Super capacitor and lithium ion battery hybrid energy storage frequency modulation system and control method thereof

Abstract

The invention discloses a super capacitor and lithium ion battery hybrid energy storage frequency modulation system and a control method thereof, and belongs to the technical field of power system frequency modulation control. The super capacitor energy storage system and the lithium ion battery energy storage system are connected to the energy storage high-voltage alternating current bus through respective bidirectional converters and boosting transformers; the output end of the power synthesis device is connected to an RTU interface of a power grid dispatching system through a boosting transformer. The coordination controller is in bidirectional communication with the super capacitor CMS, the lithium ion battery BMS, the bidirectional converter PCS, the power synthesis device and the power grid dispatching system through the communication interface module, the fire fighting system, the video monitoring system and the heating and ventilation system are connected to an auxiliary monitoring channel of the coordination controller, and the prefabricated cabin provides a physical integration platform for all subsystems. According to the invention, through cooperative control of the super capacitor and the lithium ion battery, power output is dynamically distributed in a power grid frequency modulation instruction direction and a system state, and dual objectives of quick response and energy optimization are realized.

Description

A hybrid energy storage frequency regulation system combining supercapacitors and lithium-ion batteries and its control method Technical Field

[0001] This invention belongs to the field of power system frequency regulation control technology, and particularly relates to a frequency regulation control method and system based on a hybrid energy storage system of supercapacitor and lithium-ion battery. Background Technology

[0002] As the proportion of renewable energy generation continues to increase, the demand for frequency regulation resources in the power grid is growing. Traditional thermal power units have slow frequency regulation response speed and low regulation accuracy, making it difficult to meet the needs of modern power grids for fast and precise frequency regulation. Therefore, developing efficient and rapid-response hybrid energy storage systems has become an important direction for improving the frequency regulation capability of the power grid.

[0003] Currently, common energy storage frequency regulation systems mainly include single electrochemical energy storage systems (such as lithium-ion batteries) or supercapacitor systems. Some solutions employ hybrid energy storage systems combining molten salt and electrochemical methods, using a coordinating controller to achieve power distribution. However, these systems generally suffer from the following problems: limited response speed, mismatch between energy density and power density, short system lifetime, and complex control strategies.

[0004] The existing technology has the following main drawbacks: lithium-ion batteries have a slow response speed, making it difficult to meet the requirements of high-frequency frequency modulation; supercapacitors have high power density but low energy density, while lithium-ion batteries have the opposite, making it difficult for a single system to achieve both; existing control methods are mostly static priority allocation, without considering real-time changes in system state; frequent high-power output leads to accelerated aging of lithium-ion batteries, affecting the system's economic efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of uncoordinated response speed and energy efficiency, lack of dynamic optimization of control strategy, and short system life in existing hybrid energy storage frequency regulation systems. It proposes a hybrid energy storage frequency regulation system and its control method based on the coordinated control of supercapacitor and lithium-ion battery, so as to achieve fast response, efficient energy utilization and extended system life.

[0006] This invention achieves the dual goals of rapid response and energy optimization by using the coordinated control of supercapacitors and lithium-ion batteries to dynamically allocate power output based on the direction of grid frequency regulation commands and system status.

[0007] This invention is achieved using the following technical solution: a hybrid energy storage and frequency regulation system combining supercapacitors and lithium-ion batteries. The system structure includes: a supercapacitor energy storage system with high power density, suitable for high-frequency, short-time frequency regulation response; the supercapacitor energy storage system consists of supercapacitor cells, supercapacitor modules, supercapacitor clusters, a supercapacitor management system (CMS), a fire protection system, a video monitoring system, a heating and ventilation system, and a prefabricated cabin; wherein, supercapacitor cells are connected in series and parallel to form modules, and modules are further connected to form cluster-level units, which are connected to the CMS to achieve real-time monitoring and balanced control of voltage, current, temperature, and SOC; the fire protection system uses perfluorohexanone gas extinguishing devices, arranged on the top of the cluster-level units, to respond to abnormal temperature or arc fault signals; the video monitoring system deploys infrared thermal imaging and visible light dual-spectrum cameras to cover all electrical connection points; the heating and ventilation system adopts industrial-grade air conditioning and duct design to maintain the cabin temperature within the range of 15℃-35℃; the prefabricated cabin is a steel structure fireproof cabin with a protection level of not less than IP54, supporting overall hoisting and modular expansion.

