Influence of non-linear loads on the operation and power flow of induction generators

This paper considers the analysis and operation of an autonomous three-phase squirrel cage induction generator when it is feeding linear and non-linear loads. The nonlinear load comprises of a static voltage and frequency dependent component and a three-phase diode rectifier supplying a composite load containing constant power, constant current and constant resistance components. The dynamic model of the generator accounts for the effect of the main air-gap flux linkage saturation which with the excitation capacitors determines the steady-state operating points. Extensive simulation results are provided showing the starting transients and loading dynamics of the generator. The inducement of oscillations in the frequency and waveforms of generator variables due to the presence of the three-phase diode rectifier when the generator runs at a constant rotor speed are exemplified. The flows of the real and reactive powers with the rectifier load show that although the average active powers in capacitors and inductances are zero over the switching period of the three-phase diode rectifier, they are non-zero instantaneously and time-varying. Some experimental steady-state characteristics results obtained from an induction generator feeding a rectifier and an AC load are provided.