An excitation and frequency conversion start-up multiplexing device, system and control method

Abstract

This invention discloses an excitation and frequency conversion starting multiplexing device, a synchronous generator system, and a control method, belonging to the field of synchronous motor excitation and frequency conversion starting. It includes: two voltage source converters, VSC1 and VSC2, and a DC chopper; the two VSCs are connected to the synchronous generator terminals, and the DC chopper is connected to the excitation winding; when the two VSCs are connected in series, one operates in rectification mode to provide DC voltage to the subsequent excitation chopper; the other operates in inverter mode to provide frequency conversion current to the generator stator, enabling soft starting of the generator; when the two VSCs are connected in parallel, both operate in rectification mode to provide DC voltage to the subsequent stage, increasing the capacity of the excitation system while also directly providing reactive power support to the grid; further preferably, both the VSCs and the DC chopper are fully controllable devices. This invention achieves the multiplexing of excitation and frequency conversion starting, improving the controllable capacity of the excitation system and the efficiency and stability of the frequency conversion starting system.

Description

Technical Field

[0001] This invention belongs to the field of synchronous motor excitation and frequency conversion starting, and more specifically, relates to an excitation and frequency conversion starting multiplexing device, a synchronous generator system and control method. Background Technology

[0002] To support carbon peaking and carbon neutrality efforts and accelerate the construction of a clean, low-carbon, safe, and efficient energy system, my country's power system is at a critical stage of transformation towards green and low-carbon development.

[0003] Accelerating the development of green and clean energy sources such as wind, solar, and hydropower is crucial for achieving the goal of a clean and low-carbon energy transition. The large-scale development and construction of new energy sources like wind and solar power place higher demands on the power system's regulation capabilities, flexibility, and capacity to absorb new energy. Therefore, it is imperative to accelerate the construction of a new power system adapted to the increasing proportion of new energy sources. However, new energy sources, represented by wind and solar power, are characterized by intermittency and volatility. Large-scale grid connection of these new energy sources can impact the stable operation of the power system, thus requiring energy storage to ensure grid security. Pumped hydro storage, as a safe, stable, economical, and environmentally friendly energy storage method, also possesses advantages such as flexible start-up and shutdown, rapid response, strong stability, and superior regulation performance. It will play a vital role in the construction of a new power system with an increasing proportion of new energy sources. Meanwhile, pumped storage power stations, as large-scale energy storage power sources with dual functions of peak shaving and valley filling, can effectively undertake the peak shaving tasks of the power system, reduce the investment in polluting and costly thermal power peak shaving units, and reduce the use of coal resources, thereby achieving peak shaving and carbon reduction. During periods of low electricity load, pumped storage power stations use excess electricity as pumping power, further achieving valley filling and carbon reduction, and improving the absorption capacity of new energy sources. Therefore, pumped storage power stations are a clean energy source, an energy storage source, and a regulating source.

[0004] When pumped-storage units operate as electric motors, they cannot start automatically and must rely on other starting systems. For pumped-storage units, static frequency converters (SFCs) have become the primary starting method due to their advantages such as stationary equipment, convenient operation and maintenance, large starting capacity, fast starting speed, high reliability, and low system impact. However, the main circuit of current SFCs is generally composed of semi-controlled devices (thyristors), which suffers from problems such as high harmonic content, poor control performance, and complex starting process.

[0005] In addition to the variable frequency drive (VFD) starting system, pumped storage units also require a specific excitation system for excitation. The existence of these two systems results in a large overall size and footprint for the pumped storage unit system. Furthermore, after the pumped storage unit completes its VFD start-up and begins normal operation, the VFD starting system becomes idle, leading to a significant waste of resources. This problem also exists in other synchronous units that require both VFD starting and excitation systems.

[0006] Overall, existing synchronous generator units suffer from problems such as large system size, large footprint, and resource waste due to the need to rely on different systems for frequency conversion starting and excitation. Summary of the Invention

[0007] To address the shortcomings and improvement needs of existing technologies, this invention provides an excitation and frequency conversion start multiplexing device, system, and control method. Its purpose is to improve the control performance of the frequency conversion starter while increasing the controllable capacity of the excitation system. This effectively enhances the reactive power support capability and stable operation capability of the unit, improves the overall system utilization efficiency, further reduces the construction and maintenance costs of the unit, and solves the problems of large system size, large footprint, and resource waste caused by synchronous generator units requiring different devices for frequency conversion start and excitation.

[0008] To achieve the above objectives, according to one aspect of the present invention, an excitation and frequency conversion start-up multiplexing device is provided, comprising: a converter group and a circuit breaker group; the converter group includes voltage source converters VSC1 and VSC2, a DC chopper, and transformers TR1 to TR2;

[0009] The DC side of voltage source converter VSC1, the DC side of voltage source converter VSC2, and the input terminal of DC chopper are connected in parallel; the AC side connection terminals of voltage source converters VSC1 and VSC2 are connected to the low-voltage side of transformers TR1 and TR2 respectively; the output terminal of DC chopper is used to connect to the excitation winding of synchronous generator.

