Patent ID: 8324846

Claim:
A retarding system for an electric drive machine having an engine that powers a generator, a rectifier connected to the generator, an inverter, and at least one drive motor connected to the inverter, the retarding system comprising: a direct current (DC) link connected to the rectifier and the inverter and including a first DC rail at a first voltage and a second DC rail at a second voltage; a first contactor switch in electrical communication with the first DC rail; a second contactor switch in electrical communication with the second DC rail; a first resistor grid connected in series between the first contactor switch and the second contactor switch; a controller disposed to selectively actuate the first contactor switch and the second contactor switch to conduct a waste current through the first resistor grid between the first DC rail and the second DC rail, the waste current being generated by the at least one drive motor when a motion of the electric drive machine is retarded; an inverter circuit disposed in parallel electrical connection with a portion of the first resistor grid having a resistance that is less than a grid resistance of the first resistor grid, wherein the inverter circuit is configured to control a frequency of an alternating current (AC) voltage being generated in response to a blower command provided by the controller, and wherein the inverter circuit is arranged to convert a DC voltage that is present across the portion of the first resistor grid into the AC voltage; an AC motor electrically connected to the inverter circuit and configured to operate at a variable speed in response to the frequency of the AC voltage; a blower connected to the AC motor; a chopper circuit connected to the first DC rail, and a second resistor grid connected between the chopper circuit and the second DC rail, wherein the chopper circuit is arranged to selectively control a voltage difference applied to the second resistor grid; and a switchable diode disposed in series with the second resistor grid and in parallel with the chopper circuit between the first DC rail and the second resistor grid, the switchable diode being selectively connectable between the second resistor grid with the first DC rail continuously to equalize the first and second voltages and thus deactivate the DC link during service; wherein the blower is arranged to provide convective cooling of the first resistor grid when the AC motor is operating.