Real-time digital control of PWM inverter with PI compensator for uninterruptible power supply

A method is presented for real-time digital control of PWM (pulsewidth-modulation) inverters for UPS application. Using two state variables (output voltage and load current) measured at every sampling time, the DSP (digital signal processor) carries out the real-time calculation of the inverter pulsewidth for the next sampling time. Maximum pulsewidth and robustness to the system parameter variation are obtained by using the next sampling pulsewidth calculation and the PI compensation, respectively. The control scheme was verified through simulation and experiment for various cases, including sudden load change, system parameter variation, and the nonlinear load condition, and it provides excellent transient response and robustness for various load conditions