Energy management and voltage stabilization control method for net-forming type flywheel energy storage system

Abstract

The invention provides an energy management and voltage stabilization control method for a net-forming type flywheel energy storage system, and relates to the technical field of flywheel energy storage. Multi-voltage threshold control is adopted, and the working modes of the flywheel energy storage system are intelligently switched, including a standby mode, a charging mode, an energy releasing mode and a discharging mode, so that suppression of power grid voltage fluctuation and energy management of the energy storage system are optimized. Through the cascade expansion state observer, the disturbance in the system is effectively estimated and compensated, and the self-adaptive capability and robustness of the system to the voltage fluctuation of the power grid are enhanced. The adopted control strategy can effectively cope with large fluctuation and rapid change of the power grid voltage, and the problems that a traditional PI controller is slow in dynamic response and poor in anti-interference capacity are solved. Through the method, the flywheel energy storage system can stably switch working modes and keep stable operation under various power grid working conditions, meanwhile, the charging and discharging process of the energy storage system is optimized, the electric energy quality is improved, and the stability and reliability of a power grid are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of flywheel energy storage, and in particular to an energy management and voltage stabilization control method for a grid-type flywheel energy storage system. Background Art

[0002] A grid-connected flywheel energy storage system is an electromechanical conversion system that stores energy in the form of kinetic energy. It boasts high power density, long service life, fast response, and environmental friendliness, promising broad applications in electric vehicles, microgrid systems, and aerospace. In practical applications, flywheel energy storage must not only provide instantaneous high power but also achieve stable grid connection, requiring fast dynamic response and robust interference resistance during switching operations. This performance is largely dependent on the flywheel energy storage system's DC bus voltage control.

[0003] Currently, the DC bus voltage control of flywheel energy storage systems is mainly based on the dual closed-loop structure of the PI controller, which uses the voltage outer loop to stabilize the DC bus voltage and the current inner loop to control the current output. However, the PI controller has the following problems:

[0004] (1) Poor anti-interference ability: Since the PI controller only adjusts the control output according to the voltage deviation, its anti-interference ability is weak. During the operation of the flywheel energy storage system, due to frequent charging and discharging, the steady-state operating point will drift over a large range, resulting in poor bus voltage stability. Especially when the power grid fluctuates greatly, the PI control system cannot effectively suppress the disturbance, resulting in large voltage fluctuations and affecting the system stability.

[0005] (2) Slow dynamic response: Under the condition of new energy grid connection, the grid voltage fluctuates rapidly, and the dynamic response of the PI controller is slow, making it difficult to cope with the frequent voltage changes in the grid and unable to meet the flywheel energy storage system's requirements for instantaneous high power and rapid operating condition switching.

[0006] (3) Unable to adapt to large disturbance conditions: Because PI control relies on linear models, its adaptability to complex disturbances is poor. When faced with large disturbances (such as large-scale wind power grid connection or sudden load changes), PI controllers are prone to overshoot and oscillation, making it difficult to operate stably. This is especially true in power grids with a high proportion of renewable energy, where the limitations of traditional PI controllers are even more obvious. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide an energy management and voltage stabilization control method for a grid-type flywheel energy storage system. The flywheel energy storage system can smoothly switch working modes and maintain stable operation under various grid operating conditions. At the same time, it optimizes the charging and discharging process of the energy storage system, improves the quality of electric energy, and ensures the stability and reliability of the grid.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A method for energy management and voltage regulation control of a grid-type flywheel energy storage system adopts a compensation-enhanced extended state observer (ESO) active disturbance rejection control strategy. Through a cascaded extended state observer (ESO), system disturbances are estimated and compensated in stages, achieving disturbance-free steady-state error compensation. Specifically, for ramp-type disturbances, the cascaded ESO structure achieves zero disturbance estimation error.

