A flywheel energy storage multi-machine parallel current conversion device and control method

Abstract

The present invention discloses a flywheel energy storage multi-machine parallel converter and control method in the field of power electronics technology, including: a control unit, an input unit, a voltage unit and a plurality of power branch units, wherein the power branch unit is connected to the voltage unit, the voltage unit is connected to the input unit, the input unit is externally connected to an AC power grid, the control unit is connected to the input unit, the voltage unit and the plurality of power branch units, and when the control unit detects the presence of a faulty power branch unit, the grid-side converter in the faulty power branch unit is disconnected, the machine-side converter in the faulty power branch unit is controlled to operate in a constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side converter in other power branch units is controlled to operate in a constant power according to the issued quota dispatching instruction. The present invention utilizes converters and flywheels to store and release energy, thereby realizing reasonable resource allocation, grid stability and reasonable utilization of energy.

Description

Technical Field

[0001] The invention relates to a flywheel energy storage multi-machine parallel current conversion device and a control method, belonging to the technical field of power electronics. Background Art

[0002] With the increase in the proportion of large-scale renewable energy, the system inertia decreases, the system frequency regulation capability significantly declines, the frequency stability problem of the power grid becomes increasingly prominent, and the charging load of new energy electric vehicles also increases the difficulty of power grid regulation. The power system not only faces the problems of transmission, consumption and peak regulation, but also faces the challenge of insufficient frequency regulation capability. High-quality frequency regulation resources are urgently needed to participate in the power grid to maintain its safety and stability. The importance of energy storage system as a peak regulation means becomes more and more prominent.

[0003] The flywheel energy storage system mainly consists of three parts: flywheel motor, energy conversion system, and control management system. The flywheel motor exchanges energy with the power grid through the converter, storing or releasing energy according to demand. The converter realizes the two-way exchange of energy between the flywheel motor and the power grid. Currently, it is limited by the small power of a single flywheel and cannot meet the actual engineering application. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a flywheel energy storage multi-machine parallel converter device and a control method, which utilizes the converter device and the flywheel to store and release energy, thereby achieving reasonable resource allocation, grid stability and reasonable utilization of energy.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In the first aspect, the present invention provides a flywheel energy storage multi-machine parallel conversion device, comprising: a control unit, an input unit, a voltage unit and a plurality of power branch units, wherein the power branch unit is connected to the voltage unit, the voltage unit is connected to the input unit, the input unit is externally connected to an AC power grid, the control unit is connected to the input unit, the voltage unit and the plurality of power branch units, and when the control unit detects the presence of a faulty power branch unit, the grid-side conversion unit in the faulty power branch unit is disconnected, the machine-side conversion unit in the faulty power branch unit is controlled to operate in a constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side conversion units in other power branch units are controlled to operate at a constant power according to the issued rated scheduling instructions.

[0007] Furthermore, the power branch unit also includes an absorption unit, the energy storage unit and the absorption unit are connected to the machine-side converter unit, the machine-side converter unit is connected to the grid-side converter unit, and the grid-side converter unit is connected to the voltage unit via an AC busbar.

[0008] Furthermore, the grid-side converter unit includes an input switch QF1, an input switch QF1, a charging circuit, a filtering circuit, a first bidirectional converter unit Q1, a DC support capacitor C1, a discharge resistor R4, an output switch K3 and a fuse FU1. One end of the input switch QF1 is connected to the voltage unit via the AC bus, and the other end is connected to the charging circuit. The output end of the charging circuit is connected to the midpoint of each bridge arm of the first bidirectional converter unit Q1 via the filtering circuit. The two ends of the DC support capacitor C1 and the discharge resistor R4 are respectively connected to the positive and negative poles of the DC bus, and the DC bus is connected to the input end of the fuse FU1 via the output switch K3.

[0009] Furthermore, the machine-side converter unit includes a unidirectional converter unit Q2, a second bidirectional converter unit Q3, a DC support capacitor C2, a discharge resistor R5 and an output switch QF3. The two ends of the unidirectional converter unit Q2, the second bidirectional converter unit Q3, the DC support capacitor C2 and the discharge resistor R5 are respectively connected to the positive and negative poles of the DC bus. The midpoint of the unidirectional converter unit Q2 is connected to the corresponding absorption unit, and the midpoint of each bridge arm of the second bidirectional converter unit Q3 is connected to the input end of the output switch QF3. When the power branch unit fails, the energy storage unit releases energy through the second bidirectional converter unit Q3 and the unidirectional converter unit Q2.

