Control method and device of network-constructed hybrid energy storage system and readable storage medium

Abstract

This invention relates to the field of hybrid energy storage system technology, specifically disclosing a control method, device, and storage medium for a grid-type hybrid energy storage system. The system includes a flywheel energy storage unit and an electrochemical energy storage unit, both connected to a DC bus, as well as a grid-side converter. During system startup, the control method controls the grid-side converter and flywheel energy storage unit to operate in constant voltage and constant speed modes, respectively, acquiring the grid frequency and determining and outputting the target active power based on this frequency. When the grid frequency crosses the frequency dead zone, the grid-side converter switches its operating mode, while simultaneously controlling the flywheel energy storage unit to switch its operating mode and the electrochemical energy storage unit's operating state based on the DC bus voltage changes. This invention allows for flexible adjustment of the flywheel energy storage unit's operating mode according to actual operating conditions, providing timely response when rapid support is needed, while also balancing efficient standby and millisecond-level support, making the system more intelligent and efficient, and reducing conversion losses.

Description

Technical Field

[0001] This invention relates to the field of hybrid energy storage system technology, and in particular to a control method, apparatus and computer-readable storage medium for a grid-type hybrid energy storage system. Background Technology

[0002] With the large-scale grid connection of renewable energy sources such as wind power and photovoltaics, the power system has entered a stage of dual high development: high proportion of new energy and high proportion of power electronic equipment. The system's synchronous rotational inertia and grid support capabilities have weakened significantly, making frequency and voltage stability issues increasingly prominent in weak grid and islanded scenarios, and leading to frequent occurrences of various new grid oscillation risks. Grid-based energy storage with active voltage build-up, inertia support, and islanded operation capabilities has become a core technological path to ensure the safe and stable operation of the new power system.

[0003] The current collaborative control strategy for flywheel and electrochemical hybrid energy storage grid systems also has shortcomings. Most systems operate in a single mode, such as fixed operation in constant speed mode or constant voltage mode, and cannot automatically switch operating modes according to working conditions. This results in insufficient response when rapid support is needed, and cannot take into account both efficient standby and rapid support of the system. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0005] Therefore, one objective of this invention is to propose a control method for a grid-type hybrid energy storage system. This control method can flexibly adjust the flywheel's operating mode according to actual operating conditions, achieving intelligent adaptive regulation of the energy storage operating mode and DC bus voltage. It can seamlessly and rapidly switch between flywheel speed and constant voltage mode to meet millisecond-level emergency power support requirements, and dynamically adjust the DC bus voltage based on the battery's state of charge. Relying on voltage droop characteristics, it can complete the autonomous power distribution of the energy storage unit, abandoning the traditional centralized communication control mode. The operation is shock-free and oscillating, effectively reducing the charging and discharging frequency of the electrochemical energy storage unit and significantly extending the service life of the electrochemical energy storage unit.

[0006] Therefore, a second objective of the present invention is to provide a control device for a grid-type hybrid energy storage system.

[0007] Therefore, a third objective of the present invention is to provide a computer-readable storage medium.

[0008] To achieve the above objectives, an embodiment of the first aspect of the present invention discloses a control method for a grid-type hybrid energy storage system. The grid-type hybrid energy storage system includes a flywheel energy storage unit, an electrochemical energy storage unit, and a grid-side converter. The flywheel energy storage unit and the electrochemical energy storage unit are respectively connected to a DC bus. The DC bus is connected to an AC bus through the grid-side converter. The control method includes: controlling the grid-side converter to operate in a constant voltage mode and controlling the flywheel energy storage unit to operate in a constant speed mode during operation of the hybrid energy storage system; acquiring the grid frequency; determining a target active power based on the grid frequency and outputting the target active power; controlling the grid-side converter to switch operating modes when the grid frequency crosses the frequency dead zone; controlling the flywheel energy storage unit to switch operating modes based on the voltage change of the DC bus; and controlling the operating state of the electrochemical energy storage unit.

[0009] According to the control method of the grid-type hybrid energy storage system of the present invention, during system operation, the grid-side converter is first controlled to operate in constant voltage mode, and the flywheel energy storage unit is controlled to operate in constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency crosses the frequency dead zone, the grid-side converter is controlled to switch operating modes. Simultaneously, based on the voltage change of the DC bus, the flywheel energy storage unit is controlled to switch operating modes, and the operating state of the electrochemical energy storage unit is controlled. In this way, the flywheel operating mode is flexibly adjusted according to the actual operating conditions, realizing intelligent adaptive regulation of the energy storage operating mode and the DC bus voltage, thus achieving the flywheel... The system seamlessly and rapidly switches between speed and constant voltage modes to meet millisecond-level emergency power support requirements. It can also dynamically adjust the DC bus voltage based on the state of charge of the electrochemical energy storage unit, and complete the autonomous power distribution of the energy storage unit by relying on the voltage droop characteristic. It abandons the traditional centralized communication control mode, operates without shock or oscillation, effectively reduces the frequency of battery charging and discharging, and significantly extends the service life of the electrochemical energy storage unit. On this basis, the control method of this grid-type hybrid energy storage system can flexibly adjust the operating mode of the flywheel energy storage unit according to the actual working conditions, responding promptly when rapid support is needed, while taking into account both efficient standby and millisecond-level support, making the system more intelligent and efficient, and reducing conversion losses.

[0010] Furthermore, the system controls the switching of the grid-side converter's operating mode based on grid frequency changes, and controls the switching of the flywheel energy storage unit's operating mode based on DC bus voltage changes, as well as controls the operating state of the electrochemical energy storage unit. This includes: controlling the grid-side converter to switch to constant power mode; when the flywheel energy storage unit is charging, if the DC bus voltage exceeds the upper limit of the voltage dead zone, controlling the flywheel energy storage unit to switch to constant voltage mode; after the flywheel energy storage unit switches to constant voltage mode, if the remaining rechargeable energy and the current maximum allowable charging power of the flywheel energy storage unit can meet the power demand of the grid, then controlling the electrochemical energy storage unit not to start; or, if the remaining rechargeable energy or the current maximum allowable charging power of the flywheel energy storage unit cannot meet the power demand of the grid, then the electrochemical energy storage unit supports the remaining power demand of the grid.

[0011] Furthermore, the system controls the switching of the grid-side converter's operating mode based on grid frequency changes, and controls the switching of the flywheel energy storage unit's operating mode based on DC bus voltage changes, as well as controls the operating state of the electrochemical energy storage unit. This includes: controlling the grid-side converter to switch to constant power mode; when the flywheel energy storage unit discharges, if the DC bus voltage drops to the lower limit of the voltage dead zone, controlling the flywheel energy storage unit to switch to constant voltage mode; after the flywheel energy storage unit switches to constant voltage mode, if the remaining dischargeable energy and the current maximum allowable discharge power of the flywheel energy storage unit can meet the power demand of the grid, then controlling the electrochemical energy storage unit not to start; or, if the remaining dischargeable energy or the current maximum allowable discharge power of the flywheel energy storage unit cannot meet the power demand of the grid, then the electrochemical energy storage unit supports the remaining power demand of the grid.

[0012] Furthermore, the target operating voltage of the flywheel energy storage unit and the grid-side converter in the constant voltage mode is determined based on the current voltage of the electrochemical energy storage unit; the target operating power of the grid-side converter in the constant power mode is determined based on the grid frequency.

[0013] Furthermore, when the grid frequency returns to the frequency dead zone, the grid-side converter is controlled to switch to the constant voltage mode; when the DC bus voltage returns to the voltage dead zone, the flywheel energy storage unit is controlled to switch to the constant speed mode and maintain the current speed until the flywheel energy storage unit completes charging or discharging.

[0014] Furthermore, after the flywheel energy storage unit completes charging or discharging, the method further includes: when it is determined that the grid frequency is within a preset frequency range, controlling the rotation speed of the flywheel energy storage unit to adjust to a preset rotation speed, and controlling the operating voltage of the electrochemical energy storage unit to adjust to a preset voltage, wherein the preset frequency range is used to indicate the frequency range within which the operating parameters of the energy storage unit are allowed to return to preset values.

[0015] Furthermore, controlling the rotational speed of the flywheel energy storage unit to a preset speed and controlling the operating voltage of the electrochemical energy storage unit to a preset voltage includes: adjusting the rotational speed of the flywheel energy storage unit according to a preset output power until the preset speed is reached, and then controlling the flywheel energy storage unit to operate at a constant speed at the preset speed, wherein the preset speed is the rotational speed corresponding to the flywheel energy storage unit when it is at its target SOC (State of Charge) value; adjusting the operating power of the electrochemical energy storage unit according to a preset power adjustment step size until the voltage value of the electrochemical energy storage unit reaches the preset voltage, and then controlling the flywheel energy storage unit to operate at a constant voltage at the preset voltage, wherein the preset voltage is the voltage corresponding to the electrochemical energy storage unit when it is at its target SOC value.

