Insulation Resistance Circuit for Battery Ground Fault Detection
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Solution Overview
Problem
Existing ground fault detection circuits in battery management systems for hybrid vehicles cannot accurately measure isolation breakdowns when both the positive and negative terminals of the battery are insulated, as they rely on forming a current path that is affected by battery voltage changes and assumes infinite resistance values, leading to incomplete measurement of insulation breakdowns.
Innovation Solution
A circuit that directly connects a specific power supply to either the positive or negative terminal of the battery through switches and uses operational amplifiers to sense voltage across insulation resistors between the terminals and ground, allowing for periodic switching to determine isolation breakdowns without forming a current path among the terminals, ground, and positive terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ground fault detection circuit forms a current path connecting positive terminal, ground, and negative terminal to measure insulation resistance, then the circuit can detect isolation breakdown, but the measurement accuracy deteriorates when both positive and negative terminal insulations are broken because the circuit assumes infinite resistance values
Solution Approach 1:
The patent divides the insulation resistance measurement into two separate measurements: one for the positive terminal insulation resistance (RISO+) and another for the negative terminal insulation resistance (RISO-). Instead of using a single current path that assumes infinite resistance at one terminal, the invention creates separate measurement paths for each terminal, allowing independent and accurate measurement of each insulation resistance value even when both are broken.
Solution Approach 2:
The patent inverts the traditional measurement approach by measuring each terminal's insulation resistance independently rather than measuring through a path that connects both terminals. By switching the measurement configuration to measure RISO+ and RISO- separately, the circuit eliminates the assumption of infinite resistance and can accurately detect breakdowns in either terminal.
2Adaptability or versatility
If the ground fault detection circuit uses battery voltage to alternately open and close switches for measurement, then the circuit can operate with existing power supply, but the voltage applied to operational amplifier changes with battery voltage causing measurement inconsistency
Solution Approach 1:
The patent changes the voltage parameter from variable battery voltage to a fixed reference voltage (Vref). By using a stable reference voltage source instead of the fluctuating battery voltage, the operational amplifier receives consistent voltage input regardless of battery charge state, ensuring measurement consistency while still operating with the existing power supply infrastructure.
3Device complexity
If the circuit assumes one insulation resistor has infinite resistance value during measurement, then the measurement process is simplified, but the circuit cannot normally measure isolation breakdown when both positive and negative terminal insulations are broken
Solution Approach 1:
The patent makes the measurement configuration dynamic by using switches to alternately connect different measurement paths. The circuit dynamically switches between measuring RISO+ and RISO- with appropriate reference voltages, eliminating the need for static assumptions of infinite resistance. This dynamic switching enables the circuit to adapt to different fault conditions and detect breakdowns in either or both terminals reliably.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate measurement of insulation breakdowns for both positive and negative terminals without additional circuit costs, regardless of battery charge state, and determines isolation breakdowns in real-time, improving the reliability of battery management systems.
Implementation Method 1
The first operational amplifier may sense voltage applied to an insulation resistor that is connected between the positive terminal and the ground and output the sensed voltage through an output terminal thereof. The second operational amplifier may sense voltage applied to an insulation resistor that is connected between the negative terminal and the ground and output the sensed voltage through an output terminal thereof.
Data Source
AI summary
Provided is a circuit for measuring insulation resistance, including: a first operational amplifier that is connected with a positive terminal of a battery and a second operational amplifier; a second operational amplifier that is connected with a negative terminal of the battery and the first operational amplifier; a first switch that is connected between the positive terminal and a non-inverting terminal of the first operational amplifier; and a second switch that is connected between the negative terminal and an inverting terminal of the second operational amplifier, wherein the first operational amplifier and the second operational amplifier are connected with each other through a ground.