Inertia flywheel and CAES expansion unit composite structure and operation control method

Abstract

The invention discloses an inertia flywheel and CAES expansion unit composite structure and an operation control method, the inertia flywheel and CAES expansion unit composite structure comprises a CAES expansion machine, a synchronous motor and an inertia flywheel rotor, one end of the synchronous motor is connected with the expansion machine through a clutch, and the other end of the synchronous motor is connected with an inertia flywheel through a coupler. The inertia flywheel rotor and the synchronous motor accelerate to the synchronous rotating speed through the excitation regulation self-driven system, and the system works in a reactive grid-connected state and plays the inertia supporting and phase modulation roles of the inertia phase modifier. When power grid dispatching is received and system power generation work is needed, the expansion machine is accelerated to the synchronous rotating speed under the driving of high-pressure gas, the inertia flywheel synchronous motor unit and the expansion machine are coupled to generate power, and the synchronous motor excites to adjust the self-driven system to work in an active power generation state. And when power grid dispatching is received and power generation is stopped, air supply is reduced, the expansion machine is separated from the inertia flywheel synchronous generator, and inertia supporting and phase modulation effects continue to be played. The composite structure can realize multiple functions of inertia support, phase modulation and peak regulation.

Description

Technical Field

[0001] This invention belongs to the field of power grid energy storage and stability control technology, specifically relating to a composite structure and operation control method of an inertial flywheel and compressed air energy storage system (CAES) expander unit, which is particularly suitable for integrated energy systems that improve power grid frequency stability and provide rapid phase adjustment and peak shaving capabilities. Background Technology

[0002] With the continuous expansion of the grid connection scale of renewable energy sources such as wind power and photovoltaics, the inertia level and peak-shaving capacity of the power system are declining, and operating indicators such as frequency and voltage are becoming more sensitive. This places comprehensive demands on new energy storage equipment, requiring it to simultaneously possess large-capacity peak-shaving, rapid power response, and reactive power regulation capabilities. Traditional thermal power units, under the background of gradual retirement or deep peak-shaving, struggle to balance economy and flexibility, and single-function equipment is insufficient to meet the grid's needs for multi-timescale support capabilities.

[0003] On the one hand, compressed air energy storage systems (CAES) are widely used in grid peak shaving due to their advantages such as large capacity and long lifespan. However, they have drawbacks such as slow response speed and inability to provide instantaneous inertia support. Moreover, peak-shaving energy storage technology is characterized by intermittent power generation and non-continuous grid-connected operation, resulting in insufficient utilization of generator sets. On the other hand, inertial flywheel energy storage has the characteristics of high power density, large charge-discharge rate, and fast response speed, and has millisecond-level inertia response capability. However, its energy storage capacity is limited when operating independently (usually only lasting for a few seconds to a few minutes). It is suitable for undertaking short-term, high-power dynamic support tasks, but it is difficult to independently meet the needs of medium- and long-term peak shaving or long-term energy transfer.

[0004] While existing technologies have attempted to combine different types of energy storage technologies, most are simply parallel connections at the electrical level, lacking deep integration at the mechanical level. For example, building independent flywheel power plants and compressed air power plants, although functionally complementary, results in each system having its own independent motor, converter, and auxiliary facilities. Furthermore, ensuring the unit has rapid inertial response capabilities while flexibly switching to high-capacity generation modes, and avoiding mechanical fatigue and shocks caused by frequent start-stop cycles, remains a challenge that existing single or simple hybrid energy storage technologies have not adequately addressed.

[0005] In summary, both existing compressed air energy storage systems and inertial flywheel technology have inherent defects and lack efficient integration mechanisms. Therefore, how to effectively utilize the rapid response characteristics of inertial flywheels while maintaining the advantages of large capacity and long lifespan of compressed air energy storage, and taking into account the needs of grid reactive power regulation and inertial support, and constructing an energy storage generator system that can flexibly switch under different operating scenarios and achieve multi-functional coordination of inertial support, phase regulation and peak shaving, is an urgent technical problem to be solved. Summary of the Invention

[0006] (a) Purpose of the invention To address the aforementioned deficiencies and shortcomings of existing technologies, this invention aims to provide a composite structure and operation control method for an inertial flywheel and CAES expander unit. It achieves shock-free coupling under power frequency rotation conditions through a synchronous clutch, and combines the inertial flywheel synchronous condenser (synchronous generator) with a continuous grid-connected operation mode, balancing inertial support and peak-shaving requirements. This allows for flexible switching between inertial support phase-shifting mode, peak-shaving power generation mode, and power-off mode under different operating scenarios, achieving multi-timescale coordinated control of frequency, voltage, and power balance in the power system. Furthermore, by unifying the shaft system arrangement and bearing support structure, it improves the overall mechanical reliability and energy conversion efficiency of the unit, increases equipment utilization, reduces system investment and operation and maintenance costs, and significantly enhances grid frequency stability and dynamic response performance.

