Insulation Measurement Apparatus DC Bias Compensation
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Solution Overview
Problem
Existing insulation measurement circuits using ceramic capacitors face challenges in achieving high detection accuracy due to the influence of DC bias characteristics, which complicates the measurement of insulation resistance, especially when the insulation state approaches a threshold value, leading to potential false alarms and increased costs.
Innovation Solution
The proposed insulation measurement apparatus employs a configuration where the charge resistance values during power supply voltage measurement and insulation voltage measurement are set to be the sum of the first and second resistors, ensuring that the voltage applied and the charge time periods are consistent across both modes, effectively canceling out the influence of DC bias characteristics by setting each resistor value equal to the insulation resistance threshold value, thereby improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ceramic capacitor is used as a flying capacitor in an insulation measurement circuit, then the circuit can be miniaturized and cost reduced, but the detection accuracy deteriorates due to DC bias characteristics
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement before the actual insulation resistance measurement. The calibration step measures the voltage across the ceramic capacitor when charged through a known resistance, establishing a reference value that accounts for DC bias characteristics. This preliminary measurement enables subsequent compensation for the capacitor's non-ideal behavior, thereby maintaining detection accuracy while using cost-effective ceramic capacitors.
Solution Approach 2:
The patent changes the measurement parameters by conducting measurements at two different time points: immediately after charging (to capture DC bias effects) and after a delay period (when DC bias effects have stabilized or diminished). By comparing these parameter changes over time, the system can isolate and compensate for DC bias characteristics, maintaining measurement accuracy with ceramic capacitors.
2Reliability
If the charge time period is extended to allow full charging of the capacitor, then the measurement completeness improves, but the measurement time increases
Solution Approach 1:
The patent applies partial action by charging the capacitor for a predetermined time period that is sufficient to reach the steady state influenced by DC bias characteristics, but not necessarily to complete full charging. This partial charging approach captures the essential measurement information needed for accurate insulation resistance calculation while avoiding the time penalty of waiting for complete charging, thus balancing reliability and measurement time.
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 enhances the detection accuracy of insulation resistance, preventing false alarms and reducing the overall cost by minimizing the impact of DC bias characteristics on ceramic capacitors, ensuring reliable insulation state monitoring.
Implementation Method 1
a capacitor (flying capacitor) C11 in an electrically floated state from the ground voltage G
Implementation Method 2
first to sixth resistors R11 to R16
Data Source
AI summary
An insulation measurement apparatus includes a path including a first resistor, a capacitor electrically floated from a ground, and a second resistor between a positive to a negative electrode side of a power supply, a first switching element between the power supply positive electrode side and the capacitor, a second switching element between the capacitor and the power supply negative electrode side, a detection section detecting a charge voltage on the capacitor and determining a power supply insulation state, and a voltage setting section executing a power supply voltage measurement mode controlling the first and second switching elements to charge the capacitor for a predetermined time period, and an insulation voltage measurement mode charging a terminal of a positive or negative electrode side of the capacitor via a resistor between the power supply positive or negative electrode and the ground for a predetermined time period.