The Design And Implementation Of Multi-speed Control System For Sensorless BLDCM

With the development of power electronics technology and the emergence of newkind of permanent magnetic materials, the brushless DC motor with its low-cost,high-efficiency, simple control, and superior external characteristic features is appliedwidely. Furthermore, sensorless control technology not only further reducing thevolume and cost of the motor, but also enhances its anti-jamming ability, thensignificantly widen the application range of the brushless DC motor. According to theactually demand， this paper develops a sensorless control system for BLDCM whichcan achieve multi-speed control according to Variation of the DC voltage.Firstly, this paper introduced the generation, development and applications ofbrushless DC motor and its control method were also briefly discussed. Motormathematical model based on the relationship between the system variables wasestablished after structures and operating principle of the brushless DC motor weredescribed. On the basis of analysis of the mathematical model, the sensorless controlmethods were discussed in detail: Firstly, the principle of "terminal voltage method"position detection was expounded, and the analysis of the detected error compensationmethod was followed. Secondly, a kind of current closed-loop "three-stage" startmethod was proposed in order to solve difficult problem about the self-start of themotor. Finally, according to sensorless control method a control system simulationmodel using speed¤t double closed loop control method was built andsimulation results have verified the effectiveness of the rotor position detectionmethod and the correctness of the start method.According to above control method,the structures of the main circuit of the system were completed, the control board withTI’s TMS320F2812as its core controller and driver board were designed. This paperintroduced each part of the circuit in details, and anti-jamming measures of hardwarewere also introduced.The system software program based on hardware experimental platform wascompleted using C language in the CCS compiler environment. It include motorstartup programs, dual closed-loop PI multi-speed adjustment program, AD samplinginterrupt program, commutation interrupt program, systems protection interruptprogram and so on. Among them, for the problem of multi-speed control in variable voltage environment, the software was set to continually monitor the power supplyvoltage and modify the given speed and PI parameters in real time according to thevalue of voltage, so the output speed of system can quickly follow given speed. In theback-EMF zero-crossing detecting part, this paper proposed a kind of method thatusing a30°electrical phase shifting hardware filter with secondary filter by softwarecould achieve accurate detection of the zero-crossing signal in case of90°electricalangle phase shifting depth filter method which was generally used can causewaveform distortion which would cause imprecise zero-crossing signals. Due to thecurrent sampling signal contains a large number of PWM modulation interference, inorder to get an accurate current value, the system used a mixed filter method withseveral digital filtering methods, and have achieved good results.In the end, the experimental results by running software program on thehardware experimental platform, confirmed the correctness and effectiveness of thecontrol method.