[0007] (II) Technical Solution To achieve the objective of this invention and solve its technical problems, the present invention adopts the following technical solution: The first objective of this invention is to provide a composite structure of an inertia flywheel and a CAES expander unit, used to simultaneously achieve grid inertia support, reactive power phase regulation, and active power peak shaving in a compressed air energy storage system. It includes at least a coaxially arranged CAES expander, a synchronous motor, and an inertia flywheel rotor. One end of the synchronous motor is connected to the CAES expander via a synchronous clutch, and the other end is connected to the inertia flywheel rotor via a coupling. The synchronous clutch is located on the transmission link between the synchronous motor and the CAES expander, and is configured to achieve mechanical coupling or mechanical disengagement between the CAES expander, the synchronous motor, and the inertial flywheel rotor when the speeds of the CAES expander and the synchronous motor meet the preset synchronization conditions at the power frequency rotation state. In the mechanical coupling state, the output torque of the CAES expander is transmitted to the synchronous motor and the inertial flywheel rotor to drive the synchronous motor to output active power to the grid. In the mechanical disengagement state, the CAES expander stops or stops generating electricity while the synchronous motor and the inertial flywheel rotor still rotate coaxially. The synchronous motor is configured to be powered by the grid when it is mechanically disconnected from the CAES expander in order to maintain the inertia flywheel rotor at the power frequency synchronous speed and continuously operate in grid-connected mode. It also provides inertial support to the grid through the combined rotational inertia of the synchronous motor and the inertia flywheel rotor. At the same time, the reactive power output of the synchronous motor is adjusted by the matching excitation regulation self-drive system to achieve grid voltage regulation.

[0008] The second objective of this invention is to provide an operation control method for the above-mentioned composite structure of inertia flywheel and CAES expander unit, comprising at least the following steps: S100. System Start-up and Synchronization: With the synchronous clutch in a mechanically disengaged state, the synchronous motor and inertia flywheel rotor are driven by the excitation regulation self-drive system and accelerated to the power frequency synchronous speed. The excitation current of the synchronous motor is adjusted so that its output voltage amplitude and phase meet the grid connection conditions. The grid connection switch is closed to realize the synchronous connection of the synchronous motor and inertia flywheel rotor with the power grid. S200. Inertia Support Phase Shifting Mode Operation: When connected to the grid and the synchronous clutch is still in a mechanically disengaged state, the synchronous motor is powered by the grid to maintain the inertia flywheel rotor rotating continuously at the power frequency synchronous speed. The combined rotational inertia of the synchronous motor and the inertia flywheel rotor provides inertia support to the grid to suppress frequency fluctuations. At the same time, the excitation current of the synchronous motor is dynamically adjusted by the excitation regulation self-drive system to control the reactive power output and realize grid voltage regulation. S300. Peak shaving mode activation: When a peak shaving power generation command is received from the grid dispatch, the compressed air valve connected to the CAES expander inlet is opened to drive the CAES expander to accelerate. When the difference between the speed of the CAES expander and the speed of the synchronous motor is detected to be less than the preset synchronous threshold, the synchronous clutch is closed to realize the mechanical coupling of the CAES expander with the synchronous motor and the inertial flywheel rotor. S400. Peak shaving power generation mode operation: In peak shaving power generation mode, the opening of the compressed air valve is adjusted according to the active power command of the power grid, the output power of the CAES expander is controlled, the synchronous motor is driven to output adjustable active power to the power grid, and the reactive power output is adjusted through the excitation system to achieve peak shaving power generation. S500. Exiting Power Generation Mode and Mode Switching: When a command to stop power generation or exit peak shaving is received, the compressed air valve is gradually reduced until it is closed, causing the CAES expander to unload and decelerate, controlling the synchronous clutch to disengage, and at the same time switching the synchronous motor excitation state back to reactive phase modulation mode. The synchronous motor and inertia flywheel rotor continue to operate synchronously and grid-connected and switch to inertia support phase modulation mode.

[0009] (III) Technical Effects Compared with the prior art, the inertia flywheel and CAES expander composite structure and operation control method of the present invention have the following beneficial and significant technical effects: (1) This invention integrates the CAES expander, synchronous motor and inertial flywheel rotor into a composite unit on the same axis, and uses a synchronous clutch to realize the controllable mechanical coupling between the expander and the flywheel synchronous condenser. At the structural level, it integrates the traditionally distributed peak shaving unit, synchronous condenser and flywheel energy storage device into a single unit, so that the same set of equipment can undertake the functions of inertial support, reactive phase regulation and active peak shaving respectively or in concert under different operating conditions, which significantly improves the equipment utilization rate, reduces the number of units and the system footprint, and reduces the overall investment and operation and maintenance cost of the power plant.

[0010] (2) This invention constructs a closed-loop operation control strategy of inertia support phase adjustment mode, power generation peak shaving mode and power generation exit mode, and adopts synchronous clutch control based on speed synchronization criterion and active / reactive power coordination adjustment to ensure smooth and controllable torque transmission when the CAES expander is connected and disconnected, and avoid shaft impact and electrical quantity sudden change; during non-power generation period, the synchronous motor and inertia flywheel rotor continuously operate at power frequency synchronous speed, and in conjunction with excitation regulation, realizes continuous reactive power regulation and physical inertia support, which significantly improves the frequency stability and voltage support capability of large-scale new energy power grid.

