Multi-branch parallel converter, soft starting method thereof and variable speed pumped storage unit and self-starting control method thereof

Abstract

The application relates to a soft starting method of a multi-branch parallel converter. In the case that the converter is not connected to a power grid, a soft starting circuit of each power branch in the converter is controlled to charge a DC bus capacitor of each power branch to a first preset voltage; any one of all the power branches is controlled to charge a grid-side filter capacitor of all the power branches to a second preset voltage; the grid-side filter capacitors of all the power branches are charged to be completely homologous, and are matched with a power grid voltage parameter, then the first grid connection switch is controlled to be closed, and the input ends of all the power branches are connected to the power grid, so that the synchronous deviation caused by the charging of the grid-side filter capacitors of the multi-power branches is eliminated from the root, and voltage difference impact and branch interloop current during grid connection are avoided.

Description

Technical Field

[0001] This application belongs to the field of converter control technology, and particularly relates to a soft-start method for a multi-branch parallel converter, an automatic start control method for a variable-speed pumped-storage unit, a multi-branch parallel converter, a variable-speed pumped-storage unit, and a computer program product. Background Technology

[0002] As modern industry demands ever-increasing capacity and reliability from equipment, the capacity of single-branch power conversion units is increasingly insufficient to meet the needs of ultra-high power loads. Multi-branch parallel medium-voltage converters, due to their advantages such as flexible capacity expansion and strong redundancy, have been widely used in large fans, pumps, compressors, and other applications. These converters typically consist of multiple power units (branches) isolated on the grid side by an excitation transformer and directly connected in parallel on the generator side to jointly drive a high-power motor or other load.

[0003] Typically, converters are equipped with large-capacity bus support capacitors on the DC side and filter capacitors on the grid side, both of which are capacitive loads. During system startup, directly connecting the filter (capacitive load) to the grid will generate an inrush current far exceeding the rated current (the surge current can reach 3 to 6 times the rated current). This can cause grid-side fuses to blow and switching devices to trip, or even damage core power devices such as integrated gate-commutated thyristors (IGCTs) and insulated-gate bipolar transistors (IGBTs), and interfere with the stable operation of other electrical equipment on the grid side. Therefore, during converter startup, the DC bus capacitors inside each branch power unit need to be pre-charged to prevent the massive surge current generated at the moment of closing, which could damage rectifier devices and capacitors. However, for multi-branch parallel systems, even after the DC bus capacitors are fully charged, a severe current surge problem still exists during grid connection. Summary of the Invention

[0004] The purpose of this application is to provide a soft-start method for a multi-branch parallel converter, an automatic start control method for a variable-speed pumped-storage unit, a multi-branch parallel converter, a variable-speed pumped-storage unit, and a computer program product, aiming to solve the problem that in the soft start of a multi-branch parallel converter, each power branch still faces a severe current surge during grid connection operation after the DC bus capacitor has been fully charged.

[0005] In a first aspect, embodiments of this application provide a soft-start method for a multi-branch parallel converter. The converter includes multiple power branches, the input terminals of each power branch are respectively used to connect to the power grid through a first grid-connected switch, and the output terminals of each power branch are used to connect to electrical equipment. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected sequentially. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The soft-start method includes: The soft-start circuits in each of the power branches are controlled to charge their respective DC bus capacitors to a first preset voltage. According to the grid voltage, the first power converter of the first power branch charges the grid-side filter capacitor of all the power branches to the second preset voltage. The first power branch is any one of the power branches. Control the first grid-connected switch to close, so that the input terminals of all the power branches are connected to the grid.

[0006] In one embodiment, the step of controlling the first power converter of the first power branch according to the grid voltage to charge the grid-side filter capacitors of all the power branches to a second preset voltage includes: Obtain the grid voltage; Based on the grid voltage, phase-locked loop control is performed to generate a pulse modulation wave for controlling the first power converter of the first power branch, wherein the pulse modulation wave corresponds to the frequency, phase, and amplitude of the grid voltage; Based on the pulse modulation wave, the first power converter of the first power branch outputs AC power to charge the grid-side filter capacitors of all the power branches to a second preset voltage, wherein the frequency and phase of the AC power are consistent with the grid voltage.

