Patent ID: 8743568

Claim:
A method of designing a current supply circuit applied with an AC voltage of a predetermined effective value voltage to output a polyphase AC current to a polyphase load of a predetermined rated power, said current supply circuit comprising a polyphase inverter circuit, said polyphase inverter circuit including series connection of two switching elements for each phase, and outputting said AC current of each phase from a node of said series connection, and said method comprising the steps of: (a) setting a current value as a rated current value of said polyphase inverter circuit, said current value being obtained by dividing said rated power of said polyphase load by a voltage value being twice said effective value voltage; and (b) selecting said switching element having a second breakdown voltage based on said rated current value, said second breakdown voltage being twice a first breakdown voltage required of said switching element when a DC voltage obtained by performing full-wave rectification on said AC voltage is input to said polyphase inverter circuit, wherein said switching element is an IGBT element, and in said step (b), an increment of turn-on losses in rated current value of said IGBT element having said second breakdown voltage with reference to turn-on losses in rated current value of said IGBT element having said first breakdown voltage is defined as a divisor, the product of a first value, a second value, and a third value is defined as a dividend, said first value being obtained by subtracting an increment of a saturation voltage of said IGBT element having said second breakdown voltage with reference to a saturation voltage of said IGBT element having said first breakdown voltage from said saturation voltage, said second value being a maximum value of an output current of said inverter in terms of sinusoidal wave, and said third value being π/16, and said IGBT element having said second breakdown voltage is selected in an area with a lower switching frequency of said inverter than the result obtained by dividing said dividend by said divisor.