[0010] Furthermore, each of the grid-side converter units is connected in sequence through optical fibers to form a closed loop, and each grid-side converter unit is capable of sending and receiving synchronization signals. When one of the grid-side converter units receives the synchronization signal abnormally, the next grid-side converter unit connected to it switches to the host and sends the synchronization signal.

[0011] Furthermore, when the control unit detects that the grid-side converter unit is operating in constant voltage mode, it controls the machine-side converter unit to operate in constant power mode; when the control unit detects that the machine-side converter unit is operating in constant voltage mode, it controls the grid-side converter unit to operate in constant power mode.

[0012] Furthermore, the machine-side converter unit is a four-arm converter, the first arm is a unidirectional converter unit, and the second to fourth arms are bidirectional converter units, all of which have two modes of operation: constant power mode operation and constant voltage mode operation. The constant power mode operation further includes constant power mode charging and constant power mode discharging, and each operation mode can be converted online.

[0013] Furthermore, when the control unit detects a fault in a certain energy storage unit, it controls the network-side converter unit of the branch to exit operation, controls the machine-side converter unit of the branch to operate in constant voltage mode, controls the first bridge arm of the machine-side converter unit of the branch to operate, and releases the energy of the branch energy storage unit; when the control unit detects a fault in any of the second bridge arm, the third bridge arm, and the fourth bridge arm of a machine-side converter unit, it controls the network-side converter unit of the branch to exit operation, controls the first bridge arm of the machine-side converter unit of the branch to operate, and releases the energy of the branch energy storage unit.

[0014] In a second aspect, the present invention provides a flywheel energy storage multi-machine parallel current conversion control method, which is executed by a control unit and includes:

[0015] Detecting whether there is a faulty power branch unit;

[0016] In response to a signal indicating the presence of a faulty power branch unit, the grid-side converter unit in the faulty power branch unit is disconnected, the machine-side converter unit in the faulty power branch unit is controlled to operate in constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side converter units in other power branch units are controlled to operate in constant power according to the issued rated scheduling instructions.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention is provided with a storage unit, an absorption unit and a voltage unit, and utilizes a current conversion device and a flywheel to store and release energy according to the real-time situation of the power grid, and supports direct parallel connection of a plurality of power branch units, which is convenient for engineering design and construction, thereby realizing reasonable allocation of resources, power grid stability and reasonable utilization of energy, and ultimately meeting the power grid's needs for frequency modulation and short-term peak regulation, and improving the stability of the power grid and the profitability of the power station. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a system block diagram of a flywheel energy storage multi-machine parallel converter device provided in Embodiment 1 of the present invention;

[0020] Figure 2 This is a control connection diagram of a flywheel energy storage multi-machine parallel converter device provided in Embodiment 1 of the present invention;

[0021] Figure 3 is a circuit diagram of a first power branch unit provided in Embodiment 1 of the present invention;

[0022] Figure 4 This is an optical fiber connection diagram of a grid-side converter unit provided in Embodiment 1 of the present invention;

[0023] Figure 5 It is a synchronization process control diagram provided by the first embodiment of the present invention;

[0024] Figure 6This is a startup process control diagram provided in Example 1 of the present invention.

[0025] In the figure: 1. input unit; 2. voltage unit; 3. first grid-side converter unit; 4. second grid-side converter unit; 5. third grid-side converter unit; 6. fourth grid-side converter unit; 7. first machine-side converter unit; 8. second machine-side converter unit; 9. third machine-side converter unit; 10. fourth machine-side converter unit; 11. first energy storage unit; 12. second energy storage unit; 13. third energy storage unit; 14. fourth energy storage unit; 15. first absorption unit; 16. second absorption unit; 17. third absorption unit; 18. fourth absorption unit; 19. control unit. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0027] Embodiment 1:

[0028] like Figure 1 and 2 As shown, a flywheel energy storage multi-machine parallel conversion device includes a control unit 19, an input unit 1, a voltage unit 2, a first power branch unit Z1, a second power branch unit Z2, a third power branch unit Z3, and a fourth power branch unit Z4;

[0029] The first power branch unit Z1 includes a first grid-side converter unit 3, a first generator-side converter unit 7, a first energy storage unit 11, and a first absorption unit 15. The first energy storage unit 11 and the first absorption unit 15 are connected to the first generator-side converter unit 7, and the first generator-side converter unit 7 is connected to the first grid-side converter unit 3.

