Research On Novel Space Vector Pulse Width Modulation Technique For Five-Phase Inverter

Recently,with its high power,high performance,high reliability and many other advantages,the multiphase motor drive system has been widely used in the field of electrified transportation,showing a broad application prospect.The development of high performance multiphase motor drive system depends on a number of key techniques and pulse width modulation(PWM)technique is one of them,which is the important foundation and basic premise of its realization.High performance multiphase motor drive system has put forward many new and higher requirements for PWM technique,especially with its rapid development.High bus voltage utilization and low electromagnetic noise are two important aspects.Overmodulation technique can make the multiphase inverter work in the nonlinear modulation region,improving the bus voltage utilization rate and expanding the motor speed range.Random modulation technique can suppress the electromagnetic interference from the source without the change of the topology,reducing the electromagnetic noise.Based on this background,this paper focuses on the overmodulation technique and random modulation technique of five-phase voltage source inverters.Based on the theory of multi-dimensional space decoupling,this paper describes the basic principle of five-phase space vector pulse width modulation(SVPWM)technique in detail.By analyzing and comparing several common five-phase SVPWM algorithms,the nearest four-vector SVPWM algorithm is selected,laying a foundation for the research of new modulation techniques.Then this paper makes an in-depth study on the five-phase overmodulation technique,expounds the basic concept of overmodulation technique,introduces the principle of overmodulation by the traditional synthetic vector method and analyzes the limitations of this method.From the perspective of five phase system control degrees of freedom and based on the nearest four-vector SVPWM algorithm,this paper puts forward a five phase four degrees of freedom SVPWM overmodulation algorithm.The third harmonic content which needs to be optimal controlled is deduced in detail in the overmodulation region according to the modulation ratio.The fundamental wave and the third harmonic subplanes are controlled at the same time without reducing control degrees of freedom,effectively reducing the low harmonic content of output voltage.Through simulation and experiments,effectiveness and correctness of the overmodulation strategy proposed in this paper is verified.Random switching frequency modulation is one of the most common random modulation methods at present.The effect of randomization is closely related to the variation range of switching frequency.However,a wide range of frequency variations may lead to spectrum aliasing and difficulties in regulator design.To further disperse higher harmonics in the narrow switching frequency range,this paper proposes a five-phase SVPWM algorithm with piecewise random switching frequency in half-fundamental period.By improving the random switching frequency modulation method of full fundamental wave period,the switching frequency of two half fundamental wave periods is randomized independently and high harmonics concentrated near the switching frequency and its integer multiples are further reduced,thus better suppressing the electromagnetic noise and interference.Simulation and experimental results show that the new random modulation strategy can further reduce the amplitude of high harmonics within a narrow range of switching frequency variation and realize better dispersion of higher harmonics,which is conducive to the application and promotion of random modulation strategy.In order to verify the proposed modulation strategies,a five-phase inverter experiment platform has been built and corresponding hardware circuit and software module have been designed,including the main power circuit of a five-phase inverter,DSP control circuit,random number generator and interrupt program,etc.Based on the experimental platform,a series of comparative experiments have been carried out,verifying the correctness and feasibility of the proposed new modulation strategies.