Model of a self-excited induction generator for the design of capacitor-controlled voltage regulators

The systematic design of voltage regulation systems for self-excited induction generators requires the development of a control-oriented model. The paper considers the situation where the peak magnitude of the stator voltages is regulated through adjustable capacitors connected to the windings. A transfer function model is difficult to obtain, due to the strong nonlinearity of the self-excitation phenomenon, and to unconventional features of the problem. Nevertheless, the paper succeeds in computing a transfer function relating small deviations of the capacitance to small deviations of the voltage magnitude using a clever choice of reference frame. The linearized system is found to be stable for all operating points under consideration, and the eigenvalues of the system predict rapidly-decaying oscillatory transients combined with a slower exponentially decaying component. Results of simulations of the full nonlinear model and of the linearized system demonstrate the validity of the approximation for small deviations. Experimental results also show a good match between measured data and the identified model.