Decoupled Battery Cluster SOC Calibration During Grid Frequency Response
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Solution Overview
Problem
The existing battery management systems (BMS) face challenges in accurately estimating the state of charge (SOC) of energy storage systems due to precision issues with current sensors, sampling deviations, and infrequent calibration, leading to low SOC accuracy, especially in frequency modulation scenarios where full charge or discharge conditions are rare.
Innovation Solution
A method for online SOC calibration is implemented by controlling individual battery clusters within the energy storage system to satisfy SOC calibration conditions, allowing for independent decoupling management without affecting normal system operation, using a controller to determine when a battery cluster needs calibration based on its SOC and the system's charging or discharging state, and adjusting its charging, discharging, or standby state accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the energy storage system performs charge or discharge actions based on AGC scheduling instructions in frequency modulation scenarios, then the system responds to grid frequency regulation demands, but full charge or discharge conditions are rarely met, causing SOC calibration to fail and SOC accuracy to decrease over time
Solution Approach 1:
The system segments the battery clusters into multiple independent groups, each with its own DC/DC converter. This allows individual clusters to be calibrated independently without affecting the entire system's frequency modulation response capability
Solution Approach 2:
The controller proactively identifies battery clusters that need SOC calibration based on running time and SOC deviation thresholds, and schedules their calibration before SOC accuracy degrades significantly, ensuring continuous accurate operation during frequency modulation
2Measurement precision
If SOC calibration is performed by fully charging or discharging the energy storage system, then SOC accuracy is improved, but normal system operation is disrupted and calibration frequency is reduced
Solution Approach 1:
The system divides battery clusters into multiple independent groups, allowing calibration of individual clusters without stopping the entire system. Other clusters continue to provide frequency modulation services while one cluster undergoes calibration
Solution Approach 2:
Instead of requiring full system charge/discharge for calibration, the system performs partial calibration on selected clusters by controlling them to charge or discharge independently until their SOC reaches extreme values, achieving calibration without full system shutdown
3Ease of operation
If individual battery clusters are controlled independently with one-to-one DC/DC converter correspondence, then SOC calibration can be performed on single clusters without affecting system operation, but device complexity increases
Solution Approach 1:
Each DC/DC converter is designed to handle multiple functions: normal power conversion during frequency modulation and SOC calibration during calibration mode. This multi-functionality reduces the need for separate dedicated calibration hardware
Solution Approach 2:
The system dynamically switches between normal operation mode and calibration mode for different battery clusters. The DC/DC converters adapt their operating state based on whether their associated cluster needs calibration, optimizing resource utilization despite the one-to-one configuration
Data Source
AI summary
A method for controlling an energy storage system includes: determining that a first battery cluster in a plurality of battery clusters needs to be calibrated; and controlling, based on a state of charge SOC of the first battery cluster and a current charging or discharging state of the energy storage system, the first battery cluster to be charged or discharged or to be in a standby state, so that the first battery cluster satisfies a SOC calibration condition. In the method, charging, discharging, or standby-state control needs to be performed on only one battery cluster that needs to be calibrated in the energy storage system, independent decoupling management is implemented on the battery cluster, and normal running of the energy storage system is not affected. This enables the battery cluster to quickly satisfy the SOC calibration condition and can improve SOC accuracy of the energy storage system.