This paper describes a simple control for a BLDC motor drive which provides a wide speed range without use of a position sensor. Three line-to-line voltages and two stator currents are sensed and processed in digital form to produce the stator flux linkage space vector. The angle of this vector is then used in a microcontroller to produce the appropriate stator current command signals for the current controller of the inverter. A speed signal is derived from the rate of the change of angle of the flux linkage.
The control system has been implemented on a 400-W motor using Nd-Fe-B magnets. The closed loop speed control has been shown to be effective down a frequency 5Hz, thus providing a wide range of speed control. An open loop starting program is used to accelerate the motor up to this limit frequency. The problem of drift of analog integrator is developed by using the digital integrator.