[0010] The circuit breaker group is used to control the connection between the converter group and the synchronous generator and the power supply side, as well as the connection between the voltage source converters VSC1 and VSC2;

[0011] During operation, voltage source converters VSC1 and VSC2 are connected in parallel and both operate in rectification mode, with the excitation and frequency conversion start-up multiplexing device serving as the excitation system for the synchronous unit; or, voltage source converters VSC1 and VSC2 are connected in series and operate in rectification and inversion modes respectively, with the excitation and frequency conversion start-up multiplexing device serving as the frequency conversion start-up system for the synchronous unit.

[0012] Furthermore, the switching devices in the voltage source converters VSC1 and VSC2, as well as the DC chopper, are all fully controllable devices.

[0013] Furthermore, the excitation and frequency conversion start-up multiplexing device provided by the present invention also includes: a control module;

[0014] All switching devices in the voltage source converters VSC1 and VSC2 and the DC chopper are connected to the control module.

[0015] The control module is used to generate switching signals based on the required terminal voltage feedback value of the synchronous generator and the required reactive power feedback value absorbed or injected by the power grid when the excitation and frequency conversion start-up multiplexing device is used as the excitation system of the synchronous generator. This signal controls the opening and closing of the fully controlled devices in the excitation system so that the terminal voltage of the synchronous generator and the reactive power absorbed or injected by the power grid are equal to the command value.

[0016] The control module is also used to generate switching signals based on the speed feedback value and current feedback value of the synchronous unit when the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous unit, so as to control the opening and closing of the fully controlled devices in the frequency conversion start-up system and make the speed and current of the synchronous unit equal to the command value.

[0017] Furthermore, the circuit breaker group includes: the circuit breaker group includes circuit breaker QF, and circuit breakers QF1 to QF6;

[0018] The first terminals of circuit breakers QF1, QF2, QF3, and QF6 are connected together. The second terminal of circuit breaker QF1 is used to connect to the plant power supply. The second terminal of circuit breaker QF2 is connected to the high-voltage side of transformer TR1. The second terminal of circuit breaker QF3 is connected to the high-voltage side of transformer TR2 and the first terminal of circuit breaker QF5. The second terminal of circuit breaker QF6 is used to connect to the low-voltage side of the main transformer. The second terminal of circuit breaker QF5 is used to connect to the generator terminal of the synchronous generator unit. The first terminal of circuit breaker QF1 is used to connect to the low-voltage side of the main transformer, and the second terminal of circuit breaker QF2 is used to connect to the generator terminal of the synchronous generator unit.

[0019] The first terminal of circuit breaker QF4 is connected to the output terminal of the DC chopper, and the second terminal is used to connect to the excitation winding of the synchronous generator.

[0020] Furthermore, the excitation and frequency conversion start-up multiplexing device provided by the present invention also includes: a voltage stabilizing capacitor C;

[0021] The two ends of the voltage regulator capacitor C are connected in parallel with the DC side of the voltage source converter VSC1, the DC side of the voltage source converter VSC2, and the input terminal of the DC chopper.

[0022] Furthermore, the excitation and frequency conversion start-up multiplexing device provided by the present invention also includes: a start-up unit;

[0023] The two ends of the starting unit are connected to the low-voltage side of transformer TR1 and the AC side of voltage source converter VSC1, respectively.

[0024] According to another aspect of the present invention, a synchronous generator system is provided, comprising: a synchronous generator and the excitation and frequency conversion start-up multiplexing device provided in the embodiments of the present invention.

[0025] Furthermore, the synchronous generator system provided by the present invention includes a synchronous generator motor, a synchronous condenser, or a synchronous motor of a pumped storage unit.

[0026] According to another aspect of the present invention, a control method for the above-mentioned synchronous generator system is provided. When the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous generator, the control method includes:

[0027] (S1) After the voltage source converters VSC1 and VSC2 and the DC chopper are all in normal condition, close circuit breakers QF4 and QF5. After the positions of each circuit breaker are checked and found to be normal, proceed to step (S2).

[0028] (S2) Close circuit breaker QF1 or QF6 and close circuit breaker QF2. After verifying that the positions of each circuit breaker are normal, proceed to step (S3).

[0029] (S3) Trigger the conduction voltage source converter VSC1, and after detecting that its output voltage is normal, proceed to step (S4);

[0030] (S4) Trigger the chopper to turn on, and after detecting that the rotor position is correct, proceed to step (S5);

[0031] (S5) Trigger the conduction voltage source converter VSC2 to start the unit.

[0032] Furthermore, when the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous unit, after step (S5), it also includes: when the speed of the synchronous unit reaches the synchronous set speed, proceed to step (S6);

[0033] (S6) Adjust the speed and voltage of the synchronous generator set. When the grid connection conditions are met, proceed to step (S7).

[0034] (S7) Close circuit breaker QF, open circuit breaker QF5, and lock out the output of voltage source converter VSC2 to complete synchronous grid connection and exit the frequency conversion start system.

[0035] Furthermore, when the excitation and frequency conversion start-up multiplexing device is used as the excitation system of a synchronous unit, the control method includes:

[0036] After the synchronous generator unit is in normal operation, the circuit breaker QF3 is closed, and the voltage source converter VSC2 is triggered.

[0037] According to another aspect of the present invention, a multi-machine shared system is provided, comprising: a shared rectifier, a shared transformer, a selection module, a circuit breaker QF1 for connecting to the plant power supply, N synchronous generator sets, and N voltage source converters, N DC choppers, N transformers and N circuit breaker sets corresponding one-to-one with the N synchronous generator sets; N is a positive integer greater than or equal to 2.

