The FOC (Field-Oriented Control) rotor initial position calibration for PMSM (Permanent Magnet Synchronous Motor) is a crucial step, primarily involving the initialization process of the motor controller.

When the encoder pulse count is 0, we expect the rotor's electrical angle to also be 0.

During the experiment, zeroing the rotor's initial position is performed to ensure the accuracy of vector control.

Only by knowing the precise rotor position can accurate vector control be achieved.

In FOC, we typically determine the real-time position of the rotor by reading the feedback information from the encoder.

When the encoder's pulse count is zero, logically, the rotor's electrical angle should also be zero.

In reality, due to various influencing factors (such as encoder errors, mechanical installation inaccuracies, and uneven motor magnetism), the actual electrical angle of the rotor may not precisely match the number of encoder pulses.

We typically need to perform rotor initial position zeroing to correct this error.

It is generally achieved through the following five steps:

1. Run the motor at a specific speed and load for a period of time to reach a stable state.

2. Read the number of pulses from the encoder at this moment, denoted as N.

3. Through calculation, determine the electrical angle of the motor at this speed and load (this value is typically determined experimentally). Assume the calculated electrical angle is θ.

4. Compare the number of encoder pulses N with θ. If they are not equal, zero calibration is required.

5. The zero-point calibration method involves adjusting the parameters of the controller (such as the proportional and integral coefficients of the PID controller) to make the motor's electrical angle close to θ when the encoder pulse count is N.

The zero calibration process of the FOC controller needs to be repeated multiple times until suitable controller parameters are found, ensuring that the electrical angle of the motor equals or closely approximates the encoder's pulse count.