[0030] The second power branch unit Z2 includes a second grid-side converter unit 4, a second machine-side converter unit 8, a second energy storage unit 12, and a second absorption unit 16. The second energy storage unit 12 and the second absorption unit 16 are connected to the second machine-side converter unit 8, and the second machine-side converter unit 8 is connected to the second grid-side converter unit 4.

[0031] The third power branch unit Z3 includes a third grid-side converter unit 5, a third machine-side converter unit 9, a third energy storage unit 13, and a third absorption unit 17. The third energy storage unit 13 and the third absorption unit 17 are connected to the third machine-side converter unit 9, and the third machine-side converter unit 9 is connected to the third grid-side converter unit 5.

[0032] The fourth power branch unit Z4 includes a fourth grid-side converter unit 6, a fourth machine-side converter unit 10, a fourth energy storage unit 14, and a fourth absorption unit 18. The fourth energy storage unit 14 and the fourth absorption unit 18 are connected to the fourth machine-side converter unit 10, and the fourth machine-side converter unit 10 is connected to the fourth grid-side converter unit 6.

[0033] The first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5, and the fourth grid-side converter unit 6 are connected to the voltage unit 2 via the AC busbar, the voltage unit 2 is connected to the input unit 1, and the input unit 1 is externally connected to the AC power grid;

[0034] The control unit 19 is connected to the input unit 1, the voltage unit 2, the first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5, the fourth grid-side converter unit 6, the first machine-side converter unit 7, the second machine-side converter unit 8, the third machine-side converter unit 9, the fourth machine-side converter unit 10, the first energy storage unit 11, the second energy storage unit 12, the third energy storage unit 13, and the fourth energy storage unit 14. The control unit 19 controls the output power of the first grid-side converter unit 3 to the fourth grid-side converter unit 6 or the first machine-side converter unit 7 to the fourth machine-side converter unit 10 according to the scheduling instruction and the rotation speed of the first energy storage unit 11 to the fourth energy storage unit 14.

[0035] The number of power branch units can be increased or decreased according to the actual needs of the project.

[0036] like Figure 3 As shown, the first grid-side converter unit 3 includes an input switch QF1, a charging circuit, a filter circuit, a first bidirectional converter unit Q1, a DC support capacitor C1, a discharge resistor R4, an output switch K3, and a fuse FU1; one end of QF1 is connected to the voltage unit 2 via the AC busbar, and the other end of QF1 is connected to the charging circuit. The output end of the charging circuit is connected to the midpoint of each bridge arm of the first bidirectional converter unit Q1 via the filter circuit. The DC support capacitor C1 and the discharge resistor R4 are respectively connected to the positive and negative poles of the DC bus, and the DC bus is connected to the input end of the fuse FU1 via the output switch K3. The second grid-side converter unit 4, the third grid-side converter unit 5, and the fourth grid-side converter unit 6 have the same structure and connection method as the first grid-side converter unit 3;

[0037] The first machine-side converter unit 7 includes a unidirectional converter unit Q2, a second bidirectional converter unit Q3, a DC support capacitor C2, a discharge resistor R5, and an output switch QF3; the unidirectional converter unit Q2, the second bidirectional converter unit Q3, the DC support capacitor C2, and the discharge resistor R5 are respectively connected to the positive and negative poles of the DC bus, the midpoint of the unidirectional converter unit Q2 is connected to the corresponding first absorption unit 15, and the midpoint of each bridge arm of the second bidirectional converter unit Q3 is connected to the input end of the output switch QF3. The second machine-side converter unit 8, the third machine-side converter unit 9, and the fourth machine-side converter unit 10 have the same structure and connection method as the first machine-side converter unit 7, and the machine-side converter unit is not equipped with a DC side input switch to reduce investment cost;

[0038] The first grid-side converter unit 3 to the fourth grid-side converter unit 6 are all three-bridge-arm bidirectional converter units, and at the same time, they all have reactive power support capability, and have two modes of operation: constant power mode operation and constant voltage mode operation. The constant power mode operation includes constant power mode charging and constant power mode discharging, and each operation mode can be converted online;

[0039] The first machine side converter unit 7 to the fourth machine side converter unit 10 are four-bridge arm converters, the first bridge arm is a unidirectional converter unit, and the second to fourth bridge arms are bidirectional converter units, all of which have two modes of operation: constant power mode operation and constant voltage mode operation. The constant power mode operation further includes constant power mode charging and constant power mode discharging. Each operation mode can be converted online. When a power branch unit fails, the branch energy storage unit releases energy through the second bidirectional converter unit Q3 and the unidirectional converter unit Q2.

