Patent ID: 8436563

Claim:
A control unit of a permanent magnet synchronous motor comprising: a DC power supply, an inverter for converting DC power supplied from said DC power supply to AC power, said permanent magnet synchronous motor supplied with said AC power via multi-phase output terminals of said inverter, a phase inferring means for inferring a phase of a rotor of said permanent magnet synchronous motor on the basis of a magnitude relation between an inter-line voltage, between a phase voltage having a minimum value of the multi-phase electrical potentials generated at said output terminals of said inverter and another phase voltage, and a predetermined threshold voltage when said permanent magnet synchronous motor runs free, and a rotational direction inferring means for inferring a rotational direction of said free-running permanent magnet synchronous motor on the basis of magnitude relations between said at least two different inter-line voltages and said threshold voltage.