[0008] Lithium-ion battery energy storage system: Features high energy density, suitable for medium- to long-term frequency regulation; the system consists of individual battery cells, battery modules, battery clusters, a battery management system (BMS), a fire protection system, a video monitoring system, a heating and ventilation system, and a prefabricated enclosure; individual battery cells utilize mainstream lithium iron phosphate materials (ternary lithium materials are largely obsolete), with a single cell capacity ≥280Ah. Cells are connected in series and parallel to form modules, which in turn form cluster-level units. These cluster-level units are connected to a three-tiered BMS architecture (cell-level, module-level, system-level) to achieve full lifecycle management of voltage, current, temperature, SOC, and SOH; the fire protection system employs a PACK-level detection + enclosure-level suppression scheme, with each battery pack containing a composite detector (temperature / smoke / CO), which activates perfluorohexanone fire suppression upon triggering; the video monitoring and heating and ventilation system configurations are consistent with those of the supercapacitor system; the prefabricated enclosure features a double-layer insulated fireproof structure with a fire resistance rating of at least 120 minutes, supporting online maintenance and hot-swappable replacement.

[0009] Coordination Controller: Used to receive AGC commands from the power grid, monitor system status (SOC, temperature, power output capacity, etc.) in real time, and dynamically allocate power commands. Mainstream coordination controllers adopt an industrial-grade real-time operating system, with a hardware platform of dual-core ARM+FPGA architecture, featuring 4 Ethernet interfaces, 8 CAN bus interfaces, 16 DI / DO interfaces, and 2 RS485 interfaces. The controller has built-in AGC command parsing module, SOC estimation module, power allocation algorithm module, fault diagnosis module, and log recording module. The AGC command parsing module supports IEC-104 and IEC-61850 protocols, with a response time ≤100ms. The power allocation algorithm module adopts a model predictive control (MPC) strategy, with a rolling optimization cycle of 1 second, and the objective function is to minimize the power deviation and SOC deviation penalty term.

[0010] Power combining device: used to vector combine the output power of supercapacitors and lithium-ion batteries and output it to the grid dispatch unit (RTU); it is actually an RTU substation of the energy storage system, which includes a data acquisition module, a computing module and a communication module.

[0011] Bidirectional converter (PCS) and transformer: These serve as the connection medium between supercapacitors and lithium-ion battery energy storage systems and the 6kV energy storage bus, enabling bidirectional power flow. The PCS features three operating modes: constant power, constant voltage, and constant current. It supports PQ and VF control strategies, and offers various single-unit capacities. Parallel operation is supported, with a DC side voltage range of 1000V-1500V. It is connected to the 6kV bus via a step-up transformer. The PCS communicates with the coordinating controller via a CAN bus, uploading status parameters including DC voltage, AC voltage, output power, module temperature, and fault codes.

[0012] Communication interface module: Enables information exchange with the power grid dispatching system and energy storage system. The communication interface module is an independent communication unit, supporting IEC-104, IEC-61850, and Modbus-TCP protocol conversion; it has a dual-machine hot backup mechanism with a master-slave switching time of ≤1 second; the communication unit has a built-in AGC command caching mechanism, supporting breakpoint resume and command replay protection; and it connects to the energy storage system via an Ethernet ring network.

[0013] The supercapacitor energy storage system and the lithium-ion battery energy storage system are respectively connected to the high-voltage AC bus of the energy storage system through their respective bidirectional converters (PCS) and step-up transformers; the output of the power combining device is connected to the RTU interface of the power grid dispatching system through the step-up transformer; the coordination controller communicates bidirectionally with the supercapacitor CMS, lithium-ion battery BMS, bidirectional converter (PCS), power combining device and power grid dispatching system through the communication interface module to realize command issuance and status acquisition; the fire protection system, video monitoring system and HVAC system are respectively connected to the auxiliary monitoring channel of the coordination controller for environmental anomaly linkage protection; the prefabricated cabin provides a physical integration platform for each subsystem, supporting modular deployment and online maintenance.