[0040] The first energy storage unit 11 includes a magnetic suspension permanent magnet synchronous motor, a flywheel, a cooling fan, and a magnetic suspension system. The second energy storage unit 12 , the third energy storage unit 13 , and the fourth energy storage unit 14 have the same structure as the first energy storage unit 11 .

[0041] The first absorption unit 15 includes a plurality of resistors, and the second absorption unit 16 , the third absorption unit 17 , and the fourth absorption unit 18 are consistent with the first absorption unit 15 .

[0042] like Figure 4 As shown, the first grid-side converter unit 3 uses optical fiber to connect to the second grid-side converter unit 4, the second grid-side converter unit 4 uses optical fiber to connect to the third grid-side converter unit 5, the third grid-side converter unit 5 uses optical fiber to connect to the fourth grid-side converter unit 6, and the fourth grid-side converter unit 6 uses optical fiber to connect to the first grid-side converter unit 3.

[0043] like Figure 5 As shown, after the device is powered on, the station number of the first grid-side converter unit 3 is set to A1, the station number of the second grid-side converter unit 4 is set to A2, the station number of the third grid-side converter unit 5 is set to A3, and the station number of the fourth grid-side converter unit 6 is set to A4;

[0044] Determine whether A1 receives the synchronization signal normally. If A1 receives the synchronization signal normally, A1 forwards the received synchronization signal to A2. If the synchronization signal received by A1 is abnormal, A1, as the host, generates a synchronization signal and sends it to A2. A1 reports a synchronization abnormality fault. If A3 reports a synchronization abnormality fault, the equipment trips due to a fault.

[0045] Determine whether A2 receives the synchronization signal normally. If A2 receives the synchronization signal normally, A2 forwards the received synchronization signal to A3. If the synchronization signal received by A2 is abnormal, A2 generates a synchronization signal as the host and sends it to A3. A2 also reports a synchronization abnormality fault. If A4 reports a synchronization abnormality fault, the equipment trips due to a fault.

[0046] Determine whether A3 receives the synchronization signal normally. If A3 receives the synchronization signal normally, A3 forwards the received synchronization signal to A4. If the synchronization signal received by A3 is abnormal, A3, as the host, generates a synchronization signal and sends it to A4. A3 also reports a synchronization abnormality fault. If A1 reports a synchronization abnormality fault, the equipment trips due to a fault.

[0047] Determine whether A4 receives the synchronization signal normally. If A4 receives the synchronization signal normally, A4 forwards the received synchronization signal to A1. If the synchronization signal received by A4 is abnormal, A4, as the host, generates a synchronization signal and sends it to A1. A4 also reports a synchronization abnormality fault. If A2 reports a synchronization abnormality fault, the equipment trips due to a fault.

[0048] If the first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5 and the fourth grid-side converter unit 6 operate in a constant voltage mode, the first machine-side converter unit 7, the second machine-side converter unit 8, the third machine-side converter unit 9 and the fourth machine-side converter unit 10 are controlled to operate in a constant power mode;

[0049] If the first machine-side converter unit 7, the second machine-side converter unit 8, the third machine-side converter unit 9 and the fourth machine-side converter unit 10 operate in constant voltage mode, the first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5 and the fourth grid-side converter unit 6 are controlled to operate in constant power mode.

[0050] If any one of the first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5 and the fourth grid-side converter unit 6 fails, the grid-side converter unit of the branch is controlled to exit operation, and the generator-side converter unit of the branch is controlled to operate in a constant voltage mode;

[0051] If any one of the first energy storage unit 11, the second energy storage unit 12, the third energy storage unit 13, and the fourth energy storage unit 14 fails, the branch network side converter unit is controlled to exit operation, the branch machine side converter unit is controlled to operate in a constant voltage mode, and the first bridge arm of the branch machine side converter unit is controlled to operate to release the energy of the branch energy storage unit;

[0052] If any of the second bridge arm, the third bridge arm, and the fourth bridge arm of any unit among the first machine-side converter unit 7, the second machine-side converter unit 8, the third machine-side converter unit 9, and the fourth machine-side converter unit 10 fails, the network-side converter unit of the branch is controlled to exit operation, and the first bridge arm of the machine-side converter unit of the branch is controlled to operate to release the energy of the branch energy storage unit.

