PWM Pre-Charge Circuit for Overcurrent Fault Detection
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Solution Overview
Problem
Existing pre-charge circuits in electric vehicles struggle to reliably detect overcurrent fault conditions during fast PWM-based precharge functions, especially in high-voltage systems with large capacitive loads, which can lead to component stress or damage.
Innovation Solution
An adaptive pre-charge control circuit that uses a pulse-width modulated signal to generate a current profile, monitoring the current profile to detect overcurrent faults by identifying consecutive pulses exceeding a predefined limit, and includes overvoltage protection and current limiting features, utilizing a high-voltage switch and a control circuit with a microprocessor and current sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM control is used for fast pre-charge function, then pre-charge speed is improved, but ability to detect overcurrent faults deteriorates
Solution Approach 1:
The patent applies periodic action by using PWM control to generate periodic current pulses during pre-charge. The control circuit monitors these periodic pulses and detects overcurrent faults by analyzing patterns in consecutive pulses, specifically identifying when two consecutive pulses exceed the predefined limit. This allows fast pre-charge while maintaining reliable fault detection through periodic monitoring.
Solution Approach 2:
The patent implements feedback by having the control circuit continuously monitor the current profile during PWM-based pre-charge and use this information to detect overcurrent faults. The system feeds back the current measurement information to the control logic, which then determines whether to continue or interrupt the pre-charge operation based on detected fault conditions.
2Reliability
If pre-charge circuit limits inrush current, then component damage is prevented, but charging time increases
Solution Approach 1:
The patent applies dynamics by transitioning the pre-charge circuit from a static resistance-based current limit to a dynamic PWM-controlled switch. The high-voltage switch alternates between on and off states, dynamically controlling current flow to charge the DC link capacitor. This dynamic approach reduces charging time compared to static resistance limiting while still preventing component damage through controlled current profiles.
Solution Approach 2:
The patent uses periodic action through PWM switching to achieve both fast charging and component protection. The periodic on/off switching creates a controlled average current that charges the capacitor quickly without exceeding damage thresholds. The periodic nature allows the system to deliver higher peak currents than static resistance would permit, reducing charging time while maintaining safety.
Data Source
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AI summary
Disclosed is an adaptive pre-charge control circuit, for use in a solid state battery disconnect and protection system, wherein the adaptive pre-charge control circuit includes a high-voltage switch coupled between an electric battery and a DC link capacitor of an electric vehicle, and wherein the electric vehicle is powered by the electric battery. The control circuit may be operable to issue a pulse width modulated (PWM) signal to generate a current profile wherein every other pulse exceeds a predefined limit, monitor, during pre-charging, the current profile, and to determine an overcurrent fault exists in the case that two consecutive pulses exceed the predefined limit.