the control target of the energy storage converter from PQ control (grid-connected current control mode) to DC bus voltage control (DC bus voltage support mode).

[0108] The controller sends the first mode switching command and control target to the energy storage converter. After receiving the first mode switching command, the energy storage converter switches its control algorithm from PQ control to DC bus voltage control to stabilize the DC bus voltage. The energy storage converter obtains energy from the energy storage unit and continuously supplies energy to the DC bus, providing DC-side support for the compensation converter.

[0109] This step involves the controller coordinating the control of the compensation converter and the energy storage converter to achieve stable and reliable dynamic support for the load-side voltage. The compensation converter stabilizes the load-side voltage, while the energy storage converter provides DC bus support for the compensation converter in DC bus voltage support mode. This ensures the continuity and stability of the load-side voltage during voltage dips, while simultaneously achieving efficient energy supply and safe operation of the energy storage system during the compensation process.

[0110] In one possible implementation, in step S400, according to the first mode switching instruction, the energy storage converter is controlled to switch from the grid-connected current control mode to the DC bus voltage support mode, configured as follows: S410, in response to the first mode switching instruction, latches the current operating state.

[0111] It is understandable that the grid-connected current control mode is the mode in which energy storage operates normally. The control objective is to charge and discharge according to the set active power and operate according to the set reactive power, i.e., PQ control.

[0112] The DC bus voltage support mode is the mode during sag compensation. The control objective is to stabilize the DC bus voltage and continuously supply power to the compensation converter, which is DC bus voltage control.

[0113] For example, before sending the first mode switching command to the energy storage converter, the controller can first latch the current operating state (i.e., the operating state before or immediately after the sag trigger) to avoid control abrupt changes during the energy storage converter's switch from grid-connected current control mode to DC bus voltage support mode, thereby making the switch of the energy storage converter from grid-connected current control mode to DC bus voltage support mode smooth and safe.

[0114] For example, the current operating status may include the current current setpoint, the current modulation output, the controller integral term of the current energy storage converter, the current phase, and the current DC bus voltage. The current setpoint is the output current reference value that the energy storage converter is tracking before the sag. It is either a current command issued by the controller to the energy storage converter (in grid-connected current control mode) or a target value calculated by the internal controller of the energy storage converter. When the sag is triggered, the controller latches the current setpoint so that there is a reference when switching to the DC bus voltage support mode. The current modulation output is the PWM duty cycle or modulation signal of the energy storage converter, which can be read by the controller or obtained through communication. It is used to initialize the controller parameters of the energy storage converter after the switch. The current controller integral term of the energy storage converter is the cumulative value of the integral part of the PI (or PID) controller inside the energy storage converter. The controller can latch the integral term before the mode switch so that the integral calculation can continue after the switch to avoid abrupt changes. The current phase is the current grid phase calculated above (at the moment of sag triggering). It is used to maintain the phase continuity after the switch and prevent abrupt changes in the voltage source output. The current DC bus voltage is the voltage on the DC side of the energy storage converter, reflecting the energy storage status of the energy storage unit. The controller latches the current DC bus voltage so that it can be used as a reference for the DC bus voltage support mode during the switch to avoid output jumps.

[0115] The controller can write the above parameters into the cache register or state storage unit, and call them as initial conditions during subsequent control mode switching.

[0116] S420 determines the control target after the switch based on the current operating status.

[0117] For example, before the switchover, the control target of the energy storage converter is the active / reactive power control target. That is, the controller generates the corresponding current reference quantity (i.e., the current current setpoint) according to the preset active power command and reactive power command and controls the output of the energy storage converter. When the switchover process is triggered, the controller terminates the power control target and switches the control target to the DC bus voltage control target.

[0118] The controller can determine the current DC bus voltage in the current operating state as the target DC bus voltage after switching. Alternatively, the controller can also smoothly set the target DC bus voltage after switching based on the current DC bus voltage and the system's allowable fluctuation range, so that the target value after switching and the current DC bus voltage meet a preset rate of change limit.

[0119] This step enables the energy storage converter to switch its control target from power control to DC bus voltage control, ensuring that the energy storage converter can continuously and stably supply power to the DC bus after the mode switch, thus providing stable energy support for the output compensation voltage of the compensation converter.

[0120] S430 determines the control structure after the switch based on the control objective after the switch.

