Control method of hybrid energy storage system and hybrid energy storage system

Abstract

The application discloses a control method of a hybrid energy storage system and the hybrid energy storage system, and relates to the technical field of electric energy storage systems.The control method comprises the following steps: after starting, a grid-side converter stabilizes the voltage of a DC bus to a rated value; a flywheel converter continuously monitors the voltage change rate on the DC bus; when the absolute value of the voltage change rate exceeds a first threshold value, the flywheel energy storage system enters a transient response mode; in the transient response mode, the flywheel energy storage system autonomously releases or absorbs power to suppress voltage fluctuation of the DC bus; a battery energy storage system continuously monitors the trend voltage deviation on the DC bus; when the absolute value of the trend voltage deviation exceeds a second threshold value and the duration exceeds a preset time, the battery energy storage system enters a steady-state regulation mode; in the steady-state regulation mode, the battery energy storage system autonomously performs continuous charging and discharging regulation. By adopting the method, the problem that the capacity of the battery energy storage system is accelerated to attenuate due to high-frequency charging and discharging impact can be avoided.

Description

Technical Field

[0001] This invention relates to the field of energy storage system technology, and in particular to a control method for a hybrid energy storage system and a hybrid energy storage system. Background Technology

[0002] In related technologies, existing hybrid energy storage systems mostly adopt a parallel AC-side scheme, that is, the flywheel energy storage system and the battery energy storage system are each equipped with an independent energy storage converter, which are connected in parallel on the AC low-voltage side to the step-up transformer and connected to the grid. High-frequency power fluctuations on the grid side act on the energy storage converters corresponding to the flywheel energy storage system and the battery energy storage system simultaneously through the AC bus, so that the battery energy storage system will be subjected to high-frequency charging and discharging impacts, thereby causing the capacity of the battery energy storage system to decay more rapidly. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of the present invention is to propose a control method for a hybrid energy storage system, which can avoid the problem of accelerated capacity decay caused by high-frequency charging and discharging shocks to the battery energy storage system.

[0004] To address the aforementioned problems, a first aspect of the present invention provides a control method for a hybrid energy storage system. The hybrid energy storage system includes a DC bus, a grid-side converter, a flywheel energy storage system, and a battery energy storage system. The DC side of the grid-side converter is connected to the DC bus, and the AC side of the grid-side converter is used to connect to the power grid or a load. The flywheel energy storage system is connected to the DC bus via a flywheel converter, and the battery energy storage system is connected to the DC bus and is connected in parallel with the flywheel energy storage system on the DC side. The control method includes: after startup, the grid-side converter stabilizes the voltage of the DC bus to a rated value; the flywheel converter continuously monitors the voltage changes on the DC bus. When the absolute value of the voltage change rate exceeds a first threshold, the flywheel energy storage system enters a transient response mode. In this transient response mode, the flywheel energy storage system autonomously releases or absorbs power to smooth the voltage fluctuations of the DC bus. The battery energy storage system continuously monitors the trend voltage deviation on the DC bus. When the absolute value of the trend voltage deviation exceeds a second threshold and the duration exceeds a preset time, the battery energy storage system enters a steady-state regulation mode. In this steady-state regulation mode, the battery energy storage system autonomously performs continuous charge and discharge regulation. The trend voltage deviation is the deviation of the actual voltage on the DC bus from the rated value.

[0005] According to the control method of the hybrid energy storage system of the present invention, when the voltage change rate of the DC bus is large, the flywheel energy storage system is controlled to autonomously release or absorb power to smooth the voltage fluctuation of the DC bus. When the trend voltage deviation on the DC bus is large, the battery energy storage system is controlled to autonomously perform continuous charging and discharging regulation, thereby avoiding the problem that the battery energy storage system will be subjected to high-frequency charging and discharging impacts and thus accelerate capacity decay, and also avoiding the situation of trend power imbalance in the hybrid energy storage system.

[0006] In some embodiments, the system further includes: when the absolute value of the voltage change rate does not exceed the first threshold, the flywheel energy storage system maintains a standby state or executes a smoothing scheduling command issued by the upper-level system; when the absolute value of the trend voltage deviation does not exceed the second threshold or the duration does not reach the preset time, the battery energy storage system maintains a float charging state or executes a smoothing scheduling command issued by the upper-level system.

