Analysis of a hybrid PWM based on modified space-vector and triangle-comparison methods

Abstract

A classical space-vector pulsewidth modulator (PWM) with equal duration of application of zero-state vectors V/sub 0/ and V/sub 7/ was modified. A factor-variable k/sub 0/ (proportional to the time of application of vector V/sub 7/) was introduced. By changing k/sub 0/ from zero to one, the duration of application of V/sub 7/ can be changed from 0% to 100% of the combined application time for zero-state vectors. Correlation between modified space-vector and triangle-comparison methods (with added zero sequence) was established. The influence of factor k/sub 0/ on characteristics of the PWM was investigated. An expression for the optimal value of k/sub 0/ that provides minimum ripple in the load current was derived. Salient features of the new algorithm are extended linearity (up to a modulation index of 1.154), reduced switching losses, and ability to change the current spectrum by changing k/sub 0/ every sampling time. The developed algorithm is suitable for microprocessor and analog implementation. Since the new algorithm combines the theory of space-vector PWM with the ease of implementation of a triangle-comparison PWM, it is named "hybrid" PWM (HPWM).