[0016] Furthermore, after the flywheel energy storage unit switches to constant voltage mode, the method further includes: if the SOC value of the flywheel energy storage unit is less than or equal to a first SOC threshold or greater than or equal to a second SOC threshold, then controlling the flywheel energy storage unit to shut down so that the electrochemical energy storage unit can fully support the target active power; if the SOC value of the flywheel energy storage unit is greater than the first SOC threshold and less than the second SOC threshold, then controlling the flywheel energy storage unit to maintain the constant voltage mode operation.

[0017] In summary, the control method for the grid-type hybrid energy storage system according to the present invention, during operation, firstly controls the grid-side converter to operate in constant voltage mode and the flywheel energy storage unit to operate in constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency exceeds the frequency dead zone, the grid-side converter switches its operating mode. Simultaneously, based on the voltage changes of the DC bus, the flywheel energy storage unit switches its operating mode, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristic of the constant speed mode, the flywheel can rapidly output active power according to the determined target power, exhibiting a fast short-term high-power response, quickly filling the grid power gap, and pulling the grid frequency back to a reasonable range. Simultaneously, controlling the flywheel energy storage unit's operating mode and the electrochemical energy storage unit's operating state based on the DC bus voltage changes allows the flywheel to prioritize the rapid active power support task after frequency exceedances, reducing frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and wear. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, which better meets the actual needs of the system. It responds promptly when rapid support is required, while taking into account both efficient standby and millisecond-level support, making the system more intelligent and efficient. It realizes the integrated design of boost converter, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0018] Meanwhile, the control method of this grid-type hybrid energy storage system relies on a simplified topology structure without a DC / DC (Direct Current to Direct Current Converter) common DC bus, streamlining the power conversion process, reducing operating losses and equipment investment costs, and using voltage droop to naturally drive power distribution, achieving graded power support and automatic safety fallback mechanisms. Fast and slow power are coordinated and complementary, and the two types of energy storage units are seamlessly connected for power supply. While improving the system integration and operating condition adaptability, it ensures the stable and reliable operation of the energy storage system under all operating conditions in the new energy grid scenario.

[0019] To achieve the above objectives, a second aspect of the present invention discloses a control device for a grid-type hybrid energy storage system. The grid-type hybrid energy storage system includes a flywheel energy storage unit, an electrochemical energy storage unit, and a grid-side converter. The flywheel energy storage unit and the electrochemical energy storage unit are respectively connected to a DC bus. The DC bus is connected to an AC bus through the grid-side converter. The control device includes a controller for executing the control method of the grid-type hybrid energy storage system of the above embodiment of the present invention.

[0020] The control device for a grid-type hybrid energy storage system according to an embodiment of the present invention is used to implement the control method for the grid-type hybrid energy storage system described in the above embodiments of the present invention. During operation of the grid-type hybrid energy storage system, the grid-side converter is first controlled to operate in constant voltage mode, and the flywheel energy storage unit operates in constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency exceeds the frequency dead zone, the grid-side converter is controlled to switch its operating mode. Simultaneously, based on the voltage change of the DC bus, the flywheel energy storage unit is controlled to switch its operating mode, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristic of the constant speed mode, the flywheel can quickly output active power according to the determined target power, with a fast short-term high-power response speed, quickly filling the grid power gap and pulling the grid frequency back to a reasonable range. At the same time, controlling the flywheel energy storage unit to switch its operating mode and the operating state of the electrochemical energy storage unit based on the voltage change of the DC bus allows the flywheel to prioritize the rapid active power support task after the frequency exceeds the limit, reducing frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and loss. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, which better meets the actual needs of the system. It responds promptly when rapid support is required, while taking into account both efficient standby and millisecond-level support, making the system more intelligent and efficient. It realizes the integrated design of boost converter, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0021] To achieve the above objectives, a third aspect of the present invention provides a computer-readable storage medium storing a control program for a grid-type hybrid energy storage system, wherein the control program for the grid-type hybrid energy storage system, when executed by a processor, implements the control method for the grid-type hybrid energy storage system as described in the above embodiments of the present invention.

[0022] According to an embodiment of the present invention, a computer-readable storage medium stores a control program for a grid-type hybrid energy storage system. When the control program is executed by a processor, it implements the control method for the grid-type hybrid energy storage system as described in the above embodiment of the present invention. During operation of the grid-type hybrid energy storage system, the grid-side converter is first controlled to operate in a constant voltage mode, and the flywheel energy storage unit operates in a constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency crosses the frequency dead zone, the grid-side converter is controlled to switch operating modes. Simultaneously, based on the voltage change of the DC bus, the flywheel energy storage unit is controlled to switch operating modes, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristic of the constant speed mode, the flywheel can quickly output active power according to the determined target power. It has a fast short-term high-power response speed, quickly filling the grid power gap and pulling the grid frequency back to a reasonable range. Simultaneously, the system controls the flywheel energy storage unit's operating mode switching and the electrochemical energy storage unit's operating status based on DC bus voltage changes. This allows the flywheel to prioritize rapid active power support after frequency limits are exceeded, reducing frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and wear. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, better meeting the system's actual needs. It responds promptly when rapid support is required, while also balancing efficient standby and millisecond-level support, making the system more intelligent and efficient. This achieves integrated boost converter design, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of a control method for a grid-type hybrid energy storage system according to an embodiment of the present invention; Figure 2 This is a flowchart of a control method for a grid-type hybrid energy storage system according to a specific embodiment of the present invention; Figure 3 This is a schematic diagram of the control device for a grid-type hybrid energy storage system according to an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures: 1000 - Grid-type hybrid energy storage system; 1100 - Flywheel energy storage unit; 1200 - Electrochemical energy storage unit; 1300 - Grid-side converter; 1400 - DC bus; 2000 - Control device for grid-type hybrid energy storage system; 2100 - Controller. Detailed Implementation

[0026] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. The embodiments of the present invention are described in detail below.

[0027] The following is for reference. Figure 1 A control method for a grid-type hybrid energy storage system according to an embodiment of the present invention is described.

[0028] like Figure 1 The diagram shown is a flowchart of a control method for a grid-type hybrid energy storage system according to an embodiment of the present invention. The grid-type hybrid energy storage system includes a flywheel energy storage unit (i.e., a flywheel), an electrochemical energy storage unit (i.e., a battery), and a grid-side converter (PCS, power conversion system). The flywheel energy storage unit and the electrochemical energy storage unit are respectively connected to a DC bus, and the DC bus is connected to an AC bus through the grid-side converter. The control method for this grid-type hybrid energy storage system includes: Step S11: When the grid-type hybrid energy storage system is running, the grid-side converter is controlled to operate in constant voltage mode, and the flywheel energy storage unit is controlled to operate in constant speed mode.

[0029] In a specific embodiment, the control method for this grid-based hybrid energy storage system operates the grid-side converter in constant voltage mode during system operation. The DC bus is connected to the AC bus via the grid-side converter. This grid-side converter can convert AC to DC and vice versa, achieving bidirectional AC-DC conversion and ensuring high power quality fed into the grid. Simultaneously, it stabilizes the DC bus voltage, supporting operation in weak grid conditions. The grid-side converter operates in constant voltage mode to maintain a constant DC bus voltage. Regardless of whether the DC energy comes from electrochemical energy storage units (including but not limited to lithium batteries or other electrochemical batteries), flywheels, or other loads, the grid-side converter needs to dynamically absorb or release energy from the grid to ensure the DC voltage does not fluctuate, thereby preventing malfunctions, reduced efficiency, or damage to batteries and other equipment connected to the DC bus due to voltage fluctuations.

[0030] Furthermore, the flywheel energy storage unit operates in constant-speed mode, meaning the flywheel is controlled to maintain a certain rotational speed. In the event of a grid fault, the flywheel immediately switches to discharge mode, converting mechanical energy into electrical energy to maintain the DC bus voltage and provide seamless power protection for the downstream grid. Moreover, this grid-connected hybrid energy storage system control method controls the grid-side converter to operate in constant-voltage mode and the flywheel energy storage unit to operate in constant-speed mode, avoiding frequent power adjustments by the grid-side converter and improving overall operating efficiency. The flywheel energy storage unit, with its high rotational inertia in constant-speed mode, can quickly respond to and effectively absorb or compensate for such instantaneous power disturbances.

