Motor Control Device Overcurrent Fault Determination
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Solution Overview
Problem
Motor control devices face erroneous overcurrent fault determination due to regenerative currents, especially in low voltage states where the increase in input voltage from regenerative energy is small, leading to potential misidentification of faults during normal operation.
Innovation Solution
A motor control device that includes a processor to estimate power supply current and determine overcurrent faults by comparing the current values with threshold values, stopping fault determination when the negative power supply current is below a certain threshold to avoid erroneous identification, and optionally performing a command value lowering process to suppress overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor control device stops overcurrent fault determination when input voltage is outside operating range, then erroneous determination due to regenerative energy is avoided, but fault detection reliability deteriorates in low voltage states
Solution Approach 1:
The patent changes the parameter used for fault determination from input voltage range to power supply current value. By estimating the power supply current and comparing it with a threshold, the system can accurately distinguish between normal regenerative current and actual fault conditions even in low voltage states, resolving the contradiction between avoiding erroneous determination and maintaining fault detection capability
Solution Approach 2:
The patent replaces the voltage-based fault determination mechanism with a current-based mechanism. By substituting the input voltage monitoring approach with power supply current estimation and comparison, the system achieves more reliable fault detection that works effectively across all voltage conditions including low voltage states
2Measurement precision
If overcurrent fault determination is continuously performed, then fault detection capability is maintained, but erroneous determination occurs due to regenerative current in normal operation
Solution Approach 1:
The patent introduces power supply current estimation as an intermediary parameter to mediate between the actual current and fault determination. By using the estimated power supply current as a reference, the system can distinguish between normal regenerative current and actual fault conditions, preventing erroneous determination while maintaining continuous fault detection capability
Solution Approach 2:
The patent implements a feedback mechanism where the estimated power supply current is continuously compared with the threshold value. This feedback loop enables the system to dynamically adjust fault determination based on actual operating conditions, maintaining high reliability by stopping determination during normal regenerative operation while detecting actual faults
Data Source
AI summary
A motor control device includes at least one power converter. The at least one power converter is connected between a DC power supply and a motor. The at least one power converter converts a DC electric power into a multi-phase AC electric power by operating a plurality of switching elements and supplies the multi-phase AC electric power to the motor. The motor control device calculates a command value for operating the at least one power converter to control electrical conduction to the motor. The motor control device determines an overcurrent fault when a value of a current flowing through the at least one power converter or a motor winding of the motor exceeds an overcurrent threshold value. The motor control device estimates or detects a power supply current that is a direct current flowing between the DC power supply and the at least one power converter.