Alternating current excitation device charging and discharging system and method for variable-speed pumped storage unit and medium

Abstract

The invention discloses an alternating-current excitation device charging and discharging system and method for a variable-speed pumped storage unit 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 ordered charging and discharging operation of each power sub-module, and smooth starting and shutdown of the alternating-current excitation device are realized; compared with an existing hardware scheme, the hardware cost is reduced, the size of the excitation device is reduced, and the economical efficiency, safety and stability of the system are effectively improved.

Description

Technical Field

[0001] The invention relates to a charging and discharging system, method and medium of an AC excitation device for a variable-speed pumped storage unit, and belongs to the technical field of power electronics. Background Art

[0002] Variable-speed pumped storage technology is an advancement of traditional pumped storage technology. As a more efficient and flexible peak-shaving and frequency-regulating power source, its use of a high-power AC excitation system allows the speed of its energy storage units to be continuously adjusted over a wide range. This increases the adaptable head range of the units and improves operational stability. Its efficiency can be increased by 3% to 10% under both power generation and pumping conditions, demonstrating advanced technical performance. This energy storage unit has application value in both power generation support and power auxiliary services. It will contribute to the construction and development of smart grids by meeting the needs of large-scale new energy access to the grid, supporting the development of renewable energy, enhancing the flexibility of system peak regulation, and raising the quality requirements of ultra-high voltage transmission for grid stability.

[0003] The AC excitation device contains a DC capacitor bank, such as Figure 1 The DC link shown requires smooth charging of the DC bus capacitors before the device operates. During power outages and shutdown, a discharge circuit for the capacitor bank is required. Existing charging and discharging methods include resistive charging and discharging and active inverter charging and discharging. The resistive charging and discharging method connects the power source to an energy storage element (such as a capacitor or battery) via a resistor. Based on Ohm's law, the charging current is limited to achieve charging and discharging of the energy storage element. The active inverter charging and discharging method processes the grid or other AC power source through rectification and filtering before charging and discharging the energy storage element (such as a battery or capacitor). During the charging process, a power electronic converter (such as an AC-DC converter) may be used to convert the AC power to a suitable DC voltage to charge the energy storage element. During the discharge process, the DC power stored in the battery is converted to AC power via an inverter, enabling energy feedback and utilization. Currently, the engineering application of AC variable-speed generators is in the exploratory stage, and there are no mature examples of charging and discharging methods and systems using AC excitation devices for variable-speed pumped-storage units. The aforementioned existing charging and discharging technologies have the problem of simultaneous charging of all power branches, which leads to heating of the charging transformer or excitation transformer and increased losses. Therefore, it is urgent to provide a charging and discharging method and system for the AC excitation device of a variable-speed pumped storage unit 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 an AC excitation device for a variable-speed pumped-storage unit. The system overcomes the difficulties encountered in the prior art of simultaneous charging of various power branches, which results in heating and increased losses in the charging transformer or excitation transformer. The system effectively improves the economy, safety, and stability of the system, achieves smooth starting and stopping of the AC excitation device, and reduces the size and cost of the AC excitation device.

[0005] To achieve the above-mentioned object, the technical solution adopted by the present invention is: an AC excitation device charging and discharging system for a variable-speed pumped-storage unit, comprising: an AC excitation device main circuit, a power submodule, the power submodule comprising a branch circuit breaker, an excitation transformer, a grid-side converter, a DC bus, and a machine-side converter, the branch circuit breaker being connected to the grid-side converter via the excitation transformer, the grid-side converter being connected to the DC bus, and the DC bus being connected to the variable-speed pumped-storage unit via the machine-side converter; the AC excitation device main circuit comprising an excitation main circuit breaker K1 and a main transformer low-voltage side, the excitation main circuit breaker K1 being connected to the branch circuit breaker, and further comprising:

[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 the circuit breaker K6. K6 is connected to the charging resistors R1, R2, and R3. R1 is connected to the three-phase AC phase A, R2 is connected to the three-phase AC phase B, and R3 is connected to the three-phase AC phase C. The charging resistors R1, R2, and R3 are connected to the circuit breaker K8 via the step-up transformer T1. The three-phase AC phases A and C are connected via a discharge circuit.

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

[0008] The system further comprises a controller connected to the main circuit of the AC excitation device, the power submodule, the charging circuit and the discharging circuit respectively, and used for controlling the charging and discharging of the AC excitation device.

[0009] In the above scheme, the system overcomes the problems existing in the prior art such as simultaneous charging of each power sub-module causing heating of the charging transformer or excitation transformer and increased losses, thereby improving the economy, safety and stability of the system, while reducing the size of the excitation device, effectively reducing hardware costs, and realizing orderly charging and discharging of each power sub-module, ensuring safe and reliable charging and discharging of the system.

[0010] According to the embodiments of the present invention, the present invention can be further optimized. The following is the technical solution formed after optimization:

[0011] In one preferred embodiment, the charging circuit further comprises: a circuit breaker K7; the circuit breaker K7 is connected in parallel with the charging resistors R1, R2, and R3. In the above solution, 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 the battery via the charging circuit.