[0007] In one embodiment, the first power converter controlling the first power branch charges the grid-side filter capacitors of all the power branches to a second preset voltage, further comprising: The soft-start circuit in the first power branch is controlled to maintain the charging of the DC bus capacitor of the first power branch, and the soft-start circuits in the other power branches besides the first power branch are controlled to turn off.

[0008] In one embodiment, the second preset voltage is any value between 80% and 100% of the grid voltage.

[0009] Secondly, embodiments of this application also provide a self-starting control method for a variable-speed pumped-storage unit based on the soft-start method described above. The variable-speed pumped-storage unit includes a rotor, a stator, a second grid-connected switch, and multiple excitation transformers. The input terminal of one of the power branches is connected to the first grid-connected switch via one of the excitation transformers. The rotor, as an electrical device, is connected to the output terminal of each of the power branches. The stator is used to connect to the power grid via the second grid-connected switch. The self-starting control method further includes: Based on the rotor position relative to the stator, the excitation current of each power branch is modulated to drive the rotor to accelerate smoothly. When the rotor reaches the preset speed, the second grid-connected switch is closed to connect the stator to the grid.

[0010] In one embodiment, prior to controlling the closing of the second grid-connected switch, the method further includes: The excitation voltage of the stator is modulated to match the power grid.

[0011] In one embodiment, after controlling the second grid-connected switch to close, the method further includes: Control the variable-speed pumped-storage unit to enter a steady-state power generation or drive mode.

[0012] In one embodiment, the preset speed is the speed at which the variable-speed pumped-storage unit operates in steady state under the drive of the grid voltage.

[0013] Thirdly, this application also provides a multi-branch parallel converter, including a first grid-connected switch, multiple power branches, a memory, a processor, and a computer program stored in the memory and executable on the processor. The input terminals of each power branch are respectively used to connect to the power grid through the first grid-connected switch, and the output terminals of each power branch are respectively used to connect to electrical equipment. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected in sequence. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The processor is connected to each power branch and the first grid-connected switch. When the processor executes the computer program, it implements the steps of the soft-start method for the multi-branch parallel converter described above.

[0014] Fourthly, this application also provides a variable-speed pumped-storage unit, including a rotor, a stator, a first grid-connected switch, a second grid-connected switch, multiple power branches, a memory, a processor, and a computer program stored in the memory and executable on the processor. The input terminals of each power branch are respectively used to connect to the power grid via the first grid-connected switch, and the output terminals of each power branch are respectively used to connect to the rotor. The stator is used to connect to the power grid via the second grid-connected switch. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected sequentially. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The processor is connected to each power branch, the first grid-connected switch, and the second grid-connected switch. When the processor executes the computer program, it implements the steps of the self-starting control method for the variable-speed pumped-storage unit as described above.

[0015] Fifthly, embodiments of this application also provide a computer program product that, when run on a computer, causes the computer to execute the soft-start method for multi-branch parallel converters and / or the self-start control method for variable-speed pumped-storage units as described above.

[0016] The beneficial effects of this application embodiment compared with related technologies are as follows: The soft-start method for multi-branch parallel converters provided in this application embodiment, when the converter is not connected to the grid, controls the soft-start circuit in each power branch to charge its respective DC bus capacitor to a first preset voltage; according to the grid voltage, controls any one of the power branches to charge the grid-side filter capacitor of all power branches to a second preset voltage; so that the voltage of the grid-side filter capacitor of all power branches is charged from the same source and matches the grid voltage parameters; then controls the first grid connection switch to close, so that the input terminals of all power branches are connected to the grid, thereby eliminating the synchronization deviation caused by each power branch charging its grid-side filter capacitor independently, avoiding voltage difference impact and inter-branch circulating current during grid connection, improving the severe current impact problem that each power branch still faces when performing grid connection operation after the DC bus capacitor is fully charged during the soft-start process of multi-branch parallel converters, and avoiding system protection action or equipment damage. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a multi-branch parallel converter provided in an embodiment of this application.