[0121] For example, before switching, the energy storage converter adopts a PQ control structure, that is, the controller uses active power and reactive power as the outer loop controlled variables. The power outer loop calculates the d-axis current reference value and q-axis current reference value according to the active power command and reactive power command, respectively. The current inner loop generates the modulation voltage command according to the d-axis current reference value and q-axis current reference value, and controls the output of the energy storage converter through PWM modulation.

[0122] When the switching process is triggered, the controller cancels the original power outer loop's regulation of active power and switches the controlled variable of the outer loop from active power to the DC bus target voltage (target value). The original current inner loop is retained as a fast adjustment loop, and a control structure of DC bus voltage outer loop and current inner loop is constructed. That is, after the switch, the controller collects the DC bus voltage (feedback value) in real time and constructs the DC bus voltage outer loop input based on the deviation between the target value and the feedback value. The outer loop calculates the d-axis current reference value based on the deviation. The q-axis current reference value can be kept at the latched value before the switch or set to zero according to the control requirements to reduce reactive power disturbances during the switch. The current inner loop calculates the d-axis voltage command and q-axis voltage command based on the deviation between the d-axis and q-axis current reference values ​​and the actual feedback current. The commands are then generated into drive signals through inverse coordinate transformation and PWM modulation to control the output of the energy storage converter.

[0123] S440 initializes the control parameters based on the current operating state, the control objective after the switch, and the control structure after the switch, thus obtaining the control parameters after the switch.

[0124] For example, the controller can use the actual output state at the switching moment as the initial operating point of the new controller for the energy storage converter to avoid sudden error changes when the new controller is put into operation. For the outer loop of the DC bus voltage, the controller can initialize the integral term of the outer loop of the DC bus voltage based on the d-axis current reference value in the current setpoint, so that the d-axis current value output by the new outer loop at the moment of activation is... With d-axis current reference value Equal: Assuming the outer loop of the DC bus voltage uses a PI regulator. ,in, This represents the deviation between the target DC bus voltage and the real-time DC bus voltage. , These represent the proportional coefficient and integral coefficient in the PI controller, respectively. Since the real-time DC bus voltage is the target DC bus voltage at the switching moment, we have... The controller can initialize the outer loop integral term to The q-axis current value output at the instant the new outer loop is engaged. It can be the q-axis current reference value in the current setpoint, or it can be initialized to 0.

[0125] For the inner current loop, the controller can retain or reset its integral term to match the voltage command output before the switch. For example, the initial value of the new inner loop integral term can be determined as the d-axis voltage command and q-axis voltage command latched before the switch.

[0126] The current modulation output and current phase can be used as the initial modulation output and initial phase of the new controller for the energy storage converter, respectively. The switched control parameters include the initial values ​​of the outer loop integral term, the inner loop integral term, and the d-axis current value. q-axis current value Initial modulation output, initial phase.

[0127] The above steps can effectively prevent sudden command jumps, integral saturation, and large output swings during mode switching, thereby improving the smoothness of control switching and the stability of system operation.

[0128] S450 sends the first mode switching command, the switched control target, the switched control structure, and the switched control parameters to the energy storage converter, so that the energy storage converter switches from the grid-connected current control mode to the DC bus voltage support mode.

[0129] For example, the controller can send the first mode switching command, the switched control target, the switched control structure, and the switched control parameters to the control execution unit of the energy storage converter through an internal control bus, communication interface, or dedicated signal channel.

[0130] After receiving the first mode switching command, the energy storage converter exits the original grid-connected current control mode PQ control and calls the switched control structure to establish a control loop with the DC bus voltage as the outer loop controlled variable and the d-axis and q-axis current as the inner loop controlled variables.

[0131] The energy storage converter writes the target DC bus voltage into the outer voltage loop reference register, writes the initial value of the outer loop integral term into the integrator of the DC bus voltage regulator, and writes the initial value of the inner loop integral term into the d-axis current regulator and q-axis current regulator. The d-axis current value... and q-axis current value The initial modulation output is written to the modulation module at the inner current loop input terminal, and the initial phase is written to the coordinate transformation module. The energy storage converter starts operation with the current operating point as the initial state of the new control mode at the start of the switching process, thus avoiding output shocks caused by sudden changes in control objectives, control structure, and control parameters.