[0015] The excitation main circuit breaker K1 is controlled to be open, and the circuit breakers K6, K8 and branch circuit breakers are closed. The three-phase AC power passes through the charging resistors R1, R2, R3, the step-up transformer T1, the circuit breaker K8 and the branch circuit breaker to charge the DC bus of the power sub-module, so that the DC bus voltage of the power sub-module is close to the normal operating value;

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

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

[0018] Control the excitation main circuit breaker K1 and the branch circuit breaker to close, and 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 comprises:

[0020] Step 21: Control the excitation main circuit breaker K1 and the branch circuit breaker to be disconnected, and the circuit breaker K8 to be closed;

[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, and convert the DC side power into AC power through the grid-side converter and feed it back to the three-phase AC bus.

[0022] Step 23: After the discharge is completed, the circuit breakers K6, K7 and the branch circuit breakers are controlled to be disconnected.

[0023] In one preferred embodiment, step 11 further includes: after the DC bus voltage of the power sub-module approaches a 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 comprises:

[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 on and off of power devices inside the grid-side converter of the power submodule, and dissipate heat through resistance to consume the power that cannot be connected to the grid;

[0026] Step 25: After the discharge is completed, the circuit breakers K9, K10 and the branch circuit breakers are controlled to be disconnected.

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

[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 provided with a charging and discharging circuit, so that the AC excitation device only requires one of the charging and discharging circuits to realize the orderly charging and discharging operations of each power sub-module, and realize smooth startup and shutdown of the AC excitation device. Compared with the existing hardware solution, the hardware cost is reduced, the volume of the excitation device is reduced, and the economy, safety and stability of the system are effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0032] Figure 4 1. It is a flow chart of the discharge phase of a charging and discharging method of an AC excitation device for a variable-speed pumped storage unit according to an embodiment of the present invention;

[0033] Figure 5 This is a flow chart of a power submodule in a separate discharge phase of a charging and discharging system of an AC excitation device for a variable-speed pumped storage unit according to an embodiment of the present invention;

[0034] Figure 6 FIG. 1 is a schematic diagram of a current flow path of a power sub-module 1 in a discharge stage S20 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention may be combined with each other.

[0036] Example 1

[0037] This embodiment 1 provides a variable-speed pumped storage unit AC excitation device charging and discharging system, including: a controller, an AC excitation device, which includes an AC excitation device main circuit, and a power submodule; the AC excitation device main circuit includes: a main transformer low-voltage side, 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 The system further includes a charge and discharge circuit, which includes circuit breakers K6, K7, K8, K9, and K10, a step-up transformer T1, charging resistors R1, R2, and R3, and discharging resistors R4 and R5.

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

[0039] The AC excitation device charging and discharging system for the variable-speed pumped-storage unit of this embodiment 1 includes four power sub-modules. The AC excitation device only needs to be equipped with one charging and discharging circuit to realize orderly charging and discharging operations on each power sub-module in the AC excitation device, thereby realizing centralized control and management. Compared with the existing solution in which each power sub-module is equipped 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 method for charging and discharging an AC excitation device for a variable speed pumped storage unit, including: a charging method and a discharging method. Figure 2 As shown, the steps of the charging method include:

[0041] Charging stage S1: charging each power sub-module in turn so that the DC bus voltage of each power sub-module is close to the normal operating value.

[0042] Charging stage S2: The controller controls the branch circuit breakers K1, K2, K3, K4, and K5 to close, and charges 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 stage S1 includes a power submodule individual charging stage, including:

[0044] During module charging phase A1, the controller opens the main excitation circuit breaker K1 and closes circuit breakers K8 and K6. Three-phase 400V auxiliary power flows through charging resistors R1, R2, and R3, step-up transformer T1, circuit breaker K8, and one of the branch circuit breakers K2 through K5 to charge the DC bus capacitors in each power submodule. Depending on application requirements, the controller controls the opening and closing of branch circuit breakers to enable simultaneous or sequential charging of the power submodules.

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

[0046] Module charging stage 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 stage S10: The controller controls the excitation main circuit breaker K1 and branch circuit breakers K2 to K5 to be opened, and K8 to be closed, and discharges each submodule in turn.

[0049] Discharge stage S20: control circuit breakers K7 and K6 to be disconnected, and circuit breakers K9, K10 and branch circuit breakers K2 to K5 to be closed.

[0050] Discharge stage 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 of the power submodule, including:

[0052] Module Discharge Phase B1: The controller closes K7 and K6, and one of the branch circuit breakers K2-K5. The grid-side converters in each power submodule control the DC bus voltage below its normal operating value, converting DC power into AC energy and feeding it back to the 400V auxiliary power bus. During Module Discharge Phase B1, the controller switches the power components within each power submodule through the grid-side converters, thus forming a capacitor and resistor discharge loop.

