Sine-wave drive rotates the rotor by continuously changing the voltage of the stator coil sinusoidally in accordance with the rotation angle of the rotor.
The three phases for the motor are “delayed” by a specific amount of time, depending on the frequency.
It is more efficient, creates less vibration and less noise than the square-wave drive.
Rotor position detection is required for control.
Normally, three position sensors are used to detect the position every 60 degrees, the rotor position is estimated in real time, and a sine-wave voltage that meets to the rotor position is output.
An inverter circuit is used to drive the motor, and the voltage is continuously changed by PWM control.
If you have a sine-wave of 1Hz, it takes one second to “play” this sine-wave. If you have a second wave “shifted by 120 degrees”, this second wave will start exactly 0.33 seconds after the first, which is one third of complete time. The third wave will start shifted once again by 120 degrees, meaning 0.66 seconds after the first wave started.
This is required to control the three phases U, V and W of the BLDC motor at the right time.
Depending on the time sequence of the three phases, the motor will turn clockwise or counter clockwise.