Continuous Position Estimation Technique for Optimized Torque Ripple using Low-Resolution Sensor 2021-26-0169

With electrification of transport system, high power density performance motors such as permanent magnet synchronous and variable reluctance motors are being increasingly used for traction application. These high-performance machines require continues angle variation information for appropriate control action to be performed. This continuous angle variation data is measured using sensors such as optical or magnetic encoders, which are very expensive. Moderately expensive devices such as GMR or TMR based sensors, linear hall sensors can also be used. These provide output with fair accuracy and may require suitable machine design or complex signal conditioning to improve accuracy. Bi-polar hall-based sensors are being increasingly looked for as cheap alternates to such sensors. These sensors provide position data at a low resolution and may provide inaccurate data due to improper physical mounting, which may lead to degraded machine performance. The low-resolution data can be converted to high resolution using simple interpolation-based algorithms. These algorithms often use speed or acceleration data calculated from previous state changes to interpolate high resolution position data. Angle correction is done at each instant where a hall sensor state change is detected. This angle correction leads to sudden jumps in position data which may lead to significant torque ripple at the drive end. This paper addresses with the two problems mentioned above in using bi-polar hall sensors. Back-emf based calibration is suggested to correct the inaccuracies arising due to physical mounting. To prevent jumps in position data, a correction method is proposed to the optimize the trade-off between torque ripple and data inaccuracy. The paper also proposes an overall position estimation scheme to help identify the optimal points to switch between hall based, speed interpolation based and acceleration interpolation-based method for effective drive control.