Indirect rotor angle estimation in without permanent magnet brushless dc motor with employment of the Maxwell-Wien Bridge

This paper presents a novel method to detect the rotor position of the without permanent magnet brushless dc (WPMBLDC) motor for the starting from standstill to a certain low speed. Use of assistant field replaced with permanent magnet in the rotor highlights this family of BLDC motors in comparison with conventional BLDC motors. The principle of the estimation is based on the variation of the instantaneous phase inductance information. Since the inductance parameter plays a significant role in the steady state and dynamic characteristics of electromagnetic device, the rotor position can be determined by using inductance bridge systems to measuring unknown inductance and resistance values. In this paper, we propose an improved sensorless drive method using the motor winding in Maxwell-Wien Bridge, the standard capacitor and the resistor in parallel with it must be adjusted to achieve balance in aligned position when the maximum inductance occurred. Injection extra voltage pulses periodically into unenergized phases for this AC bridge provided. The phase inductance varies with the rotor position, therefore the motor goes into unaligned position and Maxwell-Wien Bridge goes to unbalanced condition then varies the state of bridge output. It then continues to sense the rotor position while the motor running by applying the same procedure. Finally, experimental results are also presented for the motor to confirm the feasibility and practicability of the method.