[0132] This step enables the mode switching command, along with the target, structure, and parameters required for the switch, to be issued simultaneously. This allows the energy storage converter to not only switch its operating mode but also to synchronously switch its control logic and control state, thus enabling a smooth and stable transition of the energy storage converter from grid-connected current control mode to DC bus voltage support mode.

[0133] S500 acquires the load-side voltage amplitude and determines whether compensation is successful based on the load-side voltage amplitude and the grid-side rated voltage. During voltage sag compensation, the main circuit breaker is in the open state and the bypass thyristor is in the off state to isolate the grid side from the load side.

[0134] For example, the controller can obtain the load-side voltage amplitude using the same method as for obtaining the grid-side voltage amplitude. The successful compensation range, such as 0.95pu~1.05pu, can be set through the controller's parameter configuration module, where pu is a per-unit value. The controller can then calculate the per-unit value of the load-side voltage based on the load-side voltage amplitude and the grid-side rated voltage. ,in, This represents the per-unit value of the load-side voltage. This represents the voltage amplitude on the load side.

[0135] The controller can determine whether the per-unit value of the load-side voltage is within the range for successful compensation. For example, if If the compensation is successful, it can be determined that the compensation was successful; or It can be determined that the compensation has not been completed or has been overcompensated.

[0136] The controller can convert the judgment result into a logic signal to trigger subsequent control actions (such as maintaining compensation or preparing to exit compensation). It samples the load-side voltage in real time and dynamically updates the compensation status to cope with changes in grid voltage.

[0137] During voltage sag compensation, the main circuit switch is in the open state, the bypass thyristor is in the off state, the grid side and the load side are isolated and no circuit is formed.

[0138] This step enables dynamic monitoring of load voltage recovery, providing a basis for maintaining or discontinuing the compensation process.

[0139] After successful compensation, the S600 continuously acquires the voltage amplitude on the grid side. If the voltage amplitude on the grid side is greater than the voltage threshold, it determines that the grid voltage has returned to normal.

[0140] For example, the controller monitors the grid voltage in real time and calculates the corresponding grid-side voltage amplitude. It then compares the calculated grid-side voltage amplitude at each moment with a voltage threshold. This indicates that the grid voltage has returned to normal. The controller can output the judgment result as a flag signal to notify subsequent control actions.

[0141] This step enables dynamic monitoring of the grid voltage recovery status, providing triggering conditions for compensation withdrawal and system mode switching.

[0142] When the grid voltage returns to normal, the S700 controls the bypass thyristor to conduct briefly and controls the main circuit switch to close during the conduction period of the bypass thyristor; after the main circuit switch is closed, it controls the bypass thyristor to turn off and generates a second mode switching command and a shutdown command.

[0143] For example, the controller continuously monitors the flag signal. When the flag signal indicates that the grid voltage has returned to normal, the controller can send a trigger pulse to the bypass thyristor to briefly turn it on, establishing a transition current-carrying branch. At the moment the bypass thyristor turns on or after a short delay, the controller sends a closing command to the actuator of the main circuit switch. The actuator drives the main circuit switch to close, restoring the circuit to the normal grid connection path.

[0144] After the controller determines that the main circuit breaker is closed through the auxiliary contact, it stops sending trigger pulses to the bypass thyristor, causing the bypass thyristor to turn off. At this time, the main circuit breaker is closed, the bypass thyristor is turned off, and the grid side is connected to the load side.

[0145] After the controller determines that the main circuit switch is closed through the auxiliary contacts, it can generate a second mode switching command and a shutdown command.

[0146] In one possible implementation, before the main circuit breaker is closed, it is also configured as follows: S701, obtain the restored grid-side voltage amplitude and load-side voltage amplitude, as well as the restored grid phase and load phase.

[0147] For example, similarly, the controller can calculate the restored grid-side voltage amplitude and grid phase, as well as the restored load-side voltage amplitude and load phase, by executing steps S110 to S130.

[0148] S702, calculate the amplitude error based on the restored grid-side voltage amplitude and load-side voltage amplitude, and calculate the phase error based on the restored grid phase and load phase.

[0149] For example, the formula for calculating the amplitude error is as follows: ,in, This indicates the magnitude of the restored grid-side voltage. This indicates the magnitude of the load-side voltage after recovery. If This indicates that the load-side voltage amplitude is too low, and the output voltage of the compensation converter can be adjusted upwards; if This indicates that the voltage amplitude on the load side is too high, and the output voltage of the compensation converter can be adjusted downwards.

