Sensorless control of PM-assisted SyR motors

During the last 50 years the global electricity consumption has been grown about four times. Many sectors are involved in this trend: industrial, residential, transport, commercial, public services and so on. Following this trend, the global policy makers are encouraging variable speed drives (VSD) for higher efficiency. Moreover, all manufactures are moving on reduction of final price of VSD: elimination of speed/position transducer permits to achieve this target, improving also reliability. This thesis discusses the sensorless control of VSD, in particular, a PM-assisted synchronous reluctance motor. The method adopted is based on two stages: I-f control and sensorless FOC. The former is an open-loop speed control, used only to start and stop the drive, where amplitude and frequency of the imposed reference current vector are properly set: constant amplitude and ramp variation frequency. The latter is activated when motor speed is higher than a fixed threshold. It is a classical field oriented control (FOC) where speed and position feedbacks are estimated by combining hybrid flux observer (HFO), cross product method and phased locked loop (PLL). In order to ensure a smooth transition from one stage to the other, some precautions are adopted. The developed sensorless techniques are fully validated with simulation and experimental results on ABB motor: in particular, they show good performance and robustness both at no load and under rated load.