Design of speed loop
PID regulator is chosen to regulate speed of the motor, it is in the outer loop. Hall position sensor on brushless DC motor rotor can detect the position angle of rotor magnetic pole. Each circle does the rotor turns, the state of Hall signal changes for six times. Timer can determine the required time between the two adjacent states, so we can estimate the actual position and speed of rotor. Speed loop flow chart is shown in Figure 6c