Vehicle Insulation Fault Detection Circuit Using Dual Coupling Capacitors
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Solution Overview
Problem
Aluminum electrolytic capacitors used in electrical fault detection devices for electric vehicles experience increased leakage current when in a no-load state for a long time, affecting insulation resistance measurement accuracy.
Innovation Solution
The device employs two coupling capacitors, each connected between different potential points on the power storage's current path, with an AC output unit applying a voltage via an impedance element to a connection point between them, allowing continuous voltage application and reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aluminum electrolytic capacitor is used as the coupling capacitor to increase capacity at low cost, then the cost is reduced and capacity is increased, but the leakage current increases when in a no-load state for a long period of time
Solution Approach 1:
The patent applies periodic AC voltage to the coupling capacitor through the impedance element during detection periods, preventing the capacitor from remaining in a no-load state for extended periods. This periodic excitation maintains the capacitor's insulation characteristics and prevents leakage current increase, resolving the contradiction between using cost-effective aluminum electrolytic capacitors and maintaining measurement accuracy.
2Device complexity
If a single coupling capacitor is used in the detection circuit, then the circuit is simple, but the leakage current increases when in a no-load state
Solution Approach 1:
The patent divides the single coupling capacitor into two series-connected coupling capacitors. This segmentation allows AC voltage to be applied across both capacitors through the impedance element, preventing either capacitor from remaining in a no-load state. The segmented configuration maintains measurement accuracy while keeping the circuit structure relatively simple.
3Object-generated harmful factors
If AC voltage is applied frequently to prevent leakage current increase, then the leakage current is suppressed, but the detection time increases
Solution Approach 1:
The patent applies AC voltage only during the necessary detection periods rather than continuously, using partial action to prevent leakage current increase. The AC voltage is applied through the impedance element when detection is required, suppressing leakage current while minimizing the time loss associated with frequent voltage application.
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 configuration suppresses the increase in leakage current, maintaining accurate insulation resistance measurements and enhancing safety while maintaining low costs by avoiding the need for expensive high-insulation switches.
Implementation Method 1
an AC output unit configured to apply a predetermined AC voltage via an impedance element to a third connection point between the second terminal of the first coupling capacitor and the first terminal of the second coupling capacitor
Implementation Method 2
a first coupling capacitor including one cell or a plurality of cells connected in series, and having a first terminal connected to a first connection point on a current path of a power storage
Implementation Method 3
a voltage measurement unit configured to measure a voltage at the third connection point
Data Source
AI summary
In first coupling capacitor, a first terminal is connected to a first connection point on a current path of power storage in a state of being insulated from a ground. Second coupling capacitor has a second terminal connected to a second connection point that is on a current path of power storage and is lower in potential than the first connection point, and second coupling capacitor has a first terminal connected to a second terminal of first coupling capacitor. AC output unit applies a predetermined AC voltage via impedance element to third connection point between the second terminal of first coupling capacitor and the first terminal of second coupling capacitor. Voltage measurement unit measures a voltage at third connection point. Determination unit determines the presence or absence of an electrical fault on the basis of the voltage measured by voltage measurement unit.