[0011] (3) The present invention introduces a multi-condition decision logic based on grid dispatch instructions, gas storage status and unit safety constraints in the operation control method. Through comprehensive and coordinated control of compressed air valve opening, expander output power and synchronous motor excitation current, it realizes the coordinated matching of peak shaving output, inertial response and reactive power support on the time scale. In the process of grid frequency disturbance, load peak and valley changes and power generation condition switching, it can take into account high dynamic response speed, energy conversion efficiency and mechanical safety, and improve the unit's adaptability to complex grid operation scenarios and system-level operation economy. Attached Figure Description

[0012] Figure 1 The diagram shows a composite structure of an inertial flywheel and a CAES expander unit. Figure 2 The diagram shown is a flowchart of the operation control of the composite structure of the inertia flywheel and CAES expander unit.

[0013] Explanation of reference numerals in the attached diagram: 1. CAES expander; 2. Synchronous motor; 3. Inertia flywheel rotor; 4. Synchronous clutch; 5. Coupling; 6. Operation control unit. Detailed Implementation

[0014] This invention aims to provide a composite structure and operation control method for an inertia flywheel and a CAES expander unit. To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. The described embodiments are some, but not all, embodiments of this invention, and are exemplary and intended to explain this invention, and should not be construed as limiting this invention.

[0015] Example 1: Composite structure of inertia flywheel and CAES expander unit As a specific example, such as Figure 1As shown in the embodiment of the present invention, the composite structure of inertia flywheel and CAES expander unit is used to simultaneously realize grid inertia support, reactive power phase regulation and active power peak regulation in a compressed air energy storage system. It includes a coaxially arranged CAES expander 1, synchronous motor 2, and inertia flywheel rotor 3. One end of the synchronous motor 2 is connected to the CAES expander 1 via a synchronous clutch 4, and the other end is connected to the inertia flywheel rotor 3 via a coupling 5. Wherein: The CAES expander 1 is an axial-flow, centripetal, or axial-centripetal combined expander. Its inlet end is connected to the high-pressure gas storage device and the pre-stage heat exchanger via a pipeline, and a compressed air valve is installed on the inlet pipeline. The outlet end is connected to the exhaust pipeline, so that the compressed air expands and performs work after being heated by heat exchange, and provides mechanical power input to the synchronous motor 2 and the inertia flywheel rotor 3 when the synchronous clutch 4 is engaged. In addition, the number of stages of the CAES expander 1 is determined according to the gas storage pressure range, and a 2-stage to 4-stage expansion structure is usually adopted. Intermediate reheat devices are set between stages to improve the expansion work efficiency. The expander's inlet pipeline is equipped with a pressure regulating valve and a temperature sensor. The compressed air is heated to 250°C to 400°C through the pre-stage heat exchanger to avoid the risk of icing due to excessive cooling during expansion, while improving the expander's output power and thermodynamic efficiency.

[0016] Synchronous motor 2 is configured to maintain the inertia flywheel rotor 3 at the power frequency synchronous speed by being powered by the grid when it is mechanically disconnected from CAES expander 1. It also provides inertia support to the grid by combining its rotational inertia with that of the inertia flywheel rotor 3. At the same time, the reactive power output of the synchronous motor is adjusted by the matching excitation regulation self-drive system to achieve grid voltage regulation.

[0017] Preferably, the stator winding of the synchronous motor 2 is connected to the power grid through a main transformer and a grid-connected circuit breaker, and is equipped with an excitation regulation self-drive system electrically connected to the synchronous motor, including an excitation power supply, an excitation transformer, and an excitation controller. The excitation controller adjusts the magnitude of the excitation current applied to the excitation winding of the synchronous motor in real time according to the grid voltage and reactive power demand. By increasing the excitation current, the synchronous motor is put into an over-excitation state to output capacitive reactive power to the grid and achieve voltage support. By decreasing the excitation current, the synchronous motor is put into an under-excitation state to absorb inductive reactive power from the grid and achieve voltage suppression.

[0018] The inertia flywheel rotor 3 is mounted in a closed low-pressure housing with a rotating support. The low-pressure housing is created by evacuating or filling with inert gas to form a low-pressure or near-vacuum environment to reduce wind resistance loss when the inertia flywheel rotor rotates at high speed. The inertia flywheel rotor 3 is radially supported by electromagnetic bearings on both sides, and a rolling protection bearing is provided at at least one end of it. This bearing is used to mechanically limit and provide emergency support for the inertia flywheel rotor in the event of electromagnetic bearing failure, abnormal lubrication, or extreme impact load conditions, preventing the inertia flywheel rotor from contacting and rubbing against the low-pressure housing and avoiding structural damage.

