Modified PI speed controllers for series-excited dc motors fed by dc/dc boost converters

In drive systems, especially for speed regulation, the use of a series-excited dc-motor is prefered in cases where large load changes may occur. In order to design a controller that achieves a fast torque response, in this paper, a complete system consisting of a dc/dc boost converter and a series-excited dc-motor is considered. For the complete system, a modified nonlinear PI speed controller is proposed that provides directly the duty-ratio input of the converter without needing the conventional current inner-loop. In particular, the constant PI speed controller gains are multiplied by a suitable time function that substantially upgrades the whole nonlinear system dynamic performance. Taking into account the complete nonlinear system model, it is shown that the proposed controller acts on the duty-ratio input of the converter providing a continuous input signal exactly in the permitted range [0,1)[0,1), achieves precise motor speed regulation independently from system parameters' variations or load torque changes and guarantees closed-loop system stability and convergence to the desired steady-state equilibrium. Finally, the proposed PI controller performance is verified through extended simulation and experimental results under rapid changes of the reference signal and the external load.