A Kind Of Simplified Multilevel Space Vector PWM Control Strategy Based On Control Degrees Of Freedom Combination

The modular cascaded H-bridge multilevel inverters,which have the advantages of convenient installation,easy expansion and convenient maintenance are used more and more popular in medium and high power variable frequency speed regulation applications.In order to adapt to the modular structure of cascaded H-bridge multilevel inverter,this paper takes the three-phase cascaded H-bridge multilevel inverter as the research object and then the general,simplified control strategy of multilevel Space Vector Pulse Width Modulation(SVPWM)is studied in depth.Firstly,the paper introduces the technology of SVPWM.It is point out that the digital implementation of the traditional multilevel SVPWM has the characteristics that it is difficult to be realized with the increase of the number of cascaded cells.The digital realization process of the two-level SVPWM and the sinusoidal pulse width modulation(SPWM)is compared and analyzed.Then the unified theory of the two is established through formula deduction and graph inference.And the control ideology of simplified multilevel SVPWM based on control degree of freedom combination is proposed.Secondly,a kind of simplified multilevel space vector PWM which consists of vector phase shift,virtual carrier phase shift and virtual carrier phase disposition SVPWM based on two-level SVPWM,is proposed by deconstructing and reorganizing the degrees of freedom of the virtual triangular carrier and modulation wave.Then the disposition of virtual modulation wave and carrier,the distribution of switching state and sequence when synthesizing the reference vector and the perspective of vector synthesis are analyzed to describe the synthetic essence of the proposed multilevel SVPWM method.The novel algorithms based on control degrees of freedom combination changes a routine of locating and calculating the reference vector in a complicated voltage vector space by decomposing the vector with less dwell times.More importantly,it is absolutely general and can be directly applied to any voltage level of the cascaded H-bridge inverter.Finally,an experimental platform of cascaded H-bridge multilevel inverter based on Microchip’s dsPIC33EP512MU810 is built and the main power circuit and control circuit and auxiliary power supply is designed after the in-depth theoretical analysis.Both simulation and experimental results are provided to demonstrate the algorithms.