17th International Middle East Power Systems Conference, Mansoura University, Egypt, December 15-17, 2015 Comparison between Various Switching Tables for a Direct Torque Controlled Permanent Magnet Synchronous Motor (DTC-PMSM) Shady M. Sadek, Sherif A. Zaid and Mahmoud M. Abd-Elhkim Department of Electrical Power and Machines, Cairo University, Giza, Egypt {shady_mamdouh_2011& sherifzaid & mhakim1945} @yahoo.com Abstract - Direct Torque Control (DTC) of AC drives is considered one of the most interesting high dynamic response motor control strategies nowadays. Permanent Magnet Synchronous Motors (PMSM) are now replacing Induction Motors (IM) in a variety of applications due to their valuable advantages like increased efficiency and compact size. The combination of DTC and PMSM in the same drive system leads to excellent performance not only for torque dynamics but also for efficiency point of view. DTC depends on the selection of the desired stator voltage vector from a look-up table called "switching selection table" to meet the torque and flux change requirements. In the literature, there are various switching tables according to the using of zero voltage vectors and the number of hysteresis comparator levels. Each table has its own merits and demerits in terms of torque response, speed response, torque and flux ripples and switching frequency (losses). Comparisons of these various switching tables are discussed in this paper showing their effect on the drive performance through MATLAB/Simulink simulations. Keywords: Electric Drives, Direct Torque Control, Permanent Magnet Synchronous Motor (PMSM), Voltage Source Inverter (VSI), Switching Table, Matlab/Simulink. I. INTRODUCTION Nowadays, permanent magnet synchronous motors (PMSM) are replacing Induction motors (IM) in a variety of applications like vehicles, robotics, ships, windmills, and machine tools due to their desirable advantages such as higher torque output compared to IM, higher efficiency, reliability, quiet operation ,higher power density, superior P.F ,and low rotor temperature. For high performance operation, Field Oriented Control (FOC) or Direct Torque Control (DTC) could be used. According to [1] and [2], comparisons between FOC and DTC have been made and the conclusion is that DTC offers a simpler control architecture with a similar dynamic performance to FOC because in DTC, no machine parameters dependence, no reference frame transformation, no need for position sensors, no inner current control loop, and no voltage modulation scheme are used but, DTC has hysteresis controllers with switching selection table. DTC provides independent control of both the torque and flux. It selects the most appropriate inverter switching state from a pre-designed look up table which gives fast torque response. The selection is made to restrict the flux and torque errors within their hysteresis bands. The DTC has the disadvantages of high torque and flux ripples, not constant inverter switching frequency, and poor performance at low speeds. Many studies have been made to solve DTC's problems especially the torque ripples and variable switching frequency problems [3, 4]. Some studies have been introduced recently that neither use switching table nor hysteresis controllers but they calculate the voltage vector and realize it by some of the voltage modulation techniques like Space vector Modulation (SVM-DTC) [5] or Sinusoidal Pulse Width Modulation (SPWM-DTC) [6]. In [7], the voltage vector isn't applicable to the whole sampling period, but to a certain ratio of it, which reduces the torque ripples significantly; this system is called Duty Ratio Control. Model Predictive Control (MPDTC) also replaces the table and the hysteresis controllers by a prediction algorithm and a cost function. The prediction algorithm uses the machine equations to calculate the trajectory of the torque in the next sampling periods which also decreases the torque ripples [8]. In [9], a new method was proposed to optimize the selection of the voltage vectors so that maximum rate of change in torque can be achieved with constant switching frequency. Although these relatively new methods for DTC can solve various problems of the conventional method (switching table method); complexity, increased computations, and cost will be important demerits to be taken into account when implementing such schemes. These demerits appeared because most of these new techniques require the use of position sensors which increases system cost, complexity, and reduces reliability. Machine parameters dependence is also a disadvantage of these new methods, thus on-line parameter estimation, temperature rise, and saturation should be taken into account in implementing these schemes. Increased computations and control algorithm complexity require the use of powerful processors having high performance capabilities, therefore cost is badly affected. High performance control and estimation of complex