[0007] In some embodiments, under the transient response mode, the control method includes: when the voltage change rate is negative, the flywheel energy storage system releases stored energy to inject power into the DC bus; when the voltage change rate is positive, the flywheel energy storage system absorbs surplus power on the DC bus.

[0008] In some embodiments, under the steady-state regulation mode, the control method includes: when the filtered trend voltage deviation is negative, the battery energy storage system discharges to compensate for the continuous power deficit; when the filtered trend voltage deviation is positive, the battery energy storage system charges to absorb the continuous power surplus.

[0009] In some embodiments, the method further includes: when the state of charge of the flywheel energy storage system is lower than a preset lower limit, the flywheel energy storage system exits the transient response mode, and the battery energy storage system compensates for the power required for the energy recovery of the flywheel energy storage system; when the state of charge of the flywheel energy storage system is higher than a preset upper limit, the flywheel energy storage system stops absorbing power, and the surplus power on the DC bus is fed back to the DC bus by the battery energy storage system.

[0010] In some embodiments, the system further includes: when the hybrid energy storage system is operating in grid-connected mode, the grid-side converter switches to a virtual synchronous machine control strategy to actively construct voltage and frequency references at the grid connection point; the flywheel energy storage system autonomously provides inertial response and damping based on locally detected voltage change rate; and the battery energy storage system provides the continuous energy required for synchronization based on locally detected trend voltage deviation.

[0011] In some embodiments, the method further includes: when the absolute value of the voltage change rate exceeds the fault determination threshold, the flywheel energy storage system immediately stops outputting power and triggers the DC protection device to operate.

[0012] A second aspect of the present invention provides a hybrid energy storage system, comprising: a DC bus; a flywheel energy storage system connected to the DC bus via a flywheel converter, the flywheel energy storage system being configured to autonomously release or absorb power to smooth voltage fluctuations on the DC bus when the absolute value of the voltage change rate on the DC bus exceeds a first threshold, based on locally detected voltage change rate; a battery energy storage system connected to the DC bus and in parallel with the flywheel energy storage system on the DC side, the battery energy storage system being configured to autonomously perform continuous charge and discharge regulation when the absolute value of the trend voltage deviation on the DC bus exceeds a second threshold and the duration exceeds a preset time, based on locally detected trend voltage deviation; and a grid-side converter, the DC side of the grid-side converter being connected to the DC bus, and the AC side of the grid-side converter being used to connect to the power grid or a load to compensate for continuous power imbalance on the DC bus.

[0013] According to the hybrid energy storage system of the present invention, by executing the control method of the hybrid energy storage system of the above embodiments, the problem of accelerated capacity decay caused by the battery energy storage system being subjected to high-frequency charging and discharging shocks can be avoided.

[0014] In some embodiments, the hybrid energy storage system further includes a booster compartment, which houses a booster transformer, and the AC side of the grid-side converter is connected to the power grid via the booster transformer.

[0015] In some embodiments, the flywheel energy storage system includes multiple flywheel units, and the hybrid energy storage system further includes: a flywheel converter compartment, which is divided into a converter chamber and a flywheel chamber, with a fireproof structure between the converter chamber and the flywheel chamber. The converter chamber is used to integrate the grid-side converter, and the flywheel chamber adopts an open installation architecture to densely arrange multiple flywheel units. The DC outputs of the multiple flywheel units are combined and connected to the DC bus. In addition, a water-air heat exchange system and a braking resistor are provided above the flywheel chamber for heat dissipation and energy dissipation braking of the flywheel units.

[0016] 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

[0017] 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 schematic diagram of a hybrid energy storage system according to an embodiment of the present invention; Figure 2 This is a flowchart of a control method for a hybrid energy storage system according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a battery energy storage system according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a flywheel converter compartment according to an embodiment of the present invention.

[0018] Figure label: Hybrid energy storage system 100; DC bus 1; flywheel energy storage system 2; battery energy storage system 3; grid-side converter 4; flywheel converter 5; flywheel converter compartment 6; flywheel unit 21; battery unit 31; converter compartment 61; flywheel compartment 62. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below, and the embodiments described with reference to the accompanying drawings are exemplary.