[0019] The synchronous clutch 4 is installed on the transmission link between the synchronous motor 2 and the CAES expander 1, and is configured to achieve mechanical coupling or mechanical disengagement between the CAES expander 1, the synchronous motor 2 and the inertia flywheel rotor 3 when the speed of the CAES expander 1 and the synchronous motor 2 meets the preset synchronization conditions at the power frequency rotation state. In the mechanical coupling state, the output torque of the CAES expander 1 is transmitted to the synchronous motor 2 and the inertia flywheel rotor 3 to drive the synchronous motor 2 to output active power to the grid. In the mechanical disengagement state, the CAES expander 1 stops or stops generating electricity while the synchronous motor 2 and the inertia flywheel rotor 3 still rotate coaxially.

[0020] Preferably, the synchronous clutch 4 is a permanent magnet type, electromagnetic type or mechanical type, and is equipped with a speed synchronization detection device, including a first speed sensor installed on the CAES expander and a second speed sensor installed on the synchronous motor. By detecting the speed signals of the two, it is determined whether the CAES expander and the synchronous motor meet the synchronization conditions. When the speed difference between the two is less than a preset threshold and the electrical grid connection conditions are met, the synchronous clutch is triggered to perform mechanical coupling operation. When the speed difference between the two is greater than the preset threshold, the unit needs to exit power generation operation or an abnormal operating condition is detected, the synchronous clutch is triggered to perform mechanical disengagement operation.

[0021] The inertia flywheel and CAES expander composite structure of this invention also includes a unit operation control unit 6, which is communicatively connected to the synchronous motor 2, CAES expander 1, high-pressure gas storage device (not shown in the figure) and synchronous clutch 4. It is used to select the unit to operate in inertia support phase modulation mode, power generation peak shaving mode or exit power generation mode according to the active power command, reactive power command and frequency deviation information issued by the power grid, and coordinate and control the compressed air flow, synchronous clutch status and excitation current during the mode switching process.

[0022] As a preferred option, the unit operation control unit 6 incorporates unit constraint conditions and performance evaluation models. In the combined power generation and peak shaving mode, it corrects the reference value of the active power that the unit can output based on the pressure limit of the high-pressure gas storage device, the allowable inlet temperature of the expander, and the torque and thermal stress limits of the synchronous motor and inertia flywheel rotor. Under the premise of meeting the constraint conditions, it determines the active power output with the goal of optimizing the comprehensive index of grid frequency stability, peak shaving benefits, and equipment life loss. In the inertia-supported phase adjustment mode, it dynamically adjusts the reactive power output and excitation strategy of the synchronous motor based on the real-time frequency change rate and voltage deviation.

[0023] More preferably, the unit operation control unit is also configured to switch the composite structure of the inertia flywheel and CAES expander unit to islanded operation when the grid experiences disturbances or when a local grid needs a black start. The unit releases compressed air through the high-pressure gas storage device to drive the CAES expander to drive the synchronous motor to generate electricity in order to establish a local voltage and frequency reference. The high rotational inertia of the inertia flywheel rotor is used to maintain frequency stability. After the local grid voltage and frequency recover to the set range, the unit achieves synchronous grid connection with the upstream grid through the synchronous clutch and excitation regulation self-drive system.

[0024] It should be noted that in Embodiment 1, the coaxially arranged CAES expander 1, synchronous motor 2, and inertia flywheel rotor 3 form a single shaft system through synchronous clutch 4 and coupling 5, so that the power output by the expander when engaged can be superimposed on the flywheel-synchronous motor integrated rotor, realizing the coupling conversion of mechanical energy and electrical energy; the inertia flywheel rotor is arranged in the low-pressure housing and is supported by a combination of electromagnetic bearings and rolling protection bearings, which reduces wind resistance loss during high-speed rotation and improves the safety redundancy of the shaft system under abnormal operating conditions such as power failure and impact; the unit operation control unit realizes the coordinated linkage of this composite structure at the mechanical and control levels through comprehensive regulation of clutch status, gas storage pressure, and excitation current.

[0025] Example 2: Operation Control Method Based on Embodiment 1 above, Embodiment 2 further provides an operation control method for the aforementioned composite structure of inertia flywheel and CAES expander unit, such as... Figure 2 As shown, the main steps include the following: S100. System startup and grid synchronization: With the synchronous clutch in a mechanically disengaged state, the synchronous motor and inertia flywheel rotor are driven by the excitation regulation self-drive system and accelerated to the power frequency synchronous speed. The excitation current of the synchronous motor is adjusted so that the output voltage amplitude and phase meet the grid connection conditions. The grid connection switch is closed to realize the synchronous grid connection of the synchronous motor and inertia flywheel rotor with the power grid.

