Sensorless Brushless Dc Motor Speed System Based On Single-chip Microprocessors

In this paper, a speed system of brushless square wave DC motor is discussed. The system is mainly made up of 80C196MC single-chip microprocessor that is used as the principal condol device, and there are output and input circuits. In addition, IGBT is used as the main circuit's power switch component. The system fulfills the motor digital control based on PWM bridge-modulation. 80Cl96MC single-chip microprocessor is developed especially for motor control. In this paper, it is maken full use of: protective function, six channel outputs of PWM waveform, keyboard and display unit, the indirect detection of rotor position, and so on.The construction of BLDC motor lead to that it require a rotor position sensor forcommutation. The sensor,however, causes many disadvantages. As a result, manymethods are proposed to cancel the sensor. In this papef, the rotor position is based on the detection of the conducting interval of free-wheeling diodes connected inaniparallel with power component IGBT, the theory of this approach is based on theover-zero point of the back EMF of the motor. This approach is characterized by itssophisticated position detection and make it possible to be operated at a low speed.lt,furthermore, makes great contribution to simplify the Starting procedure.For the amplitude of the back EMF is proportional to the rotor speed, it isimpossible to detect the rotor position at standstill. The "three-step" starting procedure is presented that is: locating, accelerating and switching .The motor is operated at the brushless pattem by the control unit and position detective unit. The experimental results show that the approach is practicable and reliable,in another hand, it proves that the 80Cl96MC is suitable for motor control.