[0018] Figure 2This is a schematic diagram of the power branch structure in a multi-branch parallel converter provided in an embodiment of this application.

[0019] Figure 3 A flowchart of a soft-start method for a multi-branch parallel converter provided in an embodiment of this application.

[0020] Figure 4 A flowchart of a soft-start method for a multi-branch parallel converter provided in an embodiment of this application.

[0021] Figure 5 The pre-charge simulation waveform of the DC bus capacitor of a multi-branch parallel converter provided in an embodiment of this application is shown.

[0022] Figure 6 The pre-charge simulation waveform of the grid-side filter capacitor of a multi-branch parallel converter provided in an embodiment of this application is shown.

[0023] Figure 7 A flowchart of an automatic start-up control method for a variable-speed pumped storage unit provided in an embodiment of this application.

[0024] Figure 8 This is a schematic diagram of a soft-start device for a multi-branch parallel converter provided in an embodiment of this application.

[0025] Figure 9 This is a schematic diagram of the structure of a multi-branch parallel converter or variable speed pumped storage unit provided in an embodiment of this application. Detailed Implementation

[0026] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0027] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0028] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0030] In typical self-starting strategies for variable-speed pumped-storage units with multi-branch parallel converters: On the one hand, after the DC capacitors of each power branch of the converter have completed pre-charging, each power branch begins independent phase-locked loop (PLL) charging, charging its respective grid-side filter capacitors through its own DC bus capacitor. If the charging voltage output by each power branch is inconsistent with the grid voltage in amplitude, frequency, and phase, a huge inrush current will be generated on the grid-side filter capacitors and line inductance. Therefore, the above self-starting strategy struggles to achieve precise synchronization between the grid-side filter capacitor voltages of multiple power branches and the grid voltage. If there is an amplitude, phase, or frequency deviation between the filter capacitor voltages of each power branch and the grid voltage, a large inrush current will be generated at the moment of grid connection, potentially damaging power devices or affecting grid stability. On the other hand, if the voltages of the grid-side filter capacitors of each power branch are not synchronized, a large circulating current will be generated at the moment of parallel connection, leading to system protection activation or equipment damage.

[0031] To address the aforementioned shortcomings, the inventive concept of this application is to provide a soft-start method for a multi-branch parallel (type) converter. This method utilizes a two-stage control architecture, which involves independent pre-charging of the DC bus capacitors of each power branch and synchronous charging of the grid-side filter capacitors of multiple branches by a single power branch based on the grid voltage phase-locked loop. This solves the problems of large starting current surges, poor voltage synchronization, and complex control in multi-power branch parallel AC excitation systems, achieving smooth grid connection between the system and the grid without impact. Simultaneously, it reduces system operating costs and improves system reliability.

[0032] The embodiments of this application take a variable-speed pumped-storage unit as an example of an electrical device for a multi-branch parallel converter; in other embodiments, the electrical device may also be a drive motor from other fields, or it may be an energy storage device.

[0033] Please see Figure 1 The variable-speed pumped-storage unit includes a control and protection unit 101, a rotor 102, a stator 103, a first grid-connected switch 104, a second grid-connected switch 105, and multiple power branches 110. There are two or more power branches 110. The stator 103 is used to connect to the power grid 200 via the second grid-connected switch 105. The input terminals of each power branch 110 are respectively used to connect to the power grid 200 via the first grid-connected switch 104, and the output terminals of each power branch 110 are respectively used to connect to electrical equipment. In this embodiment, the electrical equipment is the rotor 102.

[0034] In one embodiment, the variable speed pumped storage unit also includes multiple excitation transformers 106, and the input terminal of a power branch 110 is connected to the first grid-connected switch 104 through an excitation transformer 106.

[0035] like Figure 2 As shown, in one embodiment, the power branch 110 includes a grid-side filter circuit 111, a first power converter 112, a second power converter 113, a DC bus capacitor C0, a machine-side filter circuit 114, and a soft-start circuit 115. The grid-side filter circuit 111, the first power converter 112, the second power converter 113, and the machine-side filter circuit 114 are sequentially connected between the input and output terminals of the power branch 110. The DC bus capacitor C0 is connected to the DC bus between the first power converter 112 and the second power converter 113. The soft-start circuit 115 is connected between the power grid 200 and the DC bus.

