Patent ID: 8884575

Claim:
A drive system of a synchronous electrical motor comprising: a synchronous electrical motor; a power converter that is connected to the synchronous electrical motor and that is constituted of a plurality of switching elements; a controller that controls the synchronous electrical motor by outputting a voltage instruction to the power converter; a voltage detection unit that detects induced voltages at respective open phases upon application of respective positive and negative pulse voltages between respective two phases out of three-phase windings of the synchronous electrical motor; an induced voltage difference calculating unit that calculates an induced voltage difference that is a difference between an induced voltage detected by the voltage detection unit at each of the open phases upon application of the positive voltage pulse between the corresponding two phases and an induced voltage detected by the voltage detection unit at the open phase upon application of the negative voltage pulse between the two phases; an induced voltage sum calculating unit that calculates an induced voltage sum that is a sum of the induced voltage detected by the voltage detection unit at each of the open phases upon application of the positive voltage pulse between the corresponding two phases and the induced voltage detected by the voltage detection unit at the open phase upon application of the negative voltage pulse between the two phases; and a rotor position determining unit that determines a rotor position based on the induced voltage difference and the induced voltage sum.