A high-low voltage ride-through control system for a flywheel energy storage device

Abstract

This invention discloses a high-low voltage ride-through coordinated control system for a flywheel energy storage device. The grid-side converter of the flywheel energy storage device operates in constant voltage mode. When the grid voltage reaches the high-low voltage ride-through threshold, it limits active power and maximizes reactive power output to support the grid. The generator-side converter operates in constant power mode. When the DC bus voltage instability reaches the threshold, it switches to constant voltage mode and simultaneously limits the upper limit of active power. After the grid voltage recovers, the grid-side converter and the generator-side converter sequentially resume their initial operating modes. This invention achieves automatic coordination and control without adding additional coordination and control equipment, utilizing the sampling and control systems of the generator-side converter and the grid-side converter themselves. This ensures that the flywheel energy storage device has the ability to remain connected to the grid and operate continuously even when the grid connection point voltage experiences sudden changes within the region.

Description

Technical Field

[0001] This invention relates to a high and low voltage ride-through control system for a flywheel energy storage device, belonging to the field of power electronics technology. Background Technology

[0002] Driven by the national strategic goals of carbon peaking and carbon neutrality, energy storage, as a crucial technology and fundamental equipment supporting the new power system, is inevitably developing on a large scale. Among various energy storage methods, flywheel energy storage has advantages over battery energy storage and supercapacitor energy storage, such as a high number of charge-discharge cycles, near-zero maintenance, and the elimination of complex fire suppression systems. Therefore, its proportion in subsequent large-scale energy storage applications will significantly increase.

[0003] According to relevant national standards, when the grid connection voltage changes abruptly within the region, the energy storage system should have the ability to operate continuously without disconnecting from the grid. However, there are currently almost no applications of high-power flywheel energy storage devices in China. When proposing high and low voltage ride-through requirements for flywheel energy storage devices, there is a lack of collaborative control logic between the machine-tested converter and the grid-side converter. For example, CN 104682764 A only studies the control of active and reactive power of the grid-side converter, which is not applicable to energy storage systems that require both grid-side and machine-side converters to participate in high and low voltage ride-through power control. CN 115051390 A describes generating power device pulse signals based on the output voltage reference value and zero-sequence voltage to achieve power distribution and ensure the system's low voltage ride-through capability, but it does not involve the collaborative control logic between the machine-tested converter and the grid-side converter. Summary of the Invention

[0004] This invention provides a high-low voltage ride-through control system for a flywheel energy storage device, which solves the problem of insufficient control strategies for high-power flywheel energy storage devices when grid voltage changes suddenly, as disclosed in the background art. It eliminates the need for additional coordination control equipment and utilizes the device's own sampling and control system to achieve engineering applications.

[0005] To solve the above-mentioned technical problems, the present invention addresses these problems through the following technical solution:

[0006] A high- and low-voltage ride-through control system for a flywheel energy storage device monitors the 6kV~35kV power grid in real time. When the voltage of the 6kV~35kV power grid changes abruptly in the region and reaches the start threshold of high-voltage ride-through or low-voltage ride-through, the system controls the flywheel energy storage device to generate or absorb reactive power to support the power grid, ensuring that it does not disconnect from the grid and operates continuously.

[0007] A high-low voltage ride-through control system for a flywheel energy storage device includes a step-up transformer, a grid-side converter, and a generator-side converter. The grid-side converter has a rated voltage of 400V and is connected to a 6kV~35kV power grid through the step-up transformer. The DC side of the generator-side converter is connected to the grid-side converter, and the AC side is connected to the flywheel energy storage device.

[0008] Step-up transformer 1 boosts the 400V voltage to 6kV~35kV.

[0009] The grid-side converter includes an AC switch QF1, a charging circuit, a filtering circuit, a first bidirectional converter unit Q1, a first DC support capacitor C1, and a DC output switch QF2. The AC switch QF1 is a three-phase switch. The charging circuit includes a charging switch K1 and a charging resistor. The charging switch K1 is a three-phase switch, and each of the three phases of the charging switch K1 is connected to a charging resistor. The filtering circuit includes a filtering resistor RC1 and a filtering inductor L1. The first DC support capacitor C1 is connected in parallel across the two ends of the first bidirectional converter unit Q1. The filtering inductor L1 is connected to the first bidirectional converter unit Q1. The AC switch QF1 is connected in series with the filtering inductor L1. The charging circuit is connected in parallel with the AC switch QF1.

