Flywheel-battery Hybrid Energy Storage Frequency Regulation System, Method, Device and Medium

Abstract

The present application discloses a flywheel-battery hybrid energy storage frequency regulation system, method, device and medium. The system includes a flywheel energy storage system and a battery energy storage system. In the startup stage, the flywheel speed rises from zero to the rated speed, and the battery energy storage system enters the standby state. In the normal state of the grid frequency, the flywheel energy storage system enters speed control to maintain the flywheel speed at the rated speed, and the battery energy storage system operates in the standby state. When the grid frequency is in an abnormal state, it enters the inertial response regulation stage, and the flywheel energy storage system adopts a virtual inertia control strategy based on the inertia of the flywheel itself and the state of the grid frequency. In the primary frequency regulation stage, the battery energy storage system adopts a droop control strategy, and the flywheel energy storage system maintains the virtual inertia control strategy. In the flywheel state of charge recovery stage, the flywheel energy storage system enters the state of charge recovery state, the battery energy storage system participates in the primary frequency regulation of the grid, and at the same time outputs additional power to match the energy absorbed during the flywheel state of charge recovery.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage and power grid system inertia and frequency response, and in particular to a flywheel-battery hybrid energy storage frequency regulation system, method, device and medium. Background Art

[0002] From the perspective of grid stability, the dynamics and stability of frequency are important indicators of grid strength and the balance between power generation and electricity consumption. In new energy grids, the access of a large number of power electronic converters leads to a reduction in the inertia of the grid system, which also means that when a frequency event occurs in the system (such as generator disconnection, load access, wind power and photovoltaic processing fluctuations), under load disturbances, the grid system is prone to faster frequency changes and larger frequency deviations. The introduction of energy storage systems can effectively control the system frequency change rate and frequency deviation when frequency events occur. Therefore, energy storage systems play an important role in frequency fluctuation smoothing and voltage stability control of the grid.

[0003] According to the phase of grid frequency change, the frequency control strategy can be divided into the inertial response phase and the primary frequency response phase. The inertial response phase is generally within tens of milliseconds to seconds after the frequency event occurs. At this time, the system will be subject to a large frequency change rate and is in a frequency deterioration period. The frequency fluctuation at this time presents high-frequency characteristics. The primary frequency response phase is usually within tens of seconds to one minute after the grid frequency event occurs. It is in the frequency recovery period. At this stage, the energy storage system is required to provide long-term energy support.

[0004] The grid frequency response puts forward different time scale power and energy requirements for the energy storage system, so the energy storage system must have both good power output characteristics and a certain capacity. It is difficult for a single type of energy storage to meet the above requirements, so a power-type energy storage system with a higher power density and an energy-type energy storage system with a large capacity and long-term energy storage capacity can be combined to form a hybrid energy storage system. As a power-type energy storage system, the flywheel energy storage system has the advantages of high power density, fast response speed, and long service life. It can participate in the grid frequency modulation at a high frequency. The flywheel energy storage has its own inertia, and the control strategy can be reasonably set to enable the flywheel energy storage system to provide damping and inertia to the grid to achieve the inertial frequency regulation of the grid; the lithium-ion battery energy storage system, as an energy-type energy storage system, can provide long-term power support to the grid and achieve the primary frequency modulation response of the grid. The hybrid energy storage system that combines the flywheel energy storage system and the lithium-ion battery system can maximize the advantages of the energy storage system and control the grid frequency changes within a reasonable range.

[0005] In the related art, most single - form energy storage systems are used to participate in the power grid frequency response. In the control strategy of the power - type energy storage system participating in the power grid inertia response, most adopt the virtual inertia control strategy based on a fixed inertia constant. This strategy fails to maximize the use of the energy storage's own parameters and the power grid frequency condition to determine the depth of the energy storage's participation in the power grid frequency regulation. In the research on related hybrid energy storage systems, most separately control and operate the power - type energy storage system and the energy - type energy storage system, without studying the output control strategy in different stages of the frequency response and the state - of - charge recovery of the power - type energy storage, thus prolonging the power grid frequency recovery time, increasing the energy storage capacity configuration, and increasing the system cost, which urgently needs to be solved.

[0006] Application Content

[0007] This application aims to solve at least one of the technical problems in the related art to some extent.

[0008] To this end, the first objective of this application is to propose a flywheel - battery hybrid energy storage frequency regulation system, which can achieve inertial response and primary frequency regulation after a power grid frequency event occurs, and can achieve the state - of - charge recovery of the flywheel energy storage system, improving the utilization efficiency of the energy storage system.

[0009] The second objective of this application is to propose a flywheel - battery hybrid energy storage frequency regulation method.

[0010] The third objective of this application is to propose an electronic device.

[0011] The fourth objective of this application is to propose a computer - readable storage medium.