[0036] In one embodiment, the grid-side filter circuit 111 includes a grid-side filter capacitor C1 and a grid-side filter inductor L1. The generator-side filter circuit 114 includes a generator-side filter capacitor C2 and a generator-side filter inductor L2. Both the first power converter 112 and the second power converter 113 are bidirectional AC / DC power converters. During the startup phase of the variable-speed pumped-storage unit, the first power converter 112 can operate in inverter mode. During the steady-state phase of the variable-speed pumped-storage unit, the first power converter 112 operates in rectification mode, and the second power converter 113 operates in inverter mode. The soft-start circuit 115 draws power directly from the grid 200, i.e., Vac.

[0037] In one embodiment, the soft-start circuit 115 includes a soft-start switch K1, a pre-charge resistor R1, a pre-charge transformer T1, and a rectifier D1, which are connected in series between the DC bus of the power grid 200.

[0038] like Figure 3 As shown, one embodiment of this application provides a soft-start method for a multi-branch parallel converter, combined with... Figures 1 to 3 Soft boot methods include: In step S110, the soft-start circuit 115 in each power branch 110 is controlled to charge their respective DC bus capacitor C0 to the first preset voltage.

[0039] Each power branch 110's soft-start circuit 115 draws power from the grid 200 to pre-charge its DC bus capacitor C0. The first preset voltage is typically 80%-100% of the rated DC bus voltage. It is understood that this step is performed when the input terminals of each power branch 110 are not connected to the grid.

[0040] In step S120, the first power converter 112 of the first power branch 110a is controlled to charge the grid-side filter capacitor C1 of all power branches 110 to the second preset voltage according to the grid voltage. The first power branch 110a is any one of the power branches 110.

[0041] In some embodiments, if it is not necessary to connect to the power grid 200 through the excitation transformer 106, the grid voltage in step S120 is the voltage of the power grid 200. In some embodiments, if it is necessary to connect to the power grid 200 through the excitation transformer 106, the grid voltage in step S120 can be the rated secondary voltage of the excitation transformer 106, which is obtained by voltage conversion based on the grid voltage and the turns ratio of the primary and secondary sides of the excitation transformer 106.

[0042] In this embodiment, the DC bus capacitor C0 of the first power branch 110a is used as the power source, and the first power converter 112 of the first power branch 110a is controlled to work in inverter mode. The output charging current charges its own grid-side filter capacitor C1 and the grid-side filter capacitor C1 of each power branch 110 through each excitation transformer 106 to the second preset voltage.

[0043] During the charging process, the first power converter 112 of the first power branch 110a is phase-locked and generates a waveform with reference to the voltage of the power grid 200 or the rated secondary voltage of the excitation transformer 106, synchronously charging each grid-side filter capacitor C1. This ensures that the voltage of each grid-side filter capacitor C1 is synchronously charged to the second preset voltage, and that the phase and frequency of each grid-side filter capacitor C1 are consistent with the voltage of the power grid or the rated secondary voltage of the excitation transformer 106, so that the first grid-connected switch 104 can perform impact-free grid connection. The second preset voltage is any value between 80% and 100% of the voltage of the power grid 200 or the rated secondary voltage of the excitation transformer 106.

[0044] In step S130, the first grid-connected switch 104 is closed to connect all the input terminals of the power branches 110 to the grid.

[0045] By synchronously charging the grid-side filter capacitors C1 of each power branch 110 to the same amplitude, and ensuring that the phase and frequency of each grid-side filter capacitor C1 are consistent with the grid 200 before connecting to the grid, the deviation in amplitude, frequency, and phase caused by the independent charging of the grid-side filter capacitors C1 by multiple power branches 110 is eliminated from the source. This avoids voltage difference surges and inter-branch circulating currents during grid connection, and improves the problem of severe current surges that each power branch 110 still faces during grid connection operation after the DC bus capacitor is fully charged during the self-starting of variable speed pumped-storage units containing multiple parallel power branches 110. This also prevents system protection actions or equipment damage.

