Digital state feedback control of a three phase sinusoidal PWM inverter

This paper proposes a method of three phase voltage control of a sinusoidal PWM (pulse width modulation) inverter. The state equation of the inverter main circuit is derived and transformed to the d-q frame. An algorithm of dead-beat control is then developed by considering only the load current as a disturbing variable. The advantage of dead-beat control is that it can control very quickly within a short time (sampling period) as compared to other methods. The main objective of the controller design is to obtain a sinusoidal voltage at the inverter output with low harmonic distortions. To compensate the calculation delay and to realize the invertor physically, a 3rd order prediction method is adopted and a new switching technique is developed. This switching technique can reduce unnecessary switching so that switching loss can be minimized. Finally, simulations are carried out under typical load conditions (rectifier with capacitor load) and harmonic analysis is also performed. Throughout all simulations, very good results are shown where total harmonic distortions (THD) are less than 5%