[0020] Currently, most existing hybrid energy storage systems adopt a parallel topology on the AC side. This means that the flywheel energy storage system and the battery energy storage system each have independent power conversion systems (PCS), which are connected in parallel on the low-voltage AC side (e.g., the 690V bus) before being connected to the grid via a step-up transformer. Physically, the flywheel energy storage system is typically arranged in an independent container or cabinet, housing the flywheel and its corresponding power conversion system, and connected to the grid via a standard AC interface. The battery compartment is also independently located, and the two systems are electrically connected in simple parallel configuration only through the AC bus.

[0021] However, in practical engineering applications and in operation for high-frequency fluctuation scenarios, the above-mentioned existing technologies have the following significant technical problems: First, the overall cycle efficiency of hybrid energy storage systems is relatively low. In the AC parallel architecture, the charging and discharging processes of both the battery energy storage system and the flywheel energy storage system require their own independent DC-AC conversion stages, resulting in two stages of power conversion losses and thus a relatively low overall cycle efficiency of the hybrid energy storage system.

[0022] Second, there are issues with response delays and coordination complexity. In existing solutions, the power allocation between flywheel energy storage systems and battery energy storage systems relies entirely on commands issued by the upper-level energy management system via the communication network. Limited by communication protocol stack processing, network transmission, and controller execution cycles, hybrid energy storage systems exhibit inherent delays ranging from milliseconds to tens of milliseconds. When the power grid experiences transient disturbances or sudden load changes, these communication delays may affect the support effect.

[0023] Third, there is insufficient protection against high-frequency shocks to the battery. High-frequency power fluctuations on the grid side directly affect the battery energy storage system and its corresponding PCS, forcing the battery energy storage system to withstand high-frequency charging and discharging current surges. Especially in application scenarios with millisecond-level load fluctuations, such as AI (Artificial Intelligence) computing centers, the battery energy storage system is under high-frequency stress for extended periods, significantly accelerating capacity degradation. Real-world examples have shown that under such conditions, battery energy storage systems using AC parallel configurations may have a cycle life of only about three years, far below design expectations, severely impacting the economic viability of hybrid energy storage systems.

[0024] Fourth, hybrid energy storage systems involve a large number of devices and require a large footprint. Flywheel energy storage systems and battery energy storage systems are independent of each other, with a large number of devices, a large footprint, a large workload for on-site installation and wiring, and high engineering costs.

[0025] Fifth, flywheel energy storage systems suffer from low space utilization and limited power density. Traditional flywheel energy storage systems mostly adopt a cabinet-style structure design, with each flywheel unit occupying its own cabinet, resulting in a large proportion of wasted space within the cabinet. Taking a standard 20-foot container as an example, it can typically only integrate 10 to 12 flywheel units, and the power density of a single cabinet encounters a bottleneck, making it difficult to meet the construction requirements of large-scale independent energy storage power stations for high power density and compact layout.

[0026] To address the aforementioned problems, a first aspect of the present invention provides a control method for a hybrid energy storage system. This method can avoid the problem of accelerated capacity decay caused by high-frequency charging and discharging shocks to the battery energy storage system.

[0027] In an embodiment, such as Figure 1 As shown, the hybrid energy storage system 100 includes a DC bus 1, a grid-side converter 4, a flywheel energy storage system 2, and a battery energy storage system 3. The DC side of the grid-side converter 4 is connected to the DC bus 1, while the AC side is used to connect to the power grid or load. The flywheel energy storage system 2 is connected to the DC bus 1 via a flywheel converter 5. The battery energy storage system 3 is connected to the DC bus 1 and is connected in parallel with the flywheel energy storage system on the DC side. The flywheel converter responds autonomously based on the local DC bus voltage signal, without waiting for communication commands, reducing the response delay from tens of milliseconds in the AC scheme to microseconds / milliseconds. The battery energy storage system responds to slower-moving trend changes in the bus voltage. The battery energy storage system is controlled by the voltage outer loop of the grid-side converter, responsible for continuous energy throughput and steady-state regulation of the bus voltage. When grid dispatch commands are issued to the grid-side converter, the grid-side converter adjusts the charging and discharging power of the battery energy storage system according to the power command and the SOC state of the battery energy storage system. Flywheel energy storage systems automatically filter high-frequency components, while battery energy storage systems only withstand smooth power curves on the order of minutes or longer.

