Study On Optimal Control Strategy Of PWM In Vector Control System

ABSTRACT Electrical Vehicle (EV) is gradually becoming the focus of research in its fieldand is a kind of ideal green vehicle as the problems of energy and environment arebecoming more and more serious in the 21st century. The energy in EV is provided bystorage batteries instead of traditional gasoline, but the dynamic characters of motorand the driving distance of EV are limited by the capacity of its storage batteries withcurrent technologies. It's the key of solving problems to study on optimal controlstrategies and to improve the working efficiency of motor driving systems at present. The aim of this thesis is to do some research on optimal control strategies ofinverters in vector control system of IM (Induction Motor). The deficiencies involtage utilities and switching frequencies of power switches (IGBT) at fixed PWMperiod of traditional voltage sinusoidal PWM (SPWM) are analyzed in detail at thefirst part of this thesis, and some concrete optimized methods are given and simulatedby computer. The working principles and concrete realization methods of SpaceVector PWM (SVPWM), which is used widely recently, are introduced at length. Thedeficiencies of SVPWM in decreasing switching losses are analyzed, and someexplicit optimized methods are given and compared by computer simulations. NormalSPWM, optimized SPWM, SVPWM and optimized SVPWM are compared based onprevious work, and the differences and relations between them are pointed outdetailedly. The optimized SVPWM of distributing the none-switching areas of eachphase of voltage, which is 60o in each half period of sinusoid, to the two sides ofcurrent peaks symmetrically is proved to be the ideal control method by theoreticalanalysis and computer simulations. The implementation methods of SVPWM andoptimized SVPWM in DSP of TMS320LF2407 are introduced at the last part of thisthesis. The experimental results in practical systems demonstrate that the efficiency ofthe controllers has been dramatically improved after adopting SVPWM strategies.