4-2. To Start with Square-Wave Drive

In the case of sensorless square-wave drive, induced electromotive force is not generated on starting, and the rotor position cannot be identified.
Therefore, the following procedure is necessary to start.

• (1) First, forcibly flow the current to the specified coil to move the rotor to the specific position.
• (2) Flow current in the coil with low voltage and with constant periods in sequence.
• (3) Rotate the rotor while gradually increasing the voltage.
• (4) The number of rotations increases, and the rotor position can be detected by the induced voltage.
• (5) Flow the current to the coil corresponding to the detected rotor position.
• (6) If a stable position can be detected, start steady operation to reach the target speed.

In steady operation, the speed can be maintained against load fluctuations by feeding back the target speed deviation.