Comparison of quasi bang-bang and sliding mode controls for a DC shunt motor with time delay

We propose a hybrid fuzzy-linear controller for a nonlinear terminal voltage-controlled DC motor. The nonlinearity includes the effect of magnetization saturation and a nonlinear fan load. The input to the proposed Fuzzy Logic Controller (FLC) is an `aggregate' error between the required and the actual rpm and its time derivatives. The FLC is designed to approximate a bang-bang controller and its coefficients are chosen as a tradeoff between short rise time, small steady-state errors, and control chattering. The FLC performance was compared to that of a well-known design; namely a sliding mode controller with a boundary layer. Although the FLC design procedure is easier, the performance of the two controllers are quite similar. Unfortunately, the FLC design was not robust enough to counter the effect of large time delays introduced by the power electronics interface.