[0150] The formula for calculating phase error is as follows: ,in, Indicates the restored power grid phase. This indicates the load phase after recovery. If This indicates that the load phase is lagging, and the output phase of the compensating converter can catch up; if This indicates that the load phase is ahead, and the output phase of the compensation converter can be adjusted backward.

[0151] S703 generates adjustment commands based on amplitude error and phase error.

[0152] For example, the controller can As the input for the output voltage regulation of the compensation converter, As the input to the output phase adjustment of the compensation converter, the voltage correction amount of the compensation converter is calculated through the adjustment algorithm. and phase correction ,Right now , ,in, , These are the amplitude regulator parameters. , These are the parameters for the phase adjuster. Adjustment commands can include voltage correction amounts. and phase correction .

[0153] S704 controls the compensation converter to adjust the output voltage and output phase according to the adjustment command.

[0154] For example, the controller can adjust the voltage correction amount. and phase correction The output voltage reference value and output phase reference value of the compensation converter are updated so that the output voltage of the compensation converter gradually approaches the voltage on the grid side. , ,in, To compensate for the original output voltage reference value of the converter, To compensate for the original output phase reference value of the converter.

[0155] The compensated converter is based on the updated output voltage reference value. and output phase reference value The PWM modulation signal is adjusted to gradually change the amplitude and phase of its output voltage, thereby making the voltage state at both ends of the main circuit switch gradually more consistent, so as to reduce the impact at the moment of closing.

[0156] S705: Obtain the voltage difference and phase difference across the main circuit switch, and determine whether the closing conditions are met based on the voltage difference and phase difference across the main circuit switch. The closing conditions include that the voltage difference across the main circuit switch is less than the amplitude difference threshold, and the phase difference across the main circuit switch is less than the phase difference threshold.

[0157] For example, during the process of the compensation converter completing dynamic adjustment, the controller can continuously acquire the voltage amplitude of the grid side and the voltage amplitude of the load side, as well as the grid phase and the load phase, and calculate the difference between the voltage amplitude of the grid side and the voltage amplitude of the load side, which is the voltage difference across the main circuit switch, and calculate the difference between the grid phase and the load phase, which is the phase difference across the main circuit switch.

[0158] The amplitude difference threshold can be set to 5%~10% of the rated voltage on the grid side; the phase difference threshold can be set according to the system's allowable synchronization deviation, such as 5°~10°. The controller can compare the voltage difference across the main switch with the amplitude difference threshold, and compare the phase difference across the main switch with the phase difference threshold. If the voltage difference across the main switch is less than the amplitude difference threshold, and the phase difference across the main switch is less than the phase difference threshold, the closing condition can be determined to be met.

[0159] If the closing conditions are not met, the controller can continue to generate adjustment commands based on the amplitude error and phase error, and control the compensation converter to continue adjusting the output voltage and output phase until the closing conditions are met at both ends of the main circuit switch.

[0160] These steps can gradually eliminate the amplitude and phase deviations at both ends of the main circuit switch after the power grid is restored, reduce the inrush current and transient disturbances when the main circuit switch is closed, and achieve a smooth recovery of the main circuit.

[0161] In one possible implementation, step S700, controlling the bypass thyristor to conduct briefly and controlling the main circuit switch to close during the bypass thyristor's conduction period, is configured as follows: When the grid voltage returns to normal, S710 generates a trigger signal after determining that the closing conditions are met, and outputs the trigger signal to the drive circuit of the bypass thyristor.

[0162] For example, when the flag signal indicates that the grid voltage has returned to normal, after confirming that the closing conditions are met, the controller can generate a corresponding trigger signal based on the flag signal and immediately output the trigger signal to the drive circuit of the bypass thyristor.

[0163] After receiving the trigger signal, the drive circuit isolates, shapes, and amplifies the signal to form a trigger pulse that meets the gate triggering conditions of the bypass thyristor. This trigger pulse is then applied between the gate and cathode of the bypass thyristor, causing it to switch from the off state to the on state, thus establishing a bypass conduction loop.

[0164] After the bypass thyristor in S720 is turned on, a closing command is generated and sent to the actuator of the main circuit breaker. The actuator then drives the main circuit breaker from the open state to the closed state according to the closing command.