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

[0054] During the discharge phase, the electrical energy on the DC side of each power sub-module is first fed back to the 400V grid in turn, and the remaining electrical energy that cannot be connected to the grid is discharged through resistance heat dissipation. Figure 6Figure 1 is a schematic diagram of the current flow path of power submodule 1 in the discharge stage S20. Taking the AC excitation device composed of a neutral point clamped three-level topology as an example, the discharge stage S20 is further explained. During the discharge stage S20, the power devices SA1 and SA2 of phase A and the power devices SC3 and SC4 of phase C in the grid-side converter are turned on, and the remaining power devices are turned off. The current flow path between the DC capacitors C1 and C2 and the discharge resistors R4 and R5 is as follows: Figure 6 The black line in the middle shows this. During this phase, the power devices in the remaining power submodules are disconnected in the same manner. The power devices SA1, SA2, SC3, and SC4 are IGBT or IGCT power semiconductor devices.

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

[0056] Special note is Figure 1 The topology of the AC excitation device can be a two-level structure, a three-level structure, a cascade structure, a modular multi-level structure or other forms.

[0057] The AC excitation device charging and discharging system for a variable-speed pumped-storage unit provided in this embodiment 1 overcomes the problems existing in the prior art such as simultaneous charging of various power branches leading to heating of the charging transformer or excitation transformer and increased losses. The AC excitation device is only equipped with an additional charging and discharging circuit to perform orderly charging and discharging operations on each power sub-module in the AC excitation device, realizing centralized control and management, reducing the complexity and cost of the circuit, and having the technical advantages of reducing hardware costs, reducing the size of the excitation device, and ensuring safe and reliable charging and discharging.

[0058] The contents described in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications to the embodiments made by those skilled in the art fall within the scope defined by the claims attached to the present invention.

Claims

1. A charging and discharging system for an AC excitation device for a variable-speed pumped storage unit, comprising: The AC excitation device main circuit and power submodule include a branch circuit breaker, an excitation transformer, a grid-side converter, a DC bus, and a machine-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, and the DC bus is connected to the variable-speed pumped storage unit via the machine-side converter. The AC excitation device main circuit includes an excitation main circuit breaker K1 and a main transformer low-voltage side. The excitation main circuit breaker K1 is connected to the branch circuit breaker. It is characterized by further comprising: Charging circuit, including: circuit breakers K6, K8, step-up transformer T1, charging resistors R1, R2, R3; The input of the charging circuit is a three-phase AC power supply, which is connected to the circuit breaker K6. K6 is connected to the charging resistors R1, R2, and R3. R1 is connected to the three-phase AC phase A, R2 is connected to the three-phase AC phase B, and R3 is connected to the three-phase AC phase C. The charging resistors R1, R2, and R3 are connected to the circuit breaker K8 through the step-up transformer T1; the three-phase AC phases A and C are connected through the discharge circuit; The discharge circuit includes: discharge resistors R4, R5, circuit breakers K9, K10; three-phase AC phase A 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 phase C of the three-phase AC power; Circuit breaker K8 is connected between the excitation main circuit breaker K1 and the branch circuit breaker; The system further comprises a controller connected to the main circuit of the AC excitation device, the power submodule, the charging circuit and the discharging circuit respectively, and used for controlling the charging and discharging of the AC excitation device.

2. The AC excitation device charging and discharging system for a variable speed pumped storage unit according to claim 1 is characterized in that: 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.

3. A charging and discharging method for an AC excitation device for a variable speed pumped storage unit, characterized in that: Including charging method and discharging method; The charging method includes: Step 11: Charge the battery via the charging circuit. The excitation main circuit breaker K1 is controlled to be open, and the circuit breakers K6, K8 and branch circuit breakers are closed. The three-phase AC power passes through the charging resistors R1, R2, R3, the step-up transformer T1, the circuit breaker K8 and the branch circuit breaker to charge the DC bus of the power sub-module, so that the DC bus voltage of the power sub-module is close to the normal operating value; After the charging circuit is charged, the control circuit breakers K6, K8 and the branch circuit breaker are disconnected; Step 12: Charge the main circuit of the AC excitation device: Control the excitation main circuit breaker K1 and the branch circuit breaker to close, and 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 comprises: Step 21: Control the excitation main circuit breaker K1 and the branch circuit breaker to be disconnected, and the circuit breaker K8 to be closed; 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, and convert the DC side power into AC power through the grid-side converter and feed it back to the three-phase AC bus. Step 23: After the discharge is completed, the circuit breakers K6, K7 and the branch circuit breakers are controlled to be disconnected.

4. The method for charging and discharging an AC excitation device for a variable speed pumped storage unit according to claim 3, characterized in that: Step 11 also includes: After the DC bus voltage of the power submodule approaches the normal operating value, the circuit breaker K7 is controlled to close; After the charging circuit is charged, the circuit breaker K7 is controlled to be disconnected.

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

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

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