Variable structure controller for AC/DC boost converter

Control of AC/DC converter in presence of unknown time-varying load is a complex task due to the strong nonlinearity inherent in the converter structure and to the ones introduced by the load. When robust control techniques are used for stabilizing converter output voltage, particular care must be used to avoid degradation of the input power factor. A variable structure controller for AC/DC boost converter ensuring both robustness to load variations and near-unity power factor is considered. Owing to the separate dynamics of the input current and of the output voltage, a cascade control structure is used. The reference for the inner current loop is a sinusoidal waveform whose amplitude is modulated by the external voltage controller. The current regulator is a hysteresis-type, in which the zero-voltage control is purposely used within the hysteresis band in order to reduce high frequency chattering and hence harmonic distortion. In the external voltage loop a dynamical sliding-mode regulator is used to guarantee system robustness without introducing discontinuous control action