Field Weakening Vector Controller for PMSM Torque Stability
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Solution Overview
Problem
Conventional field weakening vector control methods for permanent magnet synchronous motors fail to achieve high-precision, high-response, and high-stability torque control, particularly in the field weakening region, due to limitations in generating d-axis current commands and ensuring torque accuracy.
Innovation Solution
A field weakening vector controller that corrects the q-axis current command using a product of the d-axis current command and a sine signal representing the phase difference between the reference axis and the motor axis, ensuring stable operation by subtracting a stabilization signal from the q-axis current command to compensate for axis errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If d-axis and q-axis currents are controlled proportionally using a table of d-axis current command values, then the control structure is simple, but the torque accuracy is insufficient
Solution Approach 1:
The patent introduces a feedback mechanism where the actual q-axis current is detected and compared with the commanded q-axis current. The difference (error signal) is fed back to the q-axis current controller to adjust the control output, enabling precise torque control. This feedback loop transforms the open-loop proportional control into a closed-loop control system, resolving the contradiction between simple control structure and torque accuracy.
2Reliability
If d-axis current command is calculated using proportional integration of terminal voltage difference, then terminal voltage control is achieved, but d-axis current command response is slow
Solution Approach 1:
The patent calculates the d-axis current command value in advance based on the terminal voltage command and actual terminal voltage difference before the current control cycle begins. By performing this calculation preliminarily and providing the d-axis current command to the current controllers in advance, the system achieves both reliable terminal voltage control and fast current response, as the command is ready before execution is needed.
3Device complexity
If q-axis current command is not corrected for phase difference, then control calculation is simple, but torque response accuracy deteriorates
Solution Approach 1:
The patent applies a phase difference correction by multiplying the commanded q-axis current by a correction factor derived from the sine of the phase difference angle. This parameter change compensates for the angular misalignment between the control reference axis and the motor reference axis, ensuring accurate torque response. The correction is calculated efficiently using pre-stored sine values, maintaining computational simplicity while improving precision.
Data Source
AI summary
A field weakening vector controller is disclosed which calculates a d-axis current command value for a power converter to drive a permanent magnet synchronous motor. The field weakening vector controller includes a stabilization calculator, a d-axis current command calculator, a q-axis current command calculator, and a phase calculator. The d-axis current command calculator corrects the d-axis current command value, while the stabilization calculator calculates a product of the phase error and the d-axis command value. The q-axis current command calculator corrects the q-axis current command value using this product.