Autonomous Wind-Generated Electricity for Induction Motors

A wind turbine with variable-voltage, variable-frequency electrical output was used to power resistive loads and induction motors in an autonomous system. The AC system was selected because AC motors, in multiple kilowatt sizes, can be more practical than DC motors. A wind turbine which produces electricity has a lower overall efficiency than a system producing mechanical power but offers more flexibility in adapting to varying loads and in locating the wind turbine near the load. A permanent magnet alternator designed to operate with a rotor speed from 70 to 150 r/min was first operated in the laboratory. The frequency of the output varied from 30 to 65 Hz, while the voltage changed from 85 to 218 V, resulting in voltage to frequency ratios (V/f) from 2.6 to 3.3 with various loads. The alternator, with a maximum rated output of 9 kW, provided power to resistive load or induction motor loads. The tests revealed that standard three-phase, 240 V, 60 Hz, AC induction motors will operate with an input of 85 V and 30 Hz. A motor temperature rise of 40° C above ambient was not exceeded when power was supplied by the alternator to a 7.6 kW motor. System efficiencies were nearly equivalent to those obtained with utility power, even though the V/f was below that calculated from the motor’s nameplate. The wind energy conversion system (WECS) was then operated in wind-speeds of 3.5 m/s or greater. This WECS was capable of providing power to satisfactorily operate induction motors in an autonomous system.