[0012] To achieve the above objectives, the first - aspect embodiment of this application provides a flywheel - battery hybrid energy storage frequency regulation system, including a flywheel energy storage system and a lithium - ion battery energy storage system connected to the power grid. Among them,

[0013] When in the startup stage, the flywheel speed gradually rises from zero to the rated speed, and the lithium - ion battery energy storage system is controlled to enter the standby state;

[0014] If the power grid frequency is in the preset normal state, the flywheel energy storage system enters the speed control working condition, maintaining the flywheel speed at the rated speed, and the battery energy storage system operates in the standby state; and

[0015] If the power grid frequency is in the preset abnormal state, the system enters the inertial response regulation stage. The flywheel energy storage system adopts a virtual inertia control strategy based on the flywheel's own inertia and the power grid frequency state, and the system enters the primary frequency regulation stage. The battery energy storage system adopts a droop control strategy, and the flywheel energy storage system maintains the virtual inertia control strategy; and

[0016] When in the flywheel energy storage state of charge restoration phase, the flywheel energy storage system enters the state of charge restoration state, enabling the battery energy storage system to participate in the primary frequency regulation of the power grid, and simultaneously outputting additional power to match the energy absorbed during the flywheel energy storage state of charge restoration.

[0017] According to the flywheel-battery hybrid energy storage frequency regulation system of the embodiments of the present application, through the coordinated inertia and frequency response control strategy of the flywheel-battery system considering the inertia of the flywheel itself and the power grid frequency state, at the initial stage of a frequency event, the flywheel energy storage provides inertia to the power grid. During the primary frequency regulation period, the battery energy storage system and the flywheel energy storage system jointly provide frequency support to the power grid, and the state of charge restoration of the flywheel energy storage system is achieved, thereby realizing the inertia response and primary frequency regulation after the power grid frequency event occurs, and realizing the state of charge restoration of the flywheel energy storage system, improving the utilization efficiency of the energy storage system.

[0018] In addition, the flywheel-battery hybrid energy storage frequency regulation system according to the above embodiments of the present application may further have the following additional technical features:

[0019] Optionally, when in the secondary frequency regulation phase, while maintaining the current output level, the regulation system waits for other units to enter the secondary frequency regulation to restore the power grid frequency to the preset normal state.

[0020] Optionally, the flywheel energy storage system and the lithium-ion battery energy storage system are connected in parallel through a DC bus unit, and are connected to the power grid through a grid-side converter, an LCL filter, a grid-connected converter, and a transformer.

[0021] Optionally, among them,

[0022] The power grid is connected to the DC bus unit through the transformer, the LCL filter circuit, and the grid-side converter in sequence, where the grid-side converter is used to maintain the stability of the DC bus voltage, enabling bidirectional power flow between the power grid and the energy storage system.

[0023] Optionally, in the flywheel energy storage system, every three phases on the stator side of the dual three-phase permanent magnet synchronous motor form a bridge arm, and each bridge arm is provided with a machine-side filter and a machine-side converter. After the two bridge arms are connected in parallel, they are connected to the DC bus unit through a flywheel energy storage grid-connected circuit breaker. The machine-side converter adjusts the voltage input to the rotor of the flywheel energy storage motor to control physical quantities, and the rotor of the dual three-phase permanent magnet synchronous motor and the rotor of the large-inertia flywheel are connected through a rotating shaft for mechanical power transmission.

[0024] Optionally, the lithium-ion battery energy storage system is sequentially connected to a battery energy storage side DC / DC converter and a battery energy storage system grid connection breaker, and is connected to a DC bus capacitor. The DC / DC converter adjusts the voltage on the lithium-ion battery side to perform power exchange between the lithium-ion battery energy storage system and the power grid.

[0025] To achieve the above object, an embodiment of the second aspect of the present application provides a flywheel-battery hybrid energy storage frequency regulation method, which uses the above flywheel-battery hybrid energy storage frequency regulation system. The method includes the following steps:

[0026] When in the startup phase, the flywheel speed gradually rises from zero to the rated speed, and the lithium-ion battery energy storage system is controlled to enter the standby state;

[0027] If the grid frequency is in a preset normal state, the flywheel energy storage system is controlled to enter the speed control working condition, the flywheel speed is maintained at the rated speed, and the battery energy storage system is controlled to work in the standby state; and

[0028] If the grid frequency is in a preset abnormal state, the system is controlled to enter the inertial response regulation stage, so that the flywheel energy storage system adopts a virtual inertia control strategy based on the inertia of the flywheel itself and the grid frequency state, and the system enters the primary frequency regulation stage, so that the battery energy storage system adopts a droop control strategy, and the flywheel energy storage system is controlled to maintain the virtual inertia control strategy; and

[0029] When in the flywheel energy storage state of charge recovery stage, the flywheel energy storage system is controlled to enter the state of charge recovery, so that the battery energy storage system participates in the primary frequency regulation of the power grid, and at the same time outputs additional power to match the energy absorbed during the flywheel energy storage state of charge recovery.

[0030] According to the flywheel-battery hybrid energy storage frequency regulation method of the embodiments of the present application, through a coordinated inertia and frequency response control strategy of the flywheel-battery system considering the inertia of the flywheel itself and the grid frequency state, at the initial stage of a frequency event, inertia is provided to the power grid by the flywheel energy storage. During the primary frequency regulation period, the battery energy storage system and the flywheel energy storage system jointly provide frequency support to the power grid, and the state of charge recovery of the flywheel energy storage system is realized, so as to realize the inertial response and primary frequency regulation after a power grid frequency event, and realize the state of charge recovery of the flywheel energy storage system, and improve the utilization efficiency of the energy storage system.

