Motor Current Sensing Diagnosis Without a Bus Current Sensor
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Solution Overview
Problem
Existing motor control devices face challenges in accurately detecting abnormalities in current detection units of three-phase motors without a separate sensor for bus current, leading to incomplete diagnosis of phase current abnormalities.
Innovation Solution
A motor control device with a current detection unit and control unit that diagnoses abnormalities by comparing phase currents and duty ratios, determining abnormality based on differences between maximum and minimum current values or duty commands, eliminating the need for a separate bus current sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate bus current sensor is added to detect abnormalities in current detection units, then measurement precision improves, but device complexity increases
Solution Approach 1:
The current detection unit performs self-diagnosis by comparing its own phase current detection results with the bus current calculated from duty ratios and phase resistance values. This self-service mechanism enables abnormality detection without requiring additional sensors, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The control unit calculates bus current based on duty ratios and phase resistance, then feeds this calculated value back for comparison with the actual bus current detected by the current detection unit. This feedback loop enables continuous monitoring and abnormality detection using existing components, avoiding the need for separate sensors.
2Ease of manufacture
If current detection is performed on the low potential side of the motor winding, then ease of manufacture improves, but measurement precision deteriorates due to inability to detect bus current directly
Solution Approach 1:
The invention introduces an intermediary calculation method where bus current is derived from duty ratios and phase resistance values rather than measured directly. This intermediary approach enables accurate bus current determination even when the drive circuit is configured on the low potential side, resolving the contradiction between ease of manufacture and measurement precision.
Solution Approach 2:
The invention replaces direct mechanical/electrical measurement of bus current with a computational approach using duty ratios and phase resistance. This substitution allows accurate bus current determination through calculation rather than direct sensing, enabling low potential side configuration while maintaining measurement precision.
3Measurement precision
If phase current detection is performed without calculating bus current from duty ratios, then measurement precision improves through direct sensing, but device complexity increases due to additional sensors
Solution Approach 1:
The control unit performs multiple functions using the same components: it controls motor drive through duty ratios and simultaneously calculates bus current for abnormality detection. This multi-functionality enables accurate bus current determination without additional sensors, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The control unit utilizes its existing control data (duty ratios and phase resistance) to self-calculate bus current for diagnostic purposes. This self-service approach enables the system to perform both motor control and abnormality detection functions using the same components, avoiding the need for separate measurement sensors.
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
Effectively detects abnormalities in current detection units, such as drift, with high accuracy and simplicity, preventing malfunctions during shift range switching without requiring additional sensors.
Implementation Method 1
The current detection unit has current detection resistors corresponding to each phase of the motor winding
Data Source
AI summary
A motor control device includes a motor, a drive circuit, a current detection unit, and a control unit. The motor has a plurality of phases of motor windings. The drive circuit is provided on a low potential side of the motor windings. The current detection unit has current detection resistors corresponding to each phase, and is provided on a low potential side of the drive circuit. The control unit includes an actuator control unit and an abnormality diagnosis unit. The abnormality diagnosis unit determines that the current detection unit is abnormal, when a difference between a maximum current, which is a maximum value of the phase current when a same duty ratio is commanded to each phase, and a minimum current, which is a minimum value of the phase current when a same duty ratio is commanded to each phase, is equal to or greater than an abnormality determination threshold.