Closed-loop Current Offset Compensation in PMSM Drives
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Solution Overview
Problem
Current measurement offset errors in permanent magnet synchronous motor drives lead to motor position-dependent torque and current errors, resulting in torque ripple and potentially opposite motor torque direction, which affects electric power steering systems by requiring higher driver effort.
Innovation Solution
A system and method for closed-loop compensation of current measurement offset errors using a processor and memory to read output voltage signals, extract a signature of the error, and compensate for it using a feedback path, involving a current measurement offset error compensator and frame transformation to adjust current measurements in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop current control is used to minimize error between commanded and measured currents, then current tracking precision is improved, but measurement offset errors cause torque ripple and incorrect torque direction
Solution Approach 1:
The system performs preliminary detection of current measurement offset errors by analyzing the relationship between commanded currents and measured currents before they cause significant torque ripple. The offset error is identified and compensated in advance through adjustment of the current measurement signals, preventing the harmful effects from manifesting in the torque output.
Solution Approach 2:
The system implements a feedback mechanism where the output voltage signal is monitored and analyzed to detect signature patterns indicating current measurement offset errors. This feedback loop continuously adjusts the current measurements to compensate for detected offsets, ensuring reliable torque control while maintaining precise current tracking.
2Measurement precision
If current measurement offset error occurs, then current controller adjusts motor voltage to match measured current with commanded current, but actual motor currents become incorrect
Solution Approach 1:
The system converts the harmful effect of current measurement offset errors into a detectable signature pattern in the output voltage signal. By analyzing this pattern, the system identifies the presence and magnitude of offset errors and transforms this previously harmful phenomenon into a useful diagnostic indicator for compensation purposes.
Solution Approach 2:
The output voltage signal serves as an intermediary that carries information about current measurement offset errors. Instead of directly measuring current with potentially offset-prone sensors, the system uses the output voltage signal as an intermediate indicator to detect and compensate for measurement errors, thereby eliminating the source of torque errors.
3Reliability
If phase current measurement offset error exceeds threshold, then torque ripple increases and may produce torque in opposite direction from command, but system complexity increases with compensation mechanisms
Solution Approach 1:
The system implements self-service by using its own output voltage signal to detect and compensate for current measurement offset errors. The compensation mechanism leverages existing system signals and components, avoiding the need for additional complex hardware or external diagnostic systems. The system monitors itself and performs self-correction, maintaining torque control stability without significantly increasing overall system complexity.
Data Source
AI summary
Systems and methods for compensating for a current measurement offset error in a permanent magnet synchronous motor (PMSM) drive are disclosed. The systems and methods include reading an output voltage command signal, extracting a signature of a current measurement offset error from the output voltage command signal, and compensating, based on the signature, for the current measurement offset error in a closed-loop using a feedback path.