[0031] Optionally, the flywheel-battery hybrid energy storage frequency regulation method of the embodiments of the present application further includes:

[0032] When in the secondary frequency regulation stage, while controlling the regulation system to maintain the current output level, wait for other units to enter the secondary frequency regulation to restore the grid frequency to the preset normal state.

[0033] To achieve the above object, an embodiment of the third aspect of the present application provides an electronic device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are configured to execute the flywheel-battery hybrid energy storage frequency regulation method as described in the above embodiments.

[0034] To achieve the above object, an embodiment of the fourth aspect of the present application provides a computer-readable storage medium, and the computer-readable storage medium stores computer instructions for causing the computer to execute the flywheel-battery hybrid energy storage frequency regulation method as described in the above embodiments.

[0035] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present application. Description of the Drawings

[0036] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description of the embodiments in conjunction with the drawings, wherein:

[0037] Figure 1 It is a flowchart of a flywheel-battery hybrid energy storage frequency regulation method according to an embodiment of the present application;

[0038] Figure 2 It is a topological structure diagram of a flywheel-battery hybrid energy storage frequency regulation system according to an embodiment of the present application;

[0039] Figure 3 It is a schematic control block diagram of a flywheel-battery hybrid energy storage frequency regulation system according to an embodiment of the present application;

[0040] Figure 4 It is a control flowchart of a flywheel-battery hybrid energy storage frequency regulation system according to an embodiment of the present application;

[0041] Figure 5 It is a waveform schematic diagram of the grid frequency and the grid frequency change rate according to an embodiment of the present application;

[0042] Figure 6 It is a waveform diagram of the flywheel energy storage power, the flywheel energy storage virtual inertia, the flywheel energy storage state of charge, and the battery energy storage power according to an embodiment of the present application;

[0043] Figure 7Flow chart of the flywheel-battery hybrid energy storage frequency regulation method provided by the embodiment of the present application;

[0044] Figure 8 Schematic structural diagram of the electronic device provided by the embodiment of the present application. Detailed implementation manners

[0045] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, but should not be construed as a limitation to the present application.

[0046] The flywheel-battery hybrid energy storage frequency regulation system, method, device and medium proposed according to the embodiments of the present application will be described below with reference to the accompanying drawings. First, the flywheel-battery hybrid energy storage frequency regulation system proposed according to the embodiments of the present application will be described with reference to the accompanying drawings.

[0047] Specifically, Figure 1 Block diagram of a flywheel-battery hybrid energy storage frequency regulation system provided by the embodiment of the present application.

[0048] As Figure 1 shown, the flywheel-battery hybrid energy storage frequency regulation system 100 includes a flywheel energy storage system 101 and a lithium-ion battery energy storage system 102 connected to the power grid. When in the startup stage, the flywheel speed gradually rises from zero to the rated speed, and the lithium-ion battery energy storage system 102 is controlled to enter the standby state; if the grid frequency is in the preset normal state, the flywheel energy storage system 101 enters the speed control working condition to keep the flywheel speed at the rated speed, and the battery energy storage system works in the standby state; and if the grid frequency is in the preset abnormal state, the system enters the inertial response regulation stage, and the flywheel energy storage system 101 adopts a virtual inertia control strategy based on the flywheel's own inertia and the grid frequency state, and the system enters the primary frequency modulation stage. The battery energy storage system adopts a droop control strategy, and the flywheel energy storage system 101 maintains the virtual inertia control strategy; and when in the flywheel energy storage state of charge recovery stage, the flywheel energy storage system 101 enters the state of charge recovery state, enabling the battery energy storage system to participate in the primary frequency modulation of the power grid, and at the same time outputting additional power to match the energy absorbed during the flywheel energy storage state of charge recovery.

[0049] Specifically, when the flywheel-battery hybrid energy storage frequency regulation system 100 is in the startup phase (i.e., entering the power-on startup phase), the grid-connected breaker of the flywheel energy storage system 101 closes. The flywheel energy storage system 101 absorbs grid power through the flywheel energy storage machine-side converter, and the flywheel speed gradually rises from zero to the rated speed; the grid-connected breaker of the lithium-ion battery energy storage system 102 closes, and the lithium-ion battery energy storage system 102 enters the standby state.

[0050] Further, when the grid frequency is in the preset normal state, the flywheel-battery hybrid energy storage frequency regulation system 100 does not participate in grid frequency regulation; the flywheel energy storage system 101 enters speed control, maintains the flywheel speed at the rated speed, and does not emit or absorb power externally; the lithium-ion battery energy storage system 102 operates in the standby state and does not emit or absorb power externally.