[0031] Step S21: Obtain the power grid frequency.

[0032] In a specific embodiment, the control method for this grid-type hybrid energy storage system performs real-time sampling processing of the grid voltage signal according to a fixed sampling period during system operation, and collects the discrete frequency sampled value of the grid at the current moment. The system collects and stores multiple sets of discrete frequency sampling values ​​to accurately capture real-time frequency changes during power grid operation, providing accurate and reliable data for subsequent power grid frequency status determination.

[0033] Step S31: Determine the target active power based on the grid frequency, and output the target active power.

[0034] Specifically, the control method for this grid-type hybrid energy storage system can be based on the grid's rated reference frequency. Based on this, discrete frequency samples of the power grid are continuously collected and compared in real time, combined with the rated reference frequency of the power grid. The frequency deviation in discrete form is calculated to be: Consider the central difference discretization algorithm to solve for the rate of frequency change. ,in, This is the current control sampling period number. This is the sequence number of the previous control sampling period. This is the sequence number of the next control sampling period. This center difference separation algorithm can effectively characterize the degree of active power deficit in the power grid and the severity of disturbances to the power grid by identifying the magnitude of the power grid frequency change rate. The larger the frequency change rate, the larger the power deficit in the power grid and the more severe the power disturbances to the power grid operation.

[0035] Furthermore, when the collected grid frequency exceeds the grid's rated reference frequency, based on the aforementioned real-time discrete frequency deviation of the grid, the control method of this grid-type hybrid energy storage system adopts an active power-frequency droop control strategy to output the target active power. That is, it automatically adjusts the amount of active power generated based on the grid frequency: less power is generated at higher frequencies, and more power is generated at lower frequencies, without manual intervention or dispatch commands. Through joint calculation of virtual inertia and primary droop, the total active power support of the system is directly generated from the grid frequency, realizing power source-level grid-connected behavior. The calculation formula for the active power adjustment command under discrete cycles is: ,in, This refers to the change in active power that the current-cycle grid-type hybrid energy storage system needs to output, i.e., the target active power in this invention. The unit is kW or MW. The droop rate (active power-frequency droop coefficient) characterizes the response speed and adjustment amplitude of the target active power. For the real-time discrete frequency deviation of the power grid, This is the rated frequency of the power grid, with a standard value of 50Hz. The rated active power of a grid-type hybrid energy storage system is expressed in kW or MW.

[0036] Furthermore, the control method of this grid-type hybrid energy storage system monitors the grid frequency in real time through periodic sampling. When the grid frequency is within the dead zone, it is determined that the active power supply and demand of the grid are in a normal fluctuation state, and there is no need to activate emergency power support. Once the grid frequency crosses the preset dead zone, it indicates that the grid has a significant active power deficit, and the stable frequency operation state has been broken. Then, based on the frequency deviation and the above formula, the target active power is calculated, driving the energy storage units of the grid-type hybrid energy storage system to quickly transmit electrical energy to the outside, rapidly making up for the active power gap in the grid. The total active power support of the system is directly generated from the grid frequency, realizing the grid-type behavior at the power source level.

[0037] Step S41: When the grid frequency crosses the frequency dead zone, control the grid-side converter to switch operating modes, and control the flywheel energy storage unit to switch operating modes based on the voltage change of the DC bus, and control the operating status of the electrochemical energy storage unit.

[0038] In a specific embodiment, when the acquired grid frequency crosses the frequency dead zone, it indicates a mismatch between power generation and consumption. The grid-connected hybrid energy storage system controls the grid-side converter to switch to the appropriate mode to change the active power exchanged with the grid, maintaining balance. The grid-side converter's response speed is in the millisecond range, far faster than traditional generator sets (seconds to minutes). It can rapidly increase or decrease active power output, preventing further frequency degradation, such as preventing the frequency from falling to the dangerous threshold triggering low-frequency load shedding. Furthermore, through rapid and precise power regulation, the frequency can be more tightly controlled within a safe range, improving power quality.

[0039] In a specific embodiment, when the grid frequency crosses the frequency dead zone, the flywheel energy storage unit's operating mode is switched based on changes in the DC bus voltage, and the operating status of the electrochemical energy storage unit is also controlled. This grid-type hybrid energy storage system control method can pre-set a target DC reference voltage, judge changes in the DC bus voltage based on the reference voltage, and automatically command the flywheel to switch between "charging," "discharging," and "standby" modes according to the deviation between the DC bus voltage and the reference value. Therefore, by controlling the flywheel's operating mode based on changes in the DC bus voltage, rapid stabilization of the DC bus voltage and automatic system power balance can be achieved. Through the millisecond-level response of the flywheel energy storage unit to voltage deviations, it automatically charges to absorb energy when there is excess power and automatically discharges to replenish energy when there is insufficient power, thereby effectively suppressing instantaneous voltage fluctuations and ensuring DC bus voltage stability. Furthermore, the operating status of electrochemical energy storage units, such as lithium batteries, is simultaneously controlled to coordinate with the flywheel, allowing the flywheel to bear the high-frequency, instantaneous power fluctuations generated by the load or new energy sources, while the battery only responds to smooth, slow power commands. Maintaining a stable DC bus voltage also significantly reduces the number of charge / discharge cycles and stress on the battery, thus significantly extending cycle life and reducing the frequency of battery replacements and total lifespan costs.

[0040] In a specific embodiment, the control method of this grid-type hybrid energy storage system, after determining that the grid frequency has crossed the frequency dead zone and identifying the target active power, drives the flywheel energy storage unit to rapidly deliver electrical energy based on the DC bus voltage changes. This quickly fills the active power gap in the grid, efficiently suppresses frequency deviation, and helps the grid frequency quickly recover to the rated operating range. Simultaneously, the flywheel prioritizes instantaneous frequency regulation, reducing frequent high-power output from electrochemical energy storage and effectively extending battery life. Therefore, the control method of this grid-type hybrid energy storage system directly drives the flywheel to charge and discharge based on DC voltage deviation. The flywheel provides high-frequency transient support without interference, communication, or delay, while the battery provides steady-state and overload protection. This significantly reduces the number of battery cycles and extends battery life by 3–5 times.

[0041] In one embodiment of the present invention, the operation mode switching of the grid-side converter is controlled based on grid frequency changes, and the operation mode switching of the flywheel energy storage unit is controlled based on DC bus voltage changes. The operation state of the electrochemical energy storage unit is also controlled, including: controlling the grid-side converter to switch to constant power mode; when the flywheel energy storage unit is charging, if the DC bus voltage exceeds the upper limit of the voltage dead zone, controlling the flywheel energy storage unit to switch to constant voltage mode; after the flywheel energy storage unit switches to constant voltage mode, if the remaining rechargeable energy and the current maximum allowable charging power of the flywheel energy storage unit can meet the power demand of the grid, then the electrochemical energy storage unit is not turned on; or, if the remaining rechargeable energy or the current maximum allowable charging power of the flywheel energy storage unit cannot meet the power demand of the grid, then the electrochemical energy storage unit supports the remaining power demand of the grid.

[0042] In a specific embodiment, when the acquired real-time grid frequency crosses the frequency dead zone, the grid-side converter is controlled to switch to constant power mode to change the active power exchanged with the grid and maintain balance. For example, when the real-time grid frequency is below the lower limit of the dead zone, it indicates a shortage of active power in the system. The grid-side converter will switch from the normal constant voltage mode to a power mode that increases the active power supplied to the grid, such as energy storage discharge or reduced charging. When the real-time grid frequency is above the upper limit of the dead zone, it indicates an excess of active power in the system. The grid-side converter will switch to a mode that reduces the active power supplied to the grid or increases the active power absorbed from the grid, such as energy storage charging or increased charging power. Furthermore, controlling the grid-side converter to switch the corresponding operating mode provides millisecond-level active power support and inertial response, significantly improving the frequency stability of the grid and reducing the risk of large-scale power outages.

[0043] In a specific embodiment, when the DC bus voltage exceeds the upper limit of the voltage dead zone, i.e. If the system detects excess power, this method switches the flywheel energy storage unit to constant voltage mode. The flywheel automatically and quickly absorbs power, drawing electricity from the DC bus. The motor accelerates its rotation, converting excess electrical energy into mechanical energy for storage, thereby lowering the DC bus voltage until it falls back into the dead zone. Therefore, by utilizing the flywheel's millisecond-level response speed and power throughput capability, excess energy is automatically and quickly absorbed at the moment of a voltage crisis, clamping the DC bus voltage within a safe range. This protects equipment safety and significantly improves the safety and stability of the power grid and grid-connected hybrid energy storage systems.

