Interactions between Dead-Beat Controlled High-Quality Rectifiers and Input Filters

The paper analyses the stability limitations of the digital ead-beat current control applied to voltage-fed three-phase converters used as PWM rectifiers. In particular, attention is focused on the interactions between the rectifier and the input filters, which are commonly employed to eliminate the high frequency harmonic content from the line currents. The effects of the inherent model mismatch represented by the input filters, which are not normally included in the conventional dead-beat algorithm, are analysed by developing a detailed stability analysis, based on a discrete-time state space model of the controlled system. The proposed analysis allows to predict the occurrence of unstable conditions and to identify some control refinements improving the system's robustness. The results of the theoretical analysis and the validity of the proposed modifications to the control strategy are finally verified by simulations.