Voltage Software Optimization Control for Constant Frequency Commutation of a BLDC Sensorless Motor

In this paper the authors present an efficient control of the time based commutation sequence of a sensorless brushless direct current (BLDC) motor. The control is achieved using an algorithm commonly used for stepper motors, with a fixed commutation frequency and controlling the supply voltage for the three phase bridge made up of six transistors. Experiments have proven that for a fixed commutation frequency of the command signals, the motor's RPM (rotations per minute) stays constant for a wide range of values of the supply voltage during each of the six steps. Experiments have also revealed that the instantaneous current used by the motor's phases for the same torque has small variations dependent on frequency of commutations that control the motor's RPM. It results from the experiments that when increasing the motor's RPM, the needed current increases following a nonlinear function. This paper proposes a way to generate the minimum supply voltage for the three phase bridge that provides the minimum current needed to generate the engine power. An 8 bit microcontroller based solution is proposed for the theoretical and experimental model.