[0044] Furthermore, when the flywheel energy storage unit is charging and switches to constant voltage mode due to the DC bus voltage exceeding the dead zone voltage, the first step is to assess whether the flywheel currently has sufficient capacity to independently handle the power excess event. Assessment indicators may include: the flywheel's remaining rechargeable energy, i.e., the energy that can be stored corresponding to the difference between the flywheel's current speed and its maximum allowable speed; and the current maximum allowable charging power, i.e., the rated capacity limited by the flywheel's motor and its machine-side inverter. Only when the flywheel can meet the power absorption requirements of the grid in both of these dimensions will a decision be made not to activate the electrochemical energy storage unit, allowing the flywheel alone to complete the energy absorption and voltage regulation tasks. Therefore, power distribution between the flywheel and battery can be achieved through power limiting by the machine-side inverter, eliminating the need for software allocation and coefficient calculations. Allowing the flywheel to independently bear the instantaneous power excess impact avoids frequent responses from the electrochemical energy storage unit, thereby significantly reducing the battery's charge-discharge cycle count, lowering its heat generation and aging rate, and effectively extending the battery's lifespan and maintenance cycle.

[0045] In a specific embodiment, if the remaining rechargeable energy or the current maximum allowable charging power of the flywheel energy storage unit cannot meet the power demand of the power grid, the electrochemical energy storage unit will start operating to take over the remaining power that the flywheel cannot support. This achieves the synergistic principle of "flywheel priority response and battery backup supplementation," where the flywheel is responsible for absorbing instantaneous, high-frequency power surges, while the battery provides continuous, high-capacity energy support when its capacity is insufficient. Therefore, the control method of this grid-type hybrid energy storage system allows the flywheel to prioritize high-frequency fluctuations, significantly reducing the number of battery charge-discharge cycles, slowing down its aging process, and extending the system maintenance cycle. At the same time, the battery, as a backup supplement, compensates for the limited energy storage capacity of the flywheel, ensuring that the system can still maintain DC bus voltage stability under prolonged or large-capacity power surplus events. This constructs a highly reliable grid-type hybrid energy storage system with both rapid response and large-capacity support capabilities, guaranteeing safe operation under all operating conditions.

[0046] In other words, during charging, when the flywheel operates in constant speed mode, if the grid frequency exceeds the upper dead zone, the PCS will calculate the target active power in real time based on grid frequency fluctuations and absorb power from the grid in a grid-connected power closed-loop manner. During this process, the DC bus voltage is raised with the power input; when the DC bus voltage rises to the upper limit of the voltage dead zone, the flywheel switches to constant voltage mode, and the constant voltage target value is set to the current battery voltage. At this time, if the remaining rechargeable energy of the flywheel and the current maximum allowable charging power can fully support the grid-side power demand, the battery does not operate; when the remaining rechargeable energy of the flywheel or the current maximum allowable charging power is insufficient to meet the grid-side demand, the battery provides backup support.

[0047] In one embodiment of the present invention, the operation mode switching of the grid-side converter is controlled based on grid frequency changes, and the operation mode switching of the flywheel energy storage unit is controlled based on DC bus voltage changes. The operation state of the electrochemical energy storage unit is also controlled, including: controlling the grid-side converter to switch to constant power mode; when the flywheel energy storage unit discharges, if the DC bus voltage drops to the lower limit of the voltage dead zone, controlling the flywheel energy storage unit to switch to constant voltage mode; after the flywheel energy storage unit switches to constant voltage mode, if the remaining dischargeable energy and the current maximum allowable discharge power of the flywheel energy storage unit can meet the power demand of the grid, then the electrochemical energy storage unit is not turned on; or, if the remaining dischargeable energy or the current maximum allowable discharge power of the flywheel energy storage unit cannot meet the power demand of the grid, then the electrochemical energy storage unit supports the remaining power demand of the grid.

[0048] In a specific embodiment, when the voltage of the DC bus drops to the lower limit of the voltage dead zone, i.e. If an active power deficit is detected, meaning that the power consumed by the grid exceeds the power generated by the grid-type hybrid energy storage system, the method will control the flywheel energy storage unit to switch to constant voltage mode, convert the rotational kinetic energy stored in the flywheel into electrical energy and output it to the DC bus, making up for the power deficit at a speed of milliseconds, raising the DC bus voltage to the normal range, and ensuring system stability and load power supply.

[0049] Furthermore, when the flywheel energy storage unit is in a discharging state and switches to constant voltage mode due to the DC bus voltage being lower than the dead zone voltage, the first step is to assess whether the flywheel currently has sufficient capacity to independently handle the power loss event. Assessment indicators may include: the flywheel's remaining dischargeable energy, i.e., the total amount of mechanical energy currently stored in the flywheel that can still be released; and the current maximum allowable discharge power, i.e., the maximum instantaneous electrical power that the flywheel energy storage unit can sustainably output under the current conditions, limited by the inverter on the machine side. Only when the flywheel can meet the power requirements of the grid in both of these dimensions will a decision be made not to activate the electrochemical energy storage unit, allowing the flywheel alone to complete the energy output and voltage regulation tasks.

[0050] Furthermore, if the remaining dischargeable energy or the current maximum allowable discharge power of the flywheel energy storage unit cannot meet the power demand of the grid, the electrochemical energy storage unit will support the grid's remaining power demand. This also achieves the synergistic principle of "flywheel priority response, battery backup supplement," where the flywheel is responsible for compensating for instantaneous, high-frequency power shortages, while the battery provides continuous, high-capacity energy support when its capacity is insufficient. Therefore, the control method of this grid-type hybrid energy storage system prioritizes the flywheel to handle high-frequency discharge demands, significantly reducing the number of battery charge-discharge cycles, slowing down its aging process, and extending the system maintenance cycle. Simultaneously, the battery, as a backup, compensates for the inherent shortcomings of the flywheel's limited energy storage and short discharge time, ensuring that the system can maintain stable DC bus voltage even under high power shortages or long-term energy support demands. This constructs a highly reliable grid-type hybrid energy storage system with both rapid response and high-capacity support capabilities, guaranteeing safe operation under all operating conditions.

[0051] In other words, under discharge conditions, the flywheel operates in constant speed mode. When the grid frequency exceeds the lower limit of the frequency dead zone, the PCS calculates the target active power in real time based on grid frequency fluctuations and sends active power to the grid using a grid-connected power closed-loop mode. During this process, the DC bus voltage gradually decreases as power is continuously delivered. When the bus voltage drops to the lower limit of the voltage dead zone, the flywheel switches to constant voltage mode, and the constant voltage target value follows the current battery voltage. If the remaining dischargeable energy of the flywheel and the current maximum allowable discharge power can fully support the grid-side power, the battery remains stationary and does not participate in the response. When the remaining dischargeable energy of the flywheel or the current maximum allowable discharge power cannot match the grid-side power demand, the battery is deployed as a backup support.

[0052] In one embodiment of the present invention, the target operating voltage of the flywheel energy storage unit and the grid-side converter in constant voltage mode is determined based on the current voltage of the electrochemical energy storage unit; the target operating power of the grid-side converter in constant power mode is determined based on the grid frequency.

[0053] Specifically, in existing related technologies, the flywheel energy storage unit and the grid-side converter typically use a fixed DC reference voltage as a common control target in constant voltage mode. However, the control method of the grid-type hybrid energy storage system in this embodiment of the invention determines the operating target voltage of the flywheel energy storage unit and the grid-side converter in constant voltage mode based on the current voltage of the electrochemical energy storage unit. That is, this common target voltage is no longer a fixed value, but is dynamically adjusted according to the current terminal voltage of the electrochemical energy storage unit. When the battery voltage rises or falls, the reference for maintaining the stability of the DC bus of the flywheel and the grid-side converter also moves accordingly, so that the DC bus voltage is always coordinated with the battery voltage. Therefore, when the target bus voltage is consistent with the battery voltage, the voltage difference between the two is eliminated, avoiding the battery being forced and ineffectively cyclically charged and discharged, and preventing such continuous and inefficient damage.

