Battery Pack Connection Control Using SOC and OCV Estimation
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Solution Overview
Problem
Connecting multiple battery packs in a vehicle's energy storage system can lead to circulating currents and current spikes due to imbalances in terminal voltage, which reduces power capacity and poses safety risks.
Innovation Solution
A method for controlling electrical connection of battery packs based on estimating battery states such as state of charge (SOC) and open circuit voltage (OCV) to predict and prevent imbalances, using a multi-battery prediction model to determine safe connection conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple battery packs are connected in parallel to increase power capacity, then the available power for propulsion is improved, but circulation currents and current spikes occur due to terminal voltage imbalances
Solution Approach 1:
The system performs preliminary estimation of battery states (SOC and OCV) for each battery pack before attempting connection. The control unit evaluates whether connection conditions are met by comparing estimated states between battery packs, and only permits connection when the imbalance is within acceptable thresholds, thereby preventing circulation currents before they occur.
2Ease of operation
If terminal voltage measurement is used to determine connection suitability, then the control method is simple, but the measurement is unreliable during driving when battery packs are under load
Solution Approach 1:
The system introduces an intermediary estimation process that uses terminal voltage measurements combined with current and resistance information to calculate estimated open circuit voltages (EOCV) and estimated states of charge (ESOC). This intermediary step transforms the unreliable terminal voltage measurement into a more reliable indicator of actual battery state, enabling accurate connection determination while maintaining control simplicity.
3Speed
If battery packs are connected without state estimation, then the connection process is fast, but unsuccessful connection attempts reduce available power and harm battery lifetime
Solution Approach 1:
The control unit performs rapid estimation of battery states using available measurement data before initiating connection. By evaluating estimated SOC and OCV differences in advance, the system determines connection suitability quickly, permitting immediate connection when conditions are favorable and preventing unsuccessful attempts that would reduce power availability and harm battery lifetime.
Data Source
AI summary
A method for controlling electrical connection of at least two battery packs (202, 203) of an energy storage system (200) of a vehicle (201) to a common load during operation of the vehicle, each one of the battery packs being connectable to the load via at least one respective switching device, the method comprising:receiving measurement data relating to current operating conditions of the energy storage system,based on at least the measurement data, estimating at least one battery state of each one of the battery packs, wherein said at least one battery state is at least one of an open circuit voltage and a state of charge,based on the estimated at least one battery state of each one of the battery packs, controlling electrical connection of each battery pack to the load via the at least one respective switching device.