Permanent Magnet Synchronous Motors Control: Sensorless and Field-Weakening Operation

The Permanent Magnet Synchronous Motor (PMSM) has been adopted since the 1980s, mainly in low and medium power high accuracy servo drives, thanks to its high power density. Moreover, the possibility of using powerful digital controllers has allowed to exploit its inherent accuracy in torque production. In the recent years, industry has shown a renewed interest in this class of machines, mainly related to the higher efficiency achievable with respect to other kinds of motor. In fact, following an increasing trend in the energy cost, the higher initial cost represented by the purchase and installation of a PMSM with respect to typical solutions (e.g. induction and DC) has started to be covered by the lifetime consumption. This, together with the improved environmental consciousness, opened the way to new applications, characterized by lower accuracy and slower dynamics, where different requirements are set, like lower production and maintenance costs, higher reliability, energy optimized control and wider speed ranges. Among these applications, industrial ones are maybe the most relevant (e.g. fans and pumps), while emerging ones are electric and hybrid vehicles and home appliances. The impact of the adoption of these machines could be very important in the future, as most of the electrical energy consumption at present is represented by relatively low efficiency motors, and even few percentage units of increased efficiency would lead to huge savings. This thesis describes the work in the years 2010-2012, during the PhD course at the Electric Drives Laboratory of the University of Udine. The topics studied are mainly two, both regarding the digital control of electric drives for Permanent Magnet Synchronous Motors (PMSMs): the sensorless control and the flux-weakening control. Although the two topics have been an object of the research in electric drives for many years, and a strong development has started from that research, still many issues are open, and the industrial need for higher performances and efficiency of these drives keeps posing interesting challenges to researchers worldwide. “Sensorless control” is the name under which the motor control techniques aiming at the avoiding the use of mechanical sensors usually adopted. For the case of PMSM, different techniques have been considered, and some improvements have been proposed both to the analytical approach and to the techniques adopted. Different flux-weakening control feedback schemes have been compared, and a proposal for the non linearity compensation of the loop dynamics has been proposed for a class of these, mainly applicable to Interior PMSM. A perspective on the practical implementation issues has been kept all over the work, favoring simpler schemes with the less possible parameter dependence, in order to avoid the need for extensive off line tests on the single machine.