Power Conversion Device Short Circuit Location via Inductance
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Solution Overview
Problem
Existing power conversion devices cannot accurately determine the location of a short circuit between a cable and a motor, leading to difficulties in identifying the source of the fault, which hinders efficient maintenance and repair.
Innovation Solution
A power conversion device equipped with a low-speed current sensor and a control circuit that calculates inductance values to determine the location of an interphase short circuit on a cable by analyzing current waveforms and switch states, allowing for precise identification of the short circuit location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-speed current sensor is used to detect short circuit location with high precision, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the measurement parameter from direct current magnitude (requiring high-speed sensors) to inductance value (detectable by low-speed sensors). By measuring the inductance of the short-circuit path through voltage and current waveform analysis, the system achieves high-precision location detection without requiring expensive high-speed current sensors. The inductance value serves as an intermediate parameter that correlates with distance from the power conversion device.
Solution Approach 2:
The patent replaces the direct electrical measurement approach (using high-speed current sensors to detect current rise rate) with an equivalent electrical circuit analysis approach (calculating inductance from voltage and current waveforms). This substitution allows the use of low-speed current sensors while maintaining the ability to determine short circuit location with high precision through inductance-based distance calculation.
2Loss of information
If no short circuit location determination function is added, then device complexity is reduced, but loss of information occurs as users cannot identify the fault location
Solution Approach 1:
The control circuit is designed to perform multiple functions: normal PWM control of the power conversion device, overcurrent protection, and short circuit location determination. By integrating the short circuit detection function into the existing control circuit, the patent avoids adding separate dedicated hardware while still providing comprehensive fault location information to users, thereby reducing information loss without proportionally increasing device complexity.
Solution Approach 2:
The system uses its own existing sensors (voltage sensor and low-speed current sensor) and control circuitry to determine short circuit location, rather than requiring external diagnostic equipment. The control circuit calculates inductance values and determines fault locations using data already being collected during normal operation and fault conditions, enabling the system to self-diagnose without additional information loss.
3Productivity
If high-resolution short circuit location determination is implemented, then productivity is improved through faster fault identification, but device complexity increases
Solution Approach 1:
The patent changes the measurement approach from direct high-speed current sampling to inductance calculation based on voltage and current waveforms. This parameter change enables high-resolution location determination (distance calculation from inductance value) using standard low-speed sensors and conventional control circuitry, thereby improving productivity through fast fault identification without requiring complex high-speed measurement systems.
Data Source
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AI summary
According to the present invention, a low speed current sensor is used to determine where, among a motor and a cable connected to a power conversion device, a short circuit has occurred. In addition, the low speed current sensor is used to specify an interphase short circuit location on the cable with high resolution. When a direct current voltage value is a predetermined value lower than the value when a motor is being driven, the switch elements, one of which is on an upper arm and the other one of which is on a lower arm of a different phase than the upper arm, are turned on to generate in the cable, a current for short circuit investigation. Thereafter, while one of the switch elements is turned off, a current measurement value is obtained from the current sensor. On the basis of the time when both the switch elements were turned on and a current measurement value of the current sensor, a round-trip inductance value of a cable is calculated, and a short circuit location is determined from the inductance value.