[0046] This invention solves the synchronization control problem between the grid-side filter capacitor C1 of each branch and the grid voltage 200 in a multi-branch parallel converter, ensuring that the input voltage of each power branch 110 is consistent and that its phase and frequency are consistent with the grid voltage, thus improving the grid connection success rate and system stability. It also solves the current surge problem caused by the asynchronous voltage of the grid-side filter capacitor C1 and the grid voltage during the startup of the medium-voltage drive system in the multi-branch parallel converter. The self-starting control method of this application has clear control logic, high reliability, and reduces system complexity and cost.

[0047] Please see Figure 4 In one embodiment, step S120 includes: Step S121: Obtain the grid voltage.

[0048] In some embodiments, if it is not necessary to connect to the power grid 200 through the excitation transformer 106, the voltage of the power grid 200 is directly obtained as the power grid voltage in this step. In some embodiments, if it is necessary to connect to the power grid 200 through the excitation transformer 106, after obtaining the voltage of the power grid 200, the rated voltage of the secondary side of the excitation transformer 106 is obtained by transformer conversion based on the primary and secondary turns ratio of the excitation transformer 106 as the power grid voltage in this step.

[0049] Step S122: Based on the grid voltage, perform phase-locked loop control to generate a pulse modulation wave for controlling the first power converter 112 of the first power branch 110a. The frequency, phase, and amplitude of the pulse modulation wave correspond to the grid voltage.

[0050] In this embodiment, a pulse modulation wave for controlling the first power converter 112 of the first power branch 110a is generated based on the voltage of the power grid 200 or the frequency and phase of the rated voltage of the secondary side of the excitation transformer 106.

[0051] Step S123: Based on the pulse modulation wave, the first power converter 112 of the first power branch 110a outputs AC power to charge the grid-side filter capacitor C1 of all power branches 110 to the second preset voltage, wherein the frequency and phase of the AC power are consistent with the frequency and phase of the grid voltage.

[0052] In this circuit, the AC output of the first power converter 112 in the first power branch 110a is consistent with the frequency and phase of the voltage of the power grid 200, which is also consistent with the frequency and phase of the secondary voltage of the excitation transformer 106. The second preset voltage is, for example, the voltage of the power grid 200 or 80% of the rated secondary voltage of the excitation transformer 106.

[0053] For example, if the grid voltage is 20kV and the first grid-connected switch 104 is closed, the primary voltage of the excitation transformer 106 is 20kV and the secondary rated voltage of the excitation transformer 106 is 3.6kV. Then the second preset voltage can be set to 2.88kV.

[0054] In one embodiment, the first power converter 112 controlling the first power branch 110a to charge the grid-side filter capacitor C1 of all power branches 110 to a second preset voltage further includes: The soft-start circuit 115 in the first power branch 110a is controlled to maintain the charging of the DC bus capacitor C0 of the first power branch 110a, while the soft-start circuits 115 in other power branches 110 besides the first power branch 110a are controlled to be turned off, thereby reducing the energy loss and voltage drop of the DC bus capacitor C0 of the first power branch 110a during the charging process of the grid-side filter capacitor C of each power branch 110, and thus reducing the inrush current during grid connection.

[0055] The self-starting control method of this application, the simulation results of the pre-charge voltage of the DC bus capacitor C0 are as follows: Figure 5 As shown, the pre-charging of the DC bus capacitor C0 is completed within 10 seconds (approximately 8.2 seconds). Figure 5 The corresponding time for position A is shown. The pre-charge simulation results of the grid-side filter capacitor C1 are as follows. Figure 6 As shown, after the DC bus capacitor C0 has completed its pre-charge ( Figure 6 The internal network filter capacitor C1 completes pre-charging within 200-300ms (corresponding time to position A shown). Figure 6 The corresponding time at position B shown) and grid connection ( Figure 6 The position corresponding to 8.5s shown is given, and the maximum instantaneous current on the secondary side of the excitation transformer 106 during grid connection is approximately 300A, which meets the engineering requirements.