[0010] When the grid-type flywheel energy storage system is in discharge condition, a release voltage loop is added. When the renewable energy power generation is insufficient, the release voltage loop is used to jointly supply power, so that the flywheel energy storage system can be intelligently and dynamically switched among the four working modes of charging, standby, release and discharge. The dynamic switching of the working mode is based on the grid voltage amplitude, the flywheel state of charge SOC and the bus voltage fluctuation range. The specific switching logic is as follows: when When the system enters charging mode; if and , it enters standby mode; when and When, if , the system enters the energy release mode, otherwise it enters the standby mode; if , then regardless of the SOC state, it enters the discharge mode; among them, 、 、 All are set threshold voltages;

[0011] The maximum output power in each operating mode is controlled by limiting the output command of the voltage outer loop; when the flywheel state of charge (SOC) reaches the upper or lower limit, it is forced to switch to standby or energy release mode to prevent overcharging or over-discharging;

[0012] The grid-type flywheel energy storage system includes a bidirectional back-to-back converter including a machine-side converter, a grid-side converter and a DC bus capacitor C, and a grid-side inductor core and a filter capacitor C. g The grid-side filter and the flywheel energy storage unit driven by the permanent magnet synchronous motor; the electric speed increase and power generation deceleration of the motor are controlled by a bidirectional back-to-back converter; the permanent magnet synchronous motor adopts a surface-mounted rotor permanent magnet synchronous motor, combined with the d-axis current i d =0 magnetic field oriented control to improve dynamic response and power density; control signals are generated based on the space vector pulse width modulation algorithm to achieve precise adjustment of the machine-side and grid-side converters.

[0013] Furthermore, the cascaded extended state observer includes a first extended state observer ESO1 and a second extended state observer ESO2; ESO1 estimates the total disturbance of the system and passes the result to ESO2 as prior information; ESO2 further observes the remaining unknown disturbance based on the output of ESO1; by configuring the adjustable control gain of the cascaded ESO, it is ensured that there is no steady-state error for both step-type and ramp-type disturbances, meeting the dynamic performance requirements and achieving frequency domain bandwidth optimization.

[0014] Furthermore, the active disturbance rejection control is designed based on the third-order state space equation of the DC bus voltage, and the third-order state space equation of the DC bus voltage is obtained as follows:

[0015] The DC bus voltage equation is:

[0016] ;

[0017] Among them, P g is the grid-side converter output power; R s is the stator resistance, u dc is the DC bus voltage; 、 、 、 They are the dp-axis current component and inductance component of the motor respectively; is the rotor excitation flux; is the rotor electrical angular velocity;

[0018] The state space equations related to the DC bus voltage of the flywheel system are defined = ,get:

[0019] ;

[0020] The total disturbance of the system in the voltage loop is defined as ,in, represents a total disturbance function with respect to the system state x1 and time t. x3 is the derivative of the total disturbance function of the system, representing the fast-changing disturbance term that cannot be modeled in the system. The total disturbance is expanded into a new state variable, and the DC bus voltage control model is expanded into the following third-order state space equation:

[0021] ;

[0022] in, ; Control quantity , is the p-axis voltage component of the motor; system parameters .

[0023] Furthermore, the output power of the grid-side converter is obtained according to the mathematical model of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system. First, the voltage equation, electromagnetic torque equation, and rotor motion equation of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system are obtained according to the mathematical model of the surface-mounted permanent magnet synchronous motor, as follows:

[0024] The voltage equation of the surface-mounted rotor permanent magnet synchronous motor on the flywheel side in the d, q synchronous coordinate system is:

[0025] ;

[0026] in, 、 、 、 、 、 They are the dp-axis voltage component, current component, and inductance component of the motor respectively. is the rotor excitation flux, is the rotor electrical angular velocity, R s is the stator resistance, u dc is the DC bus voltage, i dc is the DC bus current; C represents the capacitance of the DC bus capacitor;

[0027] The electromagnetic torque equation is:

[0028] ;

[0029] Among them, T e is the electromagnetic torque, p is the number of pole pairs of the motor;

[0030] The mechanical motion equation is:

[0031] ;

[0032] Where J is the moment of inertia, is the mechanical angular velocity, T L is the load torque, B is the damping coefficient;

[0033] The power of the machine-side converter is:

[0034] ;

[0035] The grid-side converter is directly connected to the grid and adopts vector control based on grid electromotive force orientation. The voltage equation is obtained in the synchronous rotating coordinate system as follows:

[0036] ;

[0037] in, 、 and 、 They are the AC side of the grid-side converter Shaft voltage and current components, 、 is the three-phase electromotive force of the power grid Axis component, is the grid angular frequency, is the grid-side equivalent resistance; L g Connect inductance to the grid side;

[0038] The output power of the grid-side converter is: .