[0054] Furthermore, in existing technologies, flywheel and electrochemical hybrid energy storage systems cannot directly operate on the same DC bus. To achieve parallel coordination on the DC side, an independent DC / DC converter must be configured on the battery side to control the battery's charging and discharging current and power. This avoids passive and uncontrollable charging and discharging caused by voltage differences during direct parallel connection, leading to complex topology, increased power stages, increased energy loss, and a significant increase in equipment cost and size. However, the control method of the grid-type hybrid energy storage system in this invention determines the target operating voltage of the flywheel energy storage unit and the grid-side converter in constant voltage mode based on the current voltage of the electrochemical energy storage unit. The DC bus voltage is no longer constant but is generated in real-time by the battery's state of charge, eliminating the voltage difference between the two. This constructs a voltage-driven collaborative scheduling mechanism with extremely simple control logic, no communication, no oscillation, and high reliability. Simultaneously, there is no need to use a DC / DC converter to connect the battery and the bus, reducing hardware costs, shrinking container size, and adapting to large-scale site deployment.

[0055] In a specific embodiment, the target power output of the grid-side converter in constant power mode is no longer fixed, but dynamically adjusted according to the real-time deviation of the grid frequency. Specifically, when the grid frequency deviates from the grid's rated frequency, the total active power required by the hybrid energy storage system for the current cycle, i.e., the target active power, is calculated based on a pre-set droop rate combined with parameters such as the real-time discrete frequency deviation of the grid. This allows the grid-side converter to actively respond to frequency changes. For example, when the frequency is below the lower limit of the dead zone, the grid-side converter automatically increases the active power supplied to the grid to help raise the frequency; conversely, when the frequency is too high, it reduces output or absorbs power. Thus, through the joint calculation of virtual inertia and primary droop, the total active power of the system is directly generated from the grid frequency, realizing the grid-connected behavior of the power source level.

[0056] In one embodiment of the present invention, when the grid frequency returns to the frequency dead zone, the grid-side converter is controlled to switch to constant voltage mode; when the DC bus voltage returns to the voltage dead zone, the flywheel energy storage unit is controlled to switch to constant speed mode and maintain the current speed until the flywheel energy storage unit completes charging or discharging.

[0057] Specifically, when the grid frequency returns to the normal dead zone range due to primary frequency regulation control, the grid-side converter no longer needs to adjust active power to support the frequency. Therefore, it switches back to constant voltage mode to maintain the stability of the DC bus voltage. This achieves the logic of prioritizing grid frequency support during frequency anomalies and prioritizing the power quality of the local DC bus after the frequency returns to normal. Once the grid frequency recovers to the dead zone, it indicates that the active power supply and demand of the grid are basically balanced. At this time, the grid-side converter should switch the control target back to constant voltage mode, actively absorbing or releasing energy to smooth the DC bus voltage deviation and prevent equipment damage due to excessive voltage or load shutdown due to excessively low voltage.

[0058] Furthermore, when the DC bus voltage returns to the normal voltage dead zone range due to the charging and discharging regulation of the flywheel or battery, i.e. When the power excess or deficiency state of the hybrid energy storage system has been resolved, the control flywheel energy storage unit switches from constant voltage mode back to constant speed mode. In constant speed mode, the flywheel energy storage unit no longer actively charges or discharges the DC bus, but only maintains the current speed, i.e., the speed reached when it just exited charging or discharging, and continues to maintain this state until the upper-level dispatch command instructs it to start charging or discharging again. This achieves the effect of allowing the flywheel to quickly return to a low-power standby state after completing its task, avoiding overcharging or discharging or maintaining an ineffective working mode for a long time. When the DC bus voltage exceeds the limit, the flywheel absorbs or releases energy through rapid charging and discharging to stabilize the voltage; once the voltage returns to normal, it indicates that the power has been rebalanced. If the flywheel continues to charge and discharge at this time, it will lead to unnecessary energy loss. Therefore, timely switching back to constant speed mode and maintaining the current speed preserves the energy stored or remaining in the flywheel and puts it into a standby state, ready to respond to the next voltage limit event.

[0059] In other words, when the grid frequency falls back into the frequency dead zone, the grid-side active power drops to 0kW, the grid-side converter PCS switches to constant voltage mode, and the constant voltage target value follows the current terminal voltage of the battery; the flywheel synchronously switches to constant speed mode to maintain the current constant speed, exits the power response state, and completes the charging and discharging process.

[0060] In one embodiment of the present invention, after the flywheel energy storage unit completes charging or discharging, the method further includes: when it is determined that the grid frequency is within a preset frequency range, controlling the rotation speed of the flywheel energy storage unit to adjust to a preset rotation speed, and controlling the operating voltage of the electrochemical energy storage unit to adjust to a preset voltage, wherein the preset frequency range is used to indicate the frequency range within which the operating parameters of the energy storage unit are allowed to return to preset values.

[0061] Specifically, when the grid frequency returns to a preset normal range that indicates a stable operating state, it means that the active power of the grid has been basically balanced. At this time, there is no longer a need for grid-type hybrid energy storage units to provide emergency frequency support. Therefore, the flywheel energy storage unit and the electrochemical energy storage unit can be controlled to restore their respective operating parameters to the preset optimal standby values. This includes: controlling the rotation speed of the flywheel energy storage unit to a preset speed, which is usually the highest efficiency speed or the highest allowable speed of the flywheel, representing that the flywheel has stored the maximum mechanical energy and is in a high-energy standby state; and controlling the operating voltage of the electrochemical energy storage unit to a preset voltage, which is usually the voltage of the battery's optimal state of charge, so that the battery is neither overcharged nor over-discharged, and has a two-way adjustment margin.

[0062] Furthermore, the control method of this grid-type hybrid energy storage system, when determining that the grid frequency is within a preset frequency range, adjusts the rotational speed of the flywheel energy storage unit to a preset speed and the operating voltage of the electrochemical energy storage unit to a preset voltage. This eliminates the state deviation generated by the flywheel and electrochemical energy storage units during frequency support, restoring the system to its optimal standby reference state to cope with potential frequency disturbances. When the grid frequency exceeds the limit, the flywheel may have already consumed some energy through discharge, resulting in a decrease in rotational speed, and the battery may have experienced a decrease in terminal voltage due to discharge. If these parameters are not actively reset, the hybrid energy storage system will operate in a suboptimal state for a long time: the flywheel's available energy storage decreases, and the battery voltage is too low to charge, thus weakening its ability to cope with subsequent disturbances. Therefore, actively resetting the state after the frequency returns to normal ensures that the energy storage units always have bidirectional adjustment capabilities, while guaranteeing the long-term reliability and efficiency of the hybrid energy storage system and extending equipment lifespan.

[0063] In one embodiment of the present invention, controlling the rotational speed of the flywheel energy storage unit to a preset rotational speed and controlling the operating voltage of the electrochemical energy storage unit to a preset voltage includes: adjusting the rotational speed of the flywheel energy storage unit according to a preset output power until the preset rotational speed is reached, and then controlling the flywheel energy storage unit to operate at a constant speed at the preset rotational speed, wherein the preset rotational speed is the rotational speed corresponding to the flywheel energy storage unit when it is at its target SOC value; adjusting the operating power of the electrochemical energy storage unit according to a power adjustment step size until the voltage value of the electrochemical energy storage unit reaches a preset voltage, and then controlling the flywheel energy storage unit to operate at a constant voltage at the preset voltage, wherein the preset voltage is the voltage corresponding to the electrochemical energy storage unit when it is at its target SOC value.

[0064] In a specific embodiment, the control method of this grid-type hybrid energy storage system no longer directly controls the rotational speed of the flywheel energy storage unit. Instead, it adjusts the flywheel energy storage unit according to a preset output power, that is, controls the flywheel to charge or discharge at a constant power value. This power control mode is typically used to respond to grid dispatch commands or participate in primary frequency regulation. Driven by the aforementioned constant power, the rotational speed of the flywheel energy storage unit will continuously change in one direction, that is, it increases during charging and decreases during discharging, until a preset target rotational speed is reached. This preset rotational speed is determined based on the rotational speed corresponding to the target SOC value of the flywheel energy storage unit. The SOC is the percentage of currently stored mechanical energy relative to its maximum storable energy, used to indicate how much energy the flywheel can release and how much space it can charge, thus corresponding to a specific target rotational speed.

