Segmental rotor switched reluctance drives

Abstract

One of the well-known drawbacks of switched reluctance machines is the relatively high output torque ripple. Techniques aiming to reduce machine torque ripple either compromise the machine performance or the simplicity of the inverter and the controller. The work presented in this thesis shows that low torque ripple over a wide speed range can be achieved without severe penalties in terms of the machine performance and the size, cost and complexity of the power electronics and the controller. This is achieved by designing a 6-phase machine and driving it from a three-phase full bridge circuit. Switched reluctance motors with segmented rotors are a relatively recent advancement in the electromagnetic design of doubly-salient reluctance motors, having only been introduced in 2002. By replacing the conventional toothed rotor with individual segments, it has been proven that higher torque density than conventional switched reluctance machines could be achieved. Early work by Mecrow and El-Kharashi has demonstrated the operation of prototype machines with short-pitched and fully-pitched windings. The machine design work presented here builds on this early work by examining aspects of the machine design and its operation. Two six-phase machines – one with a segmented rotor and the other with a toothed rotor - have been designed. Performance comparisons have been made between the two six-phase machines and a three phase segmented rotor machine that was previously designed at Newcastle University. Additionally, a three phase single tooth winding and a two phase segmented rotor switched reluctance machine have been studied in simulation and experimentally. Detailed comparison of inverter ratings and machine efficiencies are made under equal conditions for a 2-phase machine driven from h-bridge and asymmetric half-bridge inverters. This is achieved with results from a test rig and the use of accurate dynamic simulation. Simulation models for 3-phase and 6-phase machines have also been generated. Detailed comparison of inverter ratings and machine efficiencies are made under equal conditions for the 3-phase and 6-phase drives in the dynamic simulation. Comparisons between simulated and measured results are shown to be very good for all of the drives.