Carrier Based Pwm-vsi Drives In The Overmodulation Region

Pulse Width Modulated Voltage Source Inverters (PWM-VSI) are widely utilized in motor drive and other three-phase power conversion applications a.s voltage/ current sources with controllable output frequency and magnitude. The choice of pulse width modulation method strongly affects the inverter energy efficiency, waveform quality, and voltage linearity. However, the dependence of these performance characteristics on the modulator type is not well understood. This thesis attempts an in-depth analysis of switching loss, waveform quality, and voltage linearity characteristics of the modern PWM methods. The analytical results aid the development of simple, yet highly efficient modulation strategies and control algorithms. A Generalized Discontinuous PWM method (GDPWM) which minimizes the switching losses and provides a wide voltage linearity range ha.s been developed. Algorithms which combine the superior performance characteristics of the GDPWM method with other high performance PWM methods have been established. Modulator voltage linearity characteristics have been thoroughly investigated. Both the per carrier cycle voltage linearity and per output voltage fundamental cycle voltage linearity characteristics have been analytically modeled. In the nonlinear modulation (overmodulation) range, the influence of the modulator nonlinearity on the drive steady state and dynamic performance ha.s been thoroughly investigated. As a result high performance overmodulation algorithms could be developed for various drives and applications. With a strong emphasis on the overmodulation region performance of both open loop voltage feedforward controlled drives and closed loop current controlled drives, all the performance characteristics could be enhanced by employing the novel modulation methods and control algorithms. The theory has been supported with computer simulations and laboratory experiments and strong correlation has been obtained. In addition to developing new modulation methods and control algorithms, this thesis establishes analytical and graphical methods for the study, performance evaluation, and design of the modern PWM methods. Also simple techniques for generating the modulation waves of the high performance PWM methods are described.