[0065] Furthermore, the control method of this grid-type hybrid energy storage system does not control the electrochemical energy storage unit to rapidly jump to the target active power. Instead, it gradually adjusts the operating power of the electrochemical energy storage unit according to a preset power adjustment step size, such as increasing or decreasing by 5kW each time at 100ms intervals. This step-by-step adjustment allows the charging and discharging power of the electrochemical energy storage unit to change smoothly, avoiding current surges caused by sudden power changes and extending the service life of the electrochemical energy storage unit. During the power adjustment process, the battery's terminal voltage will change accordingly until it reaches the preset voltage. This preset voltage is based on the voltage corresponding to the electrochemical energy storage unit at its target SOC value. For electrochemical energy storage devices such as lithium batteries, there is a definite correspondence between its open-circuit voltage and SOC. Therefore, adjusting the voltage of the electrochemical energy storage unit to this preset value means that the SOC of the electrochemical energy storage unit has been accurately restored to the preset target SOC. At this point, the electrochemical energy storage unit is neither overcharged nor over-discharged, possessing optimal bidirectional adjustment margin.

[0066] Specifically, once the voltage of the electrochemical energy storage unit reaches the preset voltage, the flywheel energy storage unit operates at a constant voltage. At this point, the flywheel switches from a potentially constant power mode to a constant voltage mode, maintaining the DC bus voltage stable at a preset value that matches the preset voltage of the electrochemical energy storage unit. This means that after the electrochemical energy storage unit completes its state reset, the flywheel energy storage unit takes over the stabilization of the DC bus voltage, allowing the electrochemical energy storage unit to remain stable in its current state without being affected by DC bus voltage fluctuations. Therefore, by gradually adjusting the operating power of the electrochemical energy storage unit in power steps rather than abruptly changing it, drastic changes in the current of the electrochemical energy storage unit are avoided, reducing damage and protecting its lifespan and safety. Furthermore, after the electrochemical energy storage unit completes its state reset, the flywheel energy storage unit immediately takes over the DC bus voltage stabilization task, enabling the grid-type hybrid energy storage system to operate more autonomously, efficiently, and safely.

[0067] In a specific embodiment, the target SOC value is, for example, but not limited to, 50%. The above process involves returning the battery SOC to the median value, thereby preparing for the next frequency regulation beyond the limit. It is understandable that if the SOC is not returned to a fixed value, for example, if the current SOC is 80%, it will quickly recharge during the next frequency regulation, failing to fully utilize the flywheel's function. Therefore, by adjusting the electrochemical energy storage unit voltage to this preset value, the electrochemical energy storage unit neither overcharges nor over-discharges, possessing optimal bidirectional regulation margin.

[0068] In other words, when the grid frequency enters the range that allows energy storage to return to a fixed SOC value (i.e., the target SOC value, for example, but not limited to 50%), the flywheel operates in constant speed mode and gradually and smoothly approaches the target speed corresponding to the fixed SOC value. Once the flywheel speed reaches the speed corresponding to the fixed SOC value, it maintains a constant speed. After the flywheel returns to the fixed SOC, the PCS uses the voltage value corresponding to the battery's fixed SOC value as a reference, makes a small adjustment, and writes it into the PCS constant voltage target value. It uses a low-power slow control method to drive the battery to return to the fixed SOC value. Following the slow rise in battery voltage, the PCS constant voltage target value is adjusted synchronously. Until the battery SOC reaches the fixed SOC value, the battery remains in a static steady state, completing the flywheel and battery SOC centering process, preparing for the next frequency regulation command.

[0069] In one embodiment of the present invention, after the flywheel energy storage unit switches to constant voltage mode, the method further includes: if the SOC value of the flywheel energy storage unit is less than or equal to a first SOC threshold or greater than or equal to a second SOC threshold, then controlling the flywheel energy storage unit to shut down so that the electrochemical energy storage unit can fully support the target active power; if the SOC value of the flywheel energy storage unit is greater than the first SOC threshold and less than the second SOC threshold, then controlling the flywheel energy storage unit to maintain constant voltage mode operation.

[0070] Specifically, when the DC bus voltage exceeds the voltage dead zone, the flywheel energy storage unit switches to constant voltage mode. When the flywheel energy storage unit is operating in constant voltage mode, if the SOC value of the flywheel energy storage unit is less than or equal to the first SOC threshold, which is usually preset as the lower limit of the flywheel SOC, for example, but not limited to, 10%, it means that the energy stored in the flywheel energy storage unit has been basically exhausted. Continuing to discharge will lead to excessively low speed, unstable output, or even damage to the equipment. Alternatively, if the SOC value is greater than or equal to the second SOC threshold, which is usually preset as the upper limit of the flywheel SOC, for example, but not limited to, 90%, it means that the flywheel energy storage unit is close to being fully charged. Continuing to charge will lead to excessive speed and excessive mechanical stress. Therefore, when the SOC of the flywheel energy storage unit meets the two preset conditions mentioned above, the flywheel energy storage unit is controlled to shut down, and the electrochemical energy storage unit automatically undertakes all the supporting active power. The electrochemical energy storage unit has a wider SOC operating range. When the flywheel exits due to exceeding the SOC limit, the electrochemical energy storage unit is capable of independently undertaking all power demands, ensuring uninterrupted system operation and thus ensuring the safety of the flywheel energy storage unit. Furthermore, if it is determined that the SOC value of the flywheel energy storage unit is greater than the first SOC threshold and less than the second SOC threshold, i.e., within the safe range, the flywheel energy storage unit is controlled to maintain constant voltage mode operation, thereby maintaining the stability of the DC bus voltage.

[0071] In the embodiments of the present invention, during the implementation of the control method for the above-mentioned grid-type hybrid energy storage system, the corresponding controller in the grid-side converter can perform grid frequency acquisition, active power calculation, and switching between constant power mode and constant voltage mode of the grid-side converter; the corresponding controller in the flywheel energy storage unit can perform flywheel speed regulation based on DC bus voltage changes, and switching between constant voltage mode and constant speed mode of the flywheel energy storage unit. Furthermore, the main control device in the grid-type hybrid energy storage system acquires the constant voltage setpoint (i.e., the constant voltage target value) and sends it to the grid-side converter and the flywheel converter on the flywheel energy storage unit side, and coordinates the energy management of the flywheel energy storage unit and the electrochemical energy storage unit (i.e., the battery), while simultaneously realizing the overall protection and status monitoring of the grid-type hybrid energy storage system. The battery energy storage unit operates in conjunction with the DC bus based on its own characteristics; that is, when the DC bus voltage is higher than the battery terminal voltage, the battery charges; conversely, the battery discharges.

[0072] The control method of the grid-type hybrid energy storage system of the present invention described above will be explained below with reference to specific embodiments. Figure 2 This is a flowchart of a control method for a grid-type hybrid energy storage system according to a specific embodiment of the present invention, such as... Figure 2 As shown in this specific embodiment, the control method of the grid-type hybrid energy storage system includes the following steps: S1: Real-time data acquisition: grid frequency f, battery SOC_bat, flywheel SOC_fly, DC voltage U_dc; S2: Calculate the frequency deviation; S3: Calculate the rate of change of frequency; S4: Calculate the target active power; S5: Calculate the DC reference voltage; S6: Determine if the DC bus voltage exceeds the limit; S7: Over-limit, the flywheel switches to constant voltage mode and calculates the flywheel power; S8: No limit exceeded, flywheel maintains constant speed mode; S9: Determine whether the flywheel SOC is less than or equal to the first pre-SOC threshold or greater than or equal to the second SOC threshold; S10: Flywheel lockout, electrochemical energy storage unit fully supports the target active power; S11: Flywheel maintains constant voltage charging and discharging mode; S12: DC bus voltage returns to the voltage dead zone, flywheel switches back to speed mode.

[0073] In this specific embodiment, the control flow description of the control method of the grid-type hybrid energy storage system includes first entering S1, then entering S2, then entering S3, then entering S4, then entering S5. If S6 is true, then enter S7; otherwise, execute S8, then execute S9. If S9 is true, then execute S10 and then S12; otherwise, execute S11 and then S12, and so on in a loop.

[0074] According to the control method of the grid-type hybrid energy storage system of the present invention, during the operation of the grid-type hybrid energy storage system, the grid-side converter is first controlled to operate in constant voltage mode and the flywheel energy storage unit is controlled to operate in constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency exceeds the frequency dead zone, the grid-side converter is controlled to switch operating modes. At the same time, the flywheel energy storage unit is controlled to switch operating modes based on the voltage change of the DC bus, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristics of the constant speed mode, the flywheel can quickly output active power according to the determined target power. The short-term high-power response speed is fast, quickly filling the grid power gap and pulling the grid frequency back to a reasonable range. At the same time, controlling the flywheel energy storage unit to switch operating modes and the operating state of the electrochemical energy storage unit based on the voltage change of the DC bus enables the flywheel to take the lead in quickly supporting active power after the frequency exceeds the limit, reducing the frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and loss. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, which better meets the actual needs of the system. It responds promptly when rapid support is required, while taking into account both efficient standby and millisecond-level support, making the system more intelligent and efficient. It realizes the integrated design of boost converter, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0075] In one embodiment of the present invention, a control device 2000 for a grid-type hybrid energy storage system is also provided.