[0026] Preferably, in step S100, an initial excitation current is applied to the excitation winding of the synchronous motor through the excitation regulation self-drive system, and a variable frequency starting power supply is applied to the stator winding of the synchronous motor to drive the synchronous motor rotor and the inertia flywheel rotor to accelerate synchronously. The actual speed of the synchronous motor and the inertia flywheel rotor is detected in real time by a speed sensor set on the rotor shaft of the synchronous motor. The starting control unit performs closed-loop regulation of the output of the excitation regulation self-drive system according to a preset acceleration slope curve, so that the synchronous motor speed smoothly rises to the synchronous speed range corresponding to the target power frequency. When the output frequency reaches the preset target power frequency of 50Hz and the speed reaches the rated synchronous speed of 1500rpm or 3000rpm, the output voltage amplitude and phase are matched by adjusting the excitation current, and a closed grid connection switch command is issued to realize the safe synchronous grid connection of the synchronous motor and the inertia flywheel rotor with the power grid.

[0027] It should be noted that the frequency regulation of the variable frequency starting power supply preferably adopts linear or S-curve slope control. The frequency rise rate is slow in the initial stage of startup to avoid excessive acceleration impact on the inertial flywheel rotor. The frequency rise rate accelerates in the middle stage to shorten the startup time, and the frequency rise rate decreases again when approaching the target frequency to achieve a smooth transition. Furthermore, a controllable power supply is simultaneously provided to the synchronous motor's excitation winding and stator winding through an excitation regulation self-drive system, enabling the synchronous motor and inertial flywheel rotor to start and accelerate off-grid. The core of this system lies in using closed-loop speed control and gradual frequency increase to ensure that the shaft system always operates within the allowable range of mechanical strength and electromagnetic transients.

[0028] S200. Inertia-supported phase modulation mode operation: When connected to the grid and the synchronous clutch is mechanically disengaged, the synchronous motor is powered by the grid to maintain the inertia flywheel rotor rotating continuously at the power frequency synchronous speed. The combined rotational inertia of the synchronous motor and the inertia flywheel rotor provides inertial support to the grid to suppress frequency fluctuations. The excitation current of the synchronous motor is dynamically adjusted by the excitation regulation self-drive system to control the reactive power output and realize grid voltage regulation.

[0029] As a preferred method, in the inertia-supported phase adjustment mode, the grid voltage is monitored in real time. When the grid voltage is lower than the preset threshold of the rated voltage, the excitation current is increased to make the synchronous motor enter the overexcitation state and output capacitive reactive power to the grid to raise the voltage. When the grid voltage is higher than the preset threshold of the rated voltage, the excitation current is reduced to make the synchronous motor enter the underexcitation state and absorb inductive reactive power from the grid to lower the voltage. When the grid voltage is within the preset fluctuation range of the rated voltage, the excitation current is kept basically unchanged. Thus, in the inertia-supported phase adjustment mode, continuous and smooth regulation of the grid voltage is achieved and reactive power abrupt changes are avoided.

[0030] It should be noted that in the inertia-supported phase-shifting mode, the synchronous motor and inertia flywheel rotor operate parallel to the grid at the power frequency synchronous speed. Inertia response to frequency disturbances is achieved through energy exchange between the power grid and the electromechanical system. Essentially, it utilizes a large equivalent rotational inertia to buffer and smooth changes in the power grid frequency. Simultaneously, the excitation regulation self-drive system adjusts the excitation current based on the voltage deviation, achieving dynamic distribution of reactive power. This allows the invention to provide inertia support while also possessing synchronous phase-shifting functionality.

[0031] S300. Power generation peak shaving mode activated: When a peak-shaving power generation command is received from the power grid dispatch, the compressed air valve connected to the air inlet of the CAES expander is opened to drive the CAES expander to accelerate. When the difference between the speed of the CAES expander and the speed of the synchronous motor is detected to be less than the preset synchronous threshold, the synchronous clutch is closed to realize the mechanical coupling of the CAES expander with the synchronous motor and the inertial flywheel rotor, and enter the power generation peak-shaving mode. Preferably, after receiving the peak-shaving power generation command, the gas pressure, temperature, and remaining energy of the high-pressure gas storage device are first detected. When all parameters are within the allowable range, a command to open the compressed air valve is output, and the valve opening is gradually increased according to the preset opening slope. The speed signal of the CAES expander is collected in real time by a first speed sensor installed on the rotor shaft of the CAES expander, and the speed signal of the synchronous motor is collected in real time by a second speed sensor installed on the rotor shaft of the synchronous motor. The speed difference Δn and the corresponding frequency difference Δf between the two are calculated in real time. When Δf is less than the preset frequency threshold and Δn is less than the preset speed threshold, it is determined that the mechanical coupling condition is met and a command to close the synchronous clutch is issued. During the execution of closing the synchronous clutch, a gradual engagement method is adopted to avoid impact loads.

[0032] It should be noted that the high-pressure gas storage device status detection and speed synchronization criteria set in step S300 are intended to ensure the safety and controllability of the power generation peak-shaving mode startup process. By constraining and judging pressure, temperature, and remaining stored energy, the unit can be prevented from being started erroneously when gas storage is insufficient or operating conditions are abnormal. By jointly judging the speed difference Δn and frequency difference Δf between the CAES expander and the synchronous motor, and by coordinating the gradual adjustment of valve opening and the flexible engagement of the synchronous clutch, the risks of mechanical and electrical shocks can be effectively reduced, and the operational stability of the unit during the mode switching phase can be improved.