[0010] The machine-side converter includes a second bidirectional converter unit Q2, a second DC support capacitor C2, and an AC output switch QF3;

[0011] The DC output switch QF2 is a bidirectional switch and is connected to the DC side of the machine-side converter. The second DC support capacitor C2 is connected in parallel across the two ends of the second bidirectional converter unit Q2. The AC output switch QF3 is connected between the second bidirectional converter unit Q2 and the flywheel energy storage device.

[0012] The flywheel energy storage device includes a magnetic levitation device and the flywheel body.

[0013] The control system of the grid-side converter includes a positive and negative sequence calculator, a detector, a first current controller, and a first signal generator;

[0014] The positive / negative sequence calculator is connected to the input terminal of the step-up transformer. The calculator separates the negative sequence component e of the 400V mains voltage. a and the positive-order component e b Negative-order component e a and the positive-order component e b As input to the detector;

[0015] The judge is based on the negative-order component e a and the positive-order component e b To determine whether to enter or exit high / low voltage ride-through, when the per-unit value U of the 400V mains voltage is... T≥1.1, enters high-voltage ride-through; when the per-unit value U of the 400V mains voltage. T ≤0.85, enter low-pressure ride-through;

[0016] Preferably, the high-voltage ride-through initiation threshold is 130%Un, and the low-voltage ride-through initiation threshold is 85%Un, where Un is the rated voltage value of 400V.

[0017] If the detector determines that a low-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (1) or (2). T The reactive current I T Input to the first signal generator:

[0018] When 0.2 T ≤0.85, (1)

[0019] When U T ≤0.2, (2)

[0020] U T This indicates the per-unit voltage value at the grid connection point of the energy storage converter;

[0021] I N Indicates the rated current of the energy storage converter;

[0022] If the detector determines that a high-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (3). T The signal is transmitted to the first signal generator:

[0023] (3)

[0024] The first signal generator is used to generate a drive pulse signal for the first bidirectional converter unit Q1; the drive pulse signal is a PWM turn-on signal, which is used to control the switching transistor of the first bidirectional converter unit Q1 to turn on, and the grid-side converter sends reactive current to the grid side.

[0025] The control system of the machine-side converter includes a voltage controller, an output limiter, a second current controller, and a second signal generator. The voltage controller monitors and controls the DC-side voltage, outputs the d-axis and q-axis reference currents Id-ref and Iq-ref from the second current controller, and transmits these reference currents to the output limiter. The output limiter restricts the d-axis reference current Id-ref from exceeding the output current I of the machine-side converter 3. 0， ​The output current I0 is fed into the second current controller; the second current controller outputs a voltage signal to form a PWM pulse based on the d-axis and q-axis reference currents Id-ref and Iq-ref, and sends it to the second signal generator; the second signal generator forms a PWM turn-on signal to control the switching transistor of the second bidirectional converter unit Q2 to turn on, thereby realizing the control of the DC side voltage.

[0026] The grid-side converter initially operates in constant voltage mode with a control voltage of U1. When the 400V grid voltage drops, the low-voltage ride-through function is activated, entering reactive power priority control mode. The active power reference current Idref output by the detector is recorded at this time, and active power output is stopped. The grid-side converter operates at a power level not exceeding 1.2 times its rated power value S. N The reactive power output ensures that the grid-side converter continues to operate and does not disconnect from the grid; the reactive power priority control mode is based on... Set the Idref value to 0, and only output the reactive reference current Iqref; where Idref and Iqref are the active reference current and reactive reference current output by the detector, and In is the rated current;

[0027] When an overvoltage occurs in the power grid, the grid-side converter activates its high-voltage ride-through function, enters reactive power priority control mode, records the active power reference current Idref output by the judgment device at this time and sets it to 0, and stops active power current output; the grid-side converter operates at a power level not exceeding 1.2 times the rated power value S. N Absorbing reactive power ensures that the converter continues to operate normally and does not disconnect from the grid.

[0028] The generator-side converter initially operates in constant power mode. When the DC-side voltage reaches the upper or lower limit, it switches from constant power to constant voltage mode (700V constant voltage mode). The voltage controller maintains the DC voltage at a given voltage value U2, and the output limiter limits the output current of the generator-side converter to I0, thereby limiting the active power output on the DC side to be less than or equal to P0. The DC voltage output in the constant voltage mode is maintained at a given voltage value U2. Wherein, P0 = U2I0, and P0 is a value less than the rated power of the generator-side converter.