[0051] Further, when the grid frequency is in the preset abnormal state (such as generator disconnection, load connection, wind power and photovoltaic power fluctuations), the flywheel-battery hybrid energy storage frequency regulation system 100 participates in grid frequency regulation, and is divided into inertial response regulation, primary frequency regulation phase, flywheel energy storage state of charge recovery phase, and secondary frequency regulation phase according to different stages of the grid frequency fluctuation. Among them, when in the inertial response regulation phase, the control unit of the flywheel energy storage system 101 detects the rate of change of the grid frequency. At this time, the flywheel energy storage system 101 responds quickly and adopts a virtual inertia control strategy based on the inertia of the flywheel itself and the state of the grid frequency to provide inertial power support to the grid and participate in grid frequency regulation; the control unit of the lithium-ion battery energy storage system 102 detects the grid frequency deviation. At this time, the system frequency deviation does not exceed the control dead zone (50 ± 0.033 Hz), and the lithium-ion battery energy storage system 102 does not emit or absorb power externally and is in the standby state; when in the primary frequency regulation phase, the control unit of the lithium-ion battery energy storage system 102 detects that the grid frequency deviation exceeds the control dead zone (50 ± 0.033 Hz), and the lithium-ion battery energy storage system 102 adopts a droop control strategy, and the droop coefficient depends on the grid frequency deviation and the rated capacity of the lithium-ion battery energy storage system 102; the control unit of the flywheel energy storage system 101 detects the rate of change of the grid frequency and maintains the virtual inertia control strategy based on the inertia of the flywheel itself and the state of the grid frequency.

[0052] Further, when in the flywheel energy storage state of charge recovery phase, the flywheel energy storage system 101 detects that the state of charge SOC of the flywheel is lower than the set rated value: SOC min = 0.25, the flywheel energy storage system 101 stops emitting power externally and starts the flywheel energy storage state of charge recovery phase, and uses a PI controller to realize the recovery of the flywheel energy storage state of charge. The flywheel energy storage state of charge is recovered to the set value SOC n= 0.75; During the process of restoring the state of charge of the flywheel energy storage, on the one hand, the lithium-ion battery energy storage system 102 continues to participate in the primary frequency regulation of the power grid, and on the other hand, it outputs additional power to match the energy absorbed during the restoration of the state of charge of the flywheel energy storage, avoiding secondary frequency dips in the power grid frequency.

[0053] Further, in some embodiments, when in the secondary frequency regulation stage, while the regulation system maintains the current output level, it waits for other units to enter the secondary frequency regulation to restore the power grid frequency to the preset normal state.

[0054] Thus, compared with the methods of the related art, the features and beneficial effects of the present application are as follows:

[0055] (1) In the grid inertia response regulation stage, a virtual inertia control strategy based on the flywheel's own inertia and the grid frequency state is adopted to provide inertial power support to the grid and participate in grid frequency regulation, which can maximize the characteristics of the flywheel energy storage system itself with large inertia and high power density, prevent the deterioration of the system frequency in a short time, and reduce the grid frequency change rate and the maximum frequency deviation.

[0056] (2) It realizes the coordinated control and complementarity of the power-type energy storage system and the energy-type energy storage system in grid frequency regulation, maximizes the advantages of the two energy storage systems, and improves the grid frequency regulation response speed and regulation effect.

[0057] (3) The control strategy considering the restoration of the state of charge (SOC) of the flywheel energy storage system can ensure the cycle times of the system, improve the system efficiency, reduce the energy storage capacity configuration, and save costs.

[0058] For ease of understanding, the components of the flywheel-battery hybrid energy storage frequency regulation system 100 will be described in detail below.

[0059] Specifically, in some embodiments, the flywheel energy storage system 101 and the lithium-ion battery energy storage system 102 are connected in parallel through a DC bus unit and are connected to the power grid through a grid-side converter, an LCL filter, a grid-connected converter, and a transformer.

[0060] Among them, the flywheel energy storage system 101 includes a flywheel energy storage grid-connected circuit breaker, two sets of flywheel energy storage machine-side converters, a flywheel energy storage machine-side LC filter, a dual three-phase permanent magnet synchronous motor, and a large inertia flywheel rotor; the lithium-ion battery energy storage system 102 includes a battery energy storage grid-connected circuit breaker, a battery energy storage side DC / DC converter, and a lithium-ion battery pack. The connection relationships of each device are as follows:

[0061] In some embodiments, the power grid is connected to the DC bus unit through a transformer, an LCL filter circuit, and a grid-side converter in sequence. The grid-side converter is used to maintain the stability of the DC bus voltage, enabling bidirectional power flow between the power grid and the energy storage system.

[0062] Optionally, in some embodiments, in the flywheel energy storage system 101, every three phases on the stator side of the dual three-phase permanent magnet synchronous motor form a bridge arm, and a machine-side filter and a machine-side converter are respectively provided on each bridge arm. After the two bridge arms are connected in parallel, they are connected to the DC bus unit through a flywheel energy storage grid connection breaker. The machine-side converter adjusts the voltage input to the rotor of the flywheel energy storage motor to control physical quantities such as the electromagnetic torque and speed of the motor. The rotor of the dual three-phase permanent magnet synchronous motor and the rotor of the large inertia flywheel are connected through a rotating shaft for mechanical power transmission.

[0063] Optionally, in some embodiments, the lithium-ion battery energy storage system 102 is sequentially connected to a battery energy storage side DC / DC converter and a battery energy storage system grid connection breaker, and is connected to a DC bus capacitor. The DC / DC converter adjusts the voltage on the lithium-ion battery side to perform power exchange between the lithium-ion battery energy storage system 102 and the power grid.

