A high-inertia variable-speed pumped storage unit

Abstract

The present invention discloses a high-inertia variable-speed pumped-storage unit, belonging to the technical field of power equipment. The unit comprises a pump-turbine, a flywheel, a motor system, and a step-up transformer, all connected in sequence. The motor system comprises a doubly-fed electric generator, a four-quadrant converter, and an excitation transformer. The flywheel is coaxially connected to the pump-turbine and doubly-fed electric generator, respectively. By adding a flywheel to the existing technology to increase the moment of inertia, the present invention can effectively increase the unit's moment of inertia and inertia time constant, thereby improving the unit's effective inertial energy storage. The doubly-fed electric generator provides an inertial torque through the rotating inertial energy storage to resist load fluctuations and power supply disturbances.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power equipment, and more specifically, relates to a high-inertia variable-speed pumped storage unit. Background Art

[0002] Pumped storage technology is currently the primary method for large-scale energy storage. It is also the most technologically mature, economically efficient, and readily amenable to large-scale development. It provides a green, low-carbon, clean, and flexible power source for the power system and has become a crucial tool for promoting my country's energy system transformation and the construction of a new power system. Variable-speed pumped storage units can operate at optimal efficiency, balancing both turbine-generator operation and pumping motor operation. This reduces cavitation, noise, vibration, and wear on the motor and prime mover, extending unit life. They also effectively increase unit response speed and enhance the power system's ability to rapidly regulate and compensate for frequency and voltage, thereby enhancing the safety, reliability, stability, and flexibility of power system operation. Therefore, as variable-speed unit technology matures and its economic advantages are widely recognized, variable-speed units are expected to gradually become the mainstream unit in pumped-storage power plants.

[0003] Renewable energy sources such as photovoltaics and wind power in new power systems are highly intermittent and volatile. Although existing variable-speed pumped storage units have basic functions such as peak regulation, frequency regulation, phase regulation, energy storage, system backup and black start, their role in addressing problems such as sudden fluctuations in instantaneous active power faced by new power systems is still relatively limited, and it is difficult to suppress system crashes that may be caused by sudden failures.

[0004] Therefore, in order to further improve the ability of pumped storage units to cope with sudden fluctuations in the system's active power and improve the system's frequency stability, it is necessary to propose a new pumped storage unit or further transform the existing pumped storage unit to significantly increase the unit's physical rotational inertia, and use the variable speed operation capability and instantaneous power output capability of the variable speed motor to provide the system with instantaneous active power absorption or release, thereby improving the system's anti-interference ability, reducing drastic frequency fluctuations, and ensuring the system's power supply quality and reliability. Summary of the Invention

[0005] In response to the defects or improvement needs of the existing technology, the purpose of the present invention is to provide a high-inertia variable-speed pumped-storage unit, which effectively improves the physical inertia of the pumped-storage unit, increases the effective inertial energy storage of the variable-speed unit itself, and has the ability to instantaneously suppress or compensate for sudden and severe fluctuations in the active power of the power system. It aims to solve the problems of insufficient synchronous inertia level and weak frequency transient support capability of the new power system, and can be applied to the construction of new pumped-storage power stations or the renovation of existing ones.

[0006] To achieve the above object, the present invention provides a high-inertia variable-speed pumped storage unit, comprising: a water pump turbine, a flywheel, a motor system and a step-up transformer connected in sequence, wherein the motor system comprises a doubly-fed motor generator, a four-quadrant converter and an excitation transformer;

[0007] The pump turbine is coaxially connected to the doubly-fed motor generator and is used to serve as a load or prime mover of the doubly-fed motor generator to achieve pumping and power generation functions;

[0008] The flywheel is coaxially connected to the doubly-fed motor generator and is used to increase the moment of inertia of the unit;

[0009] The four-quadrant converter includes a machine-side converter and a grid-side converter, wherein the machine-side converter is connected to the rotor winding of the doubly-fed electric generator, and achieves decoupling control of the active power and reactive power of the doubly-fed electric generator by adjusting the amplitude, phase, and frequency of the rotor current. When the water flow velocity changes, the rotor excitation current frequency is controlled to keep the stator terminal voltage frequency of the doubly-fed electric generator consistent with the grid; the grid-side converter is connected to the grid, and achieves decoupling control of the active power and reactive power of the doubly-fed electric generator through grid voltage vector control technology, and ensures that the DC bus voltage is stable and the grid-side current waveform is sinusoidal;

[0010] The excitation transformer is connected to the low-voltage side of the step-up transformer and the four-quadrant converter, and is used to provide a three-phase AC excitation power supply for the doubly-fed electric generator;

[0011] The step-up transformer is connected to the motor system and the power grid, and is used to achieve voltage conversion and electrical isolation between the motor system and the power grid.