[0165] For example, after confirming that the bypass thyristor is conducting and the closing conditions are met, the controller can generate a closing command and send the closing command to the actuator of the main circuit breaker. After receiving the closing command, the actuator drives the main circuit breaker to perform a closing action, changing the main circuit breaker from its original open state to a closed state, thereby connecting the main circuit.

[0166] After the controller outputs the closing command, it can confirm whether the main circuit breaker has completed the closing action through the auxiliary contacts. When the controller detects that the main circuit breaker status has changed from open to closed, it can determine that the main circuit breaker has successfully closed.

[0167] S730 stops outputting trigger signals to the drive circuit of the bypass thyristor after the main circuit switch changes from the open state to the closed state, so as to turn off the bypass thyristor.

[0168] Understandably, after the controller confirms the successful closing of the main circuit breaker via auxiliary contacts, it stops sending trigger signals to the drive circuit of the bypass thyristor and checks whether the branch current of the bypass thyristor crosses zero. If the branch current crosses zero, the controller can determine that the bypass thyristor has switched from the on state to the off state. Since the main circuit breaker has been connected, the branch current of the bypass thyristor gradually decreases and turns off when it crosses zero or falls below the current threshold, thereby restoring the composite switch from a short-term transition state to a normal power supply state where the main circuit breaker carries the load current.

[0169] These steps ensure that the main circuit recovery process has a current transition path and voltage synchronization basis, avoiding inrush current, voltage fluctuations, and system oscillations caused by direct closing of the main circuit switch. The bypass thyristor only conducts briefly during the closing transition and stops triggering and turns off after the main circuit switch is closed, improving the smoothness of the main circuit recovery process, closing reliability, and system operational stability.

[0170] In one possible implementation, after the main circuit breaker is opened or closed, it is further configured as follows: S101, stop outputting trigger signals to the drive circuit of the bypass thyristor; acquire the branch current of the bypass thyristor and determine whether the branch current of the bypass thyristor crosses zero; S102, if the branch current of the bypass thyristor crosses zero, determine that the bypass thyristor is turned off. The zero-crossing is determined by the branch current changing from positive to negative, from negative to positive, or the branch current falling below the current threshold.

[0171] For example, once the controller determines that the main circuit breaker is open / closed via its auxiliary contacts, it stops outputting trigger signals to the drive circuit of the bypass thyristor. The controller can acquire the branch current of the bypass thyristor in real time using a current sensor, current transformer, or Hall effect current detection element. The controller can then use the branch current at the current sampling moment... Branch current at the previous sampling time The comparison is performed; if the branch current at the previous sampling time is positive and the branch current at the current sampling time is negative, that is... , This indicates that the branch current has changed from positive to negative, indicating a zero-crossing. If the branch current at the previous sampling time was negative and the branch current at the current sampling time is positive, then... , This indicates that the branch current changes from negative to positive, indicating a zero-crossing; if the branch current at the current sampling time... If the absolute value is lower than the preset current threshold, it indicates that the branch current has decayed to near zero, and it can also be determined that the branch current has crossed zero. The current threshold can be set according to the sensor accuracy, sampling noise level and thyristor holding current requirements to avoid misjudgment due to noise disturbance.

[0172] After detecting that the branch current meets the zero-crossing condition, the controller can determine that the current in the bypass thyristor has dropped below the holding current, and the bypass thyristor has lost the continuous conduction condition, thus determining that the bypass thyristor is turned off. Detecting whether the bypass thyristor is turned off can be used to confirm whether the bypass branch has exited the conducting state, thereby determining whether isolation between the power grid and the load has been completed, or to determine whether the composite switch has completed the back-switching during the recovery phase.

[0173] S800, according to the shutdown command, controls the compensation converter to stop outputting compensation voltage and controls the compensation switch to open; according to the second mode switching command, controls the energy storage converter to switch from DC bus voltage support mode to grid-connected current control mode.

[0174] For example, the controller can send a shutdown command to the compensation converter, instructing it to stop outputting the compensation voltage, and simultaneously send a disconnect command to the actuator of the compensation switch, which drives the compensation switch to disconnect. After receiving the shutdown command, the compensation converter exits its current operating state, stops injecting voltage, and enters a shutdown or hibernation mode, thereby safely terminating the sag compensation process.