[0064] To enable those skilled in the art to further understand the flywheel-battery hybrid energy storage frequency regulation system of the embodiments of the present application, the following will be described in detail with specific embodiments.

[0065] Specifically, as Figure 2 shown, the topological structure of the flywheel-battery hybrid energy storage frequency regulation system of the embodiments of the present application includes: a power grid model 1, a transformer 2, an LCL filter 3, a grid-side converter 4, a DC bus capacitor 5, a flywheel energy storage grid connection breaker 6, a flywheel energy storage machine-side converter 7, a flywheel energy storage machine-side LC filter 8, a dual three-phase permanent magnet synchronous motor 9, a large inertia flywheel rotor 10, a battery energy storage grid connection breaker 11, a battery energy storage side DC / DC converter 12, and a lithium-ion battery energy storage system 102.

[0066] Specifically, the power grid 1 is connected to the DC bus capacitor 5 through a transformer 2, an LCL filter circuit 3, and a grid-side converter 4. The grid-side converter 4 maintains the voltage stability of the DC bus capacitor 5, realizing bidirectional power flow between the power grid and the hybrid energy storage system.

[0067] In the flywheel energy storage system, the stator side of the dual-three-phase permanent magnet synchronous motor 9 forms two bridge arms. An on-machine converter 7 and an on-machine filter 8 are provided on the two bridge arms, and they are connected to the DC bus capacitor 5 through the flywheel energy storage grid-connected breaker 6. The on-machine converter 7 adjusts the voltage input to the rotor of the flywheel energy storage motor and realizes the control of physical quantities such as the electromagnetic torque and speed of the motor. The rotor of the dual-three-phase permanent magnet synchronous motor 9 and the large-inertia flywheel rotor 10 are connected through a rotating shaft to realize the transmission of mechanical power. The converters in the flywheel energy storage system all adopt bidirectional AC / DC converters.

[0068] The lithium-ion battery energy storage system 102 is successively connected to the battery energy storage side DC / DC converter 12, the battery energy storage system grid-connected breaker 11 and the DC bus capacitor 5. The battery energy storage side DC / DC converter 12 adjusts the voltage on the lithium-ion battery side and realizes the power exchange between the lithium-ion battery energy storage system and the power grid.

[0069] Further, as Figure 3 and Figure 4 shown, among which, Figure 3 is a schematic control block diagram of the flywheel-battery hybrid energy storage frequency regulation system according to an embodiment of the present application, Figure 4 is the control flowchart of the flywheel-battery hybrid energy storage frequency regulation system. Combining Figures 2 to 4 it can be known that the flywheel-battery hybrid energy storage frequency regulation method of the embodiment of the present application includes the following steps:

[0070] S1. System power-on and startup stage. After power-on and startup, the flywheel-battery hybrid energy storage frequency regulation system enters the power-on and startup stage; the flywheel energy storage system grid-connected breaker 6 is closed, and the flywheel energy storage system absorbs grid power through the flywheel energy storage on-machine converter 7, and the speed of the flywheel motor gradually rises from 0 to the rated speed ω n ; the battery energy storage system grid-connected breaker 11 is closed, and the lithium-ion battery system enters the standby state.

[0071] S2. Monitor the grid frequency and judge whether a frequency event occurs in the grid. If no frequency event occurs, the flywheel-battery hybrid energy storage frequency regulation system does not participate in frequency regulation, the flywheel motor remains at the rated speed ω n , does not emit power externally, the battery energy storage system operates in the standby state and does not emit power externally; if it is detected that a frequency event occurs (the grid frequency fluctuates), then enter step S3.

[0072] S3. Detect the grid frequency change rate. If the grid frequency change rate is not detected, return to step S2; if the frequency change rate is detected, perform low-pass filtering on the frequency change rate to filter out high-frequency components. When it is determined that the product of the frequency change rate and the frequency deviation is positive, it indicates that the system is in a frequency deterioration period at this time, and the frequency control flag K flagSet 1. At this time, the flywheel energy storage SOC state is in a normal state, and flag K SOC Set 1. The system enters the inertial response stage, and the flywheel energy storage system starts to adopt a virtual inertial control strategy based on the flywheel inertia and grid frequency state to minimize the grid frequency change rate. At this time, the power output of the flywheel energy storage system can be calculated as follows:

[0073]

[0074] In the formula, P FESS_ref represents the reference active power output of the flywheel energy storage system participating in grid frequency regulation during the inertial response stage, H f represents the flywheel's own inertia, K fw represents the grid frequency deviation adjustment factor, K flag represents the grid frequency control flag, with a value of 0 or 1, K SOC represents the flywheel energy storage SOC state flag, with a value of 0 or 1, represents the per-unit value of the grid frequency change rate, P n represents the rated output power of the flywheel energy storage system.

[0075] Among them:

[0076]

[0077]

[0078]

[0079]

[0080] In the formula, J is the flywheel's own inertia, ω e is the electrical angular velocity of the flywheel, ω en is the rated electrical angular velocity of the flywheel, p n is the number of pole pairs of the flywheel motor, S base is the rated capacity of the flywheel energy storage system, f d+ is the positive dead zone of the grid frequency, generally set to 50 + 0.033 Hz according to grid requirements, f d- is the negative dead zone of the grid frequency, generally set to 50 - 0.033 Hz. Through calculation, the inertial frequency support provided by the flywheel energy storage system to the grid under different grid frequency conditions and flywheel speeds can be obtained. This calculated value comprehensively considers factors such as the grid frequency change rate, frequency deviation, and flywheel SOC, and can optimize the output of the flywheel energy storage system to the greatest extent.

