Implementation and Evaluation of a Full-Order Observer for a Synchronous Reluctance Motor
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Sensorless control of the synchronous reluctance motor has been a topic of research for more than a decade, producing several successful methods to accomplish this goal. However, a technique that has been overlooked is the full-order nonlinear observer, which is essentially a software model of the motor driven by measurements from the actual motor. Presented in this thesis is the design, implementation, and experimental testing of a full-order observer-based sensorless control technique which requires only the phase current and voltage measurements that are typically available in standard three-phase inverters. A technique is also presented for calculating a table of observer feedback gains parameterized only by the steady-state motor speed. This allows a gain-scheduling observer to be implemented which, as shown using experiments, improves the transient response of the observer over a wide speed range. The sensorless controller consists of a full-order nonlinear observer coupled with an input-output linearization speed controller. The resulting controller was implemented in Simulink and executed on a dSPACE DS1103 real-time DSP board using the Real-Time Workshop extension to Simulink. A custom built three-phase IGBT inverter was used to interface the DSP to a 100 watt synchronous reluctance motor for laboratory testing. The resulting sensorless controller was able to successfully track a varying speed reference from 150 rpm to 1800 rpm with a tracking error under 5% for most of the speed range. At the lowest speeds, the tracking error begins to increase but the observer remains stable down to 150 rpm.