[0076] Figure 3 This is a schematic diagram of the control device for a grid-type hybrid energy storage system according to an embodiment of the present invention. Figure 3 As shown, in one embodiment of the present invention, the grid-type hybrid energy storage system 1000 includes a flywheel energy storage unit 1100, an electrochemical energy storage unit 1200, and a grid-side converter 1300. The flywheel energy storage unit 1100 and the electrochemical energy storage unit 1200 are respectively connected to a DC bus 1400. The DC bus 1400 is connected to an AC bus through the grid-side converter 1300. The control device 2000 includes a controller 2100, which is used to execute the control method of the grid-type hybrid energy storage system as described in the above embodiment of the present invention.

[0077] In one embodiment of the present invention, the grid-side converter 1300 is controlled to switch operating modes based on grid frequency changes, and the flywheel energy storage unit 1100 is controlled to switch operating modes based on DC bus 1400 voltage changes, and the operating state of the electrochemical energy storage unit 1200 is controlled. This includes: controlling the grid-side converter 1300 to switch to a constant power mode; when the flywheel energy storage unit 1100 is charging, if the voltage of the DC bus 1400 exceeds the upper limit of the voltage dead zone, controlling the flywheel energy storage unit 1100 to switch to a constant voltage mode; after the flywheel energy storage unit 1100 switches to a constant voltage mode, if the remaining rechargeable energy and the current maximum allowable charging power of the flywheel energy storage unit 1100 can meet the power demand of the grid, then the electrochemical energy storage unit 1200 is not turned on; or, if the remaining rechargeable energy or the current maximum allowable charging power of the flywheel energy storage unit 1100 cannot meet the power demand of the grid, then the electrochemical energy storage unit 1200 supports the remaining power demand of the grid.

[0078] In one embodiment of the present invention, the grid-side converter 1300 is controlled to switch operating modes based on grid frequency changes, and the flywheel energy storage unit 1100 is controlled to switch operating modes based on DC bus 1400 voltage changes, and the operating state of the electrochemical energy storage unit 1200 is controlled. This includes: controlling the grid-side converter 1300 to switch to a constant power mode; when the flywheel energy storage unit 1100 discharges, if the voltage of the DC bus 1400 drops to the lower limit of the voltage dead zone, controlling the flywheel energy storage unit 1100 to switch to a constant voltage mode; after the flywheel energy storage unit 1100 switches to a constant voltage mode, if the remaining dischargeable energy and the current maximum allowable discharge power of the flywheel energy storage unit 1100 can meet the power demand of the grid, then the electrochemical energy storage unit 1200 is not turned on; or, if the remaining dischargeable energy or the current maximum allowable discharge power of the flywheel energy storage unit 1100 cannot meet the power demand of the grid, then the electrochemical energy storage unit 1200 supports the remaining power demand of the grid.

[0079] In one embodiment of the present invention, the target operating voltage of the flywheel energy storage unit 1100 and the grid-side converter 1300 in constant voltage mode is determined based on the current voltage of the electrochemical energy storage unit 1200; the target operating power of the grid-side converter 1300 in constant power mode is determined based on the grid frequency.

[0080] In one embodiment of the present invention, when the grid frequency returns to the frequency dead zone, the grid-side converter 1300 is controlled to switch to constant voltage mode; when the voltage of the DC bus 1400 returns to the voltage dead zone, the flywheel energy storage unit 1100 is controlled to switch to constant speed mode and maintain the current speed until the flywheel energy storage unit 1100 completes charging or discharging.

[0081] In one embodiment of the present invention, after the flywheel energy storage unit 1100 completes charging or discharging, the method further includes: when it is determined that the grid frequency is in a preset frequency range, controlling the rotation speed of the flywheel energy storage unit 1100 to adjust to a preset rotation speed, and controlling the operating voltage of the electrochemical energy storage unit 1200 to adjust to a preset voltage, wherein the preset frequency range is used to indicate the frequency range in which the operating parameters of the energy storage unit are allowed to return to preset values.

[0082] In one embodiment of the present invention, controlling the rotational speed of the flywheel energy storage unit 1100 to a preset speed and controlling the operating voltage of the electrochemical energy storage unit 1200 to a preset voltage includes: adjusting the rotational speed of the flywheel energy storage unit 1100 according to a preset output power until the preset speed is reached, and then controlling the flywheel energy storage unit 1100 to operate at a constant speed at the preset speed, wherein the preset speed is the rotational speed corresponding to the flywheel energy storage unit 1100 when it is at its target SOC value; adjusting the operating power of the electrochemical energy storage unit 1200 according to a power adjustment step size until the voltage value of the electrochemical energy storage unit 1200 reaches a preset voltage, and then controlling the flywheel energy storage unit 1100 to operate at a constant voltage at the preset voltage, wherein the preset voltage is the voltage corresponding to the electrochemical energy storage unit 1200 when it is at its target SOC value.

[0083] In one embodiment of the present invention, after the flywheel energy storage unit 1100 switches to constant voltage mode, the method further includes: if the SOC value of the flywheel energy storage unit 1100 is less than or equal to a first SOC threshold or greater than or equal to a second SOC threshold, then the flywheel energy storage unit 1100 is controlled to shut down so that the electrochemical energy storage unit 1200 can fully support the target active power; if the SOC value of the flywheel energy storage unit 1100 is greater than the first SOC threshold and less than the second SOC threshold, then the flywheel energy storage unit 1100 is controlled to maintain constant voltage mode operation.

[0084] In embodiments of the present invention, the controller 2100 may include a first controller, a second controller, and a third controller. The first controller may be a corresponding controller in the grid-side converter, the second controller may be a corresponding controller in the flywheel energy storage converter of the flywheel energy storage unit, and the third controller may be the main control device in the grid-type hybrid energy storage system. Specifically, the corresponding controller in the grid-side converter can perform grid frequency acquisition, active power calculation, and switching between constant power mode and constant voltage mode of the grid-side converter; the corresponding controller in the flywheel energy storage converter of the flywheel energy storage unit can perform flywheel speed regulation based on DC bus voltage changes, and switching between constant voltage mode and constant speed mode of the flywheel energy storage unit. In addition, the main control device in the grid-type hybrid energy storage system obtains the constant voltage setpoint (i.e., the constant voltage target value) and sends it to the flywheel converter on the grid-side converter and the flywheel energy storage unit side, and coordinates the energy management of the flywheel energy storage unit and the electrochemical energy storage unit (i.e., the battery), while realizing the overall protection and status monitoring of the grid-type hybrid energy storage system. The battery energy storage unit operates in conjunction with the DC bus based on its own characteristics. That is, when the DC bus voltage is higher than the battery terminal voltage, the battery is charged; otherwise, the battery is discharged.

[0085] It should be noted that the specific implementation of the control device 2000 of the grid-type hybrid energy storage system in this embodiment of the invention is similar to the specific implementation described in the control method of the grid-type hybrid energy storage system in the above embodiment of the invention. For details, please refer to the description of the control method of the grid-type hybrid energy storage system. In order to reduce redundancy, it will not be repeated here.

[0086] Specifically, the control device 2000 for a grid-type hybrid energy storage system according to an embodiment of the present invention is used to implement the control method for the grid-type hybrid energy storage system described above. During operation of the grid-type hybrid energy storage system, the grid-side converter is first controlled to operate in constant voltage mode, and the flywheel energy storage unit operates in constant speed mode. Then, the grid frequency is acquired, and the target active power is determined and output based on the grid frequency. When the grid frequency exceeds the frequency dead zone, the grid-side converter is controlled to switch its operating mode. Simultaneously, based on the voltage change of the DC bus, the flywheel energy storage unit is controlled to switch its operating mode, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristic of the constant speed mode, the flywheel can quickly output active power according to the determined target power, with a fast short-term high-power response speed, quickly filling the grid power gap and pulling the grid frequency back to a reasonable range. At the same time, controlling the flywheel energy storage unit to switch its operating mode and the operating state of the electrochemical energy storage unit based on the voltage change of the DC bus allows the flywheel to prioritize the rapid active power support task after the frequency exceeds the limit, reducing frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and wear. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, which better meets the actual needs of the system. It responds promptly when rapid support is required, while taking into account both efficient standby and millisecond-level support, making the system more intelligent and efficient. It realizes the integrated design of boost converter, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0087] In one embodiment of the present invention, a computer-readable storage medium is also provided.

