PMSM Torque Control via Speed Feedback PI
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Solution Overview
Problem
Conventional constant torque control methods for permanent magnet synchronous motors fail to compensate for changes in rotation speed, leading to unstable operation and increased noise when the load becomes heavier than expected.
Innovation Solution
A method that involves starting the motor in constant torque control mode, switching to constant speed control when the real-time speed falls below a reference speed, and returning to constant torque control when the speed difference exceeds a certain threshold, using a speed-based PI controller to adjust the current on the q-axis and maintain stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional constant torque control mode is used, then the motor operates with preset torque through current control, but the rotation speed cannot be compensated leading to unstable operation and noise when load increases
Solution Approach 1:
The control system dynamically switches between constant torque control mode and constant speed control mode based on real-time speed feedback. When speed drops below reference speed, the system transitions to constant speed control to compensate for load changes, and returns to constant torque control when speed recovers, creating an adaptive control strategy that resolves the contradiction between torque control and speed compensation
Solution Approach 2:
The invention introduces speed feedback mechanism by measuring real-time speed and comparing it with reference speed. The speed difference triggers mode switching and activates the speed-based PI controller to generate extra current, forming a closed-loop feedback system that compensates for speed deviations caused by load changes while maintaining operational stability
2Device complexity
If constant torque control mode is used, then the control is simple with current-based PI controller, but the motor produces noise and vibration when real-time speed is lower than reference speed
Solution Approach 1:
The invention introduces a speed-based PI controller as an intermediary layer between the current-based PI controller and the motor. This intermediate control stage processes speed feedback and generates extra current to compensate for speed deviations, reducing noise and vibration without significantly complicating the overall control structure
Solution Approach 2:
The invention extracts the speed compensation function from the basic constant torque control system by adding a separate speed-based PI controller that operates independently but influences the q-axis current. This modular approach addresses noise and vibration issues while maintaining the simplicity of the original current control structure
3Speed
If extra current is added to increase speed, then the motor exits constant torque control mode, but the target current becomes complex with multiple current components
Solution Approach 1:
The invention merges the given current from torque control and the extra current from speed control into a unified target current for the q-axis. The speed-based PI controller's output is directly added to the given current, creating a combined control signal that simplifies the overall current control while achieving both torque and speed control objectives
Data Source
AI summary
A constant torque control method for a permanent magnet synchronous motor. The method includes: 1) starting a motor; setting a torque T of the motor; calculating a given current iq_limit on a q-axis based on the torque T; setting a target current iq_A on the q-axis to be equal to the given current iq_limit; and allowing the motor to operate in a constant torque control mode by a current-based proportional integral (PI) controller on the q-axis; 2) presetting a reference speed Vref1 of the motor; measuring a real-time speed V of the motor; when the real-time speed V is less than the reference speed Vref1, increasing an extra current delta_iq to the given current iq_limit to intervene the real-time speed V of the motor; and 3) measuring the real-time speed V of the motor; and calculating a speed difference Err=V−Vref2.