[0056] like Figure 7 As shown, one embodiment of this application also provides an automatic start control method for a variable speed pumped-storage unit, including steps S110, S120, and S130 of the soft-start method in the above embodiment, and further including: In step S140, based on the position of rotor 102 relative to stator, the excitation current of each power branch 110 is modulated to drive rotor 102 to accelerate smoothly.

[0057] Before starting, based on the rotor position of rotor 102 relative to stator 103, the output frequency and voltage of each power branch 110 are gradually increased according to the preset speed-up curve to maintain magnetic flux stability; the excitation current is finely adjusted to suppress torque pulsation, and the excitation current is limited by closed-loop control to overcome large inertia and load resistance, so as to achieve stable speed-up of the unit.

[0058] In step S150, when the rotor 102 reaches the preset speed, the second grid-connected switch 105 is closed to connect the stator 103 to the grid.

[0059] In one embodiment, before controlling the second grid-connected switch 105 to close in step S150, the self-starting control method further includes: adjusting the stator's excitation voltage to match the grid 200. The AC excitation control module in the control and protection unit 101 adjusts the frequency, phase, and amplitude of the stator 103's excitation voltage to match the grid 200, thereby achieving shock-free grid connection of the stator 103.

[0060] In one embodiment, after controlling the second grid-connected switch 105 to close in step S150, the self-starting control method further includes: controlling the variable speed pumped storage unit to enter a steady-state power generation or drive mode, so as to achieve seamless switching between excitation start-up and grid-connected operation.

[0061] In one embodiment, the preset speed is the speed at which the variable-speed pumped-storage unit operates in steady state under the drive of the grid voltage.

[0062] like Figure 8 As shown, one embodiment of this application also provides a soft-start device for a multi-branch parallel converter. The soft-start device includes: The first pre-charge module 510 is used to control the soft-start circuit in each of the power branches to charge their respective DC bus capacitors to the first preset voltage. The second pre-charge module 520 is used to control the first power converter of the first power branch to charge the grid-side filter capacitors of all the power branches to a second preset voltage according to the grid voltage. The first power branch is any one of the converters in all the power branches. The grid connection control module 530 is used to control the closing of the first grid connection switch so that the input terminals of all the power branches are connected to the grid.

[0063] In one embodiment, the second precharge module 520 includes: Acquisition unit, used to acquire grid voltage; A modulation unit is configured to perform phase-locked loop control based on the grid voltage to generate a pulse modulation wave for controlling the first power converter of the first power branch, wherein the pulse modulation wave corresponds to the frequency, phase, and amplitude of the grid voltage. The pre-charge unit is used to drive the first power converter of the first power branch to output AC power based on the pulse modulation wave to charge the grid-side filter capacitors of all the power branches to a second preset voltage, wherein the frequency and phase of the AC power are consistent with the grid voltage.

[0064] In one embodiment, the first precharge module 510 is further configured to: The soft-start circuit in the first power branch is controlled to maintain the charging of the DC bus capacitor of the first power branch, and the soft-start circuits in the other power branches besides the first power branch are controlled to turn off.

[0065] Combination Figure 1 , Figure 2 and Figure 9 As shown, in a second aspect, embodiments of this application also provide a multi-branch parallel converter, including a first grid-connected switch 104, multiple power branches 110, a memory 120, a processor, and a computer program 121 stored in the memory 120 and executable on the processor. The input terminals of each power branch 110 are respectively used to connect the first grid-connected switch 104 to the power grid 200, and the output terminals of each power branch 110 are respectively used to connect electrical equipment. Each power branch 110 includes a grid-side filter capacitor C1, a first power converter 112, a second power converter 113, and a DC bus. The line capacitor C0, the machine-side filter capacitor C2, and the soft-start circuit 115, the grid-side filter capacitor C1, the first power converter 112, the second power converter 113, and the machine-side filter capacitor C2 are connected in sequence. The DC bus capacitor C0 is connected to the DC bus between the first power converter 112 and the second power converter 113. The soft-start circuit 115 is connected between the power grid 200 and the DC bus. The processor is connected to each power branch 110 and the first grid-connected switch 104. When the processor executes the computer program, it implements the steps of the soft-start method for the multi-branch parallel converter as described above.

