A new sensorless control scheme for brushless DC motors without phase shift circuit

This paper presents the design, analysis, and implementation of a high performance and cost effective sensorless control scheme for the extensively used brushless DC motors (BLDCMs). Taking into consideration cost and ease of implementation, the commutation signals are obtained without the motor neutral voltage, multistage analog filters, A/D converter, and the complex digital phase shift (delay) circuit which are indispensable in the conventional sensorless control algorithms. Instead of detecting the zero crossing point of the non-excited phase back EMF to the neutral voltage, the commutation signals are extracted directly from the specific average terminal voltages with simple RC circuits and comparators in this study. Since the neutral voltage is not needed, the extracted commutation signal is insensitive to the common mode noise, hence the low speed performance is superior to the conventional methods. Moreover, the complex phase shift circuit has been eliminated. As a result, the control algorithm can be easily interfaced with the cost effective commercial Hall effect sensor based commutation ICs. Because of the inherent low cost property, the proposed algorithm is particularly suitable for cost sensitive products such as air purifiers, air blowers, cooling fans, and related home appliances. Theoretical analysis and experimental results show that the proposed control algorithm exhibits superior performance over a wide operation range when compared with the conventional solutions.