[0012] Furthermore, the flywheel is preferably a high-inertia flywheel. This can be an explicit flywheel independent of the doubly-fed electric generator rotor, mechanically connected to the rotor, and thereby increasing the unit's physical moment of inertia. Alternatively, it can be an implicit flywheel integrated with the rotor, increasing the unit's physical moment of inertia by increasing the rotor's volume and weight, thereby increasing the inertia time constant and the unit's effective inertial energy storage. Doubly-fed electric generators using a high-inertia flywheel rotor can utilize magnetic bearings, as needed, to reduce weight pressure on the bearings.

[0013] The doubly-fed electric generator includes: a rotor structure and a stator structure, wherein the stator structure includes: a stator core and a stator winding; the rotor structure includes: a rotor core, a rotor winding, brushes and slip rings; the current in the rotor winding is fed in through the brushes and slip rings; the doubly-fed electric generator should have the function of generating short-term high voltage, high current or high power pulses to quickly absorb or release the instantaneous power required by the power grid.

[0014] The pump turbine is coaxially connected to the doubly-fed motor generator and is used to serve as a load or prime mover of the doubly-fed motor generator to achieve pumping and power generation functions;

[0015] The large inertia flywheel should have a larger diameter or a higher speed to increase the unit's rotational inertia and inertia time constant;

[0016] The four-quadrant converter includes a machine-side converter and a grid-side converter, wherein the machine-side converter is connected to the slip ring and the rotor winding of the doubly-fed electric generator through brushes, and can achieve flexible decoupling control of the active power and reactive power of the doubly-fed electric generator by adjusting the amplitude, phase and frequency of the rotor current, and keep the stator terminal voltage frequency of the doubly-fed electric generator consistent with the grid by controlling the rotor excitation current frequency when the water flow velocity changes; the grid-side converter is connected to the grid through a transformer, and can achieve decoupling control of the active power and reactive power of the doubly-fed electric generator through grid voltage vector control technology, and ensure that the DC bus voltage is stable and the grid-side current waveform is sinusoidal; the four-quadrant converter is a partial-power AC-DC-AC converter, and its capacity is smaller than that of the doubly-fed electric generator, which can significantly reduce system costs.

[0017] The excitation transformer is connected to the low-voltage side of the step-up transformer and the four-quadrant converter, and is used to provide a three-phase AC excitation power supply for the doubly-fed motor generator, and together with the four-quadrant converter and the doubly-fed motor generator, constitutes a motor system;

[0018] The step-up transformer is connected to the motor system and the power grid, and is used to achieve voltage conversion and electrical isolation between the motor system and the power grid.

[0019] The present invention also provides a control method for a high-inertia variable-speed pumped storage unit, which is applicable to situations where the grid frequency fluctuates, that is, the grid frequency suddenly drops or rises from a stable state in a short period of time, and includes the following steps:

[0020] When a sudden frequency drop occurs in the power grid, the flywheel provides rotational inertia to the generator set, and the doubly-fed generator provides positive inertia torque through rotating inertial energy storage, preventing the frequency from dropping and maintaining the stability of the system frequency. By adjusting the excitation current, the rotor synthetic magnetomotive force of the doubly-fed generator leads the stator synthetic magnetomotive force. The motor system outputs overload electrical energy to the outside world, converting the rotor stored energy into mechanical energy. The rotor of the doubly-fed generator slows down, providing active power compensation to the power grid and suppressing power grid frequency fluctuations.

[0021] When a sudden frequency rise occurs in the power grid, the flywheel provides rotational inertia to the unit, and the doubly-fed electric generator provides negative inertia torque through rotating inertial energy storage to prevent the frequency from rising and maintain the stability of the system frequency. By adjusting the excitation current, the rotor synthetic magnetomotive force of the doubly-fed electric generator lags behind the stator synthetic magnetomotive force. The motor system absorbs overload electrical energy from the outside world and converts excess active power into rotor energy storage. The rotor of the doubly-fed electric generator increases speed, provides active compensation to the power grid, and suppresses power grid frequency fluctuations.

[0022] The present invention also provides a control system for a high-inertia variable-speed pumped storage unit, comprising: a computer-readable storage medium and a processor;

[0023] The computer-readable storage medium is used to store executable instructions;

[0024] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the above-mentioned control method.