[0066] Secondly, this application also provides a variable-speed pumped-storage unit, including a rotor 102, a stator 103, a first grid-connected switch 104, a second grid-connected switch 105, multiple power branches 110, a memory 120, a processor, and a computer program 121 stored in the memory 120 and executable on the processor. The input terminals of each power branch 110 are respectively used to connect the first grid-connected switch 104 to the power grid 200, and the output terminals of each power branch 110 are respectively used to connect the rotor 102. The stator is used to connect to the power grid 200 through the second grid-connected switch 105. The power branch 110 includes a grid-side filter capacitor C1 and a first power converter 11. 2. The second power converter 113, DC bus capacitor C0, machine-side filter capacitor C2, and soft-start circuit 115 are connected in sequence with grid-side filter capacitor C1, first power converter 112, second power converter 113, and machine-side filter capacitor C2. The DC bus capacitor C0 is connected to the DC bus between the first power converter 112 and the second power converter 113. The soft-start circuit 115 is connected between the power grid 200 and the DC bus. The processor is connected to each power branch 110, the second grid-connected switch 105, and the first grid-connected switch 104. When the processor executes the computer program, it implements the steps of the soft-start method for the multi-branch parallel converter as described above.

[0067] It is understood that the processor is the aforementioned control and protection unit 101, or a part thereof. Those skilled in the art will understand that... Figure 6 This is merely an example of a multi-branch parallel converter or a variable-speed pumped-storage unit, and does not constitute a limitation on multi-branch parallel converters or variable-speed pumped-storage units. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components, such as input / output devices, network access devices, etc.

[0068] The processor can be a Central Processing Unit (CPU), or it can be other general-purpose controllers, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose controller can be a microcontroller or any conventional controller.

[0069] In some embodiments, memory 120 may be an internal storage unit of a multi-branch parallel converter or a variable-speed pumped-storage unit, such as a hard disk or memory of the multi-branch parallel converter or variable-speed pumped-storage unit. In other embodiments, memory 120 may be an external storage device of the multi-branch parallel converter or variable-speed pumped-storage unit, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the multi-branch parallel converter or variable-speed pumped-storage unit. Furthermore, memory 120 may include both internal storage units and external storage devices of the multi-branch parallel converter or variable-speed pumped-storage unit. Memory 120 is used to store operating systems, applications, boot loaders, data, and other programs. Memory 120 may also be used to temporarily store data that has been output or will be output.

[0070] This application also provides a computer-readable storage medium storing a computer program 121, which, when executed by a processor, can implement the steps in the above-described method embodiments.

[0071] This application provides a computer program product that, when run on a computer, causes the computer to perform the steps described in the various method embodiments above.

[0072] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above method embodiments of this application can be implemented by a computer program 121 instructing related hardware. The computer program 121 can be stored in a computer-readable storage medium. When the computer program 121 is executed by a processor, it can implement the steps of the various method embodiments described above. The computer program 121 includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, recording media, computer memory, ROM (Read-Only Memory), RAM (Random Access Memory), CD-ROM (Compact Disc Read-Only Memory), magnetic tape, floppy disk, and optical data storage devices. The computer-readable storage medium mentioned in this application can be a non-volatile storage medium; in other words, it can be a non-transient storage medium.

[0073] It should be understood that all or part of the steps of the above embodiments can be implemented by software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented in whole or in part as a computer program product. The computer program product includes one or more computer instructions. The computer instructions can be stored in the above-described computer-readable storage medium.

[0074] 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.

[0075] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0076] In the embodiments provided in this application, it should be understood that the disclosed devices / electronic devices and methods can be implemented in other ways. For example, the device / electronic device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0077] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0078] The above 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. A soft-start method for a multi-branch parallel converter, characterized in that, The converter includes multiple power branches, each power branch's input terminal being connected to the power grid via the first grid-connected switch, and each power branch's output terminal being connected to electrical equipment. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected sequentially. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The soft-start method includes: The soft-start circuits in each of the power branches are controlled to charge their respective DC bus capacitors to a first preset voltage. According to the grid voltage, the first power converter of the first power branch charges the grid-side filter capacitor of all the power branches to the second preset voltage. The first power branch is any one of the power branches. Control the first grid-connected switch to close, so that the input terminals of all the power branches are connected to the grid.