[0038] The DC side of the voltage source converter and the input terminal of the DC chopper corresponding to each synchronous generator unit are connected in parallel; the high voltage side and low voltage side of each transformer are connected to the generator terminal of the corresponding synchronous generator unit and the AC side of the voltage source converter, respectively, and the output terminal of each DC chopper is connected to the excitation winding of the corresponding synchronous generator unit.

[0039] The low-voltage side of the shared transformer is connected to the AC side of the shared rectifier, and the high-voltage side of the shared transformer is used to connect to the power supply side; the selection module includes N access switches corresponding one-to-one with N synchronous generators; after the access switch is closed, the DC side of the corresponding voltage source converter is also connected in parallel with the DC side of the shared rectifier;

[0040] The circuit breaker assembly includes: circuit breaker QF5 connected between the high-voltage side of the transformer and the generator terminal of the synchronous generator set; circuit breaker QF connected between the generator terminal of the synchronous generator set and the low-voltage side of the corresponding main transformer; circuit breaker QF4 connected between the output terminal of the DC chopper and the excitation winding of the synchronous generator set; and circuit breaker QF6 connected between the low-voltage side of the main transformer and the high-voltage side of the common transformer.

[0041] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0042] (1) The excitation and frequency conversion start-up multiplexing device provided by this invention, by changing the connection method and operating state of the two voltage source converters in the device, enables the frequency conversion start-up system and excitation system of the synchronous generator to be reused, integrating the two into one device. Specifically, when the device is used as an excitation system, VSC1 and VSC2 operate in parallel and synchronously, and the chopper is in the on state. It can provide excitation current to the synchronous generator and simultaneously inject (absorb) reactive power to the generator terminal through the two VSC converters, thereby improving the reactive power support capability and fully utilizing the power supply capacity. This invention leverages the potential of the excitation system to enhance the stability support capability of synchronous generator units. When used as a variable frequency start-up system, VSC1 is in rectification mode, VSC2 is in inverter mode, and the chopper is in synchronous generator start-up excitation control mode. VSC1 and the chopper form the excitation channel, providing excitation current to the rotor. VSC1 and VSC2 form the variable frequency start-up channel, providing variable frequency start-up current to the stator of the synchronous generator unit. Since the converter group continues to participate in excitation after the variable frequency start-up is completed, the utilization efficiency of the variable frequency system can be effectively improved, avoiding resource waste. In summary, this invention integrates excitation and variable frequency start-up, reducing system size and equipment footprint, avoiding resource waste, lowering costs, improving system operating efficiency, enhancing reactive power support capability, and strengthening the stability support capability of synchronous generator units.

[0043] (2) In the preferred embodiment of the excitation and frequency conversion start-up multiplexing device provided by the present invention, each switching device in the voltage source converter VSC1, VSC2 and DC chopper is a fully controlled device. When the device is used as an excitation system, it can improve the control capability and strong excitation capability of the excitation system and provide dual reactive power support channels, effectively improving the unit's stable support capability and excitation capacity. There is no need to add a separate excitation power supply. When the synchronous unit needs emergency braking and rapid change of operating conditions, VSC1 and VSC2 operate in parallel and work synchronously in inverter mode, quickly feeding back the rotational kinetic energy of the synchronous unit to the system, accelerating braking and stopping, making the operating condition change process faster, and also achieving energy saving. When the device is used as a frequency conversion start-up system, for some synchronous units, such as pumped storage units, the voltage source converter VSC1, VSC2 and DC chopper based on fully controlled devices can effectively reduce harmonic content and there is no problem of thyristor commutation failure, thereby improving the operating performance and reliability of the frequency conversion start-up system.

[0044] (3) The control method of the synchronous generator system provided by the present invention can coordinate the mutual cooperation between excitation, frequency conversion start-up and synchronous grid connection.

[0045] (4) The multi-machine shared system provided by the present invention enables multiple synchronous generator units to share the same rectifier on the basis of the reuse of the excitation system and the frequency conversion starting system, which can realize the turnaround starting of multiple synchronous generator units and further improve the system operating efficiency. At the same time, the switching devices in the shared rectifier can directly adopt more reliable and lower cost thyristors or diodes, which can effectively improve the operating efficiency and reliability of the system. More preferably, when the switching devices adopt thyristors, zero-start voltage boost can be achieved, so there is no need for a starting unit, which can further simplify the system structure. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the excitation and frequency conversion start-up multiplexing device provided in an embodiment of the present invention;

[0047] Figure 2 This is a topology diagram of the excitation and frequency conversion start-up multiplexing device provided in an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of a multi-machine shared system provided in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0051] To further improve the capacity of the excitation system and enhance the performance and efficiency of the variable frequency start system, this invention provides an excitation and variable frequency start multiplexing device, system, and control method. The overall concept is as follows: based on the traditional single-channel fully controlled excitation system, a parallel channel is added. The system's operating mode can be changed by altering the series-parallel connection of the two converters. Through coordinated control, it can operate in parallel as the excitation system alone, effectively improving the reactive power support capacity of the excitation system; or it can operate in series as a combined excitation and variable frequency start system, effectively improving the performance and efficiency of the variable frequency start system, and further enhancing the overall operating performance and stability of the synchronous generator unit.

