Inverter for an electric motor

Abstract

An oil-cooled inverter for an electric traction motor that uses six IGBT switches to generate 3-phase AC electrical current as its output. The switches are mounted on heat sinks that use hot motor oil (hydraulic fluid) as the heat transfer fluid. An interior of each of the heat sinks contains a heat transfer medium. The heat sink housing is made of molybdenum, which has a thermal expansion rate equal to that of silicon. This allows the circuitry of the inverter to be mounted directly on the top surface of the heat sinks, as the expansion and contraction of the heat sink housing will match that of the silicon substrate of the chips. Since both elements, the heat sink housing and the chip substrate, expand and contract at an equal rate during heating and cooling, the problem of the chip substrate cracking and breaking due to thermal flexing is eliminated. The inverter is in most ways electrically equivalent to prior art inverters, but the upper surface formed by the bank of heat sinks is electrically hot, and is used as part of the inverter circuitry. This allows the elimination of the insulating plate on which the inverter circuitry is normally mounted, as the chips of the inverter circuitry are mounted directly on the upper surface of the heat sinks of the inverter.