[0039] Furthermore, the third-order mathematical model of the first extended state observer ESO1 is as follows:

[0040] ;

[0041] in, 、 、 The DC bus voltage squared , voltage differential , the total disturbance to the system when the working condition switches Observed values ​​of is the observation error, that is, the difference between the observed voltage and the actual voltage; 、 、 is the adjustable control gain of ESO1, is a system parameter.

[0042] Furthermore, the second extended state observer ESO2 takes z3 as a “known disturbance” and the third-order mathematical model is as follows:

[0043] ;

[0044] in, 、 、 The DC bus voltage squared , voltage differential and subtraction The observed value of the external disturbance, is the ESO2 observation error, 、 、 is the adjustable control gain of ESO2.

[0045] Furthermore, in the compensation-enhanced extended state observer active disturbance rejection control strategy, the state error feedback (SEF) link adopts proportional-differential combined control to obtain the following control quantity:

[0046] ;

[0047] in, 、 are the proportional and differential control gain parameters respectively; is the set value of DC bus voltage;

[0048] The sum of the disturbance estimates obtained by ESO1 and ESO2 is compensated to the state error feedback, and the final control quantity of the system is obtained as:

[0049] ;

[0050] Then get The control voltage value of the shaft voltage loop is: .

[0051] The beneficial effects of adopting the above technical solution are: the present invention provides a grid-type flywheel energy storage system energy management and voltage stabilization control method, which adopts multi-voltage threshold control and intelligently switches the working mode of the flywheel energy storage system, including standby, charging, energy release and discharge modes, to optimize the suppression of grid voltage fluctuations and the energy management of the energy storage system. By cascading the extended state observer, the disturbances in the system are effectively estimated and compensated, and the system's adaptability and robustness to grid voltage fluctuations are enhanced. The control strategy adopted by the present invention can effectively cope with large fluctuations and rapid changes in grid voltage, avoiding the problems of slow dynamic response and poor anti-interference ability of traditional PI controllers. Through this method, the flywheel energy storage system can smoothly switch working modes and maintain stable operation under various grid conditions. At the same time, it optimizes the charging and discharging process of the energy storage system, improves the quality of electricity, and ensures grid stability and reliability. In wind power and photovoltaic grid-connected scenarios, the system can quickly smooth out power fluctuations from seconds to minutes, and support grid frequency regulation and voltage support. Under extreme operating conditions such as large-scale load fluctuations or the disconnection of renewable energy sources, bus voltage stability can be maintained, avoiding the instability risks associated with traditional PI control. This improves the grid's ability to accommodate wind and photovoltaic power, contributing to the achievement of the "dual carbon" goals. This method is not only applicable to energy storage systems connected to renewable energy sources such as wind and photovoltaic power, but also has broad application prospects, meeting the grid's needs for rapid response and high power output. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A control diagram of a grid-type flywheel energy storage system provided in an embodiment of the present invention;

[0053] Figure 2 A schematic diagram of the working mode of a flywheel energy storage system provided in an embodiment of the present invention;

[0054] Figure 3 A flow chart of mode switching based on multiple voltage thresholds provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0056] like Figure 1 As shown, the method of this embodiment is as follows.

[0057] A method for energy management and voltage stabilization control of a grid-type flywheel energy storage system adopts a compensation-enhanced extended state observer self-disturbance rejection control strategy. Through a cascaded extended state observer (cascade ESO), system disturbances are estimated and compensated in stages, and disturbance-free steady-state error compensation is achieved. That is, for ramp-type disturbances, the disturbance estimation error is zero through the cascaded extended state observer structure. A release voltage loop is added to the grid-type flywheel energy storage system during discharge operation. When the renewable energy generation is insufficient, the release voltage loop is used to jointly supply power, so that the flywheel energy storage system can intelligently and dynamically switch between the four working modes of charging, standby, release and discharge. The working modes are as follows: Figure 2 The dynamic switching of the working mode is based on the grid voltage amplitude, the flywheel charge state SOC and the bus voltage fluctuation range, as shown in Figure 3 The flywheel energy storage system monitors the grid voltage amplitude, flywheel state of charge (SOC) and DC bus voltage The real-time changes of the battery can realize intelligent dynamic switching among the four working modes of charging, standby, energy release and discharge. The specific switching logic is as follows: When the system enters charging mode; if and , it enters standby mode; when and When, if , the system enters the energy release mode, otherwise it enters the standby mode; if , then regardless of the SOC state, it enters the discharge mode. 、 、 This strategy ensures that the system responds flexibly to voltage fluctuations and energy status, ensuring power quality and system stability.