[0029] When the grid-side converter determines that the grid voltage has recovered from a drop or rise, it exits the high and low voltage ride-through function, exits the reactive power priority control mode, restores the recorded active power reference current Idref, and limits the current rise rate to 50% to avoid over / under voltage in the DC system caused by the grid-side converter's current rise rate being higher than that of the generator-side converter.

[0030] When the active power output of the grid-side converter recovers, the DC voltage is forcibly controlled from the given voltage value U2 to U1; if the DC voltage remains below U3 for t seconds, the generator-side converter exits constant voltage mode and switches to constant power mode. Otherwise, it remains in constant voltage mode.

[0031] Among them, the value range of U3 is U1 < U3 < U2, which is used as a judgment condition. U1 is the control voltage of the grid-side converter operating in constant voltage mode (650V constant voltage).

[0032] The beneficial effects achieved by this invention are as follows: The high and low voltage ride-through control system of the flywheel energy storage device proposed in this invention realizes that there is no need for the operation and maintenance background to issue a general control command. It is automatically controlled synchronously and coordinated by the generator-side converter and the grid-side converter, ensuring that the flywheel energy storage device has the ability to operate continuously without disconnecting from the grid when the voltage at the grid connection point changes suddenly in the region. It fills the gap in the field of high and low voltage ride-through control of flywheel energy storage devices and facilitates engineering applications. Attached Figure Description

[0033] Figure 1 A schematic diagram of the high and low voltage ride-through control system for a flywheel energy storage device;

[0034] Figure 2 This is a structural diagram of a high-low voltage ride-through control system for a flywheel energy storage device.

[0035] Figure 3 A control logic for high and low voltage ride-through of the grid-side converter in a high and low voltage ride-through control system for a flywheel energy storage device;

[0036] Figure 4 This document describes the control logic for high and low voltage ride-through of the machine-side converter in a high and low voltage ride-through control system for a flywheel energy storage device. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0038] like Figure 1 As shown, a high and low voltage ride-through control system for a flywheel energy storage system is characterized by: real-time monitoring of the 6kV~35kV power grid; when a sudden change in the voltage of the 6kV~35kV power grid is detected in the region and reaches the start-up threshold of high voltage ride-through or low voltage ride-through, the flywheel energy storage system is controlled to generate or absorb reactive power to support the power grid, ensuring that it does not disconnect from the grid and operates continuously.

[0039] A high-voltage ride-through control system for a flywheel energy storage system includes a step-up transformer 1, a grid-side converter 2, and a generator-side converter 3. The grid-side converter 2 has a rated voltage of 400V and is connected to a 6kV~35kV power grid through the step-up transformer 1. The DC side of the generator-side converter 3 is connected to the grid-side converter 2, and the AC side is connected to the flywheel energy storage device 4. The high-voltage ride-through initiation threshold is 130%Un, and the low-voltage ride-through initiation threshold is 85%Un, where Un is the rated voltage value of 400V.

[0040] Step-up transformer 1 boosts the 400V voltage to 6kV~35kV.

[0041] like Figure 2 As shown, the grid-side converter 2 includes an AC switch QF1, a charging circuit, a filter circuit, a first bidirectional converter unit Q1, a first DC support capacitor C1, and a DC output switch QF2; the AC switch QF1 is a three-phase switch; the charging circuit includes a charging switch K1 and charging resistors, the charging switch K1 is a three-phase switch, and each of the three phases of the charging switch K1 is connected to a charging resistor (see attached diagram). Figure 2 The filter circuit (R1-R3) includes a filter resistor RC1 and a filter inductor L1; the first DC support capacitor C1 is connected in parallel across the two ends of the first bidirectional converter unit Q1, the filter inductor L1 is connected to the first bidirectional converter unit Q1, the AC switch QF1 is connected in series with the filter inductor L1, and the charging circuit is connected in parallel with the AC switch QF1.

[0042] The machine-side converter includes a second bidirectional converter unit Q2, a second DC support capacitor C2, and an AC output switch QF3;

[0043] The DC output switch QF2 is a bidirectional switch and is connected to the DC side of the machine-side converter. The second DC support capacitor C2 is connected in parallel across the two ends of the second bidirectional converter unit Q2. The AC output switch QF3 is connected between the second bidirectional converter unit Q2 and the flywheel energy storage device 4.

