Flywheel energy storage phase modifier system based on brushless doubly-fed motor

Abstract

The invention relates to the technical field of power system equipment, in particular to a flywheel energy storage phase modifier system based on a brushless doubly-fed motor, which comprises a large-inertia flywheel, the brushless doubly-fed motor, a switch, a converter, a transformer and a power grid, according to the integrated system, the advantages of the synchronous phase modifier, the brushless doubly-fed motor and the flywheel energy storage technology are combined, the good inertia response capability is achieved, an electric brush and a sliding ring are omitted for the brushless doubly-fed motor, the reliability of high-rotating-speed operation is improved, and the operation and maintenance cost is reduced. Through flexible control of winding alternating current excitation and wide-range rotation speed interval operation, rapid active and reactive power support can be provided for a power grid, and multiple functions of power generation, energy storage, phase adjustment and the like can be realized. According to the method, the inherent inertia level of the power system can be remarkably improved, transient active-frequency support is realized in a strong disturbance scene, meanwhile, the dynamic reactive-voltage compensation capability is realized, and the frequency and voltage stability of the power system can be effectively maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of power system devices and equipment, and in particular to a flywheel energy storage phase regulator system based on a brushless doubly-fed motor. Background Art

[0002] With the influx of renewable energy into the power grid, the problem of insufficient grid inertia support has become increasingly prominent. With a high penetration of renewable energy and a relatively high proportion of power electronic interface loads, the inherent inertia level of new energy microgrids is extremely low. At the initial moment of a disturbance, the frequency change rate of the microgrid system increases dramatically. Load steps are on the time scale of 10 to 100 milliseconds, making these disturbances highly sensitive to control delays. While inverters have fast response speeds, inappropriate control strategies make it difficult to smooth out transient frequency fluctuations. Due to insufficient inertia support, the microgrid frequency may drop or rise rapidly, easily triggering protective action, exceeding the safety limit and jeopardizing stability. Therefore, other effective measures are urgently needed to improve the inertia level of the microgrid system.

[0003] Synchronous condensers are widely used to improve voltage stability and increase system inertia. However, in microgrids with low short-circuit ratios, frequency and voltage stability issues often arise simultaneously. Traditional synchronous condensers, due to their fixed speed, cannot provide active power and therefore cannot contribute to maintaining frequency stability.

[0004] Flywheel energy storage technology offers significant advantages in supporting high-transient active power. It can quickly respond to unbalanced power in the system during disturbances and is significantly effective in reducing the depth of frequency drops (when the load suddenly increases) and accelerating frequency recovery. The principle of flywheel energy storage technology is as follows: when storing energy, the motor operates as a motor, absorbing energy from the system, and the flywheel rotor accelerates to convert electrical energy into kinetic energy. When releasing energy, the motor operates as a generator, releasing energy to the system, and the flywheel rotor decelerates to convert kinetic energy into electrical energy. Compared to other energy storage methods, flywheel energy storage has the following advantages: it requires virtually no maintenance, has a long service life that is essentially unrestricted by the number of charge and discharge cycles, is easy to install, and is environmentally friendly.

[0005] The motor currently applied to the flywheel energy storage system is mainly a permanent magnet synchronous motor. The flywheel energy storage motor adopts a full-power converter, and the back-to-back frequency converter isolates the electromagnetic coupling between the flywheel motor and the power grid, so the rotational inertia of the flywheel cannot directly participate in improving the inherent inertia of the power system. The essence is to simulate the inertia response capability through power electronic converters and control algorithms, and to equivalent the fast power regulation capability of the flywheel energy storage system as rotational inertia, which needs to rely on real-time measurement and closed-loop control. In the micro-grid system with very low inherent inertia, after a large disturbance, the rate of change of frequency (RoCoF) at the initial moment is very large, resulting in a large number of distributed power sources being disconnected, which aggravates the further reduction of the system frequency. High RoCoF poses a serious threat to system stability, equipment safety and power quality. In addition, the traditional flywheel energy storage motor does not have a phase modulation function, and it is difficult to balance reactive power dynamic compensation. If the grid-side converter is used for reactive power compensation, the intervention of reactive power further increases the capacity of the full-power converter, increasing the equipment cost.

[0006] If the flywheel energy storage motor and the synchronous phase modifier are separated, independent equipment can maximize the frequency and voltage support performance, but the cost economy of the initial investment is under great pressure, the operation and maintenance cost of independent maintenance of two sets of equipment is high, and the redundancy is limited by the physical space, which is not suitable for space-sensitive occasions such as island micro-grid. SUMMARY

[0007] The purpose of the present application is to provide a flywheel energy storage phase modifier system based on a brushless doubly-fed motor, to solve the problems of insufficient inherent inertia level and frequency and voltage instability caused thereby, high equipment cost and high operation and maintenance cost existing in the prior art.