[0025] Compared with the prior art, the above technical solutions proposed by the present invention can achieve the following:

[0026] Beneficial effects:

[0027] (1) The high-inertia variable-speed pumped storage unit provided by the present invention adds a flywheel to the existing technology to increase the rotational inertia, which can effectively increase the rotational inertia and inertia time constant of the unit, and improve the effective inertial energy storage of the unit itself. The doubly fed electric generator provides an inertial torque through the rotating inertial energy storage to resist load changes and power supply disturbances. When the load in the system increases or the power supply decreases, the unit's rotating inertial energy storage enables the doubly fed electric generator to provide electric energy in a short time, offsetting the disturbance caused by the load increase, thereby maintaining the stability of the system frequency; conversely, when the load in the system decreases or the power supply increases, the rotating inertial energy storage of the doubly fed electric generator can also provide a reverse inertial torque, quickly absorbing the power of the power grid, and preventing the system frequency from rising too quickly.

[0028] (2) The high-inertia variable-speed pumped storage unit provided by the present invention has a doubly-fed electric generator with the function of releasing or absorbing instantaneous pulse power, which can be combined with a large-inertia rotor and an AC excitation control system to achieve rapid smoothing of instantaneous power fluctuations in the power system, thereby improving the anti-interference ability of the power system, reducing severe frequency fluctuations, and ensuring the quality and reliability of the system power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a high-inertia variable-speed pumped storage unit provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is 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 for explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0031] Figure 1 This is a schematic diagram of a high-inertia variable-speed pumped storage unit provided in Example 1 of the present invention.

[0032] like Figure 1As shown, the present invention provides a high-inertia variable-speed pumped-storage unit, comprising: a doubly-fed electric generator, a pump-turbine, a high-inertia flywheel, a four-quadrant converter, an excitation transformer, a step-up transformer, and the like. The doubly-fed electric generator comprises a rotor structure and a stator structure. The stator structure comprises a stator core and stator windings; the rotor structure comprises a rotor core, rotor windings, brushes, and slip rings; the current in the rotor windings is fed through the brushes and slip rings. The doubly-fed electric generator can be mechanically connected to the high-inertia flywheel to increase the unit's physical moment of inertia. Alternatively, the moment of inertia can be increased by increasing the volume and weight of the rotor body, thereby increasing the inertia time constant and enhancing the unit's effective inertial energy storage. The doubly-fed electric generator using a large flywheel rotor can utilize magnetic levitation bearings as needed to reduce weight pressure on the bearings. The doubly-fed electric generator should be capable of generating short-term high-voltage, high-current, or high-power pulses to quickly absorb or release the instantaneous power required by the power grid. The pump-turbine is coaxially connected to the doubly-fed electric generator and is used to serve as the load or prime mover of the doubly-fed electric generator to achieve pumping and power generation functions. The high-inertia flywheel should have a large diameter or a high speed to increase the unit's rotational inertia and inertia time constant. The four-quadrant converter includes a machine-side converter and a grid-side converter, wherein the machine-side converter is connected to the slip ring and the rotor winding of the doubly-fed electric generator via brushes. It can achieve flexible decoupling control of the active power and reactive power of the doubly-fed electric generator by adjusting the amplitude, phase, and frequency of the rotor current. When the water flow velocity changes, it controls the rotor excitation current frequency to maintain the stator terminal voltage frequency of the doubly-fed electric generator consistent with the grid. The grid-side converter is connected to the grid via a transformer and can achieve decoupling control of the active power and reactive power of the doubly-fed electric generator using grid voltage vector control technology, while ensuring DC bus voltage stability and grid-side current sinusoidal properties. The four-quadrant converter is a partial-power AC-DC-AC converter with a capacity smaller than that of the doubly-fed electric generator, which can significantly reduce system costs. The excitation transformer is connected to the low-voltage side of the step-up transformer and the four-quadrant converter, and is used to provide a three-phase AC excitation power supply for the doubly-fed electric generator, and together with the four-quadrant converter and the doubly-fed electric generator, constitutes a motor system; the step-up transformer is connected to the motor system and the power grid, and is used to achieve voltage conversion and electrical isolation between the motor system and the power grid.

[0033] When the pumped storage power station is operating normally, the high-inertia variable-speed pumped storage unit can cooperate with instructions to complete basic functions such as peak regulation, frequency regulation, phase regulation, energy storage, system backup and black start.

[0034] When a sudden drop in frequency causes a sudden fluctuation in the power grid, the high inertia of the high-inertia variable-speed pumped-storage unit allows the doubly-fed generator to continue providing positive inertia torque, providing inertia support for the grid and instantaneously suppressing frequency fluctuations, preventing rapid frequency drops. Furthermore, AC excitation can be used to achieve rapid pulse power control of the doubly-fed generator. By adjusting the excitation current, the rotor's synthetic magnetomotive force leads the stator's synthetic magnetomotive force. The motor system rapidly outputs high overload electrical energy to the outside world, converting the rotor's stored energy into mechanical energy. The doubly-fed generator's rotor speed is reduced, providing rapid and strong active power compensation to the grid, effectively suppressing grid frequency fluctuations.

