Auxiliary Battery SOC Estimation Using Open-Circuit Voltage
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Solution Overview
Problem
Existing state of charge estimation methods for vehicle-mounted batteries face challenges in accuracy due to electricity consumption during measurement and current sensor errors, especially when the vehicle is started after a period of parking.
Innovation Solution
A state of charge estimation device that utilizes a correlation characteristic between battery open circuit voltage and state of charge, updating a 'dark current' based on elapsed time and open circuit voltage regions to improve estimation accuracy without consuming battery electricity or introducing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charging/discharging currents are measured using a current sensor to estimate state of charge, then the state of charge can be continuously monitored, but measurement errors occur due to electricity consumption by the measurement unit and current sensor errors
Solution Approach 1:
The patent uses open circuit voltage as an intermediary parameter to indirectly determine state of charge, avoiding direct current measurement. By measuring open circuit voltage after the vehicle is parked and using the correlation characteristic between open circuit voltage and state of charge, the system obtains state of charge information without the measurement errors associated with current sensors and electricity consumption during measurement.
Solution Approach 2:
The patent replaces the electrical measurement system (current sensor) with a voltage measurement system. Instead of measuring current to determine state of charge, the system measures open circuit voltage and uses the pre-established correlation between voltage and state of charge, thereby eliminating the harmful effects of current measurement errors and power consumption.
2Duration of action of stationary object
If the vehicle is started after a period of parking, then the battery has time to stabilize, but the accuracy of state of charge estimation decreases due to accumulated measurement errors
Solution Approach 1:
The patent performs preliminary measurement of open circuit voltage during the parking period when the battery is stable and no current is flowing. This preliminary action captures accurate state of charge information before the vehicle is started, avoiding the accumulation of measurement errors that would occur during vehicle operation. The measured open circuit voltage and corresponding state of charge are stored for later use when the vehicle is started.
Data Source
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AI summary
A state of charge estimation device includes a memory section, a measurement section, a time measurement section, and an estimation section. The memory section memorizes a specified dark current, which is a current that flows at an auxiliary battery while the vehicle is parked, and a first state of charge at a most recent time the vehicle was parked before the vehicle is started. The measurement section measures an open circuit voltage. The time measurement section measures an elapsed time from the time the vehicle was parked to a time the vehicle is started. If the open circuit voltage has a value in a second region, the estimation section updates the specified dark current memorized in the memory section such that a second state of charge approaches a third state of charge. If the open circuit voltage when the vehicle is started on a subsequent occasion is in a first region, the estimation section estimates a state of charge of the auxiliary battery on the basis of the first state of charge, the specified dark current, and an elapsed time.