[0014] The control method includes the following steps: Initially, the supercapacitor's SOC is C_sc (50% ≤ C_sc ≤ 90%), and the lithium-ion battery's SOC is C_bat (30% ≤ C_bat ≤ 70%), with the system in standby mode. When the grid issues a downward frequency regulation command (reducing output power), the supercapacitor system absorbs power first. If the supercapacitor's SOC reaches its upper limit (e.g., 95%), the power absorption switches to the lithium-ion battery. When the grid issues an upward frequency regulation command (increasing output power), the supercapacitor system outputs power first. If the supercapacitor's SOC drops to its lower limit (e.g., 10%), the power output switches to the lithium-ion battery. During continuous frequency regulation, if the supercapacitor's SOC continuously falls below 10% or rises above 95%, the system rebalancing mechanism is triggered, transferring energy through the lithium-ion battery to adjust the system's power output. The supercapacitor's SOC is adjusted to a mid-range (e.g., 60%). The technical effects of this invention are as follows: This invention achieves priority response from the supercapacitor by coordinating the controller's dynamic power allocation strategy; a SOC boundary management mechanism between the supercapacitor and lithium-ion battery; and system rebalancing trigger conditions and execution logic, thus meeting the high-frequency regulation requirements of the power grid. The lithium-ion battery provides long-term energy support, preventing the supercapacitor from running out of energy. Dynamic SOC management reduces the frequency of high-power output from the lithium-ion battery. Real-time power allocation adjustment based on system status improves overall frequency regulation performance. It also possesses fault isolation and redundant control capabilities, ensuring the continuity of frequency regulation tasks. Attached Figure Description

[0015] Figure 1 is an electrical system diagram of the present invention. Detailed Implementation

[0016] This invention system calculates frequency regulation response efficiency indicators in real time, including response time, power deviation, and energy utilization rate, and dynamically optimizes power allocation strategies. Due to variations in regional regulations and electricity spot market policies, these indicators may differ slightly from region to region. Examples are as follows: 1. Response Time: Defined as the time required from receiving the AGC command to achieving 90% of the target output power. The target value is ≤1 second, and ≤0.5 seconds for supercapacitor systems with priority response. 2. Power Deviation: Defined as the difference between the actual output power and the power specified in the AGC command. 3. Energy utilization rate: defined as the ratio of effective output energy to total energy released by the energy storage system during frequency regulation, with a target value of ≥85%; 4. SOC fluctuation range: supercapacitor SOC is controlled within 5%-95%, and lithium-ion battery SOC is controlled within 10%-90%. Exceeding the range will trigger a rebalancing mechanism; 5. Cycle life protection index: the duration of high-rate (≥1C) output of lithium-ion batteries shall not exceed 15 minutes, and the cumulative proportion of high-frequency (≥0.5Hz) frequency regulation tasks shall not exceed 30%, in order to extend battery life.

[0017] If a fault or abnormality is detected in a certain energy storage system, the coordinating controller will automatically isolate it, and another system will take over all frequency regulation tasks and issue an alarm signal.

[0018] Referring to Figure 1, the working process of this invention will be described in detail below with reference to a typical 24-hour frequency regulation cycle. This embodiment is deployed on the low-voltage side of the 6kV energy storage busbar A and B sections of the 6kV high-voltage transformer 1A, 1B and 2A, 2B of a 2×330 MW coal-fired power plant. The supercapacitor has a rated capacity of 5 MW×10min, and the lithium-ion battery has a rated capacity of 15 MW / 30MWh (0.5 C). Each battery is connected in parallel to the 6kV busbar via its respective PCS and step-up transformer.

[0019] (1) 00:00 Initial standby AGC total command 320 MW, energy storage command 0 MW.

[0020] Supercapacitor SOCsc = 50% (center value), lithium-ion battery SOCbat = 50% (center value).

