Inverter apparatus and method therefor

An inverter apparatus comprising a power module case supporting a power module containing main circuit semiconductor devices, a body accommodating a printed circuit board, a setting section and a display section, and a heat sink for cooling said power module, wherein said body is disposed on said power module case and fastened to said power module case by fastening means, said printed circuit board being guided to a predetermined position on said power module case by guiding means and secured to said power module case by first screw members, and said power module case being disposed in a predetermined position on said heat sink by positioning means, and wherein said power module case and heat sink are fastened integrally from above said body by second screw members.

Method for using an inverter apparatus comprising a power module case, containing at least a portion of a converter circuit and an inverter circuit with a adjustable switching frequency, and a heat sink fitted to the cooling surface of said power module case and having a cooling capacity matched to an operating frequency, comprising:

• adjusting the switching frequency of said inverter circuits, and
• changing said heat sink such that a first heat sink higher in cooling capacity is used when the switching frequency of said inverter circuit is not less than a predetermined value, and a second heat sink lower in cooling capacity is used when the switching frequency of the inverter circuit in said inverter apparatus is less than said predetermined value.