[0052] This invention is applicable to various synchronous units. Without loss of generality, pumped storage units are used as examples in the following embodiments. The following are embodiments.

[0053] Example 1:

[0054] An excitation and frequency conversion start multiplexing device, such as Figure 1 and Figure 2 As shown, it includes: a converter group and a circuit breaker group; the converter group includes a voltage source converter (VSC), i.e. Figure 1 and Figure 2 VSC1 and VSC2, DC chopper, and transformers TR1 to TR2;

[0055] The DC side of voltage source converter VSC1, the DC side of voltage source converter VSC2, and the input terminal of DC chopper are connected in parallel; the AC side connection terminals of voltage source converters VSC1 and VSC2 are respectively connected to the low-voltage side of transformers TR1 and TR2; the output terminal of DC chopper is used to connect to the excitation winding of synchronous generator; in this embodiment, the synchronous generator is specifically a synchronous generator motor in a pumped storage unit, which can operate as both a generator and a motor;

[0056] The circuit breaker group is used to control the connection relationship between the converter group, the synchronous generator unit, and the power supply side, as well as the connection relationship between voltage source converters VSC1 and VSC2; in this embodiment, the power supply side is specifically the low-voltage side of the main transformer of the power grid or the plant auxiliary power supply; such as Figure 1 and Figure 2 As shown, in this embodiment, the circuit breaker group includes: the circuit breaker group includes circuit breaker QF, and circuit breakers QF1 to QF6;

[0057] The first terminals of circuit breakers QF1, QF2, QF3, and QF6 are connected together. The second terminal of circuit breaker QF1 is used to connect to the plant power supply. The second terminal of circuit breaker QF2 is connected to the high-voltage side of transformer TR1. The second terminal of circuit breaker QF3 is connected to the high-voltage side of transformer TR2 and the first terminal of circuit breaker QF5. The second terminal of circuit breaker QF6 is used to connect to the low-voltage side of the main transformer. The second terminal of circuit breaker QF5 is used to connect to the generator terminal of the synchronous generator unit. The first terminal of circuit breaker QF1 is used to connect to the low-voltage side of the main transformer, and the second terminal of circuit breaker QF2 is used to connect to the generator terminal of the synchronous generator unit.

[0058] The first terminal of circuit breaker QF4 is connected to the output terminal of DC chopper, and the second terminal is used to connect to the excitation winding of synchronous generator.

[0059] The excitation and frequency conversion start multiplexing device provided in this embodiment serves as either the excitation system or the frequency conversion start system for a synchronous generator unit. In this embodiment, the circuit structure can be changed by switching the states of each circuit breaker, thereby achieving the conversion between different operating modes. When QF1 (or QF6), QF2, QF4, and QF5 are closed, VSC1 operates in rectification mode, VSC2 operates in inverter mode, and the system operates in frequency conversion start mode. When QF1 (or QF6), QF2, QF3, and QF4 are closed, both VSC1 and VSC2 operate in inverter mode, and the system operates in pure excitation mode.

[0060] Considering that pumped storage units cannot self-start when operating as electric motors, and that the main circuits of commonly used static frequency converters (SFCs) are generally composed of semi-controlled devices (thyristors), which suffer from high harmonic content, poor control performance, and complex startup processes, this embodiment, as a preferred implementation, uses fully controlled switching devices (IGBTs) in the voltage source converters VSC1 and VSC2 and the DC chopper. Figure 2 As shown, in this embodiment, the voltage source converters VSC1 and VSC2 based on fully controllable devices have the same structure, both being three-phase voltage source two-level structures (this embodiment uses a two-level structure, but it is not limited to a two-level structure; a three-level structure, a five-level structure, or an MMC structure can also be used; it is also not limited to voltage source converters; a current source converter can also be used to implement it). Each phase bridge arm includes two IGBTs with two parallel diodes, denoted as T1 and T2; the emitter and collector of each IGBT are connected to the positive and negative terminals of the diodes connected in parallel, respectively.

[0061] The collector of T1 serves as the first end of the bridge arm, the emitter of T1 is connected to the collector of T2 as the midpoint of the bridge arm, and the emitter of T2 serves as the second end of the bridge arm. In the same three-phase circuit, the first ends of the three-phase bridge arms are connected as the positive terminal of the DC side of the three-phase circuit, the second ends of the three-phase bridge arms are connected as the negative terminal of the DC side of the three-phase circuit, and the midpoint of the three-phase bridge arms serves as the AC side connection terminal of the three-phase circuit. The gate of each IGBT is connected to the control system. Figure 2 As shown, VSC1 contains 6 IGBTs, numbered S1 to S6; VSC2 contains 6 IGBTs, numbered S7 to S12; the collectors of S1, S3, and S5 (S7, S9, and S11) serve as the first ends of their respective bridge arms, and the emitters of S2, S6, and S4 (S8, S12, and S10) serve as the second ends of their respective bridge arms. The emitters of S1, S3, and S5 are connected to the collectors of S2, S6, and S4, respectively, and the emitters of S7, S9, and S11 are connected to the collectors of S8, S12, and S10, respectively.

[0062] The positive and negative terminals of the DC side of VSC1 are connected to the positive and negative terminals of the DC side of VSC2, respectively.

