Semiconductor device, motor drive system, and method of starting motor

A motor drive system comprising:

• a three-phase motor;
• an inverter circuit configured to drive the three-phase motor, and comprising output nodes corresponding to each phase of the three-phase motor;
• a detection circuit coupled to the output nodes, and configured to detect a voltage generated in the output node of a non-energized phase of the three-phase;
• and
• a controller,
• wherein, at a time of starting the three-phase motor, the controller applies a drive voltage to any two phases of the three-phase motor by the inverter circuit based on an estimated magnetic pole position of a rotor in a stop state, and the controller estimates a position of the rotor based on a difference voltage between a detected voltage by the detector circuit during a drive voltage applying period and a detected voltage by the detector circuit during a regeneration period immediately after or immediately before the drive voltage applying period.

A motor starting method comprising:

• estimating a magnetic pole position of a rotor in a stop state at a time of starting a three-phase motor;
• applying a drive voltage to any two phases of the three-phase motor based on the estimated magnetic pole position of the rotor in the stop state;
• and
• estimating a position of the rotor based on a difference voltage between an induced voltage generated in non-energized phase during a drive voltage applying period and an induced voltage generated in non-energized phase during a regeneration period immediately after or immediately before the drive voltage applying period.