[0008] To achieve the above-mentioned purpose, the present application provides a flywheel energy storage phase modifier system based on a brushless doubly-fed motor, comprising:

[0009] a large-inertia flywheel, a brushless doubly-fed motor, a switch, a converter, a transformer and a power grid;

[0010] The large-inertia flywheel is used for storing kinetic energy and providing inertia support for the power grid.

[0011] The brushless doubly-fed motor comprises a stator power winding and a stator control winding, wherein the stator power winding is connected to the power grid through the switch, and the stator control winding is connected to the power grid through the converter, the transformer and the switch in turn.

[0012] The switch includes a power side switch and a control side switch. When the power side switch is closed, the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator power winding and the power side switch based on the current operating mode; when the control side switch is closed, the stator control winding controls the converter, and the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator control winding, converter, transformer and control side switch based on the current operating mode.

[0013] In some embodiments of the present application, the converter includes a machine-side converter and a grid-side converter;

[0014] One side of the grid-side converter is connected to the grid through a transformer, and the other side is connected to the DC part, which is used to maintain the constant voltage in the system's DC bus and maintain the constant DC voltage of the flywheel energy storage phase regulator system under different operating modes.

[0015] One side of the machine-side converter is connected to the DC link, and the other side is directly connected to the control winding of the brushless doubly-fed motor. The machine-side converter is used to perform AC excitation control on the brushless doubly-fed motor, and control the operating mode of the flywheel energy storage phase regulator system through input instructions, so that the brushless doubly-fed motor is maintained in different speed ranges, ensuring that different operating modes can be switched in real time.

[0016] In some embodiments of the present application, the transformer is used to adjust the grid voltage so that the DC voltage and AC voltage levels on both sides of the grid-side converter match.

[0017] In some embodiments of the present application, the monitoring subsystem of the flywheel energy storage phase condenser system collects grid parameters in real time, determines whether the grid is in a fault state based on the grid parameters, and adjusts the operation mode of the flywheel energy storage phase condenser system based on the grid fault state;

[0018] Among them, the grid parameters include: grid frequency, frequency change rate, three-phase voltage, and three-phase current.

[0019] In some embodiments of the present application, the monitoring subsystem of the flywheel energy storage phase regulator system simultaneously collects the voltage value, current value, DC bus voltage value of the stator power winding and the stator control winding, the speed and torque of the flywheel energy storage phase regulator, the temperature rise of the inverter, the temperature rise of the motor winding, the active power size, reactive power size and power factor of the interaction between the system and the power grid, and uploads the monitoring data to an external device in real time.

[0020] In some embodiments of the present application, the operating modes include: A hot standby mode, B reactive power-phase modulator mode, C active power-frequency support mode, D active-frequency-reactive-voltage coordinated control mode, E speed limiting mode, and F speed recovery mode.

[0021] In some embodiments of the application, when no power grid disturbance occurs, the A thermal standby mode is selected; when the power grid disturbance occurs, the B reactive power-phase modifier mode, the C active power-frequency support mode or the D active-frequency-reactive voltage coordinated control mode is selected based on the power grid parameters; if the system does not have overcharge or overdischarge, the above process is repeated; if the system has overcharge or overdischarge, the next step is determined, if the frequency and voltage have recovered, the F speed recovery mode is selected, if the frequency and voltage have not recovered, the E speed limiting mode is selected.

[0022] The advantages and beneficial effects of the present application over the prior art are:

[0023] 1. The control winding of the brushless doubly-fed motor is connected to the power grid through a converter and a transformer, which can quickly adjust the power output and timely compensate for the power shortage or excess of the power grid, further stabilizing the power grid frequency; by controlling the closing state of the switch, the system can flexibly switch between different operating modes to adapt to different power grid operating requirements.

[0024] 2. The thermal standby mode of the present application can effectively improve the power grid inertia level and suppress the frequency change rate; the active power-frequency support mode of the present application provides transient support for the active power-frequency of the power grid, suppresses the frequency drop depth, accelerates the frequency recovery, and improves the frequency stability; the reactive power-phase modifier mode of the present application participates in the reactive voltage regulation of the power grid, provides reactive power compensation for the power grid, and maintains voltage stability; the active-frequency, reactive-voltage coordinated control mode of the present application realizes simultaneous protection of the stability of the power grid frequency and voltage.

