A Two-Frequency Quasi Six-Phase Voltage Source Inverter Based on Space Vector PWM

With development of series multi-phase motor drives and harmonic injection technique to enhance torque fin multi-phase motor drives, there is an immense need for multifrequency PWM voltage source inverters (VSI) The PWM techniques used in the previous works are either of ramp-comparison or of hysteresis type The first suffer from implementation difficulties and the second has the high variable switching frequency drawback (difficulties of LC input EMI filter design) SVM possesses many advantages over the mentioned PWM techniques and It can he used in multiphase drive applications One of the most popular multi-phase machines is quasi six-phase (QS) machine The phasor diagram of a QS system and a two level six phase VSI are depicted in Fig I Despite the three-phase case the numbers of switching vectors are very high (refer to Fig 2) and the removal of low-order harmonics in SVM six-phase systems is so complicated In this paper, a two frequency QS SVM VSI is designed and implemented The approach improves the performance of the system in terms of total harmonic distortion (THD) and DC-bus utilization The resulted SVM VSI is used to generate two reference vectors for two series QS machines Some analysis and discussions are given through the development of the SVM technique, compute! simulation and practical results