Design of an active front-end rectifier controller with an accurate estimation for the dynamic of its deadbeat current control loop

This paper proposes a control strategy for a grid-connected single-phase Active Front-End (AFE) rectifier that deals with both of ac-side sinusoidal current quality during steady state and dc-bus voltage fluctuations under transient operation issues. This control strategy consists of two control loops. The outer one is used for the control of the dc-bus voltage and is based on a PI controller. The inner loop is used for the control of the grid current and is based on a Deadbeat Predictive (DP) controller that operates with a fixed switching frequency. In order to prevent interactions between the two control loops, the outer control loop dynamic should be at least ten times lower than that of the inner control loop dynamic. For this purpose, a theoretical approach for computing the dynamic of the deadbeat predictive current control is described. Then, the dc-bus voltage controller is designed so that the following constraints are satisfied: (a) the bandwidth of the voltage control loop must be very low with regard to that of the current control loop to prevent interaction between them; (b) the third harmonic component of the grid current resulting from the double line frequency ripples of the measured dc-bus voltage has to be mitigated complying with standards, and (c) reducing the transient fluctuations of the dc-bus voltage caused by instantaneous and high level changes of the active power consumed by the dc load. Simulation and experimental results for the control algorithm validation are also presented and discussed.