[0063] like Figure 2 As shown, in this embodiment, the DC chopper based on fully controllable devices includes two bridge arms, each of which contains two IGBTs with two parallel diodes connected at the top and bottom, denoted as T3 and T4; the emitter and collector of each IGBT are respectively connected to the positive and negative terminals of the diodes connected in parallel.

[0064] The collector of T3 serves as the first end of the bridge arm, the emitter of T3 is connected to the collector of T4 as the midpoint of the bridge arm, and the emitter of T4 serves as the second end of the bridge arm. In the excitation chopper circuit, the first ends of the two bridge arms are connected as the positive terminal of the excitation chopper circuit, the second ends of the two bridge arms are connected as the negative terminal of the excitation chopper circuit, and the midpoint of the two bridge arms serves as the output terminal of the excitation chopper circuit. The gate of each IGBT is connected to the control system. Figure 2 As shown, in this embodiment, the excitation chopper circuit includes four IGBTs, namely S13 to S16. The collectors of S13 and S15 serve as the first end of their respective bridge arms, and the emitters of S14 and S16 serve as the second end of their respective bridge arms. The emitters of S13 and S15 are connected to the collectors of S14 and S16, respectively.

[0065] The positive and negative terminals of the excitation chopper circuit are connected to the positive and negative terminals of VSC1 and VSC2, respectively.

[0066] In this embodiment, all switching devices in VSC1, VSC2 and the excitation chopper circuit are fully controllable switching devices IGBTs, which are more flexible in control, more controllable, and do not have the problem of commutation failure.

[0067] like Figure 1 and Figure 2 As shown, this embodiment also includes a voltage-stabilizing capacitor C and a startup unit;

[0068] The voltage regulator capacitor C is used to ensure the stability of the DC side voltage, to obtain the excitation current for chopping, to provide reactive power to the grid side, and to provide a stable voltage source for the inverter to obtain frequency conversion AC. The two ends of the voltage regulator capacitor C are connected in parallel with the DC side of the voltage source converter VSC1, the DC side of the voltage source converter VSC2, and the input terminal of the DC chopper.

[0069] The starting unit is used to limit the starting current during frequency conversion startup and exits after startup; the two ends of the starting unit are connected to the low-voltage side of transformer TR1 and the AC side of voltage source converter VSC1, respectively.

[0070] In this embodiment, each voltage source converter can adopt... Figure 2The single converter power cabinet shown can also adopt a multi-cabinet parallel structure to increase the capacity of the excitation system and the frequency conversion starting system, meet the needs of large-capacity pumped storage units, and further improve the operational reliability of the system.

[0071] In this embodiment, the excitation and frequency conversion starting multiplexing device is used as an excitation system. Voltage source converters VSC1 and VSC2 are connected in parallel and both operate in rectification mode. The DC chopper is also operational. The AC sides of VSC1 and VSC2 are connected to the synchronous generator motor terminals via transformers TR1 and TR2, employing a self-excitation method. The DC side is connected in parallel to the DC chopper to rectify the stepped-down AC terminal voltage into a DC voltage. Simultaneously, reactive power can be directly absorbed or injected into the grid through the generator terminals. The output of the DC chopper is connected to the excitation winding of the synchronous generator motor to regulate its excitation voltage. Compared to traditional excitation systems that only include a single-channel configuration of VSC1 and the DC chopper, this embodiment adds a parallel excitation channel, consisting of VSC2 and the DC chopper, thereby effectively improving the reactive power support capability of the excitation system. Since the excitation and frequency conversion start-up multiplexing device provided in this embodiment, when used as an excitation system, can both provide excitation current to the synchronous generator motor and inject (absorb) reactive power to the generator terminals, it can improve reactive power support capability and enhance the stability support capability of the pumped storage unit. Furthermore, when the synchronous generator motor requires emergency braking or rapid switching of operating conditions, VSC1 and VSC2 operate in parallel and synchronously in inverter mode, quickly feeding back the rotational kinetic energy of the synchronous generator motor to the system, accelerating braking and stopping, making the operating condition switching process faster, and also achieving energy savings.

[0072] When the excitation and frequency conversion starting multiplexing device provided in this embodiment is used as a frequency conversion starting system, voltage source converters VSC1 and VSC2 are connected in series and operate in rectification and inversion states, respectively. The chopper is in the excitation control state for starting the synchronous generator motor. TR1 is used as a step-down transformer and TR2 is used as a step-up transformer. The input terminal of TR1 is connected to the low-voltage side of the main transformer connected to the system bus or to the plant power supply. The output terminal is connected to the input terminal of VSC1 to reduce the voltage level and provide starting power. The output terminal of VSC1 is connected to the input terminal of VSC2 after passing through a voltage stabilizing capacitor to convert the power frequency AC to DC. The output terminal of VSC2 is connected to the stator terminal of the generator after being stepped up by TR2 to invert the DC to AC with adjustable frequency, so that the synchronous generator motor can achieve frequency conversion soft starting. In this variable frequency starting system, VCS1 and the DC chopper form the excitation channel, providing excitation current to the rotor of the synchronous generator motor. VSC1 and VSC2 form the variable frequency starting channel, providing variable frequency starting current to the stator of the synchronous generator motor. This integrates excitation and variable frequency starting, reducing costs while further improving system operating efficiency.