[0081] S4. Detect the grid frequency deviation. If the grid frequency deviation does not exceed the dead zone, the lithium-ion battery system does not emit or absorb power and is in the standby state. If the grid frequency deviation exceeds the dead zone, the flywheel energy storage system maintains the virtual inertia control strategy, and the battery energy storage system adopts the droop control strategy. At this time, the power reference of the battery energy storage system can be calculated as follows:

[0082]

[0083] Among them, D LIB is the maximum battery energy storage droop coefficient. After the battery energy storage starts the droop control, when the grid frequency reaches the lowest point, the frequency recovery stage is started.

[0084] S5. Detect whether the SOC of the flywheel energy storage exceeds the safe range. If it does not exceed, the flywheel energy storage continues to maintain the virtual inertia control strategy, and the battery energy storage continues to maintain the primary frequency modulation control strategy. If the SOC of the flywheel energy storage is lower than the lower limit of the safe range, the charge state recovery stage of the flywheel energy storage is started. At this time, the machine-side converter 7 of the flywheel energy storage adopts double-loop control. The outer loop adopts the SOC reference, and the inner loop q-axis current reference is given through PI control Among them, SOC FESS is the currently collected SOC of the flywheel energy storage, SOC ref is the reference SOC, k psoc and k isoc are the set PI parameters respectively. At this time, in addition to continuing to maintain the primary frequency modulation power output, the battery energy storage system also needs to compensate for the SOC recovery power of the flywheel energy storage. At this time, the output of the battery energy storage can be expressed as:

[0085]

[0086] Among them, is the result after the inversion of the K SOC flag, and P FESS is the actual output of the flywheel energy storage system.

[0087] When it is detected that the charge state of the flywheel energy storage has recovered to the permitted range, the system resumes to the primary frequency modulation stage, and the output reference of the battery energy storage resumes to P LIB_ref1 .

[0088] S5. When it is detected that the system frequency deviation value is stable at a constant deviation value, the flywheel energy storage and the battery energy storage system maintain the current output level and wait for other units to perform secondary frequency modulation to restore the grid frequency to the normal level.

[0089] The following is the verification of the flywheel-battery hybrid energy storage frequency regulation system of the present application embodiment.

[0090] Specifically, a digital simulation system of a flywheel-battery hybrid energy storage participating in grid inertia and frequency response is built on the MATLAB / Simulink platform to simulate the process of the flywheel energy storage system and the battery energy storage system participating in grid frequency regulation. At 0 s, the system powers on and starts up, and the speed of the flywheel motor gradually increases from 0 to the rated speed. At 0.08 s, the speed of the flywheel motor reaches the rated speed, and the system completes the startup process. From 0.08 s to 0.1 s, the grid frequency is in a normal state. The flywheel energy storage maintains the rated speed and does not emit or absorb power externally. The battery energy storage is in a standby state and does not emit or absorb power externally. At 0.1 s, based on the rated capacity of the grid, a load of 0.1 p.u. is suddenly applied, causing the grid frequency to suddenly drop, and the flywheel-battery hybrid energy storage frequency regulation system starts frequency regulation.

[0091] As Figure 5 shown, Figure 5 This is the waveform diagram of the grid frequency and the grid frequency change rate in an embodiment of the present application. At the initial stage of the frequency event, the frequency change rate changes rapidly. The flywheel energy storage system responds through inertia, quickly outputs a large amount of power in a short time, curbs the increasing trend of the frequency change rate, and reduces the maximum deviation of the grid frequency. When the grid frequency deviation exceeds the dead zone of primary frequency regulation, the battery energy storage system and the flywheel energy storage system jointly participate in primary frequency regulation to reduce the steady-state error of the grid frequency.

[0092] As Figure 6 shown, Figure 6 This is the waveform diagram of the flywheel energy storage power, the flywheel energy storage virtual inertia, the flywheel energy storage state of charge, and the battery energy storage power in an embodiment of the present application. It can be seen that in the inertia response stage, the output of the flywheel energy storage system quickly reaches the maximum value, which can fully utilize the characteristic of the large power density of the flywheel energy storage to provide inertial power support for the grid. In the primary frequency regulation stage, the flywheel and the battery jointly participate in frequency regulation to provide continuous energy for the grid and reduce the steady-state frequency deviation of primary frequency regulation. When the SOC of the flywheel energy storage is lower than the lower limit, the flywheel energy storage SOC recovery stage is started, and by reasonably setting the control strategy, the battery energy storage can match the energy recovered by the flywheel energy storage power in real time to avoid the secondary drop of the grid frequency.

