Power smoothing in a variable speed wind-diesel system

In wind-diesel systems wind speed variations can produce frequent start/stop cycles of the diesel engine in response to periods of low wind speed. Consequently, an energy buffer is very important in these schemes to avoid unnecessary deterioration of the diesel engine. In this paper, control systems for the operation of a variable speed wind-diesel system, including power smoothing, are analyzed. The power smoothing system comprises a front-end converter, a flywheel energy store and a vector controlled induction machine. The wind energy conversion system comprises a variable speed wind turbine and back to back converters for interfacing the variable speed generator to the load. Control of the power smoothing system compensates for the effects of wind variation and load disturbances. The operation of the whole system including the wind turbine, front-end converter, control of active and reactive power supply is discussed as well as the vector control system of the induction machine driving the flywheel. Simulation results for the entire system for a number of operational conditions are presented. Experimental results are provided for the control of the flywheel energy store.