[0021] (2) 02:10 Deep down frequency modulation provincial dispatch issued 12 MW / 30 min (New Energy Dafeng).

[0022] Strategy: Supercapacitors will prioritize absorbing 5 MW (limited to 10 MW), with SOCsc increasing from 50% to 86%; the remaining 7 MW will be absorbed by lithium-ion batteries, with SOCbat increasing from 50% to 56%.

[0023] The combined power of the generating unit and energy storage system is Ptotal = 308 MW, with a deviation of ≤0.2% and a response time of 0.7 s; the recorded energy utilization rate is 98.3%.

[0024] (3) At 05:30, the supercapacitor continued to absorb as the extreme value approached the rebalancing point, and the SOCsc rose to 95.2% (>95% threshold), lasting for 2 minutes.

[0025] Energy storage EMS system (coordination controller): locks in supercapacitor charging, lithium-ion battery absorbs in reverse at 3 MW, and discharges to supercapacitor through 6kV energy storage bus, with target SOCsc=70%.

[0026] After 120 minutes, SOCsc = 70.1% and SOCbat = 59%. If the AGC direction is reversed during this period, the rebalancing is interrupted first, and the supercapacitor is immediately put into discharge.

[0027] (4) At 07:45, the high-frequency gust disturbance AGC issued 6 consecutive reverse commands within 20s (±4MW, period 3.3s).

[0028] The supercapacitor responds independently, while the lithium-ion battery is locked out, resulting in a small SOCsc oscillation between 68% and 72%; the power deviation is ≤0.1MW.

[0029] The lithium-ion battery has zero cycles to avoid aging caused by high-frequency charge and discharge currents; after the disturbance, the SOCsc is 70%, and rebalancing is not triggered.

[0030] (5) 12:00 Extreme upward frequency modulation AGC step: +25MW / 1h (midday peak).

[0031] The supercapacitor discharges at full power for 5MW, and its energy is depleted within 10 minutes, with the SOCsc decreasing from 70% to 5% (reaching the lower limit and locking out); the remaining 20MW is continuously operated by the lithium-ion battery at a 0.5C rate.

[0032] SOCbat decreased from 59% to 39%; total output was 345MW.

[0033] (6) 15:00 Low value rebalancing SOCsc=5% (<5% threshold), lasting for 3 minutes.

[0034] Starting with the rebalancing mechanism: The lithium-ion battery charges the supercapacitor at 2MW, with a target SOCsc=50%; if an upward command is issued during charging, charging is interrupted first, and the supercapacitor provides an emergency 5MW with the remaining 5%.

[0035] After 150 minutes, SOCsc = 50.2% and SOCbat = 36%; the battery is equivalent to a low-rate charge of 0.18 C, which has a negligible impact on lifespan.

[0036] ( ) 18:30 Coal Mine Trip Extreme Working Condition #1 Coal Mill Trips by Explosion, Output Loss of 160 MW, Provincial Dispatch Issues Emergency Alert of +30 MW / 30 min, Requires Energy Storage to Support at Full Power.

[0037] The supercapacitor was fully discharged at 5MW, and then locked at 5% SOCsc after 2 minutes; the lithium-ion battery discharged continuously at 15MW, with a total output of 20MW.

[0038] SOCbat decreased from 36% to 11% (approaching the 10% lower limit), and the dispatcher agreed to temporarily relax it to 10% to avoid tripping the unit; after 30 minutes, Unit #1 was restarted, and the energy storage gradually reduced its power.

[0039] (8) At 22:00, the provincial dispatch center will issue a charging instruction for off-peak electricity when the nighttime SOC is restored. 15 MW / 3 h (22:00-01:00).

[0040] The lithium-ion battery is charged at a constant power of 15MW, and the SOCbat increases from 11% to 50%; the supercapacitor is naturally charged and discharged in small increments between 45% and 55% using sporadic downward commands, without the need for additional rebalancing.

[0041] The HVAC system was maintained at 25°C, and the fire protection system underwent a self-inspection every 2 hours, with no abnormalities found.

