Motor Control Device Connection Defect Detection
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Solution Overview
Problem
Conventional techniques for diagnosing defects in the connection between a motor control device and a motor cannot detect abnormalities with low resistive values, such as connector contact resistance, due to variations in power semiconductor characteristics or wire resistance changes.
Innovation Solution
A motor control device that generates current instructions to cause equal currents to flow into two phases of a three-phase motor or half the current to flow into one phase, with feedback control to compare voltage instructions across phases, determining defects by identifying voltage differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a regular inverter output voltage is applied to detect flowing current, then disconnection state can be diagnosed using regular current sensor, but abnormality with low resistive value cannot be detected due to current variation from power semiconductor characteristics or wire resistance change
Solution Approach 1:
The patent changes the type of current applied for diagnosis from AC current (regular inverter output) to DC current. This parameter change allows the use of voltage instruction comparison instead of current measurement, eliminating the influence of power semiconductor characteristics and wire resistance variations that affect AC current-based diagnosis. The DC current application enables accurate detection of low resistive value abnormalities by comparing voltage instructions across phases.
2Measurement precision
If feedback control is used to compare voltage instructions across phases, then connection defects can be detected without being affected by power semiconductor variation, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The patent implements feedback control by comparing the voltage instruction values across different phases. The current control unit generates voltage instructions based on DC current instructions, and the connection defect detection unit compares these voltage instructions to detect abnormalities. This feedback mechanism uses existing control loop components rather than adding separate detection hardware, thus improving measurement precision while limiting the increase in overall system complexity.
Solution Approach 2:
The patent makes the existing current control unit serve dual functions: normal motor control and connection defect diagnosis. By using the same current control unit to generate voltage instructions for both operational control and diagnostic comparison, the system achieves accurate defect detection without requiring separate dedicated diagnostic hardware, thereby managing system complexity effectively.
Data Source
AI summary
A numeric value control unit outputs a connection diagnostic signal to a target position switching unit to place the three-phase motor in a position at an angle that causes no torque generation upon application of a diagnostic current to the three-phase motor, and thereafter, outputs a connection diagnostic signal to a current instruction switching unit to apply a diagnostic current. Then, in order to apply a diagnostic current to the other two phases, the three-phase motor is placed in a position at an angle that causes no torque generation upon second application of a diagnostic current, and a diagnostic current is thereafter applied. When a diagnostic current is applied twice and in the case where no defect in connection is detected in either application, it is determined that connection is normal. Meanwhile, in the case where connection is detected once or twice, it is determined that connection is defective.