Electric Motor Current Sensor Offset Correction
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Solution Overview
Problem
Existing electric motor control systems cannot accurately detect and correct DC offset in current sensors during operation, leading to potential torque accuracy issues in AC motor control applications, especially in electric vehicle traction drives, as the DC offset drifts over time and temperature, remaining undetected and uncompensated.
Innovation Solution
An electric-motor-control system with three current sensors and a controller that determines x-offset and y-offset of a rotating vector, allowing for real-time detection and correction of offset-currents in each sensor while the motor is operating, using periodic measurements and signal processing to project current data onto an orthogonal frame, enabling accurate torque prediction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If DC offset correction is performed during off-state when no motor current is flowing, then correction simplicity is improved, but detection accuracy deteriorates because drift during operation remains undetected
Solution Approach 1:
The system performs preliminary DC offset correction during the off-state before motor current flows, establishing a baseline correction value. This preliminary action simplifies the correction process while the system prepares for operation, and the correction can be updated during operation to account for drift.
Solution Approach 2:
The system continuously monitors current measurements during motor operation and uses feedback to detect changes in DC offset drift. By comparing measured current values against expected values during operation, the system can detect offset drift and update corrections dynamically, maintaining accuracy despite the simplified preliminary correction approach.
2Adaptability or versatility
If current sensors are used to detect phase current for torque prediction, then torque control capability is improved, but measurement accuracy deteriorates due to DC offset bias in economical current sensors
Solution Approach 1:
The system extracts the DC offset component from the current sensor measurements by analyzing the measured current signals and separating the offset bias from the actual phase current. This extraction process removes the harmful DC offset bias while preserving the useful AC current information needed for torque prediction, enabling accurate torque control with economical current sensors.
Solution Approach 2:
The system changes the parameter representation of current measurements by transforming phase current measurements into a rotating reference frame and analyzing the DC component in this transformed domain. This parameter transformation allows the system to identify and correct DC offset bias, improving current measurement accuracy while maintaining the torque control capability provided by the current sensors.
3Adaptability or versatility
If DC offset drift occurs during operation due to temperature changes, then system adaptability to thermal conditions is improved, but current measurement accuracy deteriorates
Solution Approach 1:
The system implements dynamic DC offset correction that adapts to changing thermal conditions during motor operation. Instead of using a fixed correction value, the system continuously updates the DC offset correction based on real-time current measurements and detected drift, allowing the correction mechanism to respond dynamically to temperature changes and maintain measurement accuracy under varying thermal conditions.
Solution Approach 2:
The system uses feedback from continuous current measurements during operation to detect DC offset drift caused by temperature changes. By monitoring changes in the measured current signals and comparing them against expected values, the system can identify thermal-induced offset drift and apply compensatory corrections, maintaining current measurement accuracy despite thermal adaptation requirements.
Data Source
Figure 1
Figure 2A~3
Figure 4
AI summary
An electric-motor-control system (10) with current sensor offset correction includes three current-sensors (14) and a controller (16). Each of the three current-sensors (14) is used to detect current through one of three windings of a Y-connected motor (12). The controller (16) is in communication with the three current-sensors (14). The controller (16) records periodically measurements of sensed-current indicated by each current-sensor while variable-current flows through each of the three windings, determines an x-offset (24) and a y-offset (26) of a rotating-vector (28) indicated by a plurality of the measurements, and determines an offset-current (18) of each of the three current-sensors (14) based on the x-offset (24) and the y-offset (26).