AC excitation device charge-discharge system and method for variable speed pumped storage unit and medium

Abstract

The application discloses an alternating-current excitation device charging and discharging system and method for variable-speed pumped storage units and a medium. The system is provided with a charging and discharging circuit, so that the alternating-current excitation device only needs one charging and discharging circuit to realize the orderly charging and discharging operation of each power submodule, realizes the smooth starting and shutdown of the alternating-current excitation device, and reduces the hardware cost compared with the existing hardware scheme, reduces the volume of the excitation device, and effectively improves the economy, safety and stability of the system.

Description

Technical Field

[0001] This invention relates to the charging and discharging system, method, and medium of the AC excitation device for variable speed pumped storage units, and belongs to the field of power electronics technology. Background Technology

[0002] Variable-speed pumped storage technology represents an advancement over traditional pumped storage. As a more efficient and flexible peak-shaving and frequency-regulating power source, its high-power AC excitation system allows for continuous speed adjustment of the storage unit within a wide range. This increases the head range the unit can adapt to and improves operational stability. In both power generation and pumping modes, its efficiency can be improved by 3% to 10%, demonstrating advanced technical performance. This type of storage unit has application value in both power generation support and auxiliary power services. It will contribute to the construction and development of smart grids by meeting the needs of large-scale new energy grid integration, supporting renewable energy development, enhancing the flexibility of system peak shaving, and improving the quality requirements of UHV transmission for grid stability.

[0003] AC excitation devices include DC capacitor banks, such as Figure 1 The DC link shown requires smooth charging of the DC bus capacitors before the device operates, and a discharge circuit for the capacitor bank is needed during the power outage shutdown phase. Existing charging and discharging methods include resistive charging and discharging and active inverter charging and discharging. Resistive charging and discharging connects the power supply to the energy storage element (such as a capacitor or battery) through a resistor, limiting the charging current according to Ohm's law to achieve charging and discharging of the energy storage element. Active inverter charging and discharging uses the grid or other AC power supply after rectification and filtering to charge and discharge the energy storage element (such as a battery or capacitor). During charging, a power electronic converter (such as an AC-DC converter) may be used to convert AC to a suitable DC voltage to charge the energy storage element. During discharging, the DC energy stored in the battery is converted back to AC energy by an inverter, achieving energy feedback and utilization. Currently, the engineering application of AC variable speed units is in the exploratory stage, and there are no mature cases for charging and discharging methods and systems for AC excitation devices in variable speed pumped storage units. The aforementioned existing charging and discharging technologies suffer from problems such as increased heat generation and losses in the charging transformer or excitation transformer due to simultaneous charging of various power branches. Therefore, there is an urgent need to provide a charging and discharging method and system for AC excitation devices in variable-speed pumped storage units to effectively solve the above problems. Summary of the Invention

[0004] The present invention aims to provide a charging and discharging system, method and medium for AC excitation device of variable speed pumped storage unit. The system overcomes the problems of simultaneous charging of each power branch in the prior art, such as the overheating of the charging transformer or excitation transformer and increased loss, effectively improving the system economy, safety and stability, realizing smooth start and stop of AC excitation device, and reducing the size and cost of AC excitation device.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a charging and discharging system for an AC excitation device of a variable-speed pumped-storage unit, comprising: an AC excitation device main circuit and a power submodule, wherein the power submodule includes a branch circuit breaker, an excitation transformer, a grid-side converter, a DC bus, and a generator-side converter; the branch circuit breaker is connected to the grid-side converter through the excitation transformer, the grid-side converter is connected to the DC bus, and the DC bus is connected to the variable-speed pumped-storage unit through the generator-side converter; the AC excitation device main circuit includes an excitation main circuit breaker K1 and the low-voltage side of the main transformer, the excitation main circuit breaker K1 is connected to the branch circuit breaker, and further includes:

[0006] The charging circuit includes: circuit breakers K6 and K8, a step-up transformer T1, and charging resistors R1, R2, and R3. The input of the charging circuit is a three-phase AC power supply, which is connected to circuit breaker K6. K6 is connected to charging resistors R1, R2, and R3. R1 is connected to phase A of the three-phase AC power supply, R2 is connected to phase B of the three-phase AC power supply, and R3 is connected to phase C of the three-phase AC power supply. The charging resistors R1, R2, and R3 are connected to circuit breaker K8 through the step-up transformer T1. Phase A and phase C of the three-phase AC power supply are connected through a discharge circuit.