[0058] The maximum output power in each operating mode is controlled by limiting the output command of the voltage outer loop. When the flywheel state of charge (SOC) reaches the upper or lower limit, it is forced to switch to standby or discharge mode to prevent overcharging or over-discharging.

[0059] The grid-type flywheel energy storage system includes a bidirectional back-to-back converter including a machine-side converter, a grid-side converter and a DC bus capacitor C, and a grid-side inductor core and a filter capacitor C. g The grid-side filter and the flywheel energy storage unit driven by the permanent magnet synchronous motor. In order to realize the bidirectional orderly energy flow between the flywheel energy storage motor and the external power supply / load, the flywheel energy storage system controls the electric speed increase and power generation deceleration of the motor through a bidirectional back-to-back converter, thereby realizing charging and discharging. In this embodiment, a permanent magnet synchronous motor is selected as the control motor. The structure of the three-phase PMSM rotor magnetic circuit is different, and the operating performance, control method, manufacturing process and applicable occasions of the motor are also different. According to the position of the permanent magnet rotor, the rotor structure of the three-phase PMSM can be divided into two structures: surface-mounted and built-in. The surface-mounted rotor has the advantages of simple structure, low manufacturing cost and small moment of inertia; the built-in rotor structure can make full use of the magnetic resistance torque generated by the asymmetry of the rotor magnetic circuit, improve the power density of the motor, and improve the dynamic performance of the motor compared to the surface-mounted rotor structure. The manufacturing process is also simpler, but the leakage magnetic coefficient and manufacturing cost are larger than the surface-mounted rotor structure. Therefore, the permanent magnet synchronous motor of this embodiment adopts a surface-mounted rotor permanent magnet synchronous motor and considers its ideal working state, that is, ignoring the saturation of the motor core, the eddy current and hysteresis loss in the motor and assuming that the current in the motor is a symmetrical three-phase sinusoidal current. On this basis, its mathematical model is briefly analyzed. d =0 field-oriented control, improving dynamic response and power density. A space vector pulse width modulation algorithm is used to generate control signals for precise regulation of the generator-side and grid-side converters.

[0060] The output power of the grid-side converter is obtained based on the mathematical model of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system. First, the voltage equation, electromagnetic torque equation and rotor motion equation of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system are obtained based on the mathematical model of the surface-mounted permanent magnet synchronous motor. The control method of the surface-mounted permanent magnet synchronous motor adopts i d =0 vector control.

[0061] The voltage equation of the surface-mounted rotor permanent magnet synchronous motor on the flywheel side in the d, q synchronous coordinate system is:

[0062] ;

[0063] in, 、 、 、 、 、 They are the dp-axis voltage component, current component, and inductance component of the motor respectively. is the rotor excitation flux, is the rotor electrical angular velocity, R s is the stator resistance, u dc is the DC bus voltage, i dc is the DC bus current; C is the capacitance of the DC bus capacitor.

[0064] The electromagnetic torque equation is:

[0065] ;

[0066] Among them, T e is the electromagnetic torque, and p is the number of pole pairs of the motor.

[0067] The mechanical motion equation is:

[0068] ;

[0069] Where J is the moment of inertia, is the mechanical angular velocity, T L is the load torque, and B is the damping coefficient.

[0070] The power of the machine-side converter is:

[0071] ;

[0072] The grid-side converter is directly connected to the grid and adopts vector control based on grid electromotive force orientation. The voltage equation is obtained in the synchronous rotating coordinate system as follows:

[0073] ;

[0074] in, 、 and 、 They are the AC side of the grid-side converter Shaft voltage and current components, 、 is the three-phase electromotive force of the power grid Axis component, is the grid angular frequency, is the grid-side equivalent resistance; L g Connect the inductor to the grid side.

[0075] The grid-side converter output power is: .

