A Better Strategy For Sensorless Brushless Direct Current Motor

Brushless direct current motor has the advantage of good characteristics of speed control, high power density and high efficiency etc. Sensorless brushless direct current motor overcomes a lot of disadvantages by sensor, thereby, it has found wide applications.Based on the returns of both here and abroad, the paper makes a research on the control system of sensorless brushless direct current motor. The dissertation researchs and discusses the following problem:(1) The paper analyzes the mathematical model in detail. Firstly, a new zero-crossing detection method with software comparing with hardware is designed. The method only detects two Back-EMF zero crossings in a period. Only a zero-crossing is used to change phase and other five changes of phase are made forcedly.(2) Hareware detection circuit takes up the space of board and augments the cost of design. At one time, it also requires more interruption resource. So, pure software design method is proposed. It omits outside compare circuit and gets zero-crossing only from the soft arithmetic. The design method improves the flexibility of software design.(3) The paper analyzes the back-EMF current fluctuation of floating phase, using traditional PWM modulation methods. Based on the traditional PWM modulation methods the paper adopts a new proposed PWM modulation, which can reduce the back-EMF current fluctuation efficiently.(4) The paper analyzes conventional method to halt the motor. And bring a new method to halt the motor calmly.(5) The paper analyzes the process of start in detail. Using second position technology solves the failure of first position. The direct switch in a certain speed eliminates the trouble of detecting the difference between self-synchronization and outside synchronization. It optimizes the design of software.(6) Double closed loops control of current and speed with PI are adopted...