[0175] After the compensated converter stabilizes and shuts down, the controller, according to the second mode switching command, switches the energy storage converter from DC bus voltage support mode back to grid-connected current control mode, while simultaneously restoring the original PQ control. Upon receiving the second mode switching command, the energy storage converter switches its control algorithm, smoothly transitioning from DC bus voltage support mode back to grid-connected current control mode, and continues to operate according to the normal energy storage control strategy, realizing the conventional grid-connected charging and discharging functions of the energy storage device.

[0176] The controller controls the safe shutdown of the compensation converter through sequential instructions and coordinates the mode switching of the energy storage converter, which facilitates the smooth transition of the system after the grid voltage is restored. It terminates the compensation output and restores the normal operation of the energy storage, realizing a complete closed loop of temporary compensation and system continuity.

[0177] Please see Figure 3 This application also provides a control method for an energy storage type voltage sag compensation device. The energy storage type voltage sag compensation device 100 includes a power execution unit 10, which includes an energy storage unit 17, an energy storage converter 16, a compensation converter 15, an injection transformer 13, a composite switch, an energy storage switch 18, and a compensation switch 14. The method includes: Obtain the voltage amplitude on the grid side. If the voltage amplitude on the grid side is less than the voltage threshold, it is determined that a voltage sag has occurred on the grid. The voltage threshold is N times the rated voltage on the grid side, where N is less than 1. In the event of a voltage dip in the power grid, the bypass thyristor in the control composite switch is briefly turned on, and the main switch in the control composite switch is turned off during the period when the bypass thyristor is turned on; after the main switch is turned off, the bypass thyristor is turned off, and a first mode switching command is generated. The depth of sag is determined based on the voltage amplitude and rated voltage of the grid side, and a compensation voltage command is generated based on the depth of sag. The control compensation switch is closed, and according to the compensation voltage command, the control compensation converter outputs compensation voltage to the load side through the injection transformer; according to the first mode switching command, the control energy storage converter switches from grid-connected current control mode to DC bus voltage support mode. The load-side voltage amplitude is obtained, and the successful compensation is determined based on the load-side voltage amplitude and the grid-side rated voltage. During the voltage sag compensation period, the main circuit switch is in the open state and the bypass thyristor is in the off state to isolate the grid side from the load side. After successful compensation, the voltage amplitude on the grid side is continuously acquired. If the voltage amplitude on the grid side is greater than the voltage threshold, it is determined that the grid voltage has returned to normal. When the grid voltage returns to normal, the bypass thyristor is briefly turned on, and the main circuit switch is closed during the period when the bypass thyristor is turned on; after the main circuit switch is closed, the bypass thyristor is turned off, and a second mode switching command and a shutdown command are generated. According to the shutdown command, the compensation converter is controlled to stop outputting compensation voltage and the compensation switch is controlled to open; according to the second mode switching command, the energy storage converter is controlled to switch from DC bus voltage support mode to grid-connected current control mode.

[0178] It should be noted that the information interaction and execution process of the above methods are based on the same concept as the device embodiments of this application. For details on their specific functions and technical effects, please refer to the device embodiments section, and they will not be repeated here.

[0179] This application also provides an electronic device, which may include a controller 20. The electronic device of this embodiment includes: at least one processor, at least one memory, and a computer program stored in the at least one memory and executable on the at least one processor. When the processor executes the computer program, it causes the electronic device to implement the steps in any of the above-described control method embodiments for energy storage type voltage sag compensation devices, or causes the electronic device to implement the functions of each unit in the above-described device embodiments.

[0180] For example, the computer program may be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete this application. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in the electronic device.

[0181] The electronic device may be a combination board of FPGA (such as Xilinx Artix-7) and DSP (such as TI TMS320F28388), an industrial-grade PLC control system, etc. This electronic device may include, but is not limited to, processors and memory, and may include more or fewer components, or combinations of certain components, or different components. For example, it may also include input / output devices, network access devices, buses, etc.

[0182] The processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0183] In some embodiments, the memory may be an internal storage unit of the electronic device, such as a hard drive or RAM. In other embodiments, the memory may be an external storage device of the electronic device, such as a plug-in hard drive, smart memory card (SMC), secure digital card (SD) card, flash card, etc. Furthermore, the memory may include both internal and external storage units of the electronic device. The memory is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory can also be used to temporarily store data that has been output or will be output.