[0088] In one embodiment of the present invention, a control program for a grid-type hybrid energy storage system is stored on a computer-readable storage medium. When the control program for the grid-type hybrid energy storage system is executed by a processor, it implements the control method for the grid-type hybrid energy storage system as described in the above embodiment of the present invention.

[0089] It should be noted that when the computer-readable storage medium of the present invention executes the control program of the grid-type hybrid energy storage system through the processor, its specific implementation is similar to the specific implementation described in the control method of the grid-type hybrid energy storage system of the above embodiments of the present invention. For details, please refer to the description of the control method of the grid-type hybrid energy storage system. In order to reduce redundancy, it will not be repeated here.

[0090] Specifically, according to embodiments of the present invention, a control program for a grid-type hybrid energy storage system is stored on a computer-readable storage medium. When the control program for the grid-type hybrid energy storage system is executed by a processor, it implements the control method for the grid-type hybrid energy storage system as described in the above embodiments of the present invention. By controlling the grid-side converter to operate in constant voltage mode and the flywheel energy storage unit to operate in constant speed mode during the operation of the grid-type hybrid energy storage system, the grid frequency is acquired, and then the target active power is determined and output based on the grid frequency. When the grid frequency crosses the frequency dead zone, the grid-side converter is controlled to switch operating modes. At the same time, the flywheel energy storage unit is controlled to switch operating modes based on the voltage change of the DC bus, and the operating state of the electrochemical energy storage unit is controlled. Thus, relying on the stable operation characteristics of the constant speed mode, the flywheel can quickly output active power according to the determined target power. The short-term high-power response speed is fast, quickly filling the grid power gap and pulling the grid frequency back to a reasonable range. Simultaneously, the system controls the flywheel energy storage unit's operating mode switching and the electrochemical energy storage unit's operating status based on DC bus voltage changes. This allows the flywheel to prioritize rapid active power support after frequency limits are exceeded, reducing frequent high-power instantaneous charging and discharging of the battery and delaying battery aging and wear. Therefore, the control method of this grid-type hybrid energy storage system flexibly adjusts the flywheel's operating mode according to the actual DC bus voltage, better meeting the system's actual needs. It responds promptly when rapid support is required, while also balancing efficient standby and millisecond-level support, making the system more intelligent and efficient. This achieves integrated boost converter design, reduces conversion losses, lowers hardware costs, and comprehensively improves the dynamic support capability and operational reliability of the grid-type hybrid energy storage system.

[0091] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0092] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A control method for a grid-type hybrid energy storage system, characterized in that, The grid-type hybrid energy storage system includes a flywheel energy storage unit, an electrochemical energy storage unit, and a grid-side converter. The flywheel energy storage unit and the electrochemical energy storage unit are respectively connected to a DC bus. The DC bus is connected to an AC bus through the grid-side converter. The control method includes: When the grid-type hybrid energy storage system is running, the grid-side converter is controlled to operate in constant voltage mode, and the flywheel energy storage unit is controlled to operate in constant speed mode; Obtain the power grid frequency; The target active power is determined based on the grid frequency, and the target active power is output. When the grid frequency crosses the frequency dead zone, the grid-side converter is controlled to switch operating modes, and the flywheel energy storage unit is controlled to switch operating modes based on the voltage change of the DC bus, and the operating status of the electrochemical energy storage unit is controlled.

2. The control method for a grid-type hybrid energy storage system according to claim 1, characterized in that, Controlling the grid-side converter to switch operating modes based on grid frequency changes, controlling the flywheel energy storage unit to switch operating modes based on DC bus voltage changes, and controlling the operating status of the electrochemical energy storage unit, including: Control the grid-side converter to switch to constant power mode; When the flywheel energy storage unit is charging, if the voltage of the DC bus exceeds the upper limit of the voltage dead zone, the flywheel energy storage unit is controlled to switch to constant voltage mode. After the flywheel energy storage unit switches to the constant voltage mode, if the remaining rechargeable energy and the current maximum allowable charging power of the flywheel energy storage unit can meet the power demand of the power grid, then the electrochemical energy storage unit is controlled not to be turned on; or, if the remaining rechargeable energy or the current maximum allowable charging power of the flywheel energy storage unit cannot meet the power demand of the power grid, then the electrochemical energy storage unit supports the remaining power demand of the power grid.

3. The control method for a grid-type hybrid energy storage system according to claim 1, characterized in that, Controlling the grid-side converter to switch operating modes based on grid frequency changes, controlling the flywheel energy storage unit to switch operating modes based on DC bus voltage changes, and controlling the operating status of the electrochemical energy storage unit, including: Control the grid-side converter to switch to constant power mode; When the flywheel energy storage unit discharges, if the voltage of the DC bus drops to the lower limit of the voltage dead zone, the flywheel energy storage unit is controlled to switch to constant voltage mode. After the flywheel energy storage unit switches to the constant voltage mode, if the remaining dischargeable energy and the current maximum allowable discharge power of the flywheel energy storage unit can meet the power demand of the power grid, then the electrochemical energy storage unit is controlled not to be turned on; or, if the remaining dischargeable energy or the current maximum allowable discharge power of the flywheel energy storage unit cannot meet the power demand of the power grid, then the electrochemical energy storage unit supports the remaining power demand of the power grid.

4. The control method for a grid-type hybrid energy storage system according to claim 2 or 3, characterized in that, The target operating voltage of the flywheel energy storage unit and the grid-side converter in the constant voltage mode is determined based on the current voltage of the electrochemical energy storage unit; The target operating power of the grid-side converter in the constant power mode is determined based on the grid frequency.

5. The control method for a grid-type hybrid energy storage system according to claim 2 or 3, characterized in that, Also includes: When the grid frequency returns to the frequency dead zone, the grid-side converter is controlled to switch to the constant voltage mode; When the voltage of the DC bus returns to the voltage dead zone, the flywheel energy storage unit is controlled to switch to the constant speed mode and maintain the current speed until the flywheel energy storage unit completes charging or discharging.

6. The control method for a grid-type hybrid energy storage system according to claim 5, characterized in that, After the flywheel energy storage unit completes charging or discharging, it also includes: When the grid frequency is determined to be within a preset frequency range, the rotation speed of the flywheel energy storage unit is adjusted to a preset speed, and the operating voltage of the electrochemical energy storage unit is adjusted to a preset voltage. The preset frequency range is used to indicate the frequency range within which the operating parameters of the energy storage unit are allowed to return to preset values.

7. The control method for a grid-type hybrid energy storage system according to claim 6, characterized in that, The control of adjusting the rotational speed of the flywheel energy storage unit to a preset speed and the control of adjusting the operating voltage of the electrochemical energy storage unit to a preset voltage include: The speed of the flywheel energy storage unit is adjusted according to the preset output power until the preset speed is reached. Then, the flywheel energy storage unit is controlled to run at a constant speed of the preset speed. The preset speed is the speed corresponding to the flywheel energy storage unit when it is at its target SOC value. The operating power of the electrochemical energy storage unit is adjusted according to a preset power adjustment step size until the voltage value of the electrochemical energy storage unit reaches the preset voltage. Then, the flywheel energy storage unit is controlled to operate at a constant voltage of the preset voltage, wherein the preset voltage is the voltage corresponding to the electrochemical energy storage unit when it is at its target SOC value.

8. The control method for a grid-type hybrid energy storage system according to claim 2 or 3, characterized in that, After the flywheel energy storage unit switches to constant voltage mode, it also includes: If the SOC value of the flywheel energy storage unit is less than or equal to the first SOC threshold or greater than or equal to the second SOC threshold, then the flywheel energy storage unit is controlled to shut down so that the electrochemical energy storage unit can fully support the target active power. If the SOC value of the flywheel energy storage unit is greater than the first SOC threshold and less than the second SOC threshold, then the flywheel energy storage unit is controlled to maintain the constant voltage mode operation.

9. A control device for a grid-type hybrid energy storage system, characterized in that, The grid-type hybrid energy storage system includes a flywheel energy storage unit, an electrochemical energy storage unit, and a grid-side converter. The flywheel energy storage unit and the electrochemical energy storage unit are respectively connected to a DC bus. The DC bus is connected to an AC bus through the grid-side converter. The control device includes: A controller for performing a control method for a grid-type hybrid energy storage system as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a control program for a grid-type hybrid energy storage system, which, when executed by a processor, implements the control method for the grid-type hybrid energy storage system as described in any one of claims 1-8.

Images