[0007] The discharge circuit includes: discharge resistors R4 and R5, circuit breakers K9 and K10; the three-phase AC A phase is connected to circuit breaker K9, circuit breaker K9 is connected to discharge resistor R4, R4 is connected to discharge resistor R5, R5 is connected to circuit breaker K10, and K10 is connected to the three-phase AC C phase; circuit breaker K8 is connected between the excitation main circuit breaker K1 and the branch circuit breaker.

[0008] The system also includes a controller, which is connected to the main circuit of the AC excitation device, the power submodule, the charging circuit, and the discharging circuit, respectively, and is used to control the charging and discharging of the AC excitation device.

[0009] In the above solution, the system overcomes the problems of simultaneous charging of each power submodule leading to overheating of the charging transformer or excitation transformer and increased losses in the existing technology, improves the system's economy, safety and stability, reduces the size of the excitation device, effectively reduces hardware costs, realizes orderly charging and discharging of each power submodule, and ensures safe and reliable charging and discharging of the system.

[0010] According to embodiments of the present invention, the present invention can be further optimized, and the optimized technical solution is as follows:

[0011] In one preferred embodiment, the charging circuit further includes a circuit breaker K7; the circuit breaker K7 is connected in parallel with the charging resistors R1, R2, and R3. In the above scheme, the charging resistors R1, R2, and R3 are short-circuited by the circuit breaker K7, further improving the charging speed.

[0012] Based on the same concept, the present invention also provides a charging and discharging method for an AC excitation device for a variable speed pumped storage unit, including a charging method and a discharging method;

[0013] The charging method includes:

[0014] Step 11: Charge via the charging circuit:

[0015] When the main excitation circuit breaker K1 is opened, circuit breakers K6, K8 and branch circuit breakers are closed. The three-phase AC power is charged through charging resistors R1, R2, R3, step-up transformer T1, circuit breaker K8 and branch circuit breakers, so that the DC bus voltage of the power submodule is close to the normal operating value.

[0016] After the charging circuit is fully charged, control circuit breakers K6, K8 and branch circuit breakers are disconnected;

[0017] Step 12: Charge via the main circuit of the AC excitation device:

[0018] The main excitation circuit breaker K1 and the branch circuit breaker are closed to charge the power sub-module through the main circuit of the AC excitation device, so that the DC bus voltage of the power sub-module reaches the normal operating value.

[0019] The discharge method includes:

[0020] Step 21: Control the main excitation circuit breaker K1 and the branch circuit breaker to open, and circuit breaker K8 to close;

[0021] Step 22: Control circuit breakers K6 and K7 to close. When the DC bus voltage is lower than the normal operating value, control the branch circuit breaker to close. The DC side power will be converted into AC power through the grid-side converter and fed back to the three-phase AC bus.

[0022] Step 23: After the discharge is completed, control circuit breakers K6, K7 and branch circuit breakers to disconnect.

[0023] In one preferred embodiment, step 11 further includes: after the DC bus voltage of the power submodule approaches the normal operating value, controlling the circuit breaker K7 to close; after the charging circuit is fully charged, controlling the circuit breaker K7 to open.

[0024] In one preferred embodiment, the discharge method further includes:

[0025] Step 24: If there is excess power on the DC side that cannot be connected to the grid, control circuit breakers K9, K10 and branch circuit breakers to close, control the switching of power devices inside the grid-side converter of the power submodule, and dissipate the power that cannot be connected to the grid by releasing heat through resistors.

[0026] Step 25: After the discharge is completed, control circuit breakers K9, K10 and branch circuit breakers to disconnect.

