Robust dead-beat current control for PWM rectifiers and active filters

The paper analyses the stability limitations of the digital dead-beat current control applied to voltage-source three-phase converters used as PWM rectifiers and/or active filters. In these applications the conventional control algorithm, as used in drive applications, is not sufficiently robust and stability problems may arise for the current control loop. The current loop is, indeed, particularly sensitive to any model mismatch and to the possibly incorrect identification of the model parameters. A detailed analysis of the stability limitations of the commonly adopted dead-beat algorithm, based on a discrete-time state space model of the controlled system, is presented. A modified line voltage estimation technique is proposed, which increases the control´s robustness to parameter mismatches. The results of the theoretical analysis and the validity of the proposed modification to the control strategy are finally verified both by simulations and by experimental tests.