Easy digital control of three-phase PWM convertor

The authors describe the design of a digital controller using a digital signal processor (DSP) for a sinusoidal input current three-phase pulsewidth-modulated (PWM) converter. The controller adopts a proportional compensator for current control. The current control system lag-time caused by the DSP operation time is decreased to less than one sample period by a method which acquires the currents in the interval between consecutive samples. The PWM converter is modeled, and, using the modified z-transfer, the characteristic equation of the input current control system including the lag-time is established. Using the characteristic equation, the controller is designed by a conventional root locus method. The results of a simulation and an experiment indicate the validity of this analysis and the design method