[0027] Based on the same concept, the present invention also provides a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a controller, implement the steps of the above method.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a charging and discharging system, method and medium for an AC excitation device for a variable speed pumped storage unit. The system is equipped with a charging and discharging circuit, which enables the AC excitation device to realize the orderly charging and discharging operation of each power sub-module with only one charging and discharging circuit, and realizes the smooth start-up and shutdown of the AC excitation device. Compared with the existing hardware solutions, it reduces hardware costs, reduces the size of the excitation device, and effectively improves the system's economy, safety and stability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the charging and discharging system of an AC excitation device for a variable-speed pumped storage unit according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the charging stage of a charging and discharging method for an AC excitation device used in a variable-speed pumped storage unit according to an embodiment of the present invention.

[0031] Figure 3 This is a flowchart illustrating the individual charging stage of the power submodule in the charging and discharging method of the AC excitation device for a variable-speed pumped storage unit according to an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the discharge stage of a charging and discharging method for an AC excitation device used in a variable-speed pumped storage unit according to an embodiment of the present invention.

[0033] Figure 5 This is a flowchart illustrating the individual discharge stage of the power submodule of the charging and discharging system for an AC excitation device in a variable-speed pumped storage unit according to an embodiment of the present invention.

[0034] Figure 6 This is a schematic diagram of the current flow path of the power submodule 1 in the discharge stage S20 according to an embodiment of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] Example 1

[0037] This embodiment 1 provides a charging and discharging system for an AC excitation device in a variable-speed pumped storage unit, comprising: a controller, an AC excitation device including an AC excitation device main circuit and a power submodule; the AC excitation device main circuit includes: a low-voltage side of the main transformer, a current-limiting reactor, and an excitation main circuit breaker K1; the power submodule includes: a branch circuit breaker, an excitation transformer, a grid-side converter, and a generator-side converter, such as... Figure 1 As shown. The system also includes a charging and discharging circuit; the charging and discharging circuit includes: circuit breakers K6, K7, K8, K9, K10, step-up transformer T1, charging resistors R1, R2, R3, and discharging resistors R4, R5.

[0038] like Figure 1 As shown, the input of the charging and discharging circuit is drawn from the 400V three-phase AC power of the plant's power supply system, and the output is connected between the excitation main circuit breaker K1 and the branch circuit breakers K2, K3, K4, and K5. A discharge circuit is provided between phase A and phase C of the three-phase AC power through a discharge resistor.

[0039] The AC excitation device charging and discharging system for the variable speed pumped storage unit in this embodiment 1 includes four power sub-modules. The AC excitation device only needs to be configured with one charging and discharging circuit to realize the orderly charging and discharging operation of each power sub-module in the AC excitation device, and realize centralized control and management. Compared with the existing scheme where each power sub-module is configured with a charging and discharging circuit, the hardware cost is reduced and the size of the excitation device is reduced.

[0040] This embodiment 1 also provides a charging and discharging method for an AC excitation device used in a variable-speed pumped storage unit, including a charging method and a discharging method. For example... Figure 2 As shown, the charging method includes the following steps:

[0041] Charging phase S1: Each power submodule is charged sequentially to bring the DC bus voltage of each power submodule close to the normal operating value.

[0042] Charging phase S2: The controller controls the branch circuit breakers K1, K2, K3, K4, and K5 to close, charging each power sub-module through the main circuit of the AC excitation device. The grid-side converter of each power sub-module controls the DC bus voltage to reach the normal operating value.

[0043] like Figure 3 As shown, charging phase S1 includes a separate charging phase for the power submodule, including:

[0044] Module charging phase A1: The controller keeps the main excitation circuit breaker K1 in the open state and controls circuit breakers K8 and K6 to close. Three-phase 400V plant power flows through charging resistors R1, R2, R3, step-up transformer T1, circuit breaker K8, and one of the branch circuit breakers K2 to K5 to charge the DC bus capacitors in each power submodule. Depending on application requirements, the controller can control the opening / closing of the branch circuit breakers to achieve simultaneous or sequential charging of the power submodules.

