Low-inductance, high-efficiency induction machine and method of making same

#Embodiments of the invention relate generally to induction motors having a low leakage inductance and, more particularly, to a method and system for designing low-inductance, high-efficiency induction machines by providing power converters that include silicon carbide metal-oxide-semiconductor field effect transistors (MOSFETs).

#Induction machines are typically driven using a power converter with active silicon switching devices. The switching devices are typically operated using a pulse-width modulation (PWM) technique to convert a DC supply power to an AC power that can be used to drive the induction machine. In PWM, the switching devices are driven using a train of DC pulses. When a voltage is suddenly applied from the power converter across an inductive load, the current through the load rises almost linearly with time. When the voltage is then turned off, the current through the load does not immediately fall to zero but decreases approximately linearly with time, as the inductor's magnetic field collapses, and the current flows in a freewheeling diode. Thus, the input voltage pulses applied across the load by the power converter resembles a jagged current waveform. The variation in output current is typically known as the current ripple.

#Current ripple is generally undesirable because it wastes energy in the inductor and may cause unwanted pulsations in the load. Current ripple produces undesirable EMI and mechanical vibrations, and generates harmonic losses in the motor. The harmonic current runs through the stator and rotor conductors and gives rise to harmonic copper losses, and the harmonic flux confines itself to the surface of the cores and creates harmonic core losses in the stator and rotor teeth. The higher the current ripple, the lower the quality of the current waveform of an induction machine.

#The drawings illustrate embodiments presently contemplated for carrying out the invention.

#In the drawings:

#FIG. 1 illustrates a conventional induction machine drive system.

#FIG. 1 illustrates a conventional three-phase induction machine drive system 10. System 10 includes a DC link 12 that provides a DC input voltage that is converted or inverted to an AC waveform that powers an AC induction machine 14. An input filter capacitor 16 is coupled across the DC link 12 for filtering the voltage VDC on the DC link 12. A power converter 18 receives the input voltage from DC link 12 when power flows from the DC link 12 to the AC induction machine 14. This direction of power flow is often referred to operating in a “motoring” mode. When the direction of power flow is from the induction machine 14 to the power converter 18, the input voltage to the power converter 18 is AC from the induction machine 14, while the output from the power converter 18 is a DC voltage on the DC link 12. Operation with power flow from the AC induction machine 14 to the power converter 18 is often referred to operation in a regenerative braking mode that is useful, for example, in a vehicle where it is desirable to hold a given value of speed on a downhill grade, or while decelerating the vehicle.

#Power converter 18 is a typical 3-phase inverter having two series-connected switching devices per phase leg. For example, devices 20 and 22 form a first phase leg, devices 24 and 26 form a second phase leg, and devices 28 and 30 form a third phase leg. Devices 20-30 are conventional silicon semiconductor switching devices such as, for example, silicon IGBT, MOSFET, silicon bi-polar Darlington power transistor, GTO, SCR, or IGCT type devices that have a switching frequency of no more than 15-20 kHz depending on the power rating of induction machine 14. Diodes 32, 34, 36, 38, 40, 42 are coupled in anti-parallel relationship across respective silicon switching devices 20-30.

#FIG. 2 illustrates an induction machine drive system 44 in accordance with an embodiment of the invention. Drive system 44 includes a DC link 46 having a DC source voltage VS 48. Drive system 44 also includes a power source 50 that provides DC source voltage VS 48. In one embodiment, power source 50 includes an AC source 54 and a rectifier 52 configured to convert a voltage of AC source 54 to the DC link or source voltage VS. In another embodiment, power source 50 includes a DC power source 54, such as a battery, a fuel cell, or a flywheel with an associated power electronic converter. In yet another embodiment, power source 50 includes a DC power source 54, such as a battery, a fuel cell, an ultracapacitor, or a flywheel with associated power electronic control coupled to a bi-directional DC-to-DC voltage converter 52 that boosts the source voltage to the DC link or source voltage Vs. DC link 46 supplies a DC output voltage VDC 56 to a power converter or inverter 58, which drives an induction machine 60. An input filter capacitor 62 is illustrated between a positive DC rail 64 and a negative DC rail 66 and serves to provide a filter function for the high frequency currents from power source 50 to ensure the power quality between positive and negative rails 64, 66.