PWM Inverter Current Sampling for Early Insulation Fault Detection
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Solution Overview
Problem
Existing technologies for detecting insulation failure in rotational machines and transformers are costly due to the need for high-speed sampling of ringing waveforms.
Innovation Solution
An electric power conversion device with an inverter circuit, PWM signal generation, and a diagnostic unit that samples current at the peak or valley of a carrier signal, extracts relevant data, calculates an index value, and detects insulation deterioration using changes in capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-speed sampling is performed to directly measure ringing waveform for insulation diagnosis, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts only the necessary diagnostic information (ringing characteristics) from the current waveform by sampling at specific timing (peak/valley of carrier signal) rather than requiring complete high-speed waveform capture. This extraction approach obtains sufficient insulation diagnosis data while avoiding the need for expensive high-speed sampling equipment.
Solution Approach 2:
The invention changes the sampling parameter from continuous high-speed sampling to discrete sampling at specific carrier signal phases (peak/valley). By sampling current at these specific timing points and using the extracted values to calculate insulation index values, the system achieves diagnostic precision without requiring high-speed sampling hardware.
2Reliability
If high-speed sampling is performed to detect ringing waveform, then insulation deterioration detection capability is improved, but manufacturing cost increases
Solution Approach 1:
The invention replaces expensive high-speed sampling equipment with standard low-cost current sensors and microcontroller processing. By using existing inexpensive components to sample current at carrier signal peak/valley timing and extract diagnostic information, the system achieves reliable insulation detection at low manufacturing cost.
Solution Approach 2:
The invention substitutes hardware-based high-speed sampling systems with a software/control-based approach using standard sensors and digital signal processing. The microcontroller samples current at specific PWM carrier phases and calculates insulation indices through processing, replacing the need for specialized high-speed measurement hardware.
3Measurement precision
If current is sampled at high speed to capture ringing waveform, then diagnostic accuracy is improved, but ease of operation deteriorates due to complex setup
Solution Approach 1:
The system performs self-diagnosis by automatically sampling current at the peak/valley of the PWM carrier signal that is already present during normal motor operation. The control unit automatically identifies carrier phases and extracts current values at these timing points without requiring external test equipment or complex setup procedures, making the diagnostic function easy to operate.
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 early and cost-effective detection of insulation failure in rotational machines and transformers, reducing the need for expensive high-speed sampling equipment.
Implementation Method 1
a current sensor that detects a current fed to and received from the rotational machine or the transformer
Implementation Method 2
a PWM signal generation unit that compares a carrier signal with a voltage command value and generates a PWM signal for driving the inverter circuit
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
Provided is an electric power conversion device having a function of detecting, at low cost and at an early stage, a sign of insulation failure of a transformer or a rotational machine. This electric power conversion device is provided with an inverter circuit and a PWM signal generation unit that makes a comparison between a carrier signal and a voltage command value and generates a PWM signal for driving the inverter circuit. The electric power conversion device feeds and receives electric power through connection to a transformer or a rotational machine provided with a winding wire. The electric power conversion device is provided with: a current sensor that detects a current to be fed to or received from the transformer or the rotational machine; and a diagnostic unit that diagnoses insulation degradation of the transformer or the rotational machine. The diagnostic unit is provided with: a current sampling unit that acquires a current detection value by detecting a current of the current sensor at a timing of a peak or a timing of a valley of the carrier signal or both timings; an extraction unit that, when the detection timing of the current is in a fixed period of time from a timing at which the voltage command value and the carrier signal intersect with each other, extracts the current detection value at the corresponding detection timing as a value for insulation diagnosis; an index value calculation unit that calculates, from the extracted current detection value, an index value for use in the diagnosis; and an insulation degradation detection unit that, on the basis of a change of the calculated index value from a normal state thereof, detects the insulation degradation of the winding wire of the transformer or of the rotational machine.