Mitigating the Torque Ripple in Electric Traction using Proportional Integral Resonant Controller

Permanent magnet (PM) machines offer high efficiencies which are attractive to be used in vehicle propulsion systems, however, their design creates an inherent torque ripple. This is particularly problematic for electric vehicles (EV) due to low damping of torsional vibration which can result in reduced vehicle comfort. This can prohibit the take up of PM machines, missing opportunities for improving vehicle energy efficiency. This paper presents the application of resonant control (RC) to suppress the impact of the PM torque ripple this enabling take up of this technology and for the first time aims to demonstrate a reduction in vibration at a vehicle level. A prototype PM machine and driveline have been fitted to a light-duty off-road vehicle. Firstly an analysis of the vehicle vibration when it is driven in a speed-control mode with a conventional proportional-integral (PI) control. The main source of the vibration is identified as the 24th harmonic torque ripple of the PM machine, which originates from the cogging torque and air-gap flux harmonics. The vibration is more severe when the torque ripple frequency is close to the natural frequency of the drivetrain. The application of Resonance Control has demonstrated over 80% reduction in speed ripple even when the torque ripple frequency is close to the natural frequency of the vehicle.