PMSM Driver Phase Angle Control for Torque Linearity
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Solution Overview
Problem
Existing voltage mode driving techniques for permanent magnet synchronous motors (PMSM) face inefficiencies during transient conditions due to the non-linear relationship between the phase angle of the applied voltage and the back electromotive force (BEMF), leading to variations in the phase angle of the current, which affects motor torque and efficiency.
Innovation Solution
A method that directly controls the resistive-inductive drop of the motor winding by sensing the BEMF, reading voltage waveforms with specific phase angles, and generating a driving voltage as a product of these waveforms with coefficients determined by desired torque values, allowing for phase control of the current with respect to the BEMF, even during transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage mode driving is used for PMSM, then the driving circuit is simpler than current mode driving, but the phase angle of current varies during transient conditions affecting torque linearity
Solution Approach 1:
The patent changes the control parameter from direct voltage application to controlling the phase angle between applied voltage and BEMF. By adjusting the phase angle parameter dynamically, the system maintains current in phase with BEMF during transients, ensuring torque linearity while keeping the voltage mode driving circuit simple.
Solution Approach 2:
The patent implements a feedback mechanism where the phase angle between applied voltage and BEMF is continuously monitored and adjusted. The controller modifies the voltage waveform phase based on the detected phase difference, ensuring that current remains in phase with BEMF during both steady and transient conditions, thus maintaining torque linearity.
2Ease of operation
If the phase angle between applied voltage and BEMF is not controlled, then the driving method is simpler, but the phase angle of current varies during transients reducing efficiency
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the phase angle of the applied voltage before transient conditions occur. The system proactively sets the voltage phase angle to compensate for upcoming changes in load or speed, ensuring current remains in phase with BEMF and maintaining efficiency without complex real-time corrections.
3Use of energy by moving object
If closed-loop control circuits are used to maintain current phase with BEMF, then motor efficiency is enhanced, but the control circuit becomes more complex
Solution Approach 1:
The patent introduces an intermediary approach by using phase angle control as a mediator between the simple voltage mode driving circuit and the goal of maintaining current in phase with BEMF. Instead of directly controlling current with complex circuits, the system controls the voltage phase angle, which indirectly maintains current phase alignment, thus improving efficiency without proportionally increasing circuit complexity.
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
This approach maintains the phase angle of the current in phase with the BEMF during both steady and transient conditions, enhancing motor efficiency and torque linearity without the need for complex closed-loop control circuits, similar to current mode driving systems.
Implementation Method 1
sensing or estimating a back electromotive force induced in at least one winding of the motor by the rotation of a rotor of the motor
Data Source
AI summary
A method of driving a permanent magnet synchronous electric motor includes sensing or estimating a back electromotive force induced in at least a winding of the motor by the rotation of a rotor of the motor; and reading, from a memory, values of a first voltage waveform having a phase angle with respect to the back electromotive force. The method also includes generating a driving voltage corresponding to the sum of values of a control voltage, obtained as product of the values of the first voltage waveform by a first coefficient determined as a function of a desired value of motor torque, and values of a cancelation voltage of the back electromotive force. The method also includes applying the driving voltage at the motor winding.