On-Board Charger Protection Circuit for Leakage Current Discrimination
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Solution Overview
Problem
On-board electric vehicle battery chargers face safety issues due to leakage currents generated by electronic components, which can deceive differential switches and prevent them from activating in case of insulation loss between the charger and the vehicle chassis, relying solely on software-level safety is insufficient.
Innovation Solution
A method and circuit that detect phase and neutral voltages, generate homopolar voltage and current signals, and use square waves to determine phase alignment, generating an alarm signal when a limit voltage is exceeded, providing a hardware-based protection system to differentiate between capacitive and resistive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a compensation circuit is inserted to compensate for leakage currents, then the charging device can operate without circuit breaker intervention, but the device may deceive differential switches and prevent them from operating in case of insulation loss
Solution Approach 1:
The patent introduces an intermediary detection system that monitors the compensation current to distinguish between capacitive leakage current (safe) and resistive leakage current (dangerous). This intermediary mechanism acts as a mediator between the compensation circuit and the differential switch, allowing the system to maintain charging operation while preventing false deception of safety protection devices.
Solution Approach 2:
The patent replaces the purely software-level safety discrimination with a hardware-based detection circuit that uses electrical signal processing to differentiate between safe and dangerous currents. This substitution of mechanical/electrical detection for software control enhances the reliability of the safety protection system.
2Measurement precision
If software systems are used to discriminate between capacitive and resistive currents, then the system can differentiate between safe and dangerous currents, but the safety system becomes insufficient for critical safety points
Solution Approach 1:
The patent replaces software-based current discrimination with a hardware detection circuit that uses electrical signal processing. The detection circuit processes voltage and current signals through squaring and combining operations to generate detection signals that directly indicate the type of current present, providing a more reliable safety mechanism for critical safety points.
Solution Approach 2:
The patent introduces a hardware detection circuit as an intermediary between the compensation circuit and the safety control system. This intermediary hardware layer provides an additional level of safety verification that complements the software discrimination, ensuring that both capacitive and resistive currents are accurately identified and appropriately handled.
3Reliability
If a hardware-based protection circuit is implemented, then the safety reliability is enhanced, but the device complexity increases
Solution Approach 1:
The patent segments the protection system into distinct functional modules: a detection circuit for monitoring compensation current, a processing unit for signal squaring and combining operations, and a control unit for generating alarm signals. This segmentation allows each module to perform its specific function independently, making the overall complex system more manageable and maintainable.
Solution Approach 2:
The patent designs the detection circuit to perform multiple functions: monitoring compensation current, discriminating between capacitive and resistive currents, and generating appropriate alarm signals. This multi-functionality reduces the need for separate dedicated circuits for each safety function, thereby limiting the increase in device complexity while maintaining enhanced safety reliability.
Data Source
AI summary
A method for protecting an on-board charging device includes the steps of detecting the phase and neutral voltages coming from the grid, detecting a current signal representing a compensation current generated by a compensation circuit, combining the phase voltages together so as to obtain a homopolar voltage signal, squaring the current signal and the homopolar voltage signal so as to obtain a first square current wave and a second square voltage wave, combining the first and second square waves together so as to generate an output signal having a first logic level when the first and second square waves are in phase and a second logic level when the first and second square waves are out of phase, generating a voltage increasing in proportion to the duration of each section of the output signal having the first value, comparing the voltage value with a limit value and generating an alarm signal when the voltage level exceeds the limit value.