[0025] The technical solutions of the present application will be further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The structure diagram of the flywheel energy storage phase modifier system based on the brushless doubly-fed motor of the present application;

[0027] Figure 2 The structure diagram of the brushless doubly-fed motor with the rotor coaxially connected to the flywheel of the present application;

[0028] Figure 3 The basic structure diagram of the flywheel energy storage phase modifier system based on the brushless doubly-fed motor of the present application;

[0029] Figure 4 The main power circuit diagram of the flywheel energy storage phase modifier system based on the brushless doubly-fed motor of the present application;

[0030] Figure 5 The flowchart of different operating states and state switching determination of the present application;

[0031] Figure 6This is a block diagram of the excitation and grid-connected control of the flywheel energy storage phase regulator based on the brushless doubly-fed motor of the present invention;

[0032] Figure 7 This is a block diagram of active-reactive power decoupling control of a flywheel energy storage phase regulator based on a brushless doubly-fed motor according to the present invention;

[0033] Figure 8 The waveform diagram of PQ decoupling control, speed, and electromagnetic torque in the active-frequency and reactive-voltage coordinated control modes of the present invention;

[0034] Figure 9 This is a waveform diagram of the present invention for improving the grid inertia response and maintaining the transient frequency. DETAILED DESCRIPTION

[0035] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] like Figure 1 As shown, the present invention provides a flywheel energy storage phase regulator system based on a brushless doubly fed motor, comprising:

[0038] Large inertia flywheel, brushless doubly-fed motor, switch, converter, transformer, power grid;

[0039] The high-inertia flywheel is used to store kinetic energy and provide inertia support for the power grid;

[0040] The brushless doubly-fed motor includes a stator power winding and a stator control winding. The stator power winding is connected to the grid through a switch, and the stator control winding is connected to the grid through a converter, a transformer, and a switch in sequence.

[0041] The switch includes a power side switch and a control side switch. When the power side switch is closed, the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator power winding and the power side switch based on the current operating mode; when the control side switch is closed, the stator control winding controls the converter, and the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator control winding, converter, transformer and control side switch based on the current operating mode.

[0042] In some embodiments of the present application, the converter includes a machine-side converter and a grid-side converter;

[0043] One side of the grid-side converter is connected to the grid through a transformer, and the other side is connected to the DC part, which is used to maintain the constant voltage in the system's DC bus and maintain the constant DC voltage of the flywheel energy storage phase regulator system under different operating modes.

[0044] One side of the machine-side converter is connected to the DC link, and the other side is directly connected to the control winding of the brushless doubly-fed motor. The machine-side converter is used to perform AC excitation control on the brushless doubly-fed motor, and control the operating mode of the flywheel energy storage phase regulator system through input instructions, so that the brushless doubly-fed motor is maintained in different speed ranges, ensuring that different operating modes can be switched in real time.

[0045] In some embodiments of the present application, the transformer is used to adjust the grid voltage so that the DC voltage and AC voltage levels on both sides of the grid-side converter match.

[0046] In some embodiments of the present application, the monitoring subsystem of the flywheel energy storage phase condenser system collects grid parameters in real time, determines whether the grid is in a fault state based on the grid parameters, and adjusts the operation mode of the flywheel energy storage phase condenser system based on the grid fault state;

[0047] Among them, the grid parameters include: grid frequency, frequency change rate, three-phase voltage, and three-phase current.

[0048] In some embodiments of the present application, the monitoring subsystem of the flywheel energy storage phase regulator system simultaneously collects the voltage value, current value, DC bus voltage value of the stator power winding and the stator control winding, the speed and torque of the flywheel energy storage phase regulator, the temperature rise of the inverter, the temperature rise of the motor winding, the active power size, reactive power size and power factor of the interaction between the system and the power grid, and uploads the monitoring data to an external device in real time.

[0049] In some embodiments of the present application, the operating modes include: A hot standby mode, B reactive power-phase modulator mode, C active power-frequency support mode, D active-frequency-reactive-voltage coordinated control mode, E speed limiting mode, and F speed recovery mode.

[0050] In some embodiments of the present application, when no grid disturbance occurs, hot standby mode A is selected; when a grid disturbance occurs, reactive power-phase regulator mode B, active power-frequency support mode C or active power-frequency-reactive power-voltage coordinated control mode D is selected based on grid parameters; if the system does not have overcharge or over-discharge, the above process is repeated; if the system has overcharge or over-discharge, the next step of judgment is performed. If the frequency and voltage have recovered, speed recovery mode F is selected; if the frequency and voltage have not recovered, speed limitation mode E is selected.

[0051] The following further details the operating status of the flywheel energy storage phase regulator system in the power grid.

[0052] Hot Standby Mode: In this mode, the flywheel energy storage condenser is connected to the grid, maintaining its speed within ±2% of the rated speed, effectively keeping it within its normal operating range. In hot standby mode, when the speed falls below 0.98 of the rated speed, an acceleration command is triggered, stopping acceleration at 1.02 of the rated speed. The flywheel energy storage condenser then slowly decreases due to mechanical wear, repeating the process until it reaches 0.98 of the rated speed.

[0053] There are two purposes for setting the ±2% range of the rated speed: first, the constant speed control command is not started within the ±2% range, which avoids the reciprocating movement of the controller to maintain a constant speed value. The setting of this dead zone avoids frequent action of the controller; second, within the ±2% range, the flywheel energy storage phase regulator is in an open-loop control state. In this state, the rotational inertia of the flywheel is part of the system inertia, which directly increases the inherent inertia level of the power system and can effectively reduce the frequency change rate when a disturbance occurs.

