Torque Ripple Reduction via Phase Current Shaping
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Solution Overview
Problem
Electric motors experience torque ripple due to non-sinusoidal back-electromotive force (back-EMF) waveforms, leading to increased noise, vibration, and harshness (NVH) issues.
Innovation Solution
Determining phase currents in a direct-quadrature (DQ) frame of reference based on lumped parameters of the electric motor, including back-EMF and inductances, to eliminate or reduce torque ripple, and applying corresponding voltage waveforms to inject these currents into the motor, thereby suppressing harmonic components simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional current control methods are used, then the control system is simple, but torque ripple and NVH increase significantly
Solution Approach 1:
The patent applies parameter changes by modifying the phase current waveforms to include specific harmonic components. The controller determines phase currents that include fundamental and harmonic components, where the harmonic components are specifically designed to counteract the torque ripple caused by non-sinusoidal back-EMF. This changes the current parameters from simple sinusoidal waveforms to composite waveforms with controlled harmonic content, thereby reducing torque ripple and NVH while maintaining manageable control complexity through systematic current shaping.
2Object-generated harmful factors
If successive current injections are used to reduce harmonics, then harmonic components are reduced, but the control process becomes complex and time-consuming
Solution Approach 1:
The patent applies preliminary action by pre-calculating and determining the optimal phase current waveforms that include the necessary harmonic components before motor operation. The controller determines the phase currents that will simultaneously suppress all harmonic components based on the motor's back-EMF characteristics and inductance parameters. This preliminary determination of current waveforms eliminates the need for successive iterative current injections during operation, reducing both the control process complexity and response time while effectively reducing harmonic components.
3Object-affected harmful factors
If torque ripple is not separately analyzed, then the control is simpler, but NVH reduction is ineffective
Solution Approach 1:
The patent applies segmentation by separating the torque analysis into two distinct components: average torque and torque ripple. The controller determines the phase currents such that the torque ripple component is minimized or eliminated while maintaining the desired average torque output. This segmentation allows the control system to independently optimize for NVH reduction by specifically targeting the ripple component, without compromising the overall torque production. The separate analysis of torque ripple enables effective NVH reduction while maintaining manageable control through focused optimization.
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 effectively reduces torque ripple and associated NVH by analyzing currents and voltages as functions of rotor position, allowing for separate analysis and suppression of torque ripple from average torque values, resulting in improved motor efficiency and lower harmonic content.
Implementation Method 1
The controller generates a value expressing a back-electromotive force (back-EMF) as a function of the rotor position with respect to a rotating frame of reference
Data Source
AI summary
A motor drive system and method for controlling an electric motor. The motor drive system includes a plurality of phase lines switchably connected to the electric motor, a plurality of controllable switches, and a controller. The controller is communicatively coupled to the plurality of controllable switches and configured to receive a signal indicative of a rotor speed and a rotor position from the rotor sensor. The controller generates a value expressing a back-electromotive force (back-EMF) as a function of the rotor position with respect to a rotating frame of reference. Based on the rotor position, the controller determines a plurality of phase currents that reduce a torque ripple of the electric motor to approximately zero. The controller actuates the controllable switches to supply the electric motor with the plurality of phase currents.