Integral cycle control of stand-alone generators

Reducing the cost of small-scale stand-alone generators (up to 100kW), particularly in micro-hydro applications, is of increasing interest. Methods proposed recently include the use of electronic load governors to regulate the generated frequency, and the use of induction generators in place of the more conventional synchronous generator. The use of a load governor results in constant-flow operation of the turbine, and thus eliminates any hydraulic stability problems. Many load governors switch increments of load on a cycle-by-cycle basis. Voltage regulation of induction generators may similarly be achieved by switching steps of capacitance each cycle. This paper analyses the stability of such integral cycle methods for controlling both synchronous and induction generators. The results, along with actual system responses, illustrate the viability of these techniques provided the stability requirements discussed are met.