[0028] The following is for reference. Figure 2 A control method for a hybrid energy storage system according to embodiments of the present invention is described, such as... Figure 2 As shown, the control methods include: Step S1: After startup, the grid-side converter stabilizes the voltage of the DC bus to the rated value.

[0029] The rated value is the maximum allowable operating voltage of the DC bus, and the rated value is any value within the range of 1000V-1500V. The specific parameters are determined according to the design of the hybrid energy storage system. After the hybrid energy storage system is started, it can operate in grid-connected mode or grid-connected mode.

[0030] Specifically, after the hybrid energy storage system is started, the grid-side converter stabilizes the DC bus voltage to the rated value, thereby stabilizing the DC bus voltage and enabling timely monitoring of grid power fluctuations.

[0031] In step S2, the flywheel converter continuously monitors the voltage change rate on the DC bus. When the absolute value of the voltage change rate exceeds the first threshold, the flywheel energy storage system enters the transient response mode. In the transient response mode, the flywheel energy storage system autonomously releases or absorbs power to smooth the voltage fluctuations on the DC bus.

[0032] Among them, the voltage change rate is the instantaneous rate of change of power fluctuation, and the voltage change rate is a global quantity of the bus. The purpose of the flywheel energy storage system entering transient response mode is to smooth out transient fluctuations and protect the battery energy storage system.

[0033] Specifically, when a surge in power occurs on the power grid, meaning the grid needs to provide or receive high power instantaneously (the surge is either a rise or a fall), the voltage change rate on the DC bus changes significantly in the sub-millisecond range. This naturally matches the millisecond-level response capability of the flywheel. The flywheel energy storage system can respond before the power surge causes substantial damage to the hybrid energy storage system. Since grid-side load fluctuations are directly reflected as DC bus voltage fluctuations, and when surge loads such as AI computing centers start up with high power instantaneously, the DC bus voltage drops slightly. The flywheel converter detects an increase in the voltage change rate on the DC bus in microseconds, and the flywheel energy storage system enters transient response mode. The flywheel energy storage system instantly releases stored kinetic energy to inject power into the bus, smoothing out voltage drop spikes. The battery energy storage system experiences almost no surge current. When the load decreases instantaneously or the output of new energy sources increases suddenly, the DC bus voltage rises slightly. Based on this, the flywheel converter continuously monitors the voltage on the DC bus. When the absolute value of the voltage change rate exceeds the first threshold, it indicates that an impulsive power surge has occurred on the DC bus. The flywheel energy storage system enters a transient response mode. In this mode, the flywheel energy storage system autonomously releases or absorbs power to smooth out voltage fluctuations on the DC bus, thus completing the response before the power surge causes substantial damage to the hybrid energy storage system. Furthermore, the flywheel energy storage system consumes very little energy and can repeatedly respond to high-frequency surges, fully leveraging its high cycle life advantage. The flywheel energy storage system absorbs power instantaneously, preventing the battery energy storage system from experiencing surge current, thereby protecting it. It should be noted that the flywheel autonomously responds to high-frequency power fluctuations through DC bus voltage changes, reducing the high-frequency charge and discharge surges experienced by the battery energy storage system by more than 90%. In comparison, a single lithium battery solution consumes its cycle life in approximately 3 years in high-frequency applications in computing centers. This solution can significantly extend the battery replacement cycle and heat exchange life.

[0034] Step S3: The battery energy storage system continuously monitors the trend voltage deviation on the DC bus. When the absolute value of the trend voltage deviation exceeds the second threshold and the duration exceeds the preset time, the battery energy storage system enters the steady-state regulation mode. In the steady-state regulation mode, the battery energy storage system autonomously performs continuous charging and discharging regulation.

[0035] The trend voltage deviation is the deviation of the actual voltage on the DC bus from its rated value. This trend voltage deviation is an electrical quantity on the DC bus side that directly reflects the cumulative effect of continuous power imbalance. The steady-state regulation mode of the hybrid energy storage system is designed for low-frequency continuous power, restoring energy balance and maintaining power levels with a response speed of seconds or more.