[0076] In the traditional method: the voltage outer loop PI controller receives the set value of the DC bus voltage With actual value The deviation signal is used to adjust the q-axis current setting value , the inner loop of the d-axis current adopts zero current control, that is, setting =0, the dq axis current inner loop PI controller receives 、 The actual value of dq axis current , The deviation signal dq is used to adjust the dq axis control voltage value 、 , obtained 、 The reference control voltage value in the two-phase stationary coordinate system is obtained by park inverse transformation 、 , and then use the space vector pulse width modulation (SVPMW) algorithm to generate a PMW signal to control the on-off of the machine-side converter, thereby achieving the regulation of the DC bus voltage of the flywheel system.

[0077] The instantaneous power balance equation on the AC side and the DC side is:

[0078] ;

[0079] As the above equation shows, flywheel energy storage systems exhibit strongly coupled nonlinear characteristics in the dq rotating coordinate system. Especially during the charging and discharging process and operating mode switching, sudden changes in speed and grid-side power can lead to large and prolonged dynamic voltage deviations. Therefore, control strategies based on traditional PI algorithms are unable to meet the requirements for high-performance dynamic voltage regulation. The improved algorithm is as follows.

[0080] Active disturbance rejection control is designed based on the third-order state-space equation of the DC bus voltage. The third-order state-space equation of the DC bus voltage is obtained as follows:

[0081] The DC bus voltage equation is:

[0082] ;

[0083] Among them, P g is the grid-side converter output power; R s is the stator resistance, u dc is the DC bus voltage; 、 、 、 They are the dp-axis current component and inductance component of the motor respectively; is the rotor excitation flux; is the rotor electrical angular velocity.

[0084] The state space equations related to the DC bus voltage of the flywheel system are defined = ,get:

[0085] ;

[0086] The total disturbance of the system in the voltage loop is defined as ,in, represents a total disturbance function with respect to the system state x1 and time t. x3 is the derivative of the total disturbance function of the system, representing the fast-changing disturbance term that cannot be modeled in the system. By expanding the total disturbance into a new state variable, the DC bus voltage control model is expanded into the following third-order state space equation:

[0087] ;

[0088] in, . Control quantity , is the p-axis voltage component of the motor. System parameters .

[0089] ADRC is designed based on the third-order state equation of the DC bus voltage mentioned above. ESO is the core of ADRC. It can observe the total disturbance only by using the input and output of the system, and compensate the observed value to the controller u to realize active anti-disturbance control. The cascade extended state observer of this embodiment includes a first extended state observer ESO1 and a second extended state observer ESO2; ESO1 estimates the total disturbance of the system and passes the result to ESO2 as prior information; ESO2 further observes the remaining unknown disturbance based on the output of ESO1; by configuring the adjustable control gain of the cascade ESO, it is ensured that there is no steady-state error for both step-type and ramp-type disturbances, meeting the dynamic performance requirements and achieving frequency domain bandwidth optimization.

[0090] The third-order mathematical model of the first extended state observer ESO1 is designed as follows:

[0091] ;

[0092] in, 、 、 The DC bus voltage squared , voltage differential , the total disturbance to the system when the working condition switches Observed values ​​of is the observation error, that is, the difference between the observed voltage and the actual voltage; 、 、 is the adjustable control gain of ESO1, is a system parameter.

[0093] SEF adopts proportional-differential combined control to obtain the following control quantity:

[0094] ;

[0095] in, 、 are the proportional and derivative control gain parameters respectively. The estimated value of ESO to the total disturbance is After compensating to the output of SEF, the final control quantity of the system is:

[0096] ;

[0097] The total disturbance of the system and its estimated value Frequency domain transfer function:

[0098] ;

[0099] Consider placing the ESO poles at the bandwidth Where, there is , , the given transfer function is replaced by , when the total disturbance When the slope changes with k, the termination theorem is used to obtain the disturbance estimation error:

[0100] ;

[0101] It can be seen from this that when the total disturbance When the disturbance changes in a ramp, the traditional ADRC has a steady-state error in estimating the disturbance. Therefore, this paper will improve this problem.

[0102] The core of the studied CE-ADRC strategy lies in the introduction of two cascaded extended state observers. The first extended state observer ESO1 estimates the total disturbance suffered by the system and passes it to the second extended state observer ESO2 as the prior information of the disturbance. In this way, only the unknown disturbance needs to be paid attention to by ESO2, thereby improving the estimation efficiency and accuracy of the observer.