[0044] The flywheel energy storage device includes a magnetic levitation device and the flywheel body.

[0045] In power systems, asymmetrical voltage surges are the most common occurrence. The grid-side converter determines whether to enter or exit the high- and low-voltage ride-through function based on the degree of voltage drop or overvoltage. At the same time, it outputs a calculator to calculate the required active power setpoint and reactive power setpoint, and calculates the required active and reactive currents, and sends out the drive pulse signal of the bidirectional converter unit.

[0046] The generator-side converter control system is mainly used to monitor and control the DC bus voltage to prevent excessive energy output or absorption by the DC support capacitor, which could lead to system runaway. Once voltage recovery is detected, the system switches from constant voltage mode to constant power mode.

[0047] The control system of the grid-side converter 2 includes a positive and negative sequence calculator, a judgment unit, a first current controller, and a first signal generator;

[0048] The positive / negative sequence calculator is connected to the input terminal of step-up transformer 1. The positive / negative sequence calculator separates the negative sequence component e of the 400V mains voltage. a and the positive-order component e b Negative-order component e a and the positive-order component e b As input to the detector;

[0049] The judge is based on the negative order component e a and the positive-order component e b To determine whether to enter or exit high / low voltage ride-through, when the per-unit value U of the 400V mains voltage is... T ≥1.1, enters high-voltage ride-through; when the per-unit value U of the 400V mains voltage. T ≤0.85, enter low-pressure ride-through;

[0050] If the detector determines that a low-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (1) or (2). T The reactive current I T Input to the first signal generator:

[0051] When 0.2 T ≤0.85, (1)

[0052] When U T ≤0.2, (2)

[0053] U T This indicates the per-unit voltage value at the grid connection point of the energy storage converter;

[0054] I N Indicates the rated current of the energy storage converter;

[0055] If the detector determines that a high-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (3). T The signal is transmitted to the first signal generator:

[0056] (3)

[0057] The first signal generator is used to generate a drive pulse signal for the first bidirectional converter unit Q1; the drive pulse signal is a PWM turn-on signal, which is used to control the switching transistor of the first bidirectional converter unit Q1 to turn on, and the grid-side converter device 2 sends reactive current to the grid side;

[0058] ​The control system of the machine-side converter 3 includes a voltage controller, an output limiter, a second current controller, and a second signal generator. The voltage controller monitors and controls the DC-side voltage, outputs the d-axis and q-axis reference currents Id-ref and Iq-ref from the second current controller, and transmits the reference currents Id-ref and Iq-ref to the output limiter. The output limiter limits the d-axis reference current Id-ref from exceeding the output current I of the machine-side converter 3. 0， The output current I0 is fed into the second current controller; the second current controller outputs a voltage signal to form a PWM pulse based on the d-axis and q-axis reference currents Id-ref and Iq-ref, and sends it to the second signal generator; the second signal generator forms a PWM turn-on signal to control the switching transistor of the second bidirectional converter unit Q2 to turn on, thereby realizing the control of the DC side voltage.

[0059] The high-voltage ride-through initiation threshold is 130%Un, and the low-voltage ride-through initiation threshold is 85%Un, where Un is the rated voltage of 400V.

[0060] The grid-side converter 2 initially operates in constant voltage mode (650V constant voltage) with a control voltage of U1. When the 400V grid voltage drops, the low-voltage ride-through function is activated, entering reactive power priority control mode. The active power reference current Idref output by the detector is recorded at this time, and active power output is stopped. The grid-side converter 2 operates at a power level not exceeding 1.2 times its rated power value S. N The reactive power output ensures that the grid-side converter 2 continues to operate and does not disconnect from the grid; the reactive power priority control mode is based on... Set the Idref value to 0, and only output the reactive reference current Iqref; where Idref and Iqref are the active reference current and reactive reference current output by the detector, and In is the rated current;

[0061] When an overvoltage occurs in the power grid, grid-side converter 2 activates its high-voltage ride-through function, enters reactive power priority control mode, records the active power reference current Idref output by the judgment device at this time and sets it to 0, and stops the active power current output; grid-side converter 2 operates at a power level not exceeding 1.2 times the rated power value S N Absorbing reactive power ensures that the converter continues to operate normally and does not disconnect from the grid.

