Isolation Resistance Estimation via Complex Impedance Analysis
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Solution Overview
Problem
Existing methods for measuring isolation resistance in electric vehicles with high voltage batteries are unreliable, complex, and costly, often requiring multiple measurement points and stable capacitance values.
Innovation Solution
A method involving a single measurement point using a measurement circuit with a known resistance and capacitance, applying a known input signal, and determining isolation resistance through complex impedance analysis, allowing for reliable measurement without assuming capacitance value knowledge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a measurement circuit with coupling capacitance is used to measure isolation resistance, then the measurement can be performed, but the measurement becomes unreliable because capacitance values vary with temperature, voltage, and age
Solution Approach 1:
The patent changes the approach from assuming a fixed capacitance value to measuring the actual capacitance value dynamically. By using the relationship between input voltage, output voltage, and the measured capacitance value in the differential equation, the system adapts to the actual capacitance conditions rather than relying on assumed stable values, thereby resolving the contradiction between measurement reliability and capacitance stability.
2Reliability
If multiple measurement points are used in the measurement circuit, then the measurement can be performed, but the measurement becomes complex
Solution Approach 1:
The patent extracts the essential measurement function to a single measurement point. By using the voltage divider relationship and measuring only the output voltage at one point, the system eliminates the need for multiple measurement points while maintaining measurement capability. The complex interactions are resolved through mathematical modeling rather than physical complexity.
3Reliability
If a stable capacitance is used to ensure reliable measurement, then measurement reliability improves, but the cost increases
Solution Approach 1:
The patent accepts that ordinary capacitance values vary with time and conditions, rather than requiring expensive stable capacitance components. By measuring the actual capacitance value dynamically and using it in the differential equation calculation, the system achieves reliable measurements using inexpensive ordinary capacitance components, resolving the contradiction between reliability and manufacturing cost.
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 simple and reliable measurement of isolation resistance using ordinary capacitance, reducing complexity and cost while maintaining measurement accuracy.
Implementation Method 1
determination of a complex impedance of a dipole composed of the capacitance and of the isolation resistance
Implementation Method 2
said measurement circuit comprising a resistance of known value and a capacitance
Implementation Method 3
measurement of an output voltage between ground and a point situated between the resistance of known value and the capacitance
Data Source
AI summary
A method for estimating insulation resistance between a terminal of a battery and an electrical ground, including: connecting a measuring circuit to one terminal of the battery, the measuring circuit including a resistance of known value and a capacitance; application of a known input signal having an input voltage; measurement of an output voltage between the ground and a point located between the resistance of known value and the capacitance; determination of a complex impedance of a dipole of the capacitance and the insulation resistance or determination of parameters of a differential equation; and determination of the insulation resistance from the parameters of the differential equation or the complex impedance.