Patent ID: 7508089

Claim:
An over speed control circuit for a wind turbine generator system configured to be connected to a power grid, said wind turbine generator system having a generator for generating an output voltage as a function of the speed of the generator, said generator having at least one pair of output terminals and a first switch coupled across the output terminals of said generator which opens for a predetermined time thereby disconnecting said generator from said power grid in response to an overspeed control signal; the control circuit comprising: a measurement circuit for sensing the generator output voltage at the output terminals of said generator; a second switch coupled across the output terminals of said generator which closes in response to a control signal; and a control circuit, responsive to said measurement circuit, for generating a control signal to close said second switch when said generator output voltage is greater than a threshold and generating a control signal to open said second switch when said generator output voltage drops below said threshold defining a pulse width modulated (PWM) control signal, said control signal selected to cause said second switch to close at a lower voltage than said first switch.