[0045] Module charging stage A2: The controller controls the circuit breaker K7 to close, causing the charging resistors R1, R2, and R3 to short-circuit, further increasing the charging speed.

[0046] Module charging phase A3: The controller controls circuit breakers K6, K7, K8 and branch circuit breakers to disconnect.

[0047] like Figure 4 As shown, the steps of the discharge method include:

[0048] Discharge phase S10: The controller controls the excitation main circuit breaker K1 and branch circuit breakers K2 to K5 to open and K8 to close, discharging each sub-module in sequence.

[0049] Discharge phase S20: Control circuit breakers K7 and K6 are opened, and circuit breakers K9, K10 and branch circuit breakers K2 to K5 are closed.

[0050] Discharge phase S30: The controller controls K9, K10 and all branch circuit breakers to disconnect.

[0051] like Figure 5 As shown, the discharge stage S10 includes a separate discharge stage for the power submodule, including:

[0052] Module discharge phase B1: The controller closes circuit breakers K7 and K6, and one of the branch circuit breakers K2 to K5 closes. Through the grid-side converters of each power submodule, the DC bus voltage is controlled to be lower than the normal operating value, converting DC power into AC power and feeding it back to the 400V plant auxiliary power bus. In module discharge phase B1, the controller controls the switching of internal power devices in each power submodule through the grid-side converters, thus forming a capacitor and resistor discharge circuit.

[0053] Module discharge stage B2: The controller controls one of K7, K6, or branch circuit breakers K2 to K5 to disconnect.

[0054] During the discharge phase, the electrical energy on the DC side of each power submodule is first fed back to the 400V grid in sequence, and the remaining electrical energy that cannot be connected to the grid is discharged by dissipating heat through resistors. Figure 6This diagram illustrates the current flow path of power submodule 1 during discharge phase S20. Taking an AC excitation device with a neutral-point clamped three-level topology as an example, the discharge phase S20 is further explained. During discharge phase S20, power devices SA1 and SA2 in phase A and power devices SC3 and SC4 in phase C of the grid-side converter are turned on, while the remaining power devices are turned off. The current flow path between DC capacitors C1 and C2 and discharge resistors R4 and R5 is as follows: Figure 6 As shown by the black lines in the middle. In this stage, the switching on and off of power devices in the remaining power sub-modules is the same. Among them, power devices SA1, SA2, SC3, and SC4 are IGBT or IGCT power semiconductor devices.

[0055] Figure 1 This is merely an example of a charging and discharging method and system for an AC excitation device used in a variable-speed pumped-storage unit, and does not constitute a limitation on such a method and system. It may include more or fewer components than shown in the figure, or combine certain components, or different components, such as input / output devices, network access devices, etc.

[0056] It should be noted that Figure 1 The topology of the AC excitation device can be a two-level structure, a three-level structure, a cascaded structure, or a modular multilevel structure, or other forms.

[0057] The AC excitation device charging and discharging system for variable speed pumped storage units provided in Embodiment 1 overcomes the problems of existing technologies, such as the simultaneous charging of each power branch leading to overheating of the charging transformer or excitation transformer and increased losses. The AC excitation device is equipped with only one additional charging and discharging circuit, which performs orderly charging and discharging operations on each power sub-module in the AC excitation device, realizes centralized control and management, reduces the complexity and cost of the circuit, and has the technical advantages of reducing hardware costs, reducing the size of the excitation device, and ensuring safe and reliable charging and discharging.

[0058] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present embodiments by those skilled in the art will fall within the scope defined by the appended claims.

