Patent ID: 8222857

Claim:
A motor controlling device that controls an alternating-current motor by outputting a pulse width modulation signal to a switching element included in an inverter that is connected to a direct-current power source and is operable to output an alternating current having an arbitrary frequency and an arbitrary voltage to the alternating-current motor, the motor controlling device comprising: a pulse mode controlling unit that is operable to selectively switch among a plurality of pulse modes each of which can serve as an output pattern of the pulse width modulation signal, the plurality of pulse modes including a synchronous pulse mode, an asynchronous pulse mode, and a one-pulse mode, wherein the pulse mode controlling unit switches between the synchronous pulse mode and the asynchronous pulse mode based on a quantity related to an output voltage amplitude of the inverter and a quantity related to an output frequency of the inverter, the pulse mode controlling unit switches from the asynchronous pulse mode to the synchronous pulse mode in a situation where the quantity related to the output voltage amplitude of the inverter has become equal to or larger than a first set value or in a situation where the quantity related to the output frequency of the inverter has become equal to or larger than a second set value, and the pulse mode controlling unit switches from the synchronous pulse mode to the asynchronous pulse mode in a situation where the quantity related to the output voltage amplitude of the inverter has become smaller than the first set value, and also, the quantity related to the output frequency of the inverter has become smaller than the second set value.