[0036] Specifically, when a hybrid energy storage system experiences a persistent power deficit or surplus, the actual voltage of the DC bus will continuously deviate from its rated value, forming a measurable trend voltage deviation. The amplitude and duration of this trend voltage deviation directly reflect the cumulative degree of power imbalance in the power grid, perfectly aligning with the battery energy storage system's task of compensating for persistent energy deficits. Based on this, the battery energy storage system continuously monitors the trend voltage deviation on the DC bus. When the absolute value of the trend voltage deviation exceeds a second threshold and its duration exceeds a preset time, it is determined that the hybrid energy storage system exhibits a trend power imbalance. The battery energy storage system then enters a steady-state regulation mode. In this mode, the battery energy storage system autonomously performs continuous charge and discharge regulation, thereby preventing the hybrid energy storage system from exhibiting a trend power imbalance.

[0037] Therefore, the flywheel converter can autonomously respond within microsecond to millisecond timescales by detecting the voltage change rate and trend voltage deviation of the DC bus, without communication. This means it instantly releases energy when the voltage drops and instantly absorbs energy when the voltage rises, smoothing out peak voltage fluctuations on the bus. The flywheel energy storage system responds autonomously based on the locally detected DC bus voltage change rate, while the battery energy storage system responds autonomously based on the locally detected filtered voltage deviation. The two achieve frequency separation and coordination without communication, without relying on a centralized control unit to issue commands through a communication interface. The flywheel and battery energy storage systems do not require communication coordination; they achieve natural functional decoupling and coordination solely through their different frequency response characteristics to the DC bus voltage signal.

[0038] According to the control method of the hybrid energy storage system of the present invention, when the voltage change rate of the DC bus is large, the flywheel energy storage system is controlled to autonomously release or absorb power to smooth the voltage fluctuation of the DC bus. When the trend voltage deviation on the DC bus is large, the battery energy storage system is controlled to autonomously perform continuous charging and discharging regulation, thereby avoiding the problem that the battery energy storage system will be subjected to high-frequency charging and discharging impacts and thus accelerate capacity decay, and also avoiding the situation of trend power imbalance in the hybrid energy storage system.

[0039] In some embodiments, the system further includes: when the absolute value of the voltage change rate does not exceed a first threshold, the flywheel energy storage system maintains a standby state or executes a smoothing dispatch command issued by the upper-level system; when the absolute value of the trend voltage deviation does not exceed a second threshold or the duration does not reach a preset time, the battery energy storage system maintains a float charging state or executes a smoothing dispatch command issued by the upper-level system.

[0040] Specifically, when the absolute value of the voltage change rate does not exceed the first threshold, it indicates that the grid power and DC bus voltage are fluctuating normally. In this case, the flywheel energy storage system maintains standby mode or executes the smoothing dispatch command issued by the upper-level system. That is, the flywheel energy storage system does not need to enter the transient response mode, or the flywheel energy storage system is controlled to complete the smoothing dispatch task. When the absolute value of the trend voltage deviation does not exceed the second threshold or the duration does not reach the preset time, it indicates that the cumulative degree of grid power imbalance is low. In this case, the battery energy storage system maintains floating charge mode or executes the smoothing dispatch command issued by the upper-level system. That is, the battery energy storage system does not enter the steady-state regulation mode, or the battery energy storage system is controlled to complete the smoothing dispatch task.

[0041] In some embodiments, under transient response mode, the control method includes: when the rate of voltage change is negative, the flywheel energy storage system releases stored energy to inject power into the DC bus; when the rate of voltage change is positive, the flywheel energy storage system absorbs surplus power from the DC bus.

[0042] Specifically, when the voltage change rate is negative, the DC bus voltage experiences a momentary drop. The flywheel energy storage system releases its stored energy to inject power into the DC bus. In other words, the flywheel energy storage system autonomously releases its stored kinetic energy into the DC bus within a microsecond to millisecond timescale to mitigate the voltage drop. When the voltage change rate is positive, the DC bus voltage experiences a momentary rise. The flywheel energy storage system absorbs the excess power on the DC bus. In other words, the flywheel energy storage system autonomously absorbs the excess power on the DC bus within a millisecond timescale to mitigate the voltage rise.

[0043] In addition, it should be noted that the power injection or absorption of the flywheel energy storage system is completed autonomously by the flywheel local controller based on the DC bus voltage signal, without the need for communication and coordination with the grid-side converter or battery energy storage system, and the response delay is only limited by the switching speed of the power devices.

[0044] In some embodiments, under steady-state regulation mode, the control method includes: when the filtered trend voltage deviation is negative, the battery energy storage system discharges to compensate for the continuous power deficit; when the filtered trend voltage deviation is positive, the battery energy storage system charges to absorb the continuous power surplus.

