Design And Implementation On Brushless DC Starter System

Brushless DC motor (BLDCM) is distinguishably featured not only by the advantage of AC motor, such as the simple structure, high power density, reliable operation and easy maintenance, but also by the good performance of speed regulation and high starting-torque of brush dc motor. BLDCM is recognized as the first choice of starter and generator for the energy conversion in the plane. The brushless DC motor with sensor isn’t operated properly in the liquid, high temperature, upper air and corrosive environment. The sensorless BLDCM overcomes such disadvantages, it has found the wide application in many fields.The basic operation principal of BLDCM is described in this thesis, and the switch control logic is analyzed with the main circuit. The mathematical model is studied so as to design the model based on the S-function with the simulation module in Matlab/Simulink. The sensorless starting algorithm is selected for the purpose of less requirement of starting system. When starting initially, the winds are trigged by the fixed sequence in order to spin the rotor. The last state is considered as the initial position when motor is still. The ramp-up routine is executed following the initial position detection. PWM pulses are distributed to gain max torque while with little peak of current. The system is changed into the back EMF control procedure just the moment that the duty cycle of PWM is more than the min duty cycle corresponding to the back EMF control.The controller consists the simple structure hardware based on the main control chip dsPIC30F4012. The back EMF is converted into digital signal and filtered by the filter algorithm, which is uncontrolled by the hardware. The digital filter, commutation and adjustable speed are realized using the software algorithm. The control algorithm of back EMF zero-crossing is analyzed in details, the filter is designed based on the majority function in order to cancel the false zero-crossing events. The time lagging of the zero-crossing is counted by 30°electrical angle, the delaying time caused by soft filter is also counted, which avoids the delay or advantage of the commutation.In the end, a joint debugging work between the hardware and software system of the position sensorless BLDCM based on the environment of MPLAB IDE is introduced. Experiments are done in order to illustrate the efficiency of this new start-up method, and it proves to operate well. This method is proposed to solve the start-up problem of the position brushless DC motor.