[0062] The generator-side converter 3 initially operates in constant power mode. When the DC-side voltage reaches the upper or lower limit, it switches from constant power to constant voltage mode (700V constant voltage mode). The voltage controller maintains the DC voltage at a given voltage value U2, and the output limiter limits the output current of the generator-side converter 3 to I0, thereby limiting the active power output on the DC side to be less than or equal to P0. The DC voltage output in the constant voltage mode is maintained at a given voltage value U2. Wherein, P0 = U2I0, and P0 is a value less than the rated power of the generator-side converter 3.

[0063] When the grid-side converter 2 determines that the grid voltage has recovered from a drop or rise, it exits the high and low voltage ride-through function, exits the reactive power priority control mode, restores the recorded active power reference current Idref, and limits the current rise rate to 50% to avoid over / under voltage in the DC system caused by the current rise rate of the grid-side converter being higher than that of the generator-side converter.

[0064] When the active power output of the grid-side converter 2 is restored, the DC voltage is forcibly controlled from the given voltage value U2 to U1; if the DC voltage remains below U3 for t seconds, the generator-side converter exits the constant voltage mode and switches to constant power mode. Otherwise, it remains in constant voltage mode.

[0065] Among them, the value range of U3 is U1 < U3 < U2, which is used as a judgment condition. U1 is the control voltage of the grid-side converter 2 when it is operating in constant voltage mode (650V constant voltage).

[0066] like Figure 3 The grid-side converter 2 initially operates in constant voltage mode, with a DC side control voltage of 650 V. It monitors the AC grid voltage in real time. When a voltage drop or overvoltage is detected, it activates the low-voltage or high-voltage ride-through function, entering reactive power priority control mode. It records the active power reference current value Idref1 at this time and stops active power output. Since the grid-side converter can operate under 1.2 times overload for 1 minute, it can further operate at no more than 1.2 times the rated power S. N The reactive power output supports the converter to continue working and not disconnect from the grid, but at the same time, it loses its ability to stabilize the DC bus voltage. Subsequently, the DC bus voltage drops or rises rapidly. The corresponding flywheel energy storage device experiences a voltage drop when it is in the charging state and a voltage rise when it is in the discharging state.

[0067] When the grid-side converter determines that the grid voltage has recovered from a drop or rise, it exits the high and low voltage ride-through function, restores the active power reference current Idref1, and limits the current rise rate to 50% to avoid over / under voltage in the DC system caused by the grid-side converter's current rise rate being higher than that of the generator-side converter.

[0068] like Figure 4The machine-side converter 3 shown operates in constant power mode, monitoring the DC bus voltage in real time. When the voltage rises to the upper limit of 720 V or falls to the lower limit of 500 V, it switches from constant power mode to constant voltage mode, controlling the voltage at 700 V and limiting the active power output of the DC side to no more than 100 kW.

[0069] Since the power of the generator-side converter 3 is limited to less than that of the grid-side converter 2, the grid-side converter 2 can further control the DC bus voltage from 700 V to 650 V. If the voltage controller of the generator-side converter 2 detects that the DC bus voltage drops below 680 V and remains below it for 2 seconds, the generator-side converter 3 exits the constant voltage mode and switches to constant power mode. If the 2-second period is less than 2 seconds, it remains in constant voltage mode to avoid misjudgments by the control system caused by voltage fluctuations.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, any technical solutions obtained by equivalent substitution or equivalent transformation without departing from the technical principle of the present invention should also be considered within the scope of protection of the present invention.

[0071] Similarly, it should be understood that, in order to streamline this disclosure and aid in understanding one or more of the various aspects of the invention, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0072] Those skilled in the art will understand that the modules, units, or groups of devices in the examples disclosed herein can be arranged in the device as described in this embodiment, or alternatively, can be located in one or more devices different from the device in this example. The modules in the foregoing examples can be combined into a single module or, in addition, can be divided into multiple sub-modules.

[0073] Those skilled in the art will understand that modules in the device of the embodiments can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or groups in the embodiments can be combined into a single module, unit, or group, and further, they can be divided into multiple sub-modules, sub-units, or sub-groups. Except where at least some of such features and / or processes or units are mutually exclusive, any combination can be used to combine all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or units of any method or device so disclosed. Unless expressly stated otherwise, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature that serves the same, equivalent, or similar purpose.

[0074] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0075] Furthermore, some of the embodiments described herein are methods or combinations of method elements that can be implemented by a processor of a computer system or by other means of performing the functions. Therefore, a processor having the necessary instructions for implementing the methods or method elements forms means for implementing the methods or method elements. Furthermore, the elements described herein in the apparatus embodiments are examples of means for implementing the functions performed by elements for the purposes of carrying out the invention.