Claims

1. A hybrid energy storage and frequency regulation system combining a supercapacitor and a lithium-ion battery, characterized in that, include: The supercapacitor energy storage system and the lithium-ion battery energy storage system are connected to the high-voltage AC bus of the energy storage system through their respective bidirectional converters (PCS) and step-up transformers. The output of the power combining device is connected to the RTU interface of the power grid dispatching system through the step-up transformer. The coordination controller communicates bidirectionally with the supercapacitor CMS, lithium-ion battery BMS, bidirectional converters (PCS), power combining device, and power grid dispatching system through the communication interface module to realize command issuance and status acquisition. The fire protection system, video surveillance system, and HVAC system are connected to the auxiliary monitoring channel of the coordination controller. The prefabricated cabin provides a physical integration platform for each subsystem, supporting modular deployment and online maintenance.

2. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The supercapacitor energy storage system consists of supercapacitor cells, supercapacitor modules, supercapacitor clusters, supercapacitor management system (CMS), fire protection system, video surveillance system, HVAC system, and prefabricated cabin. Supercapacitor cells are connected in series and parallel to form modules, which are further divided into cluster-level units. The cluster-level units are connected to the supercapacitor management system (CMS) to realize real-time monitoring and equalization control of voltage, current, temperature, and SOC.

3. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The fire protection system uses perfluorohexanone gas extinguishing devices, which are installed at the top of the cluster-level units.

4. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, A lithium-ion battery energy storage system consists of individual battery cells, battery modules, battery clusters, a battery management system (BMS), a fire protection system, a video surveillance system, a heating, ventilation, and air conditioning (HVAC) system, and a prefabricated cabin.

5. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 4, characterized in that, The battery cells use mainstream lithium iron phosphate material system with a single cell capacity of ≥280Ah. They are connected in series and parallel to form modules, and the modules form cluster-level units. The cluster-level units are connected to the three-level architecture BMS at the single cell level, module level, and system level.

6. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The coordinating controller adopts an industrial-grade real-time operating system and a hardware platform based on a dual-core ARM+FPGA architecture. It features 4 Ethernet interfaces, 8 CAN bus interfaces, 16 DI / DO interfaces, and 2 RS485 interfaces. The controller integrates an AGC command parsing module, a SOC estimation module, a power allocation algorithm module, a fault diagnosis module, and a log recording module. The AGC command parsing module supports IEC-104 and IEC-61850 protocols and has a response time of ≤100ms.

7. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 6, characterized in that, The power allocation algorithm module adopts the Model Predictive Control (MPC) strategy, with a rolling optimization cycle of 1 second. The objective function is to minimize the power deviation and SOC deviation penalty term.

8. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The power combining device includes a data acquisition module, a computing module, and a communication module. It performs vector combining of the output power of the supercapacitor and the lithium-ion battery and outputs it to the grid dispatching unit (RTU).

9. The hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The communication interface module is an independent communication unit that supports IEC-104, IEC-61850, and Modbus-TCP protocol conversion; it has a dual-machine hot backup mechanism with a master-slave switching time of ≤1 second; the communication unit has a built-in AGC command caching mechanism that supports breakpoint resume and command anti-replay function; and it is connected to the energy storage system via an Ethernet ring network.

10. A control method for a hybrid energy storage and frequency regulation system of supercapacitor and lithium-ion battery according to claim 1, characterized in that, The control method includes the following steps: In the initial state, the supercapacitor SOC is C_sc (50% ≤ C_sc ≤ 90%), the lithium-ion battery SOC is C_bat (30% ≤ C_bat ≤ 70%), and the system is in standby mode. When the grid issues a downward frequency regulation command to reduce the output power, the supercapacitor system absorbs power first. If the supercapacitor SOC reaches the upper limit, the power is switched to the lithium-ion battery. When the grid issues an upward frequency regulation command to increase the output power, the supercapacitor system outputs power first. If the supercapacitor SOC drops to the lower limit, the power is switched to the lithium-ion battery. During continuous frequency regulation, if the supercapacitor SOC continuously falls below 10% or rises above 95%, the system rebalancing mechanism is triggered, and energy is transferred through the lithium-ion battery to adjust the supercapacitor SOC to the intermediate range.

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