[0073] like Figure 1 and Figure 2 As shown, this embodiment also includes: a control module; the voltage source converters VSC1 and VSC2 and each switching device in the DC chopper are all connected to the control module;

[0074] The control module is used to generate switching signals based on the required terminal voltage feedback value of the synchronous generator and the required reactive power feedback value absorbed or injected by the power grid when the excitation and frequency conversion start-up multiplexing device is used as the excitation system of the synchronous generator. This signal controls the opening and closing of the fully controlled devices in the excitation system so that the terminal voltage of the synchronous generator and the reactive power absorbed or injected by the power grid are equal to the command value.

[0075] The control module is also used to generate switching signals based on the speed feedback value and current feedback value of the synchronous unit when the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous unit, so as to control the opening and closing of the fully controlled devices in the frequency conversion start-up system and make the speed and current of the synchronous unit equal to the command value.

[0076] In summary, this embodiment employs two voltage source converters based on fully controllable devices. By changing the series-parallel connection method of the two converters, the excitation system and the frequency converter starting system of the fully controllable devices are reused. That is, when the two converters are connected in parallel, they are used as the excitation system, improving the controllable capacity of the excitation system, enhancing reactive power support capability, and realizing inverter energy feedback. When the two converters are connected in series, they can be used as both the excitation system and the frequency converter starting system, achieving the function of two channels with one structure, improving system efficiency and stability. At the same time, since this embodiment integrates the frequency converter starting system and the excitation system into one device through reuse, it can effectively reduce equipment size and floor space, thereby reducing the maintenance cost of auxiliary equipment for pumped storage. Furthermore, after the pumped storage unit is in normal operation, by controlling the circuit breaker of the circuit breaker group, the two converters and DC chopper will continue to work as the excitation system, thus avoiding the problem of resource waste.

[0077] It is easy to understand that the excitation and frequency conversion start-up multiplexing device provided in this embodiment can also be applied to other types of synchronous units such as synchronous condensers and synchronous motors.

[0078] Example 2:

[0079] A synchronous generator system includes: a synchronous generator and the excitation and frequency conversion start-up multiplexing device provided in Embodiment 1 above; in this embodiment, the synchronous generator is specifically a synchronous generator motor in a pumped storage unit, and the connection relationship between the synchronous generator motor and the excitation and frequency conversion start-up multiplexing device is as follows. Figure 1 and Figure 2 As shown, specifically, the excitation winding of the synchronous generator motor is connected to the output terminal of the DC chopper via circuit breaker QF4, and the motor terminal of the synchronous generator motor is connected to the second terminal of circuit breakers QF and QF5.

[0080] Example 3:

[0081] The control method for the synchronous generator system provided in Embodiment 2 above is used to coordinate the cooperation between excitation, frequency conversion starting, and synchronous grid connection. The control method includes:

[0082] (1) VSC1, VSC2 and the chopper check their own equipment status. When there is no fault, no alarm and no external interlock signal input, they send a "ready" signal to the monitoring system.

[0083] (2) The monitoring system outputs the "close circuit breaker QF4, QF5" signal and checks whether the circuit breaker position is normal;

[0084] (3) The monitoring system outputs the signal “close circuit breaker QF1 or QF6 and close circuit breaker QF2” and checks whether the circuit breaker position is normal.

[0085] (4) VSC1 is triggered to conduct and the voltage output is checked to see if it is normal;

[0086] (5) The chopper is triggered to conduct and sends a "excitation has been put into operation" signal to the monitoring system;

[0087] (6) Perform rotor position detection. If the detection is correct, trigger VSC2 to conduct, the frequency converter outputs current, and the unit starts.

[0088] (7) When the unit speed reaches the set synchronous speed, the monitoring system outputs a “synchronization engaged” signal;

[0089] (8) The synchronizing device sends an adjustment signal to regulate the unit speed and voltage;

[0090] (9) When the synchronizing device determines that the grid connection conditions are met, it sends the “circuit breaker QF closed, QF5 opened” signal and sends the “lockout output” signal to VSC2 to complete the synchronizing grid connection and exit the frequency conversion system;

[0091] (10) After the unit is running normally, close the circuit breaker QF3 again, VSC2 will be triggered to conduct and enter the excitation-only working mode.

[0092] Example 4:

[0093] A multi-machine shared system, such as Figure 3 As shown, it includes: a shared rectifier, a shared transformer TR1, a selection module, a circuit breaker QF1 for connecting to the plant power supply, N synchronous generator sets, and N voltage source converters VSC2-1 to VSC2-N, N DC choppers, N transformers TR2-1 to TR2-N, and N circuit breaker sets corresponding to the N synchronous generator sets; in this embodiment, N=2, and the two synchronous generator sets included are both synchronous generator motors in pumped storage units, i.e. Figure 3 Synchronous generator motor 1 and synchronous generator motor 2 in the middle;

[0094] like Figure 2 As shown, the DC side of the voltage source converter and the input terminal of the DC chopper corresponding to each synchronous generator unit are connected in parallel; the high voltage side and low voltage side of each transformer are connected to the generator terminal of the corresponding synchronous generator unit and the AC side of the voltage source converter, respectively, and the output terminal of each DC chopper is connected to the excitation winding of the corresponding synchronous generator unit.

