Torque Ripple Reduction of a PM Synchronous Motor for Electric Power Steering using a Low Resolution Position Sensor

Abstract

MDPS (motor driven power steering) systems have been widely used in vehicles due to their improved fuel efficiency and steering performance when compared to conventional hydraulic steering. However, the reduction of torque ripples and material cost are important issues. A low resolution position sensor for MDPS is one of the candidates for reducing the material costs. However, it may increases the torque ripple due to the current harmonics caused by low resolution encoder signals. In this paper, the torque ripple caused by the quantized rotor position of the low resolution encoder is analyzed. To reduce the torque ripples caused by the quantization of the encoder signals, the rotor position and the speed are estimated by measuring the frequency of the encoder signals. In addition, the compensating q-axis current is added to the current command so that the 6 th order torque harmonic is attenuated. The reduction of torque ripples by applying the estimated rotor position and the compensated q-axis current is verified through experimental results.

Analysis of Torque Ripple and Cogging Torque Reduction in Electric Vehicle Traction Platform Applying Rotor Notched Design

“…Therefore, when a notch is added to the rotor's surface, the notch acts in the same way as the air gap. As a result of acting as the air gap, it changes the distribution of the gap permeance function, G(θ, z), and as the number of active slots is changed, G nN L is also changed, which results in reducing the cogging torque This has the effect of reducing the energy changes due to the rotation of the motor, thereby reducing the cogging torque and torque ripple [26,27].…”

Review of BLAC Motor and Drive Technology for Electric Power Steering of Vehicles

“…In [30], using the low resolution encoder signals, the Further cost reduction can be achieved by removing the incremental encoder for the rotor speed detection [31][32][33][34], although the feasibility of the application to the EPS system was not reported. Then the rotor position can be detected by only hall-effect sensors, therefore, the rotor position information can be detected every 60 electric degrees, similar to the BLDC drives.…”

A Study on Accurate Initial Rotor Position Offset Detection for a Permanent Magnet Synchronous Motor Under a No-Load Condition

“…Inaccurate position information causes torque control errors as speed increases, making appropriate torque control impossible and resulting in poor efficiency and noise, vibration, and harshness (NVH) characteristics. In particular, the EV traction motor has a maximum speed specification equivalent to a maximum of 4 to 5 times the rated speed due to the system's characteristics to ensure controllability in the high-speed range, and an exact offset setting is required [10].…”