[0035] When a sudden and violent frequency fluctuation occurs in the power grid, the high-inertia variable-speed pumped-storage unit's large rotational inertia allows the doubly-fed generator to continue providing negative inertia torque, providing inertia support for the grid and preventing a rapid increase in frequency. Furthermore, AC excitation can be used to achieve rapid pulse power control of the doubly-fed generator. By adjusting the excitation current, the rotor's synthetic magnetomotive force lags the stator's synthetic magnetomotive force. The motor system quickly absorbs high overload electrical energy from the outside world, converting excess active power into rotor energy storage. The doubly-fed generator's rotor speed increases, providing rapid and strong active power compensation to the grid and quickly suppressing grid frequency fluctuations.

[0036] It will be easily understood by those skilled in the art 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 in the scope of protection of the present invention.

Claims

1. A control method for a high-inertia variable-speed pumped-storage unit, the high-inertia variable-speed pumped-storage unit comprising a pump-turbine, a flywheel, a motor system, and a step-up transformer connected in sequence, the motor system comprising a doubly-fed motor generator, a four-quadrant converter, and an excitation transformer; The pump turbine is coaxially connected to the doubly-fed motor generator and is used to serve as a load or prime mover of the doubly-fed motor generator to achieve pumping and power generation functions; The flywheel is coaxially connected to the doubly-fed motor generator and is used to increase the moment of inertia of the unit; The four-quadrant converter includes a machine-side converter and a grid-side converter, wherein the machine-side converter is connected to the rotor winding of the doubly-fed electric generator, and achieves decoupling control of the active power and reactive power of the doubly-fed electric generator by adjusting the amplitude, phase, and frequency of the rotor current. When the water flow velocity changes, the rotor excitation current frequency is controlled to keep the stator terminal voltage frequency of the doubly-fed electric generator consistent with the grid; the grid-side converter is connected to the grid, and achieves decoupling control of the active power and reactive power of the doubly-fed electric generator through grid voltage vector control technology, and ensures that the DC bus voltage is stable and the grid-side current waveform is sinusoidal; The excitation transformer is connected to the low-voltage side of the step-up transformer and the four-quadrant converter, and is used to provide a three-phase AC excitation power supply for the doubly-fed electric generator; The step-up transformer is connected to the motor system and the power grid to achieve voltage conversion and electrical isolation between the motor system and the power grid; It is characterized in that The following steps are involved: When a sudden frequency drop occurs in the power grid, the flywheel provides rotational inertia to the generator set, and the doubly-fed generator provides positive inertia torque through rotating inertial energy storage, preventing the frequency from dropping and maintaining the stability of the system frequency. By adjusting the excitation current, the rotor synthetic magnetomotive force of the doubly-fed generator leads the stator synthetic magnetomotive force. The motor system outputs overload electrical energy to the outside world, converting the rotor stored energy into mechanical energy. The rotor of the doubly-fed generator slows down, providing active power compensation to the power grid and suppressing power grid frequency fluctuations. When a sudden frequency rise occurs in the power grid, the flywheel provides rotational inertia to the unit, and the doubly-fed electric generator provides negative inertia torque through rotating inertial energy storage to prevent the frequency from rising and maintain the stability of the system frequency. By adjusting the excitation current, the rotor synthetic magnetomotive force of the doubly-fed electric generator lags behind the stator synthetic magnetomotive force. The motor system absorbs overload electrical energy from the outside world and converts excess active power into rotor energy storage. The rotor of the doubly-fed electric generator increases speed, provides active compensation to the power grid, and suppresses power grid frequency fluctuations.

2. The control method according to claim 1, characterized in that: The doubly-fed electric generator comprises a rotor structure and a stator structure. The stator structure comprises a stator core and a stator winding. The rotor structure comprises a rotor core, a rotor winding, brushes and a slip ring. The current in the rotor winding is fed in through the brushes and the slip ring.

3. The control method according to claim 1, wherein: The four-quadrant converter is an AC-DC-AC converter, and its capacity is smaller than that of the doubly-fed motor generator.

4. The control method according to claim 2, characterized in that: The flywheel is independent of the rotor body of the doubly-fed electric generator and is connected to the rotor body of the doubly-fed electric generator through mechanical transmission, or is integrated with the rotor body of the doubly-fed electric generator.

5. The control method according to claim 2, characterized in that: The double-fed electric generator adopts a magnetic suspension bearing.

6. A control system for a high-inertia variable-speed pumped storage unit, characterized in that: include: Computer-readable storage media and processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the control method according to any one of claims 1 to 5.

Images