| PhD Seminar

Name of the Speaker: Mr. Devjyoti Roy (EE21D026)
Guide: Dr. Kamalesh Hatua
Online meeting link: https://meet.google.com/ijd-ojjo-mss
Date/Time: 26th Aug 2025 (Tuesday), 3:00 PM
Title: I-f control based low-speed sensorless operation of SynRMs and Multipolar PMaSynRMs

Abstract :

Synchronous reluctance machines (SynRMs) have emerged as a strong candidate for rare-earth element (REE)-free industrial applications, offering high efficiency, low cost, and minimal maintenance. In line with this, SynRMs and their permanent magnet assisted variants (PMa-SynRMs) have gained widespread adoption, ranging from cost-effective fans and compressors to advanced and sophisticated electric vehicle (EV) motors.

Most control strategies for SynRMs depend on accurate rotor position feedback from encoders to operate effectively. Consequently, in recent decades, sensorless control methods have attracted significant attention, motivated by the goal of eliminating expensive encoders while improving the overall reliability of the drive. Among the major sensorless control schemes for synchronous machine drives, back-EMF based methods like Extended EMF and Active-Flux estimation schemes are popular due to their simplicity, but they lose effectiveness at low speeds as they suffer from integrator dc-drift issues at lower frequencies. Moreover, these methods are highly parameter sensitive and in SynRMs the inductance variations are inevitable at higher loads. High-frequency signal injection (HFSI) techniques provide accurate rotor position detection in the low-speed range; however, their algorithmic complexity limits their use in cost-sensitive applications like pumps, fans, and compressors, where simplicity and reliability are prioritized over precision. Hence, starting and low-speed sensorless control of SynRMs has considerable challenges to offer.

In the first part of the seminar, we will introduce a new, reliable open-loop sensorless starting method for SynRM drives that uses I-f control. A key feature is the proposed torque controller, which manipulates the reference frequency rate to guarantee stable starting, even under varying load conditions. To enhance the efficiency of this method, a two-stage optimal current injection approach is discussed. The first stage calculates the ideal operating current based on an estimated torque value. Subsequently, the second stage employs a speed-band-based algorithm to precisely fine-tune the current determined in the first stage.

The second part of the seminar introduces a new position estimation scheme for multipolar six-phase PMaSynRMs. These types of machines offer an inherent low-speed position estimation advantage. The 4-pole SynRM has been propelled in I-f control and the 12-pole PMSM is utilized to find the exact position of the rotor utilizing a zero-current injection based position error correction algorithm. The small-signal stabilization studies have also been performed for ensuring stability.

All the above control schemes have been thoroughly validated using a combination of simulation models and physical experimental results.