Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-06-19
2001-07-17
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C318S802000
Reexamination Certificate
active
06262896
ABSTRACT:
TECHNICAL FIELD
The present invention relates to power supply systems for lower voltage auxiliary systems on an electric vehicle that use power drawn from a high voltage bus.
BACKGROUND OF THE INVENTION
Electric vehicles, including battery, hybrid, and fuel cell electric vehicles, typically use an inverter in the form of a switch-mode power supply to provide three phase operating power to the vehicle's electric drive motor. The inverter design most commonly used is a pulse width modulated (PWM) voltage source inverter which utilizes power transistors that can supply the high currents needed to satisfy the torque demands required by the vehicle drive motor. The inverter switches power to the motor windings from a high voltage bus of approximately 350-400 Vdc.
In addition to the drive motor used to power the vehicle wheels, an electric vehicle normally includes various auxiliary drive motors to operate a variety of different vehicle systems. Some examples of these auxiliary drive motors include liquid coolant pumps, traction control motors, climate control compressor motors, electronic power steering pumps, as well as other blowers and fans. Although suitable DC motors are commercially available that can operate directly off the 350-400 volt bus, this high voltage operation is generally considered undesirable for various reasons including, for example, reduced motor life due to arcing and other commutation problems. Accordingly, lower voltage motors are sometimes used that can be driven from an intermediate voltage power bus operating at, for example, a fixed 42-48 Vdc. This intermediate voltage supply can be produced using a DC—DC converter that draws operating power from the high voltage bus and develops the fixed DC voltage using conventional DC—DC conversion techniques.
In addition to the intermediate voltage supply, some of the auxiliary power systems utilized on an electric vehicle require a standard vehicle voltage supply of 12 Vdc. This lower voltage bus is typically produced by a separate DC—DC converter that also draws its operating power from the high voltage bus. While providing a more desirable low voltage operation of the various auxiliary vehicle power systems, these 12 and 42 volt dedicated DC—DC converters bring with them a number of inherent disadvantages as well. In particular, each of the DC—DC converters used typically include their own input filter, control circuitry, and power transistors, the last of which requires its own thermal management—usually by way of connecting the converter into the liquid coolant system used for cooling the inverter power transistors. As a result, the DC—DC converters not only take up substantial room in the vehicle power electronics chassis, but also add significantly to the overall vehicle power system cost.
Apart from the use of DC—DC converters operating off the high voltage bus, rotary converters operating off the drive motor are sometimes used to generate the intermediate and lower voltage supplies needed by the vehicle. However, these converters are generally bulky, heavy, and inefficient. Moreover, for rotary converters in the form of an “alternator” that operates off the vehicle heat engine, the converter will not work when the engine is stopped. Where the rotary converter is run off the shaft of an electric motor, a custom design is generally required since most automotive alternators cannot run at the high speeds (8,000-15,000 rpm) of a drive motor.
It is therefore a general object of this invention to provide an electric vehicle power system that eliminates the need for dedicated DC—DC converters to generate the intermediate and/or low voltage supplies utilized for the vehicle's auxiliary power systems.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an electric power system which overcomes the above-noted disadvantages of known systems that use dedicated DC—DC converters to provide auxiliary power conversion. The electric power system of the invention includes a high voltage bus, electric drive motor, auxiliary power circuit, and an inverter that draws operating power from the high voltage bus. The inverter includes a controller and power switching devices coupled to the controller, with the power switching devices being connected in circuit to switch power from the high voltage bus to the drive motor via an output of the inverter. The auxiliary power circuit includes an input coupled to the inverter output and a rectifier having a DC output for supplying DC operating power to one or more auxiliary vehicle systems. The controller operates the power switching devices at upper and lower frequencies to provide lower frequency drive power to the drive motor and upper frequency operating power to the auxiliary power circuit. The drive motor is operable to provide rotation in response to the lower frequency drive power and the auxiliary power circuit is operable to convert the upper frequency operating power to a DC voltage that is supplied to the DC output.
This arrangement eliminates the need for one or more dedicated DC—DC converters by using the controller to inject a high frequency drive signal into the inverter's power switching devices, with the auxiliary power circuit then rectifying the outputted high frequency voltage to thereby provide the desired low and/or intermediate DC voltages. The high frequency is chosen to be a suitably high value that it does not substantially affect operation of the motor and the auxiliary power circuit preferably includes a high pass filter to block the lower frequency drive signals used to operate the motor.
In one embodiment, the auxiliary power circuit is connected directly to the inverter output with a power transformer being used to provide galvanic isolation for the auxiliary power circuit and a step down of the high voltage power to the appropriate peak voltage for subsequent rectification into the desired DC voltage. The transformer can have multiple windings to produce different DC voltages in the event more than one lower voltage DC bus is required or desired. In another embodiment, a dual winding drive motor is used with the auxiliary power circuit being connected to the drive motor's secondary winding. This can eliminate the need for a separate power transformer in the auxiliary power circuit.
REFERENCES:
patent: 5151641 (1992-09-01), Shamoto
patent: 5350994 (1994-09-01), Kinoshita et al.
patent: 6163127 (2000-12-01), Patel et al.
Hiti Silva
Nagashima James
Stancu Constantin C.
General Motors Corporation
Laxton Gary L.
Simon Anthony Luke
Wong Peter S.
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