Capacitive Insulation Resistance Measurement for High-Voltage Battery Systems
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Solution Overview
Problem
Existing methods for measuring insulation resistance in high-voltage systems suffer from electrical isolation issues and wear on relays, as they require resistive connections that can alter the insulation resistance and are prone to wear.
Innovation Solution
A method using a series circuit of a decoupling capacitor and a measuring capacitor to form a low-pass filter, allowing for electrical isolation and measurement of insulation resistance without direct resistive connection, utilizing an AC voltage source and evaluation unit to determine the insulation resistance based on capacitance and voltage measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistive measurements are used to determine insulation resistance, then the measurement can be performed, but the insulation resistance is negatively influenced and electrical connection to ground is established
Solution Approach 1:
The patent replaces the mechanical/electrical resistive measurement system with a capacitive measurement system. Instead of using resistors to measure insulation resistance, the invention uses capacitors (coupling capacitor and measuring capacitor) to perform the measurement through capacitive coupling, thereby avoiding direct electrical connection to ground and maintaining electrical isolation.
Solution Approach 2:
The patent introduces a coupling capacitor as an intermediary element between the high-voltage system and the measurement circuit. This coupling capacitor allows the measurement signal to pass through while blocking direct electrical connection to ground, thus maintaining electrical isolation while enabling measurement.
2Measurement precision
If relays are used for insulation resistance measurements, then the measurement can be performed, but the relays are subject to wear
Solution Approach 1:
The patent replaces mechanical relays with solid-state electronic components (capacitors and electronic switches). The measurement is performed using capacitive coupling and electronic signal processing, eliminating the need for mechanical relay contacts and thus eliminating wear-related failures.
3Device complexity
If direct resistive connection is used for measurement, then the measurement circuit is simple, but electrical isolation is compromised
Solution Approach 1:
The coupling capacitor serves as an intermediary that maintains electrical isolation while enabling measurement. It allows AC measurement signals to pass through capacitive coupling without creating a direct DC electrical connection to ground, thus preserving both isolation and measurement capability.
Solution Approach 2:
The patent changes the measurement parameter from resistive (DC) to capacitive (AC). By using AC signals and capacitive coupling, the system achieves electrical isolation while maintaining measurement functionality, as capacitors block DC but pass AC signals.
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
This approach ensures electrical isolation of HV+ and HV− from ground, reduces wear, and accurately determines insulation resistance using known quantities and a microcontroller-based evaluation unit.
Implementation Method 1
a decoupling capacitor (4) having a first capacitance and a measuring capacitor (5) having a second capacitance are connected to the test object (3) to form a series circuit in such a way that the decoupling capacitor (4) and the measuring capacitor (5), together with the insulation resistance (2) of the test object (3), form a low-pass filter
Implementation Method 2
the decoupling capacitor (4) and the measuring capacitor (5), together with the insulation resistance (2) of the test object (3), form a low-pass filter
Implementation Method 3
an alternating current ('AC') voltage source (10) which supplies an AC voltage at a predetermined frequency as the predetermined voltage is additionally connected in series with the measuring capacitor (5) and the decoupling capacitor (4), wherein the insulation resistance of the test object is determined by means of the evaluation unit (7), taking additional account of the AC voltage and the frequency of the AC voltage
Data Source
AI summary
The invention relates to a method for ascertaining an insulation resistance (2) of a test object (3) to be examined, wherein a decoupling capacitor (4) having a first capacity, and a measuring capacitor (5) having a second capacity are connected in series with the test object (3) in such a way that the decoupling capacitor (4) and the measuring capacitor (5) form a low-pass with the insulation resistance (2) of the test object (3), wherein a predetermined voltage (9) is applied to the series connection, the measuring capacitor voltage (8) declining on the measuring capacitor (5) is ascertained, and, by means of an evaluation unit (7), considering the first capacity, the second capacity and the ascertained measuring capacitor voltage (8), the insulation resistance (2) of the test object (3) is determined. The invention also relates to a device (1) for ascertaining an insulation resistance (2) of a test object (3) to be examined, said device (1) having a circuit assembly, a measuring unit (6) and an evaluation unit (7). The invention further relates to a high-voltage battery system having a device (1) according to the invention for ascertaining an insulation resistance (2).