[0045] The filtering method can be either passive or active filtering, and there are no restrictions on this.

[0046] Specifically, in steady-state regulation mode, when the filtered trend voltage deviation is negative, the DC bus voltage remains low, and the battery energy storage system discharges to compensate for the persistent power deficit. Conversely, when the filtered trend voltage deviation is positive, the DC bus voltage remains high, and the battery energy storage system charges to absorb the persistent power surplus. Therefore, by controlling the charging and discharging of the battery energy storage system in steady-state regulation mode, the problem of accumulated grid power imbalance can be avoided, thus achieving grid power balance. Furthermore, using the filtered trend voltage deviation for judgment allows for accurate identification of accumulated grid power imbalance.

[0047] In some embodiments, the method further includes: when the state of charge of the flywheel energy storage system is lower than a preset lower limit, the flywheel energy storage system exits the transient response mode and the battery energy storage system compensates for the power required for the energy recovery of the flywheel energy storage system; when the state of charge of the flywheel energy storage system is higher than a preset upper limit, the flywheel energy storage system stops absorbing power and the surplus power on the DC bus is fed back to the DC bus by the battery energy storage system.

[0048] Specifically, when the state of charge (SOC) of the flywheel energy storage system is lower than the preset lower limit, the flywheel energy storage system is too low to provide power to the DC bus. In this case, the flywheel energy storage system is controlled to exit the transient response mode, and the battery energy storage system compensates for the power required for the flywheel energy storage system to restore energy, thereby improving the SOC of the flywheel energy storage system. When the SOC of the flywheel energy storage system is higher than the preset upper limit, the flywheel energy storage system is too high to absorb power from the DC bus. In this case, the flywheel energy storage system is controlled to stop absorbing power, and the surplus power on the DC bus is fed back to the DC bus by the battery energy storage system.

[0049] In some embodiments, the system further includes: when the hybrid energy storage system is operating in grid-connected mode, the grid-side converter switches to a virtual synchronous machine control strategy to actively construct voltage and frequency references at the grid connection point; the flywheel energy storage system autonomously provides inertial response and damping based on locally detected voltage change rate; and the battery energy storage system provides the continuous energy required for synchronization based on locally detected trend voltage deviation.

[0050] Specifically, when the hybrid energy storage system operates in grid-connected mode, the grid-side converter switches to voltage source control mode and adopts a virtual synchronous machine control strategy to actively construct voltage and frequency references at the grid connection point. The flywheel energy storage system autonomously provides inertial response and damping based on locally detected voltage change rate to respond to grid frequency change rate. The battery energy storage system provides the continuous energy required for synchronization based on locally detected trend voltage deviation. The flywheel energy storage system and the battery energy storage system work together to present the external characteristics of grid-connected energy storage. Thus, in grid-connected mode, the grid-side converter operates as a voltage source to provide physical inertia and damping through the flywheel energy storage system, enabling the hybrid energy storage system to possess true grid-connected external characteristics.

[0051] In some embodiments, the method further includes: when the absolute value of the voltage change rate exceeds the fault determination threshold, the flywheel energy storage system immediately stops outputting power and triggers the DC protection device to operate.

[0052] Specifically, during the operation of the hybrid energy storage system, if the absolute value of the voltage change rate of the DC bus exceeds the preset fault judgment threshold, that is, the voltage change rate is far beyond the normal load fluctuation range, then a short circuit fault is determined to have occurred on the DC bus side. The flywheel energy storage system is then controlled to immediately stop outputting power, triggering the DC protection device to operate, thereby controlling the hybrid energy storage system to enter the fault isolation state to ensure the safety of the hybrid energy storage system.

[0053] A second aspect of the present invention provides a hybrid energy storage system, such as... Figure 1 As shown, the hybrid energy storage system 100 includes: a DC bus 1, a flywheel energy storage system 2, a battery energy storage system 3, and a grid-side converter 4, as follows: Figure 3 As shown, the battery energy storage system 3 includes multiple battery cells 31.

