Load-frequency control of isolated wind-diesel-microhydro hybrid power systems (WDMHPS)

We examine load-frequency control of isolated WDMHPS provided with conventional proportional-plus-integral controllers. The parameters of the controller are optimised for system performance with step or realistic disturbances using an integral-square-error (ISE) criterion. Non-optimum gain settings may result if only step changes are assumed in input wind power or in load. The controller works for a continuous hybrid power system in either a continuous or a discrete mode. System performance deteriorates for discrete control. To evaluate the performance of the hybrid system producing electric power from wind and microhydro by operating with an induction generator and from diesel by using a synchronous alternator, we must consider for the state space model of the hybrid system the load-frequency and blade-pitch controllers in the continuous or discrete mode. A study of the transient responses of the system shows that transient changes in input wind power settle in 12 s while disturbances in load take only 4 s to stabilise.