Large signal models and control design for high power-factor preconditioners

Large signal models are derived for a boost converter operating as a single-phase high power-factor preconditioner. A design procedure is presented for a PWM system with nested control loops for input current and output voltage. The inner (current) loop model is found to be linear in the large, consisting of the often used small signal model and a distortion term. The switching effects are accounted for by the insertion of a PWM describing function block in the feedback path. It is shown that careful controller design is required to avoid input current distortion or subharmonic oscillation. Controllers for the voltage loop are evaluated by analysis of the linearised plant and simulation of the full nonlinear model. The effect of input voltage feedforward with finite response time filters is investigated. Experimental results are used to corroborate the majority of the analysis