[0033] S400. Power generation peak shaving mode operation: In peak power generation mode, the opening of the compressed air valve is adjusted according to the active power command of the power grid, the output power of the CAES expander is controlled, and the synchronous motor is driven to output adjustable active power to the power grid. At the same time, the reactive power output is adjusted through the excitation system to realize peak power generation based on the composite structure.

[0034] As a preferred method, in the peak power generation mode, the system receives the target active power command issued by the power grid dispatching system, calculates the required compressed air mass flow rate based on the power characteristic curve of the CAES expander, controls the intake flow rate by adjusting the opening of the compressed air valve, uses PID control algorithm or model predictive control algorithm to perform closed-loop regulation of the valve opening, monitors the actual output power of the synchronous motor in real time and compares it with the target power, and dynamically adjusts the valve opening to make the actual output power track the target power.

[0035] More preferably, during peak power generation operation, the unit operation control unit optimizes the operating parameters in real time based on the built-in unit constraints and performance evaluation model. It dynamically corrects the reference value of the unit's output active power according to the upper and lower pressure limits of the high-pressure gas storage device, the maximum allowable intake temperature of the CAES expander, the maximum torque limit of the synchronous motor and inertial flywheel rotor, and thermal stress limitations. Under the premise of satisfying all constraints, and with the goal of optimizing the comprehensive indicators of grid frequency stability, peak power generation revenue, and equipment fatigue life loss, a multi-objective optimization algorithm determines the optimal active power output and compressed air flow rate, achieving synergistic optimization of technical performance and economic benefits.

[0036] It should be noted that the closed-loop regulation of the compressed air valve based on the active power command of the power grid in step S400 is not a simple proportional correspondence. Instead, it combines the power-flow characteristic curve of CAES expander 1 and the pressure change characteristics of the high-pressure gas storage device. By combining feedforward setting and feedback correction, it can ensure rapid power tracking while limiting the valve opening change rate and expander load ramp rate.

[0037] S500. Exiting power generation mode and mode switching: When a command to stop power generation or exit peak shaving is received, the compressed air valve is gradually reduced until it is closed, causing the CAES expander to unload and decelerate, controlling the synchronous clutch to disengage, and at the same time switching the excitation state of the synchronous motor back to the reactive phase adjustment condition. The synchronous motor and the inertia flywheel rotor continue to operate synchronously and grid-connected and switch to the inertia support phase adjustment mode.

[0038] As a preferred method, when executing the exit from power generation mode and mode switching, before issuing the command to close the compressed air valve, the active power reference value of the synchronous motor is gradually reduced according to the preset time constant to smoothly reduce the load on the expander; after the compressed air valve is closed and the expander speed drops to the predetermined safe value, the control command to disengage the synchronous clutch is issued to achieve mechanical disengagement; then, the reactive power reference value and excitation current of the synchronous motor are reset according to the grid frequency and voltage status to ensure that the synchronous motor and the inertia flywheel rotor do not generate step disturbances in voltage and frequency when switching back to the inertia support phase modulation mode.

[0039] It should be noted that the sequential control in step S500, which involves first reducing active power, then closing the valve, and delaying the clutch disengagement, is primarily used to achieve dual buffering on both the mechanical and electrical sides. This prevents shaft torsional vibration, grid voltage jumps, or significant frequency fluctuations caused by rapid unloading or sudden grid disconnection. The time constant, power slope, and clutch disengagement criteria of the aforementioned exit strategy can all be parameterized according to grid characteristics and unit capacity, optimizing peak-shaving flexibility while meeting safety constraints.

[0040] S600. Orphanage Operation and Black Boot Mode (Preferred Steps): When a severe disturbance to the power grid is detected, causing the regional power grid to disconnect, or when a black start command for the local power grid is received, the unit operation control unit switches the composite structure of the inertia flywheel and CAES expander to the islanded operation mode. Compressed air is released through the high-pressure gas storage device to drive the CAES expander, which drives the synchronous motor to generate electricity to establish a local voltage and frequency reference. The high rotational inertia of the inertia flywheel rotor is used to maintain frequency stability and provide emergency power supply for critical loads of the local power grid.

[0041] As a preferred method, in islanded operation and black start mode, the grid-connected circuit breaker is first opened to disconnect the unit from the faulty grid, keeping the synchronous clutch in a disengaged state. The energy stored in the inertial flywheel rotor is used to maintain the synchronous motor's no-load operation. Then, the compressed air valve is opened according to the preset start-up procedure, driving the CAES expander to accelerate to synchronous speed and achieving mechanical coupling with the synchronous motor through the synchronous clutch, establishing a stable islanded grid voltage and frequency. The excitation current is adjusted by the excitation regulation self-drive system to stabilize the output voltage at the rated value, and the output frequency is stabilized within the range of 50Hz±0.2Hz by adjusting the compressed air flow. After the voltage and frequency have stabilized, the critical loads of the local grid are gradually connected, and the high rotational inertia of the inertial flywheel rotor is used to suppress the frequency fluctuations at the moment of load connection.