[0095] The low-voltage side of the shared transformer is connected to the AC side of the shared rectifier, and the high-voltage side of the shared transformer is used to connect to the power supply side; the selection module includes two access switches that correspond one-to-one with the two synchronous generators; after the access switches are closed, the DC side of the corresponding voltage source converter is also connected in parallel with the DC side of the shared rectifier;

[0096] The circuit breaker assembly includes: circuit breaker QF5 connected between the high-voltage side of the transformer and the generator terminal of the synchronous generator set; circuit breaker QF connected between the generator terminal of the synchronous generator set and the low-voltage side of the corresponding main transformer; circuit breaker QF4 connected between the output terminal of the DC chopper and the excitation winding of the synchronous generator set; and circuit breaker QF6 connected between the low-voltage side of the main transformer and the high-voltage side of the common transformer.

[0097] This embodiment, based on the reuse of the excitation system and the frequency converter starting system, enables the sequential starting of multiple synchronous units. Specifically, when starting the first unit, the common rectifier is switched to the first unit via the access switch corresponding to the first unit in the selection module. The VSC2-1 of the first unit operates in inverter mode. The common rectifier and the excitation chopper form the excitation channel, and the common rectifier and VSC2-1 form the frequency converter starting channel. Its specific operation process is similar to that of Embodiment 2 above. When starting the second unit, the common rectifier is switched to the second unit. At this time, the VSC2-2 of the second unit operates in inverter mode. The common rectifier and the excitation chopper form the excitation channel, and the common rectifier and VSC2-2 form the frequency converter starting channel. Its specific operation process is similar to that of Embodiment 2 above. It should be noted that in other embodiments of the present invention, multiple synchronous generators can be shared. The synchronous generators can also be synchronous condensers, synchronous generators, or other synchronous generators. The synchronous generators can be the same or different. By connecting the shared rectifier to different synchronous generators, the startup and excitation of different generators can be achieved. The specific working principle and process are similar to those in Embodiment 2 above, and will not be repeated here.

[0098] Overall, the multi-unit shared system described in this embodiment, based on the advantages of reusing the excitation system and the frequency conversion starting system, can enable multiple pumped storage units to start in turn, further improving the system's operating efficiency. At the same time, the switching devices in the shared rectifier can directly use more reliable and lower-cost thyristors or diodes. If a thyristor converter is used, zero-start voltage boost can also be achieved, thus eliminating the need for a starting unit, further simplifying the system structure, and effectively improving the system's operating efficiency and reliability.

[0099] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multiplexed device for excitation and frequency conversion starting, characterized in that, include: The converter group and the circuit breaker group; the converter group includes voltage source converters VSC1 and VSC2, a DC chopper, and transformers TR1~TR2; The DC side of the voltage source converter VSC1, the DC side of the voltage source converter VSC2, and the input terminal of the DC chopper are connected in parallel; the AC side connection terminals of the voltage source converters VSC1 and VSC2 are respectively connected to the low-voltage side of the transformers TR1 and TR2; and the output terminal of the DC chopper is used to connect to the excitation winding of the synchronous generator. The circuit breaker group is used to control the connection relationship between the converter group and the synchronous generator and the power supply side, as well as the connection relationship between the voltage source converters VSC1 and VSC2; During operation, the voltage source converters VSC1 and VSC2 operate in parallel and both operate in rectification mode, with the excitation and frequency conversion start-up multiplexing device serving as the excitation system of the synchronous generator set; or, the voltage source converters VSC1 and VSC2 operate in series and operate in rectification and inversion modes respectively, with the excitation and frequency conversion start-up multiplexing device serving as the frequency conversion start-up system of the synchronous generator set.

2. The excitation and frequency conversion start-up multiplexing device as described in claim 1, characterized in that, The switching devices in the voltage source converters VSC1 and VSC2, as well as the DC chopper, are all fully controllable devices.

3. The excitation and frequency conversion start-up multiplexing device as described in claim 2, characterized in that, Also includes: Control module; The voltage source converters VSC1 and VSC2, as well as each switching device in the DC chopper, are all connected to the control module. The control module is used to generate a switching signal based on the required terminal voltage feedback value of the synchronous generator and the required reactive power feedback value absorbed or injected by the power grid when the excitation and frequency conversion start-up multiplexing device is used as the excitation system of the synchronous generator. This signal is used to control the opening and closing of the fully controlled devices in the excitation system, so that the terminal voltage of the synchronous generator and the reactive power absorbed or injected by the power grid are equal to the command value. The control module is also used to generate switching signals based on the speed feedback value and current feedback value of the synchronous unit when the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous unit, so as to control the opening and closing of the fully controlled devices in the frequency conversion start-up system and make the speed and current of the synchronous unit equal to the command value.

4. The excitation and frequency conversion start-up multiplexing device as described in claim 3, characterized in that, The circuit breaker group includes: the circuit breaker group includes circuit breaker QF, and circuit breakers QF1 to QF6; The first terminals of circuit breakers QF1, QF2, QF3, and QF6 are connected together. The second terminal of circuit breaker QF1 is used to connect to the plant power supply. The second terminal of circuit breaker QF2 is connected to the high-voltage side of transformer TR1. The second terminal of circuit breaker QF3 is connected to the high-voltage side of transformer TR2 and the first terminal of circuit breaker QF5. The second terminal of circuit breaker QF6 is used to connect to the low-voltage side of the main transformer. The second terminal of circuit breaker QF5 is used to connect to the generator terminal of the synchronous generator unit. The first terminal of circuit breaker QF1 is used to connect to the low-voltage side of the main transformer, and the second terminal of circuit breaker QF6 is used to connect to the generator terminal of the synchronous generator unit. The first end of the circuit breaker QF4 is connected to the output end of the DC chopper, and the second end is used to connect to the excitation winding of the synchronous unit.