[0093] According to the flywheel-battery hybrid energy storage frequency regulation system proposed in the embodiment of the present application, through the coordinated inertia and frequency response control strategy of the flywheel-battery system considering the inertia of the flywheel itself and the grid frequency state, at the initial stage of the frequency event, the flywheel energy storage provides inertia to the grid. During primary frequency regulation, the battery energy storage system and the flywheel energy storage system jointly provide frequency support to the grid, and the state of charge recovery of the flywheel energy storage system is realized, so as to achieve the inertia response and primary frequency regulation after the grid frequency event, and realize the state of charge recovery of the flywheel energy storage system, improving the utilization efficiency of the energy storage system.

[0094] Next, a flywheel-battery hybrid energy storage frequency regulation method according to an embodiment of the present application will be described with reference to the accompanying drawings.

[0095] Figure 7 It is a flowchart of the flywheel-battery hybrid energy storage frequency regulation method according to an embodiment of the present application.

[0096] As Figure 7 shown, for the flywheel-battery hybrid energy storage frequency regulation method, the above-mentioned flywheel-battery hybrid energy storage frequency regulation system is adopted, wherein the method includes the following steps:

[0097] S701, when in the startup stage, the flywheel speed gradually rises from zero to the rated speed, and the lithium-ion battery energy storage system is controlled to enter the standby state;

[0098] S702, if the grid frequency is in the preset normal state, the flywheel energy storage system is controlled to enter the speed control working condition, the flywheel speed is maintained at the rated speed, and the battery energy storage system is controlled to work in the standby state; and

[0099] S703, if the grid frequency is in the preset abnormal state, the control system enters the inertia response regulation stage, so that the flywheel energy storage system adopts a virtual inertia control strategy based on the flywheel's own inertia and the grid frequency state, and the system enters the primary frequency regulation stage, so that the battery energy storage system adopts a droop control strategy, and the flywheel energy storage system is controlled to maintain the virtual inertia control strategy; and

[0100] S704, when in the flywheel energy storage state of charge recovery stage, the flywheel energy storage system is controlled to enter the state of charge recovery, so that the battery energy storage system participates in the primary frequency regulation of the grid, and at the same time outputs additional power to match the energy absorbed during the flywheel energy storage state of charge recovery.

[0101] Optionally, the flywheel-battery hybrid energy storage frequency regulation method according to an embodiment of the present application further includes:

[0102] When in the secondary frequency regulation stage, while controlling the regulation system to maintain the current output level, wait for other units to enter the secondary frequency regulation to restore the grid frequency to the preset normal state.

[0103] It should be noted that the foregoing explanation of the flywheel-battery hybrid energy storage frequency regulation system embodiment also applies to the flywheel-battery hybrid energy storage frequency regulation method of this embodiment, and will not be repeated here.

[0104] The flywheel-battery hybrid energy storage frequency regulation method proposed according to the embodiments of the present application adopts a coordinated inertia and frequency response control strategy for the flywheel-battery system by considering the inertia of the flywheel itself and the grid frequency state. In the initial stage of a frequency event, the flywheel energy storage provides inertia to the grid. During the primary frequency regulation period, the battery energy storage system and the flywheel energy storage system jointly provide frequency support to the grid, and the state of charge of the flywheel energy storage system is restored, thereby realizing the inertial response and primary frequency regulation after the grid frequency event occurs, and realizing the state of charge restoration of the flywheel energy storage system, and improving the utilization efficiency of the energy storage system.

[0105] Figure 8 The structural schematic diagram of the electronic device provided by the embodiment of the present application. The electronic device may include:

[0106] A memory 801, a processor 802, and a computer program stored on the memory 801 and executable on the processor 802.

[0107] When the processor 802 executes the program, it implements the flywheel-battery hybrid energy storage frequency regulation method provided in the above embodiment.

[0108] Further, the electronic device further includes:

[0109] A communication interface 803 for communication between the memory 801 and the processor 802.

[0110] The memory 801 is used to store a computer program executable on the processor 802.

[0111] The memory 801 may include a high-speed RAM memory, and may also include a non-volatile memory, such as at least one disk memory.

[0112] If the memory 801, the processor 802, and the communication interface 803 are independently implemented, the communication interface 803, the memory 801, and the processor 802 may be interconnected through a bus and communicate with each other. The bus may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. The bus may be divided into an address bus, a data bus, a control bus, etc. For the sake of simplicity of representation, Figure 8 only a thick line is shown in the figure, but it does not mean that there is only one bus or one type of bus.

[0113] Optionally, in a specific implementation, if the memory 801, the processor 802, and the communication interface 803 are integrated on a single chip, the memory 801, the processor 802, and the communication interface 803 can communicate with each other through an internal interface.

[0114] The processor 802 may be a central processing unit (CPU for short), or an application specific integrated circuit (ASIC for short), or one or more integrated circuits configured to implement the embodiments of the present application.

[0115] This embodiment also provides a computer-readable storage medium storing computer instructions for causing a computer to execute the flywheel-battery hybrid energy storage frequency regulation method as described in the above embodiments.

[0116] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, without conflict, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples.

[0117] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0118] Any process or method description in a flowchart or described in other ways herein can be understood to represent a module, segment, or portion of code including one or more executable instructions for implementing a customized logic function or process, and the scope of the preferred embodiments of the present application includes additional implementations, where the functions may be executed in a substantially simultaneous manner or in a reverse order according to the involved functions, rather than in the order shown or discussed, which should be understood by those skilled in the art of the embodiments of the present application.