[0042] More preferably, after the local grid voltage recovers to 95% to 105% of its rated value and the frequency recovers to 49.5Hz to 50.5Hz and continues to operate stably for more than a preset time, the unit operation control unit initiates the synchronization and grid connection procedure with the upstream grid. By monitoring the voltage amplitude, frequency, and phase of the upstream grid in real time, the excitation current of the synchronous motor and the compressed air flow of the CAES expander are adjusted to ensure that the amplitude, frequency, and phase of the unit's output voltage are precisely synchronized with the upstream grid. When the voltage amplitude difference is less than ±2%, the frequency difference is less than ±0.05Hz, the phase difference is less than ±5°, and the synchronization condition is met for a duration exceeding a preset threshold, the grid connection circuit breaker is closed to achieve synchronous grid connection with the upstream grid, completing a smooth transition from islanded operation to grid-connected operation.

[0043] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A composite structure of an inertia flywheel and a CAES expander unit, characterized in that, It includes at least a CAES expander, a synchronous motor, and an inertial flywheel rotor arranged coaxially. One end of the synchronous motor is driven by the CAES expander via a synchronous clutch, and the other end is driven by the inertial flywheel rotor via a coupling, wherein: The synchronous clutch is located on the transmission link between the synchronous motor and the CAES expander, and is configured to achieve mechanical coupling or mechanical disengagement between the CAES expander, the synchronous motor, and the inertial flywheel rotor when the speeds of the CAES expander and the synchronous motor meet the preset synchronization conditions at the power frequency rotation state. In the mechanical coupling state, the output torque of the CAES expander is transmitted to the synchronous motor and the inertial flywheel rotor to drive the synchronous motor to output active power to the grid. In the mechanical disengagement state, the CAES expander stops or stops generating electricity while the synchronous motor and the inertial flywheel rotor still rotate coaxially. The synchronous motor is configured to be powered by the grid when it is mechanically disconnected from the CAES expander in order to maintain the inertia flywheel rotor at the power frequency synchronous speed and continuously operate in grid-connected mode. It also provides inertial support to the grid through the combined rotational inertia of the synchronous motor and the inertia flywheel rotor. At the same time, the reactive power output of the synchronous motor is adjusted by the matching excitation regulation self-drive system to achieve grid voltage regulation.

2. The composite structure of inertia flywheel and CAES expander unit according to claim 1, characterized in that, The inertia flywheel rotor is mounted in a closed low-pressure housing with rotational support. The low-pressure housing is formed into a low-pressure or near-vacuum environment by evacuating or filling with inert gas. The inertia flywheel rotor is radially supported by electromagnetic bearings on both sides and has a rolling protection bearing at at least one end for mechanical limiting and emergency support of the inertia flywheel rotor in the event of electromagnetic bearing failure, abnormal lubrication, or extreme impact load.

3. The composite structure of inertia flywheel and CAES expander unit according to claim 1, characterized in that, The CAES expander is an axial flow, centripetal, or axial-centripetal combined expander. Its inlet end is connected to the high-pressure gas storage device and the pre-stage heat exchanger through a pipeline, and a compressed air valve is installed on the inlet pipeline. The outlet end is connected to the exhaust pipeline, and it provides mechanical power input to the synchronous motor and the inertial flywheel rotor when the synchronous clutch is engaged.

4. The composite structure of inertia flywheel and CAES expander unit according to claim 1, characterized in that, The synchronous clutch is a permanent magnet, electromagnetic, or mechanical type, and is equipped with a speed synchronization detection device, including a first speed sensor installed on the CAES expander and a second speed sensor installed on the synchronous motor. By detecting the speed signals of the two, it is determined whether the CAES expander and the synchronous motor meet the synchronization conditions. When the speed difference between the two is less than a preset threshold and the electrical grid connection conditions are met, the synchronous clutch is triggered to perform mechanical coupling operation. When the speed difference between the two is greater than the preset threshold, the unit needs to exit power generation operation, or an abnormal operating condition is detected, the synchronous clutch is triggered to perform mechanical disengagement operation.

5. The composite structure of inertia flywheel and CAES expander unit according to claim 1, characterized in that, The stator winding of the synchronous motor is connected to the power grid through a main transformer and a grid-connected circuit breaker, and is equipped with an excitation regulation self-drive system electrically connected to the synchronous motor, including an excitation power supply, an excitation transformer, and an excitation controller. The excitation controller adjusts the magnitude of the excitation current applied to the excitation winding of the synchronous motor in real time according to the grid voltage and reactive power demand. By increasing the excitation current, the synchronous motor is put into an over-excitation state to output capacitive reactive power to the grid and achieve voltage support. By decreasing the excitation current, the synchronous motor is put into an under-excitation state to absorb inductive reactive power from the grid and achieve voltage suppression.

