Patent ID: 8232751

Claim:
A drive system of a synchronous motor comprising: an inverter outputting a sine-wave AC current; a three-phase synchronous motor connected to the inverter; a first controller detecting a neutral-point potential of the three-phase synchronous motor and outputting a pulse-width modulation signal to the inverter based on a result of the detection, thereby controlling the inverter; a second controller provided with a circuit that detects or estimates an induced voltage of the three-phase synchronous motor and outputting a pulse-width modulation signal to the inverter based on a detection value or an estimation value of the induced voltage, thereby controlling the inverter; and a virtual neutral-point circuit which generates a virtual neutral-point potential with respect to an output voltage of the inverter, wherein the first controller includes a sample/hold circuit which derives a sampling value by synchronizing the neutral-point potential of the three-phase synchronous motor with the pulse-width modulation signal, wherein the sample/hold circuit receives a value with respect to a difference between the virtual neutral-point potential generated by the virtual neutral-point circuit and a three-phase coil connecting point potential of the three-phase synchronous motor, and wherein, based on the sampling value, the first controller estimates a position of a rotor of the three-phase synchronous motor.