[0119] The logic and / or steps represented in the flowchart or otherwise described herein can, for example, be considered as a definitional sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or used in conjunction with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in conjunction with an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include the following: an electrical connection portion (electronic device) having one or N wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, as the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other suitable processing as necessary, and then stored in a computer memory.

[0120] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having suitable combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0121] Those of ordinary skill in the art of this technology can understand that all or part of the steps carried by the methods of the above embodiments can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiments.

[0122] In addition, each functional unit in various embodiments of the present application may be integrated into one processing module, or each unit may exist physically alone, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. When the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0123] The above-mentioned storage medium may be a read-only memory, a magnetic disk, an optical disc, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A flywheel-battery hybrid energy storage frequency regulation system, characterized in that, The system includes a flywheel energy storage system and a lithium-ion battery energy storage system connected to the power grid. Among them, When in the startup phase, the flywheel speed gradually increases from zero to the rated speed, and the lithium-ion battery energy storage system is controlled to enter the standby state; If the grid frequency is in the preset normal state, the flywheel energy storage system enters the speed control condition, maintaining the flywheel speed at the rated speed, and the battery energy storage system operates in the standby state; and If the grid frequency is in the preset abnormal state, the system enters the inertial response regulation phase. The flywheel energy storage system adopts a virtual inertia control strategy based on the flywheel's own inertia and the grid frequency state, and the system enters the primary frequency regulation phase. The battery energy storage system adopts a droop control strategy, and the flywheel energy storage system maintains the virtual inertia control strategy; and When in the flywheel energy storage state of charge recovery phase, the flywheel energy storage system enters the state of charge recovery state, enabling the battery energy storage system to participate in the grid primary frequency regulation, and simultaneously outputting additional power to match the energy absorbed during the flywheel energy storage state of charge recovery; The flywheel energy storage system and the lithium-ion battery energy storage system are connected in parallel through a DC bus unit and are connected to the power grid through a grid-side converter, an LCL filter, a grid-connected converter, and a transformer; the power grid is connected to the DC bus unit through the transformer, the LCL filter circuit, and the grid-side converter in sequence, where the grid-side converter is used to maintain the stability of the DC bus voltage, enabling bidirectional power flow between the power grid and the energy storage system; In the flywheel energy storage system, each three-phase on the stator side of the dual three-phase permanent magnet synchronous motor forms a bridge arm, and each bridge arm is provided with a machine-side filter and a machine-side converter. After the two bridge arms are connected in parallel, they are connected to the DC bus unit through a flywheel energy storage grid-connected circuit breaker. The machine-side converter adjusts the voltage input to the flywheel energy storage motor rotor to control physical quantities, and the rotor of the dual three-phase permanent magnet synchronous motor and the large-inertia flywheel rotor are connected through a rotating shaft to transmit mechanical power.

2. The system according to claim 1, characterized in that, When in the secondary frequency regulation phase, while maintaining the current output level, the regulation system waits for other units to enter the secondary frequency regulation to restore the grid frequency to the preset normal state.

3. The system according to claim 1, wherein The lithium-ion battery energy storage system is sequentially connected to a battery energy storage side DC / DC converter, a battery energy storage system grid-connected circuit breaker, and a DC bus capacitor. The DC / DC converter adjusts the voltage on the lithium-ion battery side to perform power exchange between the lithium-ion battery energy storage system and the power grid.

4. A flywheel-battery hybrid energy storage frequency regulation method, characterized in that, Adopt the flywheel-battery hybrid energy storage frequency regulation system as described in any one of claims 1-3, where the method includes the following steps: When in the startup phase, the flywheel speed gradually increases from zero to the rated speed, and the lithium-ion battery energy storage system is controlled to enter the standby state; If the grid frequency is in the preset normal state, control the flywheel energy storage system to enter the speed control condition, maintaining the flywheel speed at the rated speed, and control the battery energy storage system to operate in the standby state; and If the grid frequency is in a preset abnormal state, control the system to enter the inertial response regulation stage, so that the flywheel energy storage system adopts a virtual inertia control strategy based on the inertia of the flywheel itself and the grid frequency state, and the system enters the primary frequency regulation stage, so that the battery energy storage system adopts a droop control strategy, and control the flywheel energy storage system to maintain the virtual inertia control strategy; and When in the flywheel energy storage state of charge recovery stage, control the flywheel energy storage system to enter the state of charge recovery, so that the battery energy storage system participates in the primary frequency regulation of the power grid, and at the same time outputs additional power to match the energy absorbed during the flywheel energy storage state of charge recovery.

5. The method according to claim 4, wherein It further includes: When in the secondary frequency regulation stage, control the regulation system to maintain the current output level while waiting for other units to enter the secondary frequency regulation to restore the grid frequency to the preset normal state.

6. An electronic device, characterized in that, It includes: A memory, a processor, and a computer program stored on the memory and executable on the processor, and the processor executes the program to implement the flywheel-battery hybrid energy storage frequency regulation method according to any one of claims 4-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by the processor to be used to implement the flywheel-battery hybrid energy storage frequency regulation method according to any one of claims 4-5.

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