2. The soft-start method as described in claim 1, characterized in that, The step of controlling the first power converter of the first power branch according to the grid voltage to charge the grid-side filter capacitors of all the power branches to the second preset voltage includes: Obtain the grid voltage; Based on the grid voltage, phase-locked loop control is performed to generate a pulse modulation wave for controlling the first power converter of the first power branch, wherein the pulse modulation wave corresponds to the frequency, phase, and amplitude of the grid voltage; Based on the pulse modulation wave, the first power converter of the first power branch outputs AC power to charge the grid-side filter capacitors of all the power branches to a second preset voltage, wherein the frequency and phase of the AC power are consistent with the grid voltage.

3. The soft-start method as described in claim 2, characterized in that, The first power converter controlling the first power branch charges the grid-side filter capacitors of all the power branches to a second preset voltage, further comprising: The soft-start circuit in the first power branch is controlled to maintain the charging of the DC bus capacitor of the first power branch, and the soft-start circuits in the other power branches besides the first power branch are controlled to turn off.

4. The soft-start method as described in claim 2, characterized in that, The second preset voltage is any value taken from 80% to 100% of the grid voltage.

5. A self-starting control method for a variable-speed pumped-storage unit based on the soft-start method as described in any one of claims 1 to 4, characterized in that, The variable-speed pumped-storage unit includes a rotor, a stator, a second grid-connected switch, and multiple excitation transformers. The input terminal of one of the power branches is connected to the first grid-connected switch through one of the excitation transformers. The rotor, as an electrical device, is connected to the output terminal of each of the power branches. The stator is used to connect to the power grid through the second grid-connected switch. The self-starting control method further includes: Based on the rotor position relative to the stator, the excitation current of each power branch is modulated to drive the rotor to accelerate smoothly. When the rotor reaches the preset speed, the second grid-connected switch is closed to connect the stator to the grid.

6. The self-starting control method as described in claim 5, characterized in that, Before the control of closing the second grid-connected switch, the method further includes: The excitation voltage of the stator is modulated to match the power grid.

7. The self-starting control method as described in claim 5, characterized in that, After controlling the first grid-connected switch to close, the following steps are also included: Control the variable-speed pumped-storage unit to enter a steady-state power generation or drive mode.

8. The self-starting control method as described in claim 5, characterized in that, The preset speed is the speed at which the variable-speed pumped-storage unit operates in a steady state under the drive of the grid voltage.

9. A multi-branch parallel converter, characterized in that, The system includes a first grid-connected switch, multiple power branches, a memory, a processor, and a computer program stored in the memory and executable on the processor. The input terminals of each power branch are respectively used to connect to the power grid via the first grid-connected switch, and the output terminals of each power branch are respectively used to connect to electrical equipment. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected sequentially. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The processor is connected to each power branch and the first grid-connected switch. When the processor executes the computer program, it implements the steps of the soft-start method for a multi-branch parallel converter as described in any one of claims 1 to 4.

10. A variable-speed pumped-storage unit, characterized in that, The system includes a rotor, a stator, a first grid-connected switch, a second grid-connected switch, multiple power branches, a memory, a processor, and a computer program stored in the memory and executable on the processor. The input terminals of each power branch are connected to the power grid via the first grid-connected switch, and the output terminals of each power branch are connected to the rotor. The stator is connected to the power grid via the second grid-connected switch. Each power branch includes a grid-side filter capacitor, a first power converter, a second power converter, a DC bus capacitor, a machine-side filter capacitor, and a soft-start circuit. The grid-side filter capacitor, the first power converter, the second power converter, and the machine-side filter capacitor are connected sequentially. The DC bus capacitor is connected to the DC bus between the first power converter and the second power converter. The soft-start circuit is connected between the power grid and the DC bus. The processor is connected to each power branch, the first grid-connected switch, and the second grid-connected switch. When the processor executes the computer program, it implements the steps of the self-starting control method for the variable-speed pumped-storage unit as described in any one of claims 5 to 8.

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