6. The composite structure of inertia flywheel and CAES expander unit according to claim 3, characterized in that, It also includes a unit operation control unit, which is connected to the synchronous motor, CAES expander, high-pressure gas storage device and synchronous clutch respectively. It is used to select the unit to operate in inertia support phase modulation mode, power generation peak shaving mode or exit power generation mode according to the active power command, reactive power command and frequency deviation information issued by the power grid, and coordinate and control the compressed air flow, synchronous clutch status and excitation current during the mode switching process.

7. The composite structure of inertia flywheel and CAES expander unit according to claim 6, characterized in that, The unit operation control unit incorporates unit constraint conditions and performance evaluation models. In the combined power generation and peak shaving mode, it corrects the reference value of the active power that the unit can output based on the pressure limit of the high-pressure gas storage device, the allowable inlet temperature of the expander, and the torque and thermal stress limits of the synchronous motor and inertia flywheel rotor. Under the premise of meeting the constraint conditions, it determines the active power output with the goal of optimizing the comprehensive index of grid frequency stability, peak shaving benefits, and equipment life loss. In the inertia-supported phase adjustment mode, it dynamically adjusts the reactive power output and excitation strategy of the synchronous motor based on the real-time frequency change rate and voltage deviation.

8. The composite structure of inertia flywheel and CAES expander unit according to claim 6 or 7, characterized in that, The unit operation control unit is also configured to switch the composite structure of the inertia flywheel and CAES expander unit to islanded operation when the grid is disturbed or a local grid needs a black start. The unit releases compressed air through the high-pressure gas storage device to drive the CAES expander to drive the synchronous motor to generate electricity in order to establish a local voltage and frequency reference. The high rotational inertia of the inertia flywheel rotor is used to maintain frequency stability. After the local grid voltage and frequency recover to the set range, the unit achieves synchronous grid connection with the upstream grid through the synchronous clutch and excitation regulation self-drive system.

9. A method for operating and controlling the composite structure of an inertial flywheel and a CAES expander unit as described in any one of claims 1 to 8, characterized in that, It should include at least the following steps: S100. When the synchronous clutch is in a mechanically disengaged state, the synchronous motor and inertia flywheel rotor are driven by the excitation regulation self-drive system and accelerated to the power frequency synchronous speed. The excitation current of the synchronous motor is adjusted so that the output voltage amplitude and phase meet the grid connection conditions. The grid connection switch is closed to realize the synchronous grid connection of the synchronous motor and inertia flywheel rotor with the power grid. S200. When connected to the grid and the synchronous clutch is still in a mechanically disengaged state, the synchronous motor is powered by the grid to maintain the inertia flywheel rotor rotating at the power frequency synchronous speed. The combined rotational inertia of the two provides inertia support for the grid to suppress frequency fluctuations. At the same time, the excitation current of the synchronous motor is dynamically adjusted by the excitation regulation self-drive system to control the reactive power output and realize grid voltage regulation. S300. When receiving the peak-shaving power generation command issued by the power grid dispatch, the compressed air valve connected to the air inlet of the CAES expander is opened to drive the CAES expander to accelerate. When the difference between the speed of the CAES expander and the speed of the synchronous motor is detected to be less than the preset synchronous threshold, the synchronous clutch is closed to realize the mechanical coupling of the CAES expander with the synchronous motor and the inertial flywheel rotor, and enter the power generation peak-shaving mode. S400. In peak power generation mode, the opening of the compressed air valve is adjusted according to the active power command of the power grid, the output power of the CAES expander is controlled, and the synchronous motor is driven to output adjustable active power to the power grid. At the same time, the reactive power output is adjusted through the excitation regulation self-drive system. When S500 receives a command to stop power generation or exit peak shaving, it gradually reduces and eventually closes the compressed air valve, causing the CAES expander to unload and decelerate, controlling the synchronous clutch to disengage, and simultaneously switching the synchronous motor excitation state back to reactive phase adjustment mode. The synchronous motor and inertia flywheel rotor maintain synchronous grid-connected operation and switch to inertia support phase adjustment mode.

10. The method according to claim 9, characterized in that, In step S100, an initial excitation current is applied to the excitation winding of the synchronous motor through the excitation regulation self-drive system, and a variable frequency starting power supply is applied to the stator winding of the synchronous motor to drive the synchronous motor rotor and the inertia flywheel rotor to accelerate synchronously. The actual speed of the synchronous motor and the inertia flywheel rotor is detected in real time by a speed sensor installed on the synchronous motor. The output of the excitation regulation self-drive system is adjusted in a closed loop according to a preset acceleration slope curve to make the synchronous motor speed smoothly rise to the synchronous speed range corresponding to the target power frequency. When the output frequency reaches the preset target power frequency of 50Hz and the speed reaches the rated synchronous speed of 1500rpm or 3000rpm, the output voltage amplitude and phase are matched by adjusting the excitation current, and a closed grid connection switch command is issued to realize the safe synchronous grid connection of the synchronous motor and the inertia flywheel rotor with the power grid.

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