5. A synchronous generator system, characterized in that, include: Synchronous generator set and excitation and frequency conversion start-up multiplexing device as described in any one of claims 1 to 4.

6. The synchronous generator system as described in claim 5, characterized in that, The synchronous unit is a synchronous generator motor, synchronous condenser, or synchronous motor of a pumped storage unit.

7. The control method for a synchronous generator system as described in claim 5 or 6, characterized in that, The circuit breaker group in the excitation and frequency conversion start-up multiplexing device of the synchronous generator system includes: the circuit breaker group includes circuit breaker QF, and circuit breakers QF1 to QF6; The first terminals of circuit breakers QF1, QF2, QF3, and QF6 are connected together. The second terminal of circuit breaker QF1 is used to connect to the plant power supply. The second terminal of circuit breaker QF2 is connected to the high-voltage side of transformer TR1. The second terminal of circuit breaker QF3 is connected to the high-voltage side of transformer TR2 and the first terminal of circuit breaker QF5. The second terminal of circuit breaker QF6 is used to connect to the low-voltage side of the main transformer. The second terminal of circuit breaker QF5 is used to connect to the generator terminal of the synchronous generator unit. The first terminal of circuit breaker QF1 is used to connect to the low-voltage side of the main transformer, and the second terminal of circuit breaker QF6 is used to connect to the generator terminal of the synchronous generator unit. The first terminal of circuit breaker QF4 is connected to the output terminal of the DC chopper, and the second terminal is used to connect to the excitation winding of the synchronous unit. Furthermore, when the excitation and frequency conversion start-up multiplexing device serves as the frequency conversion start-up system for the synchronous generator unit, the control method includes: (S1) After the voltage source converters VSC1 and VSC2 and the DC chopper are all in normal condition, close circuit breakers QF4 and QF5. After the positions of each circuit breaker are checked and found to be normal, proceed to step (S2). (S2) Close circuit breaker QF1 or QF6 and close circuit breaker QF2. After verifying that the positions of each circuit breaker are normal, proceed to step (S3). (S3) Trigger the conduction of the voltage source converter VSC1, and after detecting that its output voltage is normal, proceed to step (S4). (S4) Trigger the chopper to turn on, and after detecting that the rotor position is correct, proceed to step (S5). (S5) Trigger the conduction of the voltage source converter VSC2 to start the unit.

8. The control method as described in claim 7, characterized in that, When the excitation and frequency conversion start-up multiplexing device is used as the frequency conversion start-up system of the synchronous unit, after step (S5), the process further includes: when the speed of the synchronous unit reaches the synchronous set speed, proceeding to step (S6). (S6) Adjust the speed and voltage of the synchronous generator set. When the grid connection conditions are met, proceed to step (S7). (S7) Close circuit breaker QF, open circuit breaker QF5, and lock out the output of voltage source converter VSC2 to complete synchronous grid connection and exit the frequency conversion start system.

9. The control method as described in claim 8, characterized in that, When the excitation and frequency conversion start-up multiplexing device is used as the excitation system of the synchronous generator, the control method includes: After the synchronous generator unit is in normal operation, the circuit breaker QF3 is closed, and the voltage source converter VSC2 is triggered to conduct.

10. A multi-machine shared system, characterized in that, include: A shared rectifier, a shared transformer, a selection module, and a circuit breaker QF1 for connecting to the plant power supply. N Synchronous generator units, and with N Each synchronous generator unit corresponds to one N A voltage source converter N A DC chopper, N A transformer and N A set of circuit breakers; N It is a positive integer greater than or equal to 2; The DC side of the voltage source converter and the input terminal of the DC chopper corresponding to each synchronous generator unit are connected in parallel; the high voltage side and low voltage side of each transformer are connected to the generator terminal of the corresponding synchronous generator unit and the AC side of the voltage source converter, respectively, and the output terminal of each DC chopper is connected to the excitation winding of the corresponding synchronous generator unit. The low-voltage side of the shared transformer is connected to the AC side connection terminal of the shared rectifier, and the high-voltage side of the shared transformer is used to connect to the power supply side; the selection module includes... N Each synchronous generator unit corresponds to one N One access switch; After the access switch is closed, the DC side of the corresponding voltage source converter is still connected in parallel with the DC side of the common rectifier; The circuit breaker assembly includes: circuit breaker QF5 connected between the high-voltage side of the transformer and the generator terminal of the synchronous generator set; circuit breaker QF connected between the generator terminal of the synchronous generator set and the low-voltage side of the corresponding main transformer; circuit breaker QF4 connected between the output terminal of the DC chopper and the excitation winding of the synchronous generator set; and circuit breaker QF6 connected between the low-voltage side of the main transformer and the high-voltage side of the common transformer. At work, N Each synchronous generator unit starts up in turn.

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