A low-cost sensorless control for reduced-parts, brushless DC motor drives

Brushless DC (BLDC) motor is attracting much interest due to its good performance for many applications. Moreover, cost reducing of the drive is more attractive for low cost applications. This paper presents the design and implementation of a reduced parts BLDC motor drive. Part reducing is achieved by elimination of three Hall Effect position sensors and reducing the number of power switches to four switches. For current commutation, a low cost sensorless control based on line voltages is developed. Two second-order Butterworth low-pass filters with little phase delay are designed to eliminate of high frequency PWM and calculation of average terminal voltages. Proposed sensorless control doesnpsilat need to any 30deg or 90deg phase shift that is prevalent in other sensorless methods. Moreover, to make the rectangular phase current waveforms, direct phase current control is used in which the currents of two phases A and B are controlled independently. The performance of the developed algorithms is verified via simulation and implementation. It is shown that the main source of the estimation error is drop voltage on the stator impendence in which at low speeds and for heavy loads it increases. Experimental results show that the developed sensorless control is effective and can be used for low cost applications.