[0076] The various techniques described herein can be implemented in combination with hardware or software, or a combination thereof. Thus, the methods and apparatus of the present invention, or certain aspects or portions thereof, can take the form of program code (i.e., instructions) embedded in a tangible medium, such as a floppy disk, CD-ROM, hard disk, or any other machine-readable storage medium, wherein when the program is loaded into and executed by a machine such as a computer, the machine becomes an apparatus for practicing the present invention.

[0077] When the program code is executed on a programmable computer, the computing device generally includes a processor, a processor-readable storage medium (including volatile and non-volatile memory and / or storage elements), at least one input device, and at least one output device. The memory is configured to store program code; the processor is configured to execute the system's methods according to instructions in the program code stored in the memory.

[0078] By way of example, and not limitation, computer-readable media include computer storage media and communication media. Computer storage media stores information such as computer-readable instructions, data structures, program modules, or other data. Communication media generally embodies computer-readable instructions, data structures, program modules, or other data in the form of modulated data signals such as carrier waves or other transmission mechanisms, and includes any information delivery medium. Any combination of the above is also included within the scope of computer-readable media.

[0079] As used herein, unless otherwise specified, the use of ordinal numbers such as “first,” “second,” “third,” etc., to describe ordinary objects merely indicates different instances of similar objects and is not intended to imply that the objects being described must have a given order in time, space, ordering, or any other manner.

[0080] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

Claims

1. A high-low voltage ride-through control system for a flywheel energy storage device, characterized in that: Real-time monitoring of the 6kV~35kV power grid; when a sudden change in voltage of the 6kV~35kV power grid is detected in the region and reaches the start threshold of high voltage ride or low voltage ride, the flywheel energy storage device is controlled to generate or absorb reactive power to support the power grid and achieve continuous operation without disconnecting from the grid. It includes a step-up transformer (1), a grid-side converter (2) and a machine-side converter (3); the grid-side converter (2) has a rated voltage of 400V and is connected to the 6kV~35kV power grid through the step-up transformer (1); the DC side of the machine-side converter (3) is connected to the grid-side converter (2), and the AC side is connected to the flywheel energy storage device (4). The step-up transformer (1) raises the voltage from 400V to 6kV~35kV; The control system of the grid-side converter (2) includes a positive and negative sequence calculator, a judgment unit, a first current controller and a first signal generator; The positive and negative sequence calculator is connected to the input terminal of the step-up transformer (1), and the positive and negative sequence calculator separates the negative sequence component e of the 400V grid voltage. a and the positive-order component e b Negative-order component e a and the positive-order component e b As input to the detector; The judge is based on the negative order component e a and the positive-order component e b To determine whether to enter or exit high / low voltage ride-through, when the per-unit value U of the 400V mains voltage is... T ≥1.1, enters high-voltage ride-through; when the per-unit value U of the 400V mains voltage. T ≤0.85, enter low-pressure ride-through; If the detector determines that a low-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (1) or (2). T The reactive current I T Input to the first signal generator: When 0.2 T ≤0.85, (1);​ This U T ≤0.2, (2); U T This indicates the per-unit voltage value at the grid connection point of the energy storage converter; I N Indicates the rated current of the energy storage converter; If the detector determines that a high-voltage ride-through has occurred, the first current controller obtains the reactive current I according to equation (3). T The signal is transmitted to the first signal generator: （3）； The first signal generator is used to generate a drive pulse signal for the first bidirectional converter unit Q1; the drive pulse signal is a PWM turn-on signal, which is used to control the switching transistor of the first bidirectional converter unit Q1 to turn on, and the grid-side converter device (2) sends reactive current to the grid side. The control system of the machine-side converter (3) includes a voltage controller, an output limiter, a second current controller, and a second signal generator. The voltage controller is used to monitor and control the DC-side voltage, output the d-axis and q-axis reference currents Id-ref and Iq-ref of the second current controller, and transmit the reference currents Id-ref and Iq-ref to the output limiter. The output limiter is used to limit the d-axis reference current Id-ref from exceeding the output current I of the machine-side converter (3) that is limited by the limiter. 0， The output current I0 is fed into the second current controller; the second current controller outputs a voltage signal to form a PWM pulse based on the d-axis and q-axis reference currents Id-ref and Iq-ref, and sends it to the second signal generator; the second signal generator forms a PWM turn-on signal to control the switching transistor of the second bidirectional converter unit Q2 to turn on, thereby realizing the control of the DC side voltage.