[0184] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0185] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. An energy storage type voltage sag compensation device, characterized by, include: The power execution unit includes an energy storage unit, an energy storage converter, a compensation converter, an injection transformer, a composite switch, an energy storage switch, and a compensation switch. The composite switch includes a main circuit switch and a bypass thyristor. One side of the main circuit switch is connected to the grid side, and the other side is connected to the series winding of the injection transformer. The series winding of the injection transformer is connected to the load side, forming a main circuit. The bypass thyristor is connected in parallel on both sides of the main circuit switch, forming the composite switch. One side of the energy storage switch is connected to the AC side of the energy storage converter, and the other side is connected to the grid side. The DC side of the energy storage converter is connected to the DC bus. The energy storage unit is connected to the DC bus. The converter-side winding of the injection transformer is connected to one side of the compensation switch, and the other side of the compensation switch is connected to the AC side of the compensation converter. The DC side of the compensation converter is connected to the DC bus. The controller is configured as follows: Obtain the voltage amplitude on the grid side. If the voltage amplitude on the grid side is less than a voltage threshold, determine that a voltage sag has occurred on the grid. The voltage threshold is N times the rated voltage on the grid side, where N is less than 1. In the event of a voltage dip in the power grid, the bypass thyristor in the composite switch is briefly turned on, and the main switch in the composite switch is turned off during the period when the bypass thyristor is turned on; after the main switch is turned off, the bypass thyristor is turned off, and a first mode switching command is generated. The sag depth is determined based on the grid-side voltage amplitude and the grid-side rated voltage, and a compensation voltage command is generated based on the sag depth. The compensation switch is closed, and the compensation converter is controlled to output compensation voltage to the load side through the injection transformer according to the compensation voltage command; the energy storage converter is controlled to switch from grid-connected current control mode to DC bus voltage support mode according to the first mode switching command. The load-side voltage amplitude is obtained, and the compensation is determined to be successful based on the load-side voltage amplitude and the grid-side rated voltage. During the voltage sag compensation period, the main circuit switch is in the open state and the bypass thyristor is in the off state to isolate the grid side from the load side. After successful compensation, the voltage amplitude on the grid side is continuously acquired. If the voltage amplitude on the grid side is greater than the voltage threshold, it is determined that the grid voltage has returned to normal. When the grid voltage returns to normal, the bypass thyristor is briefly turned on, and the main circuit switch is closed during the period when the bypass thyristor is turned on; after the main circuit switch is closed, the bypass thyristor is turned off, and a second mode switching command and a shutdown command are generated. According to the shutdown command, the compensation converter is controlled to stop outputting the compensation voltage, and the compensation switch is controlled to open; according to the second mode switching command, the energy storage converter is controlled to switch from DC bus voltage support mode to grid-connected current control mode.

2. The energy storage type voltage sag compensation device as described in claim 1, characterized in that, The acquisition of the grid-side voltage amplitude is configured as follows: Acquire the three-phase voltage signal from the grid side, and calculate the current grid phase based on the three-phase voltage signal from the grid side using a phase-locked loop; Based on the current grid phase, the three-phase voltage signal on the grid side is subjected to coordinate transformation to obtain the d-axis voltage component and the q-axis voltage component; wherein, the d-axis voltage component and the q-axis voltage component are voltage components in the dq coordinate system; The voltage amplitude on the grid side is calculated based on the d-axis voltage component and the q-axis voltage component.

3. The energy storage type voltage sag compensation device as described in claim 1, characterized in that, The control of the bypass thyristor in the composite switch to be briefly turned on, and the control of the main switch in the composite switch to be turned off during the period when the bypass thyristor is turned on, is configured as follows: When a voltage dip occurs in the power grid, a trigger signal is generated and output to the drive circuit of the bypass thyristor; wherein, the drive circuit applies a trigger pulse to the bypass thyristor according to the trigger signal, so that the bypass thyristor switches from the off state to the on state; After the bypass thyristor is turned on, a tripping command is generated and sent to the actuator of the main circuit switch; wherein, the actuator drives the main circuit switch from a closed state to an open state according to the tripping command; After the main circuit switch changes from the closed state to the open state, the output of trigger signal to the drive circuit of the bypass thyristor is stopped, so as to turn off the bypass thyristor.