[0053] The control unit 19 includes several CPUs, the specific number of which is determined according to the actual situation. Figure 2 Two CPUs (CPU1, CPU2) are arranged, one of which controls the input unit 1, the voltage unit 2, the first grid-side converter unit 3, the second grid-side converter unit 4, the third grid-side converter unit 5, and the fourth grid-side converter unit 6, and the other controls the first machine-side converter unit 7, the second machine-side converter unit 8, the third machine-side converter unit 9, the fourth machine-side converter unit 10, the first energy storage unit 11, the second energy storage unit 12, the third energy storage unit 13, and the fourth energy storage unit 14. The two CPUs are connected via a Category 6 network cable to establish a communication connection and share information data.

[0054] like Figure 6 As shown, when the device is normal and has no faults, the equipment is started, the high-voltage switch of the input unit 1 is closed, and the first grid-side converter unit 3 to the fourth grid-side converter unit 6 obtain a 400V three-phase AC voltage through the voltage unit 2. If a power branch fails, the control unit 19 removes the faulty branch and controls the grid-side converter units of each normal branch to start in a constant voltage mode (given a DC voltage value of 680V), and the grid-side converter unit switches QF1 and K3 are closed successively, and then K2 is closed. Each grid-side converter unit charges the DC busbar of the grid-side converter unit and the machine-side converter unit of the same branch through resistors R1 to R3. After 5 seconds, if the voltage difference between the input end of K1 and the output end of K1 is less than 30V, the control switch K1 is closed and the switch K2 is disconnected (the main circuit is connected and the DC buffer circuit is disconnected), and the charging is completed. The grid-side converter unit is controlled to operate normally in the constant voltage mode, and the operating voltage is 680V;

[0055] The control unit 19 controls the generator-side converter unit of the normal branch to start in constant power mode (given the rated power value Pn of the generator-side converter), the switch QF3 is closed, the generator-side converter unit charges the energy storage unit of the same branch, and the flywheel starts to rotate;

[0056] When the charging power of the machine-side converter unit reaches the threshold value X1 (80% of the upper limit of the flywheel's storage power), the control unit 19 detects the flywheel speed of the energy storage unit. If the flywheel speed does not reach Y1 (the speed corresponding to 75% of the flywheel's storage power), the control unit 19 controls the branch to exit operation; when the flywheel speed reaches Y1, the control unit 19 limits the maximum output of the current loop of its machine-side converter unit, and the current maximum operating power is reduced to 40% of its rated power Pn, and the machine-side converter unit is controlled to switch to constant voltage mode operation, with a given DC voltage value of 670V;

[0057] The control unit 19 controls the grid-side converter unit to operate in a constant power charging mode, and the operating power is 20% of the rated power Pn of the same branch machine-side converter;

[0058] The control unit 19 controls the generator-side current conversion unit to cancel the restriction on the maximum output power of its current loop;

[0059] The control unit 19 controls each grid-side converter unit to operate at constant power according to the issued rated dispatch instruction;

[0060] When a power branch of the first power branch Z1 to the fourth power branch Z4 fails, the control unit 19 controls the network-side converter unit KM1 of the power branch to disconnect, disconnects the power branch from the voltage unit 2 (forbids sending a start-up command to the faulty branch network-side converter unit), controls the second bidirectional converter unit Q3 of the power branch to operate in constant voltage mode with an operating voltage of 550V, controls the unidirectional converter unit Q2 of the power branch to work, releases the energy of the energy storage unit of the same power branch through the absorption unit, and the remaining power branches operate normally.

[0061] The control unit 19 of the above device controls the grid-side converter units 3 to 6 to store and release electric energy according to actual needs and on-site working conditions, so as to meet the real-time energy needs of the power grid and improve the stability of the power system and the profitability of the new energy station.

[0062] Embodiment 2:

[0063] A flywheel energy storage multi-machine parallel current conversion control method can be implemented by a flywheel energy storage multi-machine parallel current conversion device described in embodiment 1, comprising:

[0064] Detecting whether there is a faulty power branch unit;

[0065] In response to a signal indicating the presence of a faulty power branch unit, the grid-side converter unit in the faulty power branch unit is disconnected, the machine-side converter unit in the faulty power branch unit is controlled to operate in constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side converter units in other power branch units are controlled to operate in constant power according to the issued rated scheduling instructions.

