Optimal nonlinear firing angle control of converter-fed DC drive systems

A firing angle control of DC drive systems consisting of a DC motor fed by a three-phase thyristor rectifier is proposed. The two main types of DC machine, namely the series-connected and the shunt-connected, are considered and their complete nonlinear continuous-time models together with the nonlinear model of the rectifier are used. For control purposes, suitable nonlinear transformations are introduced to modify the nonlinear models of the DC drive systems into partly linear ones. Consequently, feedback linearisation methods combined with optimal control designs are applied to provide proportional-integral control strategies. However, since the firing angle control is in practice applied at distinct instants, the resulting continuous-time control schemes are transformed into discrete-time ones with the sampling time varying in accordance to the firing angle changes. Extensive simulation studies have been conducted to evaluate the effectiveness of the proposed method