[0054] Among them, the flywheel energy storage system 2 is connected to the DC bus 1 through the flywheel converter 5. The flywheel energy storage system 2 is configured to release or absorb power autonomously to smooth the voltage fluctuation of the DC bus 1 when the absolute value of the voltage change rate on the DC bus 1 exceeds a first threshold, based on the locally detected voltage change rate. The battery energy storage system 3 is connected to the DC bus 1 and is connected in parallel with the flywheel energy storage system 2 on the DC side. The battery energy storage system 3 is configured to perform continuous charging and discharging regulation autonomously when the absolute value of the trend voltage deviation of the DC bus 1 exceeds a second threshold and the duration exceeds a preset time, based on the locally detected trend voltage deviation. The DC side of the grid-side converter 4 is connected to the DC bus 1, and the AC side of the grid-side converter 4 is used to connect to the grid or load to compensate for the continuous power imbalance of the DC bus 1.

[0055] According to the hybrid energy storage system of the present invention, by executing the control method of the hybrid energy storage system of the above embodiment, the problem of accelerated capacity decay caused by the battery energy storage system 3 being subjected to high-frequency charging and discharging impacts can be avoided.

[0056] In some embodiments, the hybrid energy storage system further includes a booster compartment, which houses a booster transformer, and the AC side of the grid-side converter is connected to the power grid via the booster transformer.

[0057] In some embodiments, such as Figure 1 As shown, the flywheel energy storage system 2 includes multiple flywheel units 21, such as... Figure 4As shown, the hybrid energy storage system 100 also includes: a flywheel converter compartment 6, which is divided into a converter chamber 61 and a flywheel chamber 62. A fireproof structure is provided between the converter chamber and the flywheel chamber. The converter chamber is used to integrate grid-side converters. The flywheel chamber adopts an open installation architecture without cabinets to densely arrange multiple flywheel units. The DC outputs of multiple flywheel units are combined and connected to the DC bus. In addition, a water-air heat exchange system and a braking resistor are also provided above the flywheel chamber for heat dissipation and energy dissipation braking of the flywheel units.

[0058] In this embodiment, the flywheel converter compartment uses a 30-foot standard container, internally divided into two functional areas: a converter room and a flywheel room. The converter room integrates four grid-side converters designed on the same platform as the grid / network structure. The DC side of the grid-side converters is led out to an external DC junction box, and the AC side of the grid-side converters is connected to an external step-up transformer. It also integrates a power distribution unit, a main control unit, a chopper braking unit, and the flywheel room, adopting an open installation architecture with no cabinets and only horizontal and vertical beams. It integrates 16 flywheel units with high density. The flywheel units can be magnetic levitation flywheel units, with a rated total power of 2.66MW and a stored energy of 22.16kWh. It is equipped with a water-air heat exchange system and a braking resistor. The water-air heat exchange system is installed on the top. The booster compartment includes a booster transformer and a high-voltage switchgear. The voltage of the booster transformer is 690V / 10kV or 35kV. The AC side of the grid-side converter in the flywheel converter compartment is connected to the low-voltage side of the booster transformer. The DC junction box of the flywheel converter compartment and the DC junction box of the battery compartment are directly connected in parallel via the shortest path DC cable or copper busbar, forming a common DC bus. The flywheel units in the flywheel energy storage system do not pass through an independent grid-side converter; their outputs are directly connected to this DC bus or after in-compartment DC-AC conversion, achieving strong DC-side coupling with the battery system. The DC side of the flywheel converter is connected to this DC bus, and the AC side is connected to a step-up transformer for grid connection.

[0059] 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.

[0060] 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 hybrid energy storage system, characterized in that, The hybrid energy storage system includes a DC bus, a grid-side converter, a flywheel energy storage system, and a battery energy storage system. The DC side of the grid-side converter is connected to the DC bus, and the AC side of the grid-side converter is used to connect to the power grid or a load. The flywheel energy storage system is connected to the DC bus via a flywheel converter. The battery energy storage system is connected to the DC bus and is connected in parallel with the flywheel energy storage system on the DC side. The control method includes: After startup, the grid-side converter stabilizes the voltage of the DC bus to the rated value; The flywheel converter continuously monitors the voltage change rate on the DC bus. When the absolute value of the voltage change rate exceeds a first threshold, the flywheel energy storage system enters a transient response mode. In the transient response mode, the flywheel energy storage system autonomously releases or absorbs power to smooth out voltage fluctuations on the DC bus. The battery energy storage system continuously monitors the trend voltage deviation on the DC bus. When the absolute value of the trend voltage deviation exceeds a second threshold and the duration exceeds a preset time, the battery energy storage system enters a steady-state regulation mode. In the steady-state regulation mode, the battery energy storage system autonomously performs continuous charge and discharge regulation. The trend voltage deviation is the deviation of the actual voltage on the DC bus from the rated value.

