Colloquium on Modelling, Analysis and Control of Switched Reluctance Motors

Speaker: THIRUMALASETTY MOULI . of Ph.D. (Engg) in Electrical Engineering under Electrical Engineering

Date/Time: Jan 17 / 16:00:00

Location: Multi Media Class Room (MMCR), EE Department

Research Supervisor: Narayanan G

Abstract:
Switched reluctance machine (SRM) is known for many advantages such as permanent magnet-free operation, robust structure, low rotor inertia, low manufacturing cost, and excellent fault-tolerant capability. Hence, SRM has been adopted in many applications such as, electric vehicles, aerospace, and robotics. Nonlinear characteristics and pulsations in torque developed are well-known problems, rendering modelling and control of the SRM challenging. This thesis focuses on the modelling, characterization and control of switched reluctance machines. Current, torque, and speed control are all part of the scope of study. Conventionally rotors with laminations are used in SRM. In certain applications where the shaft temperature increases very significantly, the thermal expansion of the different constituent materials in a typical laminated would be at different rates. This creates stress in the rotor assembly and could reduce the reliability of the machine. Hence, in such applications, rotors made from a single piece of magnetic material are potential candidates. Solid-rotor and recently proposed slitted-rotor SRMs are prospective candidates for high temperature applications. However, research on solid- and slitted-rotor SRMs remains relatively limited. In this thesis, solid and slitted rotor SRMs are systematically compared through comprehensive 3D transient finite element analysis (FEA) and experimental evaluations under both static and dynamic conditions. Blocked rotor experiments and 3D finite element analyses reported show that the slitted-rotor SRM has lower core loss and higher torque density than the solid-rotor SRM. High torque density is essential for applications such as electric vehicles and aerospace systems. This thesis compares several methods to enhance laminated-rotor SRMs torque density through FEA simulations. Various magnetic structure-based techniques, including multi-toothed stators, tapered poles, non-uniform air gaps, flux barriers, and segmental rotors, are analyzed. Additionally, the performance of two winding configurations—double-layer conventional (DLC) and double-layer mutually coupled (DLMC)—is compared under unipolar and bipolar excitations, respectively. The DLMC winding concept is applied to solid- and slitted-rotor SRMs to enhance torque output. These machines are reconfigured from conventional windings to a DLMC configuration. Due to the absence of existing literature on mutually coupled solid- and slitted-rotor SRMs, FEA simulations and extensive blocked-rotor experiments are conducted to evaluate their performance under bipolar current excitation. Comparative analysis with conventionally wound counterparts reveals a significant enhancement in torque characteristics achieved through the DLMC winding connection. Two new current control schemes are proposed in this research work. In the first part, an extended horizon model-based predictive current controller is proposed for SRM. An analytical equation is reported for real-time computation of the optimal duty ratio to minimize the RMS error between the future current references and predicted currents over a horizon. The proposed controller demonstrates lower RMS error in current tracking and robustness to parameter variations, with experimental validation on a laboratory prototype drive, over an existing dead-beat predictive controller. Further, a fixed-frequency, model-independent predictive current control for SRM is proposed. Unlike traditional approaches, this method does not require any pre-measured characteristics of the SRM. Instead, it only requires two constants: the optimal value of equivalent inductance and the moving average window period. Hence this method eliminates the need for time consuming characterization experiments, multi-dimensional lookup tables, and offline curve fitting to model the flux-linkage characteristics of the SRM for current control. A high-performance torque control scheme for SRMs is presented, incorporating a PI controller, feedforward compensation, high-frequency compensation, and optimized gating functions. This controller achieves significant reduction in pulsating torque and outperforms state-of-the-art techniques across various operating conditions. Further improvement in performance is achieved through a novel PWM-based optimal predictive direct torque control scheme. In this work, a cost function, encompassing the instantaneous torque error and the RMS values of phase currents is formulated to be minimized. An analytical expression for the optimal duty ratio towards this objective is derived resulting in improved computational efficiency. This controller delivers improved torque tracking, higher torque per ampere, and lower sound pressure levels compared to existing methods. A novel experimental method for determining the combined moment of inertia and frictional torque characteristics of an SRM coupled to a load, utilizing a low torque ripple controller. The identified mechanical parameters are leveraged to develop a systematic design procedure for a PI-based speed controller, achieving fast speed reference tracking and robust disturbance rejection. The controller’s effectiveness is validated through simulations and experiments, demonstrating its effectiveness in improving SRM drive performance.