[0054] In hot standby mode, the flywheel energy storage condenser maintains near rated speed, drawing only a small amount of power from the grid to balance system losses. The flywheel stores rated kinetic energy, ready to provide voltage and frequency support for microgrids with a high proportion of renewable energy. An overall speed control strategy ensures a stable and reliable standby state, maintaining speed near the set rated value.

[0055] B Reactive power-Phase modulator mode: In this mode, the flywheel energy storage phase modulator is still in speed control state, and the machine side converter adjusts the amplitude of the excitation current according to the instruction to control the exchange of reactive power between the flywheel energy storage phase modulator and the power system. When the voltage fluctuation occurs in the renewable energy power station, the flywheel energy storage phase modulator will obtain the reactive power instruction according to the reactive power-voltage (Q-U) droop characteristic, and emit or absorb a certain amount of reactive power according to the instruction. When the grid voltage is significantly lower than the normal level, the flywheel energy storage phase modulator system control emits inductive reactive power to achieve reactive power compensation; when the grid voltage is significantly higher than the normal level, the flywheel energy storage phase modulator system control emits capacitive reactive power to absorb excess reactive power.

[0056] In the reactive power-phase modulator mode, the flywheel energy storage phase modulator can also be a long-term load as a phase modulator. According to the reactive power instruction given by the operating system, the flywheel energy storage phase modulator system becomes a constant power form of reactive load, and the reactive load type can be flexibly switched between capacitive and inductive, and the size of the load reactive power can also be flexibly set within a certain range of rated capacity, which has a significant effect on maintaining long-term reactive power balance and voltage stability of the power system.

[0057] If a frequency fluctuation occurs at this time, the flywheel energy storage phase modulator system will switch to the active-frequency and reactive-voltage coordinated control mode to provide reactive and active power support for the microgrid.

[0058] C Active power-frequency support mode: In this mode, the flywheel energy storage phase modulator is between the highest speed and the lowest speed, and the monitoring system real-time concerns the frequency change of the grid. When the frequency fluctuation exceeds the normal range, the upper instruction will switch the machine side converter to the power control mode. When the grid frequency drops, the flywheel energy storage phase modulator will obtain the active power instruction according to the active power-frequency (P-f) droop characteristic, and the flywheel energy storage will release the corresponding active power according to the instruction to support the active power demand of the renewable energy station, compensate the unbalanced management of the grid and suppress the frequency fluctuation. When the grid frequency rises, the flywheel energy storage phase modulator will also follow the active power instruction to store the excess energy in the flywheel, and absorb the power surplus of the grid to maintain the frequency stability.

[0059] For instantaneous strong step disturbance, the flywheel energy storage phase modifier system will provide strong transient active power support. According to the actual situation, the flywheel energy storage phase modifier has the ability to overload 3 times the rated power for a short time. The flywheel energy storage phase modifier system provides fast and strong active power support for the power grid, suppresses the frequency drop as much as possible, speeds up the recovery speed of the frequency, supports the rapid passage of abnormal frequency of renewable energy units and maintains forced operation, makes the frequency recover quickly to maintain the stable operation of each distributed energy unit, and provides reliable guarantee for the transient stability of frequency. Therefore, the flywheel energy storage phase modifier system has the advantages of fast response, fast suppression and fast recovery in maintaining frequency stability when dealing with short-time high-frequency strong transient step disturbance.

[0060] Due to the high randomness of frequency fluctuations, the flywheel energy storage phase modifier will alternate between charging and discharging states, which will cause the flywheel rotor to accelerate or decelerate repeatedly, causing speed fluctuations. Therefore, in the active power-frequency support mode, if the flywheel energy storage phase modifier speed changes greatly, making the speed higher than the overcharge lower limit or lower than the overdischarge upper limit, the flywheel energy storage phase modifier enters the overcharge or overdischarge state, and the control instruction will switch the flywheel energy storage phase modifier system to the speed limit mode, at this time the absorption or emission of active power will be reduced until stopped. If the frequency fluctuation disappears and the power grid no longer needs active power support, the flywheel energy storage phase modifier will again return to the hot standby mode to deal with the next disturbance.

[0061] D Active-frequency, reactive-voltage coordinated control mode: In a microgrid system with low short-circuit ratio, frequency and voltage stability problems can easily occur at the same time. When frequency and voltage are abnormal at the same time, or frequency fluctuation occurs during reactive phase modulation stable operation, the flywheel energy storage phase modifier system will enter the active-frequency, reactive-voltage coordinated control mode.

[0062] In this mode, there are four quadrant operating states of active-reactive (P-Q): inductive power generation state, capacitive power generation state, inductive energy storage state, and capacitive energy storage state. In this mode, the flywheel energy storage phase modifier system needs to provide both reactive and active support to the grid to simultaneously alleviate voltage and frequency fluctuations. The control logic in this mode is the same as the active power-frequency support mode in the reactive power-phase modifier mode.

