A new multiple-loops control scheme for a three-phase/switch/level PWM rectifier based on the input/output feedback linearization technique

In this paper, a new nonlinear control system is developed and applied to a three-phase, three-switch, three-level AC-to-DC converter. The derivation of the proposed control law is based on a fourth-order low-frequency time-invariant nonlinear state model of the converter. This mathematical model, expressed in a rotating frame, is obtained using averaging techniques over a double time base. The proposed control law is designed on the basis of a multiple-loops control strategy, where an exact input-output feedback linearization is applied to the inner and outer loops. The regulators are designed in order to ensure the shaping of the line-currents, the regulation of the DC output voltage and the compensation of the DC load unbalance. The performances of the proposed control law in steady state and transient regimes are then analyzed by numerical simulations. In this purpose, a digital version of the converter is implemented in the Matlab/Simulink framework, using the switching function approach. The obtained simulation results show a nearly zero current harmonic distortion, a unity displacement factor, a low output voltage ripple, and a high robustness to DC load unbalance.