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PWM control of multi-phase inverter is one of the key technologies in the ships electrical propulsion. In this paper, a novel discontinuous space vector PWM (DSVPWM) method of multiphase inverter is proposed by arranging the two zero vectors skillfully. Comparing with the continuous space vector PWM (CSVPWM) method the DSVPWM use only one zero vector in one switching period, so the switching loss is only four fifths of the CSVPWM. However, the output target line voltages of DSVPWM are still sine wave, the harmonic performance is excelled that of traditional SVPWM (TSVPWM) therefore. Several classic DSVPWM realization methods are given, and the operation characteristic, adapted load types and total harmonic distortion rate of them are analyzed and simulated.Index Terms--multiphase inverter; discontinuous space vector PWM; zero vector; total harmonic distortion rate

Aiming at five-phase permanent magnetism synchronous motor (PMSM), this paper sets up the variablefrequency variable-speed system supplied with three-level inverter and makes study about PWM control algorithm of five-phase three-level inverter. In multilevel inverter, Switching Frequency Optimal PWM(SFOPWM) has many advantages such as high voltage usage and simple control, but the calculation of zero-sequence component in the fivephase three-level inverter need to be studied. This paper propose a calculation method of zero-sequence component in five-phase inverter, which is proved in SFOPWM. For multi-phase multi-level inverter, the numbers of voltage vector and switching state grow rapidly with the increment of phase and level. On the basis of profound analysis about characteristic and rule of five-phase three-level inverter's voltage vector, a simple and practical control algorithm of voltage space vector PWM(SVPWM) is put forward, and it is proved by simulation experiment.Index Terms-five-phase three-level inverter,SFOPWM, SVPWM.

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