[0063] E Speed ​​Limit Mode: In active-frequency support mode, the rotor speed of the flywheel energy storage phase regulator will fluctuate within a large range. Due to the mechanical strength of the flywheel rotor and the maximum slip rate of the doubly fed generator, in order to ensure safe operation, the rotor speed of the flywheel energy storage phase regulator should be controlled between the upper and lower limits. To prevent the rotor speed from exceeding the upper and lower limits due to long-term charging and discharging, when entering the overcharge or over-discharge state, the upper command will switch the flywheel energy storage phase regulator system to speed limit mode and limit the charge and discharge power. The specific control logic is as follows:

[0064] When the flywheel is overcharged, the flywheel energy storage condenser's maximum charging power is limited to prevent the rotor speed from exceeding the maximum. As the speed increases, the maximum charging power decreases linearly until it reaches zero, at which point the flywheel can no longer charge. However, the flywheel energy storage condenser's discharge power is unrestricted, allowing it to continue providing output active power and frequency control support to the renewable energy grid at its maximum discharge power.

[0065] When the flywheel is in an over-discharge state, the maximum discharge power of the flywheel energy storage condenser is limited to prevent the rotor speed from falling below the minimum value. As the speed increases, the maximum discharge power decreases linearly until it reaches zero, at which point the flywheel can no longer discharge. At this point, the charge power of the flywheel energy storage condenser is not limited.

[0066] Speed ​​Recovery Mode: When the flywheel energy storage condenser system is in an overcharge or overdischarge state, and the grid frequency disturbance has recovered for a period of time, the upper control command switches the system to speed recovery mode. In this mode, the flywheel energy storage condenser absorbs or releases active power to gradually restore the speed to near the rated speed. Afterward, the flywheel energy storage condenser system switches back to hot standby mode. To prevent the flywheel charging and discharging process from causing further fluctuations in the grid frequency, the upper control command adjusts the charge and discharge power limits in speed recovery mode to appropriately control the speed of speed recovery.

[0067] The following describes the selection and determination of different operating states of the flywheel energy storage condenser system. According to the speed of the flywheel energy storage condenser, it is divided into over-discharge state, normal state and over-charge state. The switching between different states of the flywheel energy storage condenser system is based on Figure 5 The flowchart in .

[0068] The hot standby mode of the present invention can effectively improve the inertia level of the power grid and suppress the frequency change rate. The active power-frequency support mode of the present invention provides transient support for the active power-frequency of the power grid, suppresses the depth of frequency drop, accelerates frequency recovery, and improves frequency stability. The reactive power-phase modulator mode of the present invention participates in the reactive power-voltage regulation of the power grid, performs reactive power compensation on the power grid, and maintains voltage stability. The active power-frequency and reactive power-voltage coordinated control modes of the present invention achieve the goal of simultaneously ensuring the stability of the power grid frequency and voltage.

[0069] The beneficial effects of the present invention are:

[0070] 1. The control winding of the brushless doubly-fed motor is connected to the grid through a converter and transformer. This allows for rapid adjustment of power output, timely compensation for power shortages or surpluses in the grid, and further stabilization of the grid frequency. By controlling the closed state of the switch, the system can flexibly switch between different operating modes to adapt to varying grid operation requirements.

[0071] 2. The hot standby mode of the present invention can effectively improve the inertia level of the power grid and suppress the frequency change rate; the active power-frequency support mode of the present invention provides transient support for the active power-frequency of the power grid, suppresses the depth of frequency drop, accelerates frequency recovery, and improves frequency stability; the reactive power-phase modulator mode of the present invention participates in the reactive power-voltage regulation of the power grid, performs reactive power compensation on the power grid, and maintains voltage stability; the active power-frequency and reactive power-voltage coordinated control modes of the present invention achieve the simultaneous guarantee of the stability of the power grid frequency and voltage.

[0072] The following describes the implementation of the present invention in detail with reference to specific examples.

[0073] The flywheel energy storage phase regulator of the present invention is based on the traditional phase regulator, and adopts the method of adding a flywheel, on the one hand, to increase the rotational inertia of the phase regulator system, and on the other hand, to realize the energy storage function. This project uses a brushless doubly fed motor and a flywheel installed on the rotor to form a flywheel energy storage phase regulator. The flywheel energy storage phase regulator system is an electromechanical energy conversion and storage device. The present invention is mainly composed of an inertia wheel with large rotational inertia and high speed, a high-speed bearing supporting the rotor, a brushless doubly fed motor that realizes the mutual conversion of electrical energy and mechanical energy, a grid-side converter, a machine-side converter, a transformer, a control device, an upper operating platform, etc. By controlling the conversion of flywheel mechanical energy and electrical energy, it can cope with various disturbances in the frequency and voltage of the power grid, participate in transient support, and maintain the stable and reliable operation of the power system. The structural schematic diagram of the present invention is shown as follows. Figures 2-3 shown.