Claims

1. A charging and discharging system for an AC excitation device in a variable-speed pumped storage unit, comprising: The AC excitation device includes a main circuit and a power submodule. The power submodule comprises a branch circuit breaker, an excitation transformer, a grid-side converter, a DC bus, and a generator-side converter. The branch circuit breaker is connected to the grid-side converter via the excitation transformer. The grid-side converter is connected to the DC bus. The DC bus is connected to the variable-speed pumped-storage unit via the generator-side converter. The main circuit of the AC excitation device includes an excitation main circuit breaker K1 and the low-voltage side of the main transformer. The excitation main circuit breaker K1 is connected to the branch circuit breaker. The device is characterized by further comprising: The charging circuit includes: circuit breakers K6 and K8, step-up transformer T1, and charging resistors R1, R2, and R3; The input to the charging circuit is a three-phase AC power supply, which is connected to circuit breaker K6. K6 is connected to charging resistors R1, R2, and R3. R1 is connected to phase A of the three-phase AC power supply, R2 is connected to phase B of the three-phase AC power supply, and R3 is connected to phase C of the three-phase AC power supply. The charging resistors R1, R2, and R3 are connected to circuit breaker K8 through step-up transformer T1. Phase A and phase C of the three-phase AC power supply are connected through a discharge circuit. The discharge circuit includes: discharge resistors R4 and R5, circuit breakers K9 and K10; the three-phase AC A phase is connected to circuit breaker K9, circuit breaker K9 is connected to discharge resistor R4, R4 is connected to discharge resistor R5, R5 is connected to circuit breaker K10, and K10 is connected to the three-phase AC C phase. Circuit breaker K8 is connected between the main excitation circuit breaker K1 and the branch circuit breaker; The system also includes a controller, which is connected to the main circuit of the AC excitation device, the power sub-module, the charging circuit, and the discharging circuit, respectively, and is used to control the charging and discharging of the AC excitation device, so that the AC excitation device can realize the orderly charging and discharging of each power sub-module with only one charging and discharging circuit.

2. The AC excitation device charging and discharging system for a variable-speed pumped storage unit according to claim 1, characterized in that, The charging circuit also includes: circuit breaker K7; circuit breaker K7 is connected in parallel with charging resistors R1, R2, and R3.

3. A charging and discharging method for an AC excitation device used in a variable-speed pumped-storage unit, applied to the charging and discharging system for an AC excitation device used in a variable-speed pumped-storage unit as described in claim 2, characterized in that... This includes charging methods and discharging methods; The charging method includes: Step 11: Charge via the charging circuit: When the main excitation circuit breaker K1 is opened, circuit breakers K6, K8 and branch circuit breakers are closed. The three-phase AC power is charged through charging resistors R1, R2, R3, step-up transformer T1, circuit breaker K8 and branch circuit breakers, so that the DC bus voltage of the power submodule is close to the normal operating value. After the charging circuit is fully charged, control circuit breakers K6, K8 and branch circuit breakers are disconnected; Step 12: Charge via the main circuit of the AC excitation device: The main excitation circuit breaker K1 and the branch circuit breaker are closed to charge the power sub-module through the main circuit of the AC excitation device, so that the DC bus voltage of the power sub-module reaches the normal operating value. The discharge method includes: Step 21: Control the main excitation circuit breaker K1 and the branch circuit breaker to open, and circuit breaker K8 to close; Step 22: Control circuit breakers K6 and K7 to close. When the DC bus voltage is lower than the normal operating value, control the branch circuit breaker to close. The DC side power will be converted into AC power through the grid-side converter and fed back to the three-phase AC bus. Step 23: After the discharge is completed, control circuit breakers K6, K7 and branch circuit breakers to disconnect.

4. The charging and discharging method for the AC excitation device of the variable-speed pumped storage unit according to claim 3, characterized in that, Step 11 also includes: Once the DC bus voltage of the power submodule approaches its normal operating value, the control circuit breaker K7 closes. After the charging circuit completes charging, the control circuit breaker K7 disconnects.

5. The charging and discharging method for the AC excitation device of the variable-speed pumped storage unit according to claim 3, characterized in that, The discharge method further includes: Step 24: If there is remaining power on the DC side and it cannot be connected to the grid, control the circuit breakers K9, K10 and the branch circuit breaker to close, control the on and off of the internal power devices through the grid-side converter, and dissipate the power that cannot be connected to the grid by releasing heat through the discharge resistors R4 and R5. Step 25: After the discharge is completed, control circuit breakers K9, K10 and branch circuit breakers to disconnect.

6. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the controller, they implement the steps of any of the methods described in claims 3 to 5.

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