4. The energy storage type voltage sag compensation device as described in claim 2, characterized in that, The step of generating a compensation voltage command based on the sag depth is configured as follows: If the sag depth is less than the depth threshold, a compensation voltage command corresponding to the in-phase compensation is generated based on the grid-side rated voltage and the grid-side voltage amplitude. If the sag depth is greater than or equal to the depth threshold, a compensation voltage command corresponding to full compensation is generated based on the grid-side voltage amplitude and the current grid phase.

5. The energy storage type voltage sag compensation device as described in claim 4, characterized in that, The step of generating a compensation voltage command corresponding to in-phase compensation based on the grid-side rated voltage and the grid-side voltage amplitude is configured as follows: Calculate the compensation voltage based on the grid-side rated voltage and the grid-side voltage amplitude; A compensation voltage command is generated based on the compensation voltage and the current grid phase.

6. The energy storage type voltage sag compensation device as described in claim 4, characterized in that, The step of generating a compensation voltage command corresponding to full compensation based on the grid-side voltage amplitude and the current grid phase is configured as follows: Obtain the grid-side voltage and the corresponding grid phase before the voltage sag, and calculate the voltage phasor before the voltage sag based on the grid-side voltage and the grid phase before the voltage sag. Calculate the residual voltage phasor of the power grid based on the voltage amplitude on the grid side and the current grid phase; The compensation voltage is calculated based on the voltage phasor before the voltage dip and the residual voltage phasor of the power grid through the phasor difference relationship. Calculate the compensation voltage phase based on the grid-side voltage before the voltage sag, the grid-side voltage amplitude before the voltage sag, and the current grid phase; The compensation voltage command is generated based on the compensation voltage and the compensation voltage phase.

7. The energy storage type voltage sag compensation device as described in claim 1, characterized in that, The step of controlling the energy storage converter to switch from grid-connected current control mode to DC bus voltage support mode according to the first mode switching command is configured as follows: In response to the first mode switching command, the current running state is latched; Based on the current operating status, determine the control target after the switch; Based on the control objective after the switch, determine the control structure after the switch; Based on the current operating state, the switched control objective, and the switched control structure, the control parameters are initialized to obtain the switched control parameters; The first mode switching command, the switched control target, the switched control structure, and the switched control parameters are sent to the energy storage converter so that the energy storage converter switches from the grid-connected current control mode to the DC bus voltage support mode.

8. The energy storage type voltage sag compensation device as described in claim 2, characterized in that, Before the main circuit switch is closed, it is also configured to: Obtain the restored voltage amplitude on the grid side and the voltage amplitude on the load side, as well as the restored grid phase and load phase; Based on the restored grid-side voltage amplitude and load-side voltage amplitude, the amplitude error is calculated, and based on the restored grid phase and load phase, the phase error is calculated. An adjustment command is generated based on the amplitude error and the phase error; According to the adjustment command, the compensation converter is controlled to adjust the output voltage and output phase; The voltage difference and phase difference across the main circuit switch are obtained, and the closing conditions are determined based on the voltage difference and phase difference across the main circuit switch. The closing conditions include the voltage difference across the main circuit switch being less than the amplitude difference threshold and the phase difference across the main circuit switch being less than the phase difference threshold.

9. The energy storage type voltage sag compensation device as described in claim 8, characterized in that, The control of briefly turning on the bypass thyristor and closing the main circuit switch during the bypass thyristor's conduction period is configured as follows: When the grid voltage returns to normal, and the closing conditions are met, a trigger signal is generated and output to the drive circuit of the bypass thyristor. After the bypass thyristor is turned on, a closing command is generated and sent to the actuator of the main circuit switch; wherein, the actuator drives the main circuit switch from the open state to the closed state according to the closing command; After the main circuit switch changes from the open state to the closed state, the output of trigger signals to the drive circuit of the bypass thyristor is stopped, so as to turn off the bypass thyristor.

10. The energy storage type voltage sag compensation device as described in claim 1, characterized in that, After the main circuit switch is opened or closed, it is further configured to: Stop outputting trigger signals to the drive circuit of the bypass thyristor; obtain the branch current of the bypass thyristor and determine whether the branch current of the bypass thyristor has crossed zero. If the branch current of the bypass thyristor crosses zero, the bypass thyristor is determined to be turned off; wherein, the zero crossing is determined by the branch current changing from positive to negative, from negative to positive, or the branch current falling below a current threshold.

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