Digital AFC Control of a Three-Phase Three-Wire Unity-Power-Factor PWM Rectifier

Nowadays, ac/dc power converters must fulfill more and more design constraints with respect to the electrical grid: harmonics reduction, operation with sags and swells and/or high grid impedances, etc. This is a challenge for the controllers, since they must be robust enough to ensure the stability of the system, specially when working the conditions are not the ideal ones. In this paper, a discrete-time control technique based on Adaptive Feed-forward Cancellation (AFC) is proposed for a three-phase three-wire rectifier with a LCL input filter. The continuous-time design method for resonators has been translated into the discrete-time domain. Thus, the controller has been entirely designed in discrete-time, avoiding approximate conversions of the controller from the continuous-time domain. Besides, the usual unit computational delay in sampled-data control systems is taken into account. The simulation results show that this kind of resonant control is not only robust, but also presents a good performance.