Brushless DC motor control without position and speed sensors

The control strategy using a DSP-TMS320C25 is developed on the basis of the instantaneous voltage equation of the brushless DC motor. Without a position sensor, the controller has no information about rotor position: therefore, the controller determines the applied voltage according to the hypothetical rotor position, which is not necessarily coincident with the actual rotor position. Since the voltage supplied through the inverter is the actual applied voltage, it can be measured. Under the ideal condition that the hypothetical rotor position is coincident with the actual rotor position, the ideal applied voltage can be calculated by using the instantaneous voltage equation of the motor and the detected current. The difference between the actual and the ideal voltages is proportional to the angular difference of the hypothetical and actual rotor positions. Therefore, self-synchronization is possible by reducing the angular difference to zero. Once the rotor position is estimated, the motor can be operated without position and speed sensors.<>