[0074] The flywheel energy storage phase modifier system of the application is connected with the power grid through two groups of three-phase switches, one group of switches is connected between the power winding of the brushless doubly-fed motor and the power grid, and the other group of switches is connected between the transformer and the power grid. The voltage of the power grid is reduced through the transformer, passes through the buffer resistance and the electric reactance, and then passes through the grid-side transformer, the DC bus capacitor, the motor-side converter, and finally the AC outlet of the motor-side converter is connected with the control winding of the brushless doubly-fed motor.

[0075] In the flywheel system of the application, the large inertia flywheel is coaxially connected with the rotor of the brushless doubly-fed motor through a transmission shaft, and the high-speed bearing supports the flywheel rotor. The flywheel rotor hub material needs to meet the requirements of high strength and low density to cope with the load caused by high-speed rotation. Aluminum alloy is one of the representatives of such materials and is also the flywheel hub material used in the application.

[0076] Reference Figure 4 The main power circuit diagram of the flywheel energy storage phase modifier system of the application, and the strong electric operation control steps of the application are mainly described by the diagram.

[0077] The starting mode of the flywheel energy storage phase modifier system based on the brushless doubly-fed motor of the application is direct starting through series resistance, without the need for a complex starting control scheme, which is simple and easy to operate. The specific operation is as follows: close the starting resistance at the outlet of the control winding of the brushless doubly-fed motor, the resistance value of the starting resistance is generally several ohms, which is used to improve the starting torque of the flywheel motor. After closing, the switch between the power winding and the power grid is closed, and direct starting is realized. During the starting process, the speed of the flywheel energy storage phase modifier continuously rises and finally maintains at the natural synchronous speed:

[0078]

[0079] In the above formula, f p is the frequency of the power grid, generally 50Hz, p p is the pole pair number of the power winding, p c is the pole pair number of the control winding, and n0 is the natural synchronous speed.

[0080] After the flywheel energy storage phase modifier of the application is successfully started, the first priority of the next step is to make the motor run in double-fed mode. The frequency, size and phase of the voltage of the power winding and the control winding of the brushless doubly-fed motor need to meet a specific matching relationship, which is the key condition for the stable operation of the brushless doubly-fed motor. There is a strict "synchronous" corresponding relationship between the frequency of the power winding, the frequency of the control winding and the motor speed:

[0081]

[0082] The specific embodiment adopted for the flywheel energy storage phase modifier to enter double-fed stable operation is as follows: after the motor is started, when the rotating speed approaches the natural synchronous speed, the starting resistance at the end of the control winding is disconnected, and the switch between the power winding and the power grid is disconnected, the excitation and grid-connection control is started, the closed-loop control of the excitation current is performed on the machine-side converter, and the control block diagram is shown in the accompanying drawing Figure 6 .

[0083] When the excitation control is performed, the power winding machine end will induce a voltage, the voltage across the switch is observed, the amplitude, frequency, phase, phase sequence and waveform of the grid voltage and the machine end excitation induced voltage are compared, when the voltage waveforms on both sides of the switch are highly overlapped and meet the grid-connection conditions, the grid-connection instruction can be issued, the switch is closed, and at this time the power winding is successfully connected to the power grid.

[0084] When the flywheel energy storage phase modifier of the application is in stable double-fed operation, the upper operation platform issues a rotating speed control instruction, at this time the rotating speed of the motor can be stabilized near the rated rotating speed through the rotating speed closed-loop control. When the rotating speed of the flywheel energy storage phase modifier enters the interval of ±2% of the rated rotating speed, the flywheel energy storage phase modifier system can enter the hot standby state.

[0085] When the voltage and frequency of the power grid are normal, the flywheel energy storage phase modifier system of the application is in hot standby in the power grid, and the hot standby state is the normal state in most time. In the hot standby mode, the flywheel energy storage phase modifier is connected with the power grid, and the flywheel only absorbs a small amount of power from the power grid to balance its own loss. The rotating speed of the rotor is stabilized in the range of 0.98-1.02 times of the rated rotating speed. The operation mechanism is as follows: when the rotating speed drops to 0.98 times of the rated rotating speed, the system starts the acceleration control until the rotating speed rises to 1.02 times of the rated rotating speed and stops; then the rotating speed slowly drops due to mechanical loss, and the above process is repeated.

[0086] The ±2% "dead zone" design can avoid frequent action of the controller, and the constant rotating speed control instruction is not triggered in the interval. When the rotating speed rising instruction stops, the flywheel is in the open-loop control state, the moment of inertia of the flywheel directly participates in the inherent inertia support of the power system, and the frequency variation rate under disturbance is effectively reduced.

