Battery State-of-Charge Estimation via Scheduled Disconnection
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Solution Overview
Problem
Repetitive charging and discharging of batteries in electrical energy storage systems leads to degradation, making it difficult to accurately measure and predict changes in battery state-of-charge and operating parameters, which affects their ability to participate in frequency regulation programs.
Innovation Solution
An electrical energy storage system that includes a battery, a switch, and a controller to disconnect the battery from an external system, measure open circuit voltage, and estimate state-of-charge based on predicted usage, uncertainty thresholds, and regulation signals to optimize battery operation and minimize disruption to frequency response operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the battery is continuously connected to the external system for frequency regulation, then the battery can participate in frequency regulation programs and provide energy storage services, but the battery undergoes repetitive charging and discharging which causes degradation and reduces battery life
Solution Approach 1:
The system performs preliminary disconnection of the battery from the external system at scheduled times to enable open circuit voltage measurements before the battery is fully degraded. This preliminary action allows for state-of-charge estimation and uncertainty assessment, which informs subsequent operational decisions to optimize between frequency regulation participation and battery life preservation.
2Measurement precision
If the battery is disconnected from the external system to measure open circuit voltage, then accurate state-of-charge estimation can be obtained, but the battery operation is interrupted and frequency regulation capability is reduced
Solution Approach 1:
The system dynamically adjusts the disconnection schedule based on predicted future usage patterns and current state-of-charge uncertainty levels. When uncertainty is high, disconnection for measurement is prioritized; when uncertainty is low and usage is predicted to be minimal, disconnection is scheduled to minimize impact on frequency regulation capability. This dynamic optimization resolves the contradiction between measurement accuracy and productivity.
Solution Approach 2:
The system uses feedback from state-of-charge estimates and uncertainty assessments to determine optimal disconnection times. The controller continuously monitors battery parameters, predicts future usage, and adjusts the disconnection schedule accordingly, ensuring that measurements are taken when they provide maximum value while minimizing disruption to frequency regulation operations.
3Quantity of substance
If the battery operates at high capacity to maximize energy storage, then the battery can provide more energy for frequency regulation, but the charging and discharging cycles accelerate battery degradation
Solution Approach 1:
The system changes operational parameters by adjusting the state-of-charge range and disconnection timing based on battery health status and predicted usage. Instead of continuously operating at maximum capacity, the system dynamically modifies operating parameters to balance energy storage provision with degradation mitigation, using open circuit voltage measurements to inform these parameter changes.
Data Source
AI summary
An electrical energy storage system includes a battery configured to store electrical energy and discharge the stored electrical energy to an external system, a switch electrically connected to the battery and operable to connect the battery to the external system and disconnect the battery from the external system, a sensor configured to measure an open circuit voltage of the battery while the battery is disconnected from the external system, and a controller. The controller is configured to predict usage of the battery at a plurality of future times, schedule a time to disconnect the battery from the external system based on the predicted usage of the battery at the plurality of future times, operate the switch to disconnect the battery at the scheduled time, and obtain a measurement of the open circuit voltage of the battery while the battery is disconnected.