2. The control method for the hybrid energy storage system according to claim 1, characterized in that, Also includes: When the absolute value of the voltage change rate does not exceed the first threshold, the flywheel energy storage system maintains a standby state or executes a smooth scheduling command issued by the upper-level system. When the absolute value of the trend voltage deviation does not exceed the second threshold or the duration does not reach the preset time, the battery energy storage system maintains the float charging state or executes the smooth scheduling command issued by the upper-level system.

3. The control method for the hybrid energy storage system according to claim 1, characterized in that, In the transient response mode, the control method includes: When the voltage change rate is negative, the flywheel energy storage system releases the stored energy to inject power into the DC bus; When the voltage change rate is positive, the flywheel energy storage system absorbs the surplus power on the DC bus.

4. The control method for the hybrid energy storage system according to claim 1, characterized in that, In the steady-state regulation mode, the control method includes: When the filtered trend voltage deviation is negative, the battery energy storage system discharges to compensate for the continuous power deficit. When the filtered trend voltage deviation is positive, the battery energy storage system charges to absorb the continuous power surplus.

5. The control method for the hybrid energy storage system according to claim 1, characterized in that, The method further includes: When the state of charge of the flywheel energy storage system is lower than the preset lower limit, the flywheel energy storage system exits the transient response mode, and the battery energy storage system compensates for the power required for the energy recovery of the flywheel energy storage system. When the state of charge of the flywheel energy storage system is higher than the preset upper limit, the flywheel energy storage system stops absorbing power, and the surplus power on the DC bus is fed back to the DC bus by the battery energy storage system.

6. The control method for the hybrid energy storage system according to claim 1, characterized in that, Also includes: When the hybrid energy storage system is operating in grid-connected mode, the grid-side converter switches to a virtual synchronous machine control strategy to actively construct voltage and frequency references for the grid connection point; The flywheel energy storage system autonomously provides inertial response and damping based on locally detected voltage change rate; The battery energy storage system provides the continuous energy required for synchronization based on locally detected trend voltage deviations.

7. The control method for a hybrid energy storage system according to claim 1, characterized in that, Also includes: When the absolute value of the voltage change rate exceeds the fault determination threshold, the flywheel energy storage system immediately stops outputting power and triggers the DC protection device to operate.

8. A hybrid energy storage system, characterized in that, include: DC bus; A flywheel energy storage system is connected to the DC bus via a flywheel converter. The flywheel energy storage system is configured to release or absorb power autonomously to smooth voltage fluctuations on the DC bus when the absolute value of the voltage change rate exceeds a first threshold, based on locally detected voltage change rate on the DC bus. A battery energy storage system is connected to the DC bus and is connected in parallel with the flywheel energy storage system on the DC side. The battery energy storage system is configured to perform continuous charge and discharge regulation autonomously when the absolute value of the trend voltage deviation of the DC bus exceeds a second threshold and the duration exceeds a preset time, based on locally detected trend voltage deviation. A grid-side converter, wherein the DC side of the grid-side converter is connected to the DC bus, and the AC side of the grid-side converter is used to connect to the power grid or load to compensate for the continuous power imbalance of the DC bus.

9. The hybrid energy storage system according to claim 8, characterized in that, The hybrid energy storage system also includes a booster compartment, which houses a booster transformer. The AC side of the grid-side converter is connected to the power grid via the booster transformer.

10. The hybrid energy storage system according to claim 8, characterized in that, The flywheel energy storage system includes multiple flywheel units, and the hybrid energy storage system further includes: The flywheel converter compartment is divided into a converter chamber and a flywheel chamber, with a fireproof structure between them. The converter chamber is used to integrate the grid-side converter, and the flywheel chamber adopts an open installation architecture to densely arrange multiple flywheel units. The DC outputs of the multiple flywheel units are combined and connected to the DC bus. In addition, a water-air heat exchange system and a braking resistor are installed above the flywheel chamber for heat dissipation and energy dissipation braking of the flywheel units.

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