[0087] The reactive power-phase modifier mode is based on speed control, the amplitude of the excitation current is dynamically adjusted through the machine-side converter, and the reactive power interaction with the power grid is realized. When the voltage fluctuation occurs in the renewable energy power station, the system generates a reactive power instruction based on the reactive power-voltage (Q-U) droop characteristic: if the grid voltage is low, the inductive reactive power compensation is output; if the voltage is high, the capacitive reactive power is output to absorb the excess reactive power.

[0088] In addition, this mode supports the flywheel to run as a constant reactive load for a long time, the reactive type (capacitive / inductive) and capacity can be flexibly adjusted within the rated range, and plays a key role in maintaining the long-term reactive power balance and voltage stability of the power system.

[0089] In the active power-frequency support mode, the flywheel speed dynamically changes between the upper and lower limits, and the system monitors the grid frequency in real time. When the frequency fluctuation exceeds the normal range, the machine-side converter switches to the power control mode: if the frequency drops, the grid lacks active power, and the active-power-frequency droop characteristic is used to generate instructions, and the flywheel releases active power to compensate for the shortage and suppress the frequency drop; if the frequency rises, the grid has excess power, and the flywheel absorbs excess power to store and maintain the frequency stability.

[0090] For instantaneous strong step disturbance, the system has an overload capacity of 3 times the rated power for a short time, which can quickly suppress frequency drop and accelerate recovery, support renewable energy units to pass through abnormal frequency and stabilize operation. If the speed fluctuates greatly due to frequent charging and discharging, exceeding the lower limit of overcharging or the upper limit of overdischarging, the system will switch to the "speed limit mode"; when the frequency disturbance disappears, it will return to the "hot standby mode".

[0091] The active power-frequency and reactive power-voltage coordinated control mode is suitable for microgrids with low short-circuit ratio, where frequency and voltage stability problems often occur simultaneously, or in the "reactive power-phase modifier mode" under frequency fluctuation.

[0092] The system needs to provide active and reactive power support and operate in the active-reactive (P-Q) four-quadrant state (inductive generation, capacitive generation, inductive storage, capacitive storage). The control logic integrates the strategies of "active power-frequency support" and "reactive power-phase modifier" modes to simultaneously alleviate frequency and voltage fluctuations. The active and reactive decoupling control of the flywheel energy storage phase modifier based on the brushless doubly-fed motor of the present invention is shown in the accompanying drawings. Figure 7 .

[0093] The speed limit mode is a protection mechanism triggered in the "active power-frequency support mode" when the speed exceeds the mechanical strength or the double-fed motor slip rate limit. In the overcharge state (speed close to the upper limit), the maximum charging power is limited and decreases linearly to zero as the speed increases, but the discharging power is not limited and can still provide active support at full power. In the overdischarge state (speed close to the lower limit), the maximum discharging power is limited and decreases linearly to zero as the speed decreases, but the charging power is not limited. By limiting the power, the speed is prevented from exceeding the limit, ensuring safe operation of the system.

[0094] When the flywheel is in the overcharge / overdischarge state and the grid frequency disturbance has been restored for a period of time, the system switches to the speed recovery mode, gradually adjusts the speed to the rated value through absorbing or releasing active power, and then switches back to the "hot standby mode". To avoid secondary frequency fluctuations during the recovery process, the charging and discharging power limits need to be dynamically adjusted to control the speed recovery rate.

[0095] The flywheel energy storage phase shifter system based on the brushless doubly-fed motor of the present invention provides inertia support, frequency stabilization, and voltage regulation for the power grid. Based on the above six operating modes, the system is described in detail as follows:

[0096] The hot standby mode, active power-frequency support mode, reactive power-phase regulator mode and active-reactive coordination mode together constitute the three-dimensional support system of the flywheel energy storage phase regulator for the power grid, which improves the reliability of the power grid from three dimensions: inertia support, frequency stability and voltage regulation: in the hot standby mode, the flywheel is maintained in the rated speed range of ±2%, and the "dead zone" design is used to avoid frequent action of the controller. Its rotational inertia is directly used as part of the inherent inertia of the power grid to participate in the operation. Under disturbance, it releases or absorbs kinetic energy through slight changes in speed, slows down the frequency change rate, and enhances the anti-disturbance resilience of the power grid; the active power-frequency support mode monitors the power grid frequency in real time. When the fluctuation exceeds the limit, the base The system dynamically releases (frequency drops) or absorbs (frequency rises) active power based on the Pf droop characteristic, especially under strong step disturbances, with a short-term overload capacity of three times the rated power. This can quickly suppress the depth of frequency drops, accelerate frequency recovery, and support renewable energy units in traversing abnormal frequencies to avoid grid disconnection, further ensuring stable frequency recovery. The reactive power-phase modulator mode adjusts the excitation current through the machine-side converter and dynamically outputs inductive (voltage is too low) or capacitive (voltage is too high) reactive power based on the QU droop characteristic. This not only provides rapid compensation for transient voltage fluctuations, but also can flexibly adjust the reactive power type and capacity as a constant reactive load over the long term, maintaining long-term reactive power balance and voltage stability in the grid. The three work together to form a comprehensive support for "inertia-frequency-voltage", significantly improving the stability and risk resistance of power grids with a high proportion of renewable energy.