[0066] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0067] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0068] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0069] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A flywheel energy storage multi-machine parallel converter, characterized in that: include: A control unit, an input unit, a voltage unit, and a plurality of power branch units, wherein the power branch unit is connected to the voltage unit, the voltage unit is connected to the input unit, the input unit is externally connected to an AC power grid, the control unit is connected to the input unit, the voltage unit, and the plurality of power branch units, and when the control unit detects that there is a faulty power branch unit, the grid-side converter unit in the faulty power branch unit is disconnected, the machine-side converter unit in the faulty power branch unit is controlled to operate in a constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side converter units in other power branch units are controlled to operate in a constant power according to the issued rated dispatch instruction; The grid-side converter unit includes an input switch QF1, an input switch QF1, a charging circuit, a filtering circuit, a first bidirectional converter unit Q1, a DC support capacitor C1, a discharge resistor R4, an output switch K3 and a fuse FU1. One end of the input switch QF1 is connected to the voltage unit via the AC busbar, and the other end is connected to the charging circuit. The output end of the charging circuit is connected to the midpoint of each bridge arm of the first bidirectional converter unit Q1 via the filtering circuit. Both ends of the DC support capacitor C1 and the discharge resistor R4 are respectively connected to the positive and negative poles of the DC busbar, and the DC busbar is connected to the input end of the fuse FU1 via the output switch K3; The machine-side converter unit includes a unidirectional converter unit Q2, a second bidirectional converter unit Q3, a DC support capacitor C2, a discharge resistor R5 and an output switch QF3. The two ends of the unidirectional converter unit Q2, the second bidirectional converter unit Q3, the DC support capacitor C2 and the discharge resistor R5 are respectively connected to the positive and negative poles of the DC bus. The midpoint of the unidirectional converter unit Q2 is connected to the corresponding absorption unit. The midpoint of each bridge arm of the second bidirectional converter unit Q3 is connected to the input end of the output switch QF3. When the power branch unit fails, the energy storage unit releases energy through the second bidirectional converter unit Q3 and the unidirectional converter unit Q2.

2. The flywheel energy storage multi-machine parallel converter device according to claim 1 is characterized in that: The power branch unit also includes an absorption unit, the energy storage unit and the absorption unit are connected to a machine-side converter unit, the machine-side converter unit is connected to a grid-side converter unit, and the grid-side converter unit is connected to a voltage unit via an AC busbar.

3. The flywheel energy storage multi-machine parallel converter device according to claim 1 is characterized in that: The grid-side converter units are connected in sequence through optical fibers to form a closed loop, and each grid-side converter unit can send and receive synchronization signals. When one of the grid-side converter units receives the synchronization signal abnormally, the next grid-side converter unit connected to it switches to the host and sends the synchronization signal.

4. The flywheel energy storage multi-machine parallel converter device according to claim 1 is characterized in that: When the control unit detects that the grid-side converter unit is operating in constant voltage mode, the control unit controls the generator-side converter unit to operate in constant power mode; when the control unit detects that the generator-side converter unit is operating in constant voltage mode, the control unit controls the grid-side converter unit to operate in constant power mode.

5. The flywheel energy storage multi-machine parallel converter device according to claim 1 is characterized in that: The machine-side converter unit is a four-arm converter, the first arm is a unidirectional converter unit, and the second to fourth arms are bidirectional converter units, all of which have two modes of operation: constant power mode operation and constant voltage mode operation. The constant power mode operation further includes constant power mode charging and constant power mode discharging, and each operation mode can be converted online.

6. The flywheel energy storage multi-machine parallel converter device according to claim 5 is characterized in that: When the control unit detects a fault in a certain energy storage unit, it controls the network-side converter unit of the branch to exit operation, controls the machine-side converter unit of the branch to operate in constant voltage mode, controls the first bridge arm of the machine-side converter unit of the branch to operate, and releases the energy of the branch energy storage unit; when the control unit detects a fault in any of the second bridge arm, the third bridge arm, and the fourth bridge arm of a machine-side converter unit, it controls the network-side converter unit of the branch to exit operation, controls the first bridge arm of the machine-side converter unit of the branch to operate, and releases the energy of the branch energy storage unit.

7. A control method for the flywheel energy storage multi-machine parallel converter device according to claim 1, characterized in that: Executed by the control unit, including: Detecting whether there is a faulty power branch unit; In response to a signal indicating the presence of a faulty power branch unit, the grid-side converter unit in the faulty power branch unit is disconnected, the machine-side converter unit in the faulty power branch unit is controlled to operate in constant voltage mode, the energy of the energy storage unit in the faulty power branch unit is released, and the grid-side converter units in other power branch units are controlled to operate in constant power according to the issued rated scheduling instructions.

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