[0103] Similar to the structure of ESO1, the second extended state observer ESO2 uses z3 as a "known disturbance" and further observes the remaining unknown disturbances based on the output of ESO1 to improve the efficiency and accuracy of disturbance estimation. Its third-order mathematical model is designed as follows:

[0104] ;

[0105] in, 、 、 The DC bus voltage squared , voltage differential and subtraction The observed value of the external disturbance, is the ESO2 observation error, 、 、 is the adjustable control gain of ESO2.

[0106] In the improved compensation-enhanced extended state observer active disturbance rejection control strategy, the state error feedback (SEF) link adopts proportional-differential combined control, and the following control quantity is obtained:

[0107] ;

[0108] in, 、 are the proportional and differential control gain parameters respectively; is the set value of the DC bus voltage.

[0109] The sum of the disturbance estimates obtained by ESO1 and ESO2 is compensated to SEF, and the final control quantity of the system is obtained as:

[0110] ;

[0111] Then get The control voltage value of the shaft voltage loop is: .

[0112] The mathematical model of ESO2 is transformed into the following form by frequency domain transformation:

[0113] ;

[0114] The total disturbance of the improved system is obtained from the above formula: and its estimated value The frequency domain transfer function is:

[0115] ;

[0116] in, ;

[0117] ;

[0118] When the total disturbance Slope When the slope changes, the final value theorem is used to obtain the disturbance estimation error:

[0119] .

[0120] It can be seen from this that when the total disturbance Slope When the slope changes, the disturbance estimation error of the cascade extended state observer is 0.

[0121] The control method of this embodiment adopts multi-voltage threshold control, and optimizes the suppression of grid voltage fluctuations and the energy management of the energy storage system by intelligently switching the working modes of the flywheel energy storage system, including standby, charging, energy release and discharge modes. In particular, through the cascaded extended state observer, the disturbances in the system are effectively estimated and compensated, thereby enhancing the system's adaptability and robustness to grid voltage fluctuations. Specifically, the adopted control strategy can effectively cope with large fluctuations and rapid changes in grid voltage, avoiding the problems of slow dynamic response and poor anti-interference ability of traditional PI controllers. Through this method, the flywheel energy storage system can smoothly switch working modes and maintain stable operation under various grid conditions. At the same time, it optimizes the charging and discharging process of the energy storage system, improves the power quality, and ensures the stability and reliability of the grid. This method is not only applicable to energy storage systems under the conditions of grid connection of renewable energy sources such as wind power and photovoltaics, but also has broad application prospects and can meet the grid's needs for fast response and high power output.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the present invention.

Claims

1. A method for energy management and voltage stabilization control of a grid-type flywheel energy storage system, characterized by: The method adopts a compensation enhanced extended state observer active disturbance rejection control strategy, which estimates and compensates system disturbances in stages through a cascaded extended state observer, i.e., a cascaded ESO, and achieves disturbance-free steady-state error compensation. That is, for ramp-type disturbances, the disturbance estimation error is zero through the cascaded extended state observer structure. When the grid-type flywheel energy storage system is in discharge condition, a release voltage loop is added. When the renewable energy power generation is insufficient, the release voltage loop is used to jointly supply power, so that the flywheel energy storage system can be intelligently and dynamically switched among the four working modes of charging, standby, release and discharge. The dynamic switching of the working mode is based on the grid voltage amplitude, the flywheel state of charge SOC and the bus voltage fluctuation range. The specific switching logic is as follows: when When the system enters charging mode; if and , it enters standby mode; when and When, if , the system enters the energy release mode, otherwise it enters the standby mode; if , then regardless of the SOC state, it enters the discharge mode; among them, 、 、 All are set threshold voltages; The maximum output power in each operating mode is controlled by limiting the output command of the voltage outer loop; when the flywheel state of charge (SOC) reaches the upper or lower limit, it is forced to switch to standby or energy release mode to prevent overcharging or over-discharging; The grid-type flywheel energy storage system includes a bidirectional back-to-back converter including a machine-side converter, a grid-side converter and a DC bus capacitor C, and a grid-side inductor core and a filter capacitor C. g The grid-side filter and the flywheel energy storage unit driven by the permanent magnet synchronous motor; the electric speed increase and power generation deceleration of the motor are controlled by a bidirectional back-to-back converter; the permanent magnet synchronous motor adopts a surface-mounted rotor permanent magnet synchronous motor, combined with the d-axis current i d =0 magnetic field oriented control to improve dynamic response and power density; control signals are generated based on the space vector pulse width modulation algorithm to achieve precise adjustment of the machine-side and grid-side converters.

2. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 1, characterized in that: The cascaded extended state observer includes a first extended state observer (ESO1) and a second extended state observer (ESO2); ESO1 estimates the total disturbance of the system and transmits the result to ESO2 as prior information; ESO2 further observes the remaining unknown disturbance based on the output of ESO1; by configuring the adjustable control gain of the cascaded ESO, it is ensured that there is no steady-state error for both step-type and ramp-type disturbances, meeting dynamic performance requirements and achieving frequency domain bandwidth optimization.

3. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 2, characterized in that: The active disturbance rejection control is designed based on the third-order state-space equation of the DC bus voltage. The third-order state-space equation of the DC bus voltage is obtained as follows: The DC bus voltage equation is: ； Among them, P g is the grid-side converter output power; R s is the stator resistance, u dc is the DC bus voltage; 、 、 、 They are the dp-axis current component and inductance component of the motor respectively; is the rotor excitation flux; is the rotor electrical angular velocity; The state space equations related to the DC bus voltage of the flywheel system are defined = ,get: ； The total disturbance of the system in the voltage loop is defined as ,in, represents a total disturbance function with respect to the system state x1 and time t. x3 is the derivative of the total disturbance function of the system, representing the fast-changing disturbance term that cannot be modeled in the system. The total disturbance is expanded into a new state variable, and the DC bus voltage control model is expanded into the following third-order state space equation: ； in, ; Control quantity , is the p-axis voltage component of the motor; system parameters .

4. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 3, characterized in that: The grid-side converter output power is obtained according to the mathematical model of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system. First, the voltage equation, electromagnetic torque equation, and rotor motion equation of the surface-mounted permanent magnet synchronous motor in the d, q synchronous coordinate system are obtained according to the mathematical model of the surface-mounted permanent magnet synchronous motor, as follows: The voltage equation of the surface-mounted rotor permanent magnet synchronous motor on the flywheel side in the d, q synchronous coordinate system is: ； in, 、 、 、 、 、 They are the dp-axis voltage component, current component, and inductance component of the motor respectively. is the rotor excitation flux, is the rotor electrical angular velocity, R s is the stator resistance, u dc is the DC bus voltage, i dc is the DC bus current; C represents the capacitance of the DC bus capacitor; The electromagnetic torque equation is: ； Among them, T e is the electromagnetic torque, p is the number of pole pairs of the motor; The mechanical motion equation is: ； Where J is the moment of inertia, is the mechanical angular velocity, T L is the load torque, B is the damping coefficient; The power of the machine-side converter is: ； The grid-side converter is directly connected to the grid and adopts vector control based on grid electromotive force orientation. The voltage equation is obtained in the synchronous rotating coordinate system as follows: ； in, 、 and 、 They are the AC side of the grid-side converter Shaft voltage and current components, 、 is the three-phase electromotive force of the power grid Axis component, is the grid angular frequency, is the grid-side equivalent resistance; L g Connect inductance to the grid side; The output power of the grid-side converter is: .

5. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 4, characterized in that: The third-order mathematical model of the first extended state observer ESO1 is as follows: ； in, 、 、 The DC bus voltage squared , voltage differential , the total disturbance to the system when the working condition switches Observed values ​​of is the observation error, that is, the difference between the observed voltage and the actual voltage; 、 、 is the adjustable control gain of ESO1, is a system parameter.

6. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 5, characterized in that: The second extended state observer ESO2 takes z3 as a “known disturbance” and the third-order mathematical model is as follows: ； in, 、 、 The DC bus voltage squared , voltage differential and subtraction The observed value of the external disturbance, is the ESO2 observation error, 、 、 is the adjustable control gain of ESO2.

7. The energy management and voltage stabilization control method of a grid-type flywheel energy storage system according to claim 6, characterized in that: In the compensation-enhanced extended state observer active disturbance rejection control strategy, the state error feedback link adopts proportional-differential combined control to obtain the following control quantity: ； in, 、 are the proportional and differential control gain parameters respectively; is the set value of the DC bus voltage; The sum of the disturbance estimates obtained by ESO1 and ESO2 is compensated to the state error feedback, and the final control quantity of the system is obtained as: ； Then get The control voltage value of the shaft voltage loop is: .

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