SVPWM Based Multilevel Inverter for PMSM Drive

Abstract

The conventional PWM inverters are able to generate mostly two-level output waveforms. Many improvements have been proposed to classic configuration as regards the circuit structures, the control schemes, but the inverter performance was limited by the available number of levels to build the output voltage. To overcome these difficulties several topologies of multilevel inverter have been recently designed and they are now capturing the attention of many industries, specially for high power converters on account of certain advantages that these inverters have as compared to conventional PWM inverters like less switching losses, reduced harmonic losses, etc. In spite of these advantages some problems are also associated with these inverters. Out of these, capacitor voltage unbalance is prominent one. In this thesis, the Space Vector Pulse Width Modulation (SVPWM) technique has been applied to Permanent Magnet Synchronous Motor (PMSM) to formulate the switching pattern mainly for three-level inverter that minimizes the harmonic distortion at the inverter output.

PMSM are widely used in low and mid power applications such as computer peripheral equipments, robotics, adjustable speed drives and electric vehicles. The growth in the market of PMSM motor drives has demanded the need of simulation tool capable of handling motor drive simulations. There is a need for controllable AC device which can supply required variable AC voltage to the drives. This controllable AC voltage is obtained from an inverter. The voltage in an inverter is controlled by various controlling techniques. This thesis mainly concerns to a controlling technique known as Space Vector Pulse Width Modulation which is computationally intensive and efficient method and is proved that, SVPWM technique will generate less number of harmonics than the conventional Sinusoidal PWM method. It has been proved that in a three-level inverter, speed remains unchanged irrespective of change in the load and less number of harmonics will be generated compared to a two-level inverter.