2. The high and low voltage ride-through control system for a flywheel energy storage device according to claim 1, characterized in that: The grid-side converter (2) includes an AC switch QF1, a charging circuit, a filter circuit, a first bidirectional converter unit Q1, a first DC support capacitor C1, and a DC output switch QF2; The AC switch QF1 is a three-phase switch; the charging circuit includes a charging switch K1 and a charging resistor. The charging switch K1 is a three-phase switch, and each of the three phases of the charging switch K1 is connected to a charging resistor. The filtering circuit includes a filtering resistor RC1 and a filtering inductor L1. The first DC support capacitor C1 is connected in parallel across the two ends of the first bidirectional converter unit Q1. The filtering inductor L1 is connected to the first bidirectional converter unit Q1. The AC switch QF1 is connected in series with the filtering inductor L1. The charging circuit is connected in parallel with the AC switch QF1. The machine-side converter (3) includes a second bidirectional converter unit Q2, a second DC support capacitor C2, and an AC output switch QF3; The DC output switch QF2 is a bidirectional switch. The DC output switch QF2 is connected to the DC side of the machine-side converter. The second DC support capacitor C2 is connected in parallel to both ends of the second bidirectional converter unit Q2. The AC output switch QF3 is connected between the second bidirectional converter unit Q2 and the flywheel energy storage device (4).

3. The high and low voltage ride-through control system for a flywheel energy storage device according to claim 1, characterized in that: The high-voltage ride-through initiation threshold is 130%Un, and the low-voltage ride-through initiation threshold is 85%Un, where Un is the rated voltage of 400V.

4. The high and low voltage ride-through control system for a flywheel energy storage device according to claim 1, characterized in that: The grid-side converter (2) initially operates in constant voltage mode with a control voltage of U1. When the 400V grid voltage drops, it activates the low-voltage ride-through function, enters the reactive power priority control mode, records the active power reference current Idref output by the judgment device at this time, and stops the active power output. The grid-side converter (2) operates at a voltage not exceeding 1.2 times its own rated power value S. N The reactive power output ensures that the grid-side converter (2) continues to operate and does not disconnect from the grid; the reactive power priority control mode is based on... Set the Idref value to 0, and only output the reactive reference current Iqref; where Idref and Iqref are the active reference current and reactive reference current output by the detector, and In is the rated current; When an overvoltage occurs in the power grid, the grid-side converter (2) activates the high-voltage ride-through function, enters the reactive power priority control mode, records the active power reference current Idref output by the judgment device at this time and sets it to 0, and stops the active power output; the grid-side converter (2) operates at a power level not exceeding 1.2 times the rated power value S N Absorbing reactive power ensures that the converter continues to operate normally and does not disconnect from the grid.

5. The high and low voltage ride-through control system for a flywheel energy storage device according to claim 1, characterized in that: The machine-side converter (3) initially operates in constant power mode. When the DC side voltage is detected to reach the upper or lower limit, it switches from constant power to constant voltage mode. The voltage controller controls the DC voltage to be maintained at the given voltage value U2. The output limiter limits the output current of the machine-side converter (3) to I0, and limits the active power output on the DC side to be less than or equal to P0. The DC voltage output in the constant voltage mode is maintained at the given voltage value U2. Wherein, P0=U2I0, and P0 is a value less than the rated power of the machine-side converter (3).

6. The high and low voltage ride-through control system for a flywheel energy storage device according to claim 1, characterized in that: When the grid-side converter (2) determines that the grid voltage has recovered from a drop or rise, it exits the high and low voltage ride-through function, exits the reactive power priority control mode, restores the recorded active power reference current Idref, and limits the current rise rate to 50% to avoid over / under voltage of the DC system due to the current rise rate of the grid-side converter being higher than that of the machine-side converter. When the active power output of the grid-side converter (2) is restored, the DC voltage is forcibly controlled from the given voltage value U2 to U1; if the DC voltage is maintained below U3 for t seconds, the machine-side converter exits the constant voltage mode and switches to the constant power mode; otherwise, it remains in the constant voltage mode. Among them, the value range of U3 is U1 < U3 < U2, and U1 is the control voltage of the grid-side converter (2) in constant voltage mode.

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