[0097] The application of the present invention in a microgrid system is further described below. The flywheel energy storage phase regulator system based on a brushless doubly fed motor of the present invention is suitable for power grid scenarios where inertia support is insufficient and frequency and voltage stability problems are easily generated. This specific implementation scenario selects a microgrid system with a rated capacity of 400kVA and an AC bus voltage of 400V. The entire microgrid system does not have a synchronous generator (the diesel engine should be used as a cold standby), and the distributed renewable energy units are dominated by virtual synchronous generator control. The inertia level of the microgrid system tends to zero.

[0098] The flywheel energy storage phase regulator system based on the brushless double-fed motor of the present invention is applied to the microgrid system. Figure 8 The waveform diagram of PQ decoupling control, speed, and electromagnetic torque in the active-frequency and reactive-voltage coordinated control mode of the present invention is shown. The speed and accuracy of the active and reactive output response can meet the frequency and voltage regulation requirements of the microgrid system.

[0099] Figure 9The waveform diagram for improving power grid inertia response and maintaining transient frequency. Due to the inertia support in the hot standby mode of the application, the power grid frequency change rate at the initial disturbance moment is significantly reduced from 4.17 Hz / s to 2.93 Hz / s, the frequency drop depth is improved from 48.45 Hz to 49.12 Hz, and the frequency recovery time is reduced from 5.6 s to 3.3 s.

[0100] In the present application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. If there is an inconsistency, the meaning as explained in the specification or derived from the content described in the specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0101] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A flywheel energy storage phase regulator system based on a brushless doubly fed motor, characterized in that: include: Large inertia flywheel, brushless doubly-fed motor, switch, converter, transformer, power grid; The high-inertia flywheel is used to store kinetic energy and provide inertia support for the power grid; The brushless doubly-fed motor includes a stator power winding and a stator control winding. The stator power winding is connected to the grid through a switch, and the stator control winding is connected to the grid through a converter, a transformer, and a switch in sequence. The switch includes a power side switch and a control side switch. When the power side switch is closed, the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator power winding and the power side switch based on the current operating mode; when the control side switch is closed, the stator control winding controls the converter, and the flywheel energy storage phase condenser system exchanges power with the power grid in sequence through the stator control winding, converter, transformer and control side switch based on the current operating mode.

2. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 1, characterized in that: The converter includes a machine-side converter and a grid-side converter; One side of the grid-side converter is connected to the grid through a transformer, and the other side is connected to the DC part, which is used to maintain the constant voltage in the system's DC bus and maintain the constant DC voltage of the flywheel energy storage phase regulator system under different operating modes. One side of the machine-side converter is connected to the DC link, and the other side is directly connected to the control winding of the brushless doubly-fed motor. The machine-side converter is used to perform AC excitation control on the brushless doubly-fed motor, and control the operating mode of the flywheel energy storage phase regulator system through input instructions, so that the brushless doubly-fed motor is maintained in different speed ranges, ensuring that different operating modes can be switched in real time.

3. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 2, characterized in that: The transformer is used to adjust the grid voltage so that the DC voltage and AC voltage levels on both sides of the grid-side converter match.

4. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 3, characterized in that: The monitoring subsystem of the flywheel energy storage phase condenser system collects grid parameters in real time, determines whether the grid is in a fault state based on the grid parameters, and adjusts the operating mode of the flywheel energy storage phase condenser system based on the grid fault state; Among them, the grid parameters include: grid frequency, frequency change rate, three-phase voltage, and three-phase current.

5. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 4, characterized in that: The monitoring subsystem of the flywheel energy storage phase regulator system simultaneously collects the voltage and current values ​​of the stator power winding and stator control winding, the DC bus voltage value, the speed and torque of the flywheel energy storage phase regulator, the temperature rise of the converter, the temperature rise of the motor winding, the active power and reactive power of the interaction between the system and the power grid, and uploads the monitoring data to external equipment in real time.

6. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 5, characterized in that: The operating modes include: A hot standby mode, B reactive power-phase regulator mode, C active power-frequency support mode, D active power-frequency-reactive power-voltage coordinated control mode, E speed limit mode, and F speed recovery mode.

7. A flywheel energy storage phase regulator system based on a brushless doubly fed motor according to claim 6, characterized in that: When there is no grid disturbance, hot standby mode A is selected; When a grid disturbance occurs, select B reactive power-phase regulator mode, C active power-frequency support mode or D active-frequency-reactive-voltage coordinated control mode based on grid parameters; if the system does not have overcharge or over-discharge, repeat the above process; if the system has overcharge or over-discharge, proceed to the next step of judgment. If the frequency and voltage have recovered, select F speed recovery mode; if the frequency and voltage have not recovered, select E speed limit mode.

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