Research Of Control Strategies For Sensorless Pm Brushless DC Motors

Permanent magnet brushless DC motor(PM BLDCM) has been widely used in modern industry, because it has some excellent performance such as high torque^high efficiency and so on. However, the existence of position sensor brights many disadvantages to the motor and the torque ripple also limit its application in high precision to some extent. This paper analyzes the some common non-position sensorless control technologies, focuses on back EMF method, and analysis of the low speed running motor non commutation torque ripple suppression problem.The paper introduces the control principle ofPM BLDCM and establishes mathematical model Based on the above results, the back-EMF method and PWM_ON_PWM pulse width modulation control strategy are presented. In the back EMF method, a detailed analysis of the simulation of neutral point zero-crossing detection method is introduced. For the commutation torque ripple, the paper analyzes operation characteristics of permanent magnet brushless DC motor at low speed, the commutation torque ripple of the stage can be effectively suppressed, the PWMONPWM modulation mode is given to inhibition non commutation torque ripple. The simulation model is established in Matlab/Simulink simulation environment to study control strategy. The simulation results show that the designed control system can get good performance and the PWM_ON_PWM pulse width modulation can reduce the non-commutation torque ripple effectively.Based on the result of the simulation, the designed hardware circuit of the control system consists of the power drive circuit and the rotor position signal detecting circuit as the main two parts. With drive chip IR21367as the core structure, the power drive circuit is built. Meanwhile, the optocoupler isolation circuit and the over-current and over-voltage protection circuit are both included as the secondary parts. As an important part of the non-position sensor control system, the paper designs the virtual neutral point zero crossing detection circuit for the rotor position detection circuit, to reach the purpose in detecting the zero-cross ing.The control system software programming is completed by C language in the CCS3.1software compile environment. The designed soft system has good versatility and scalability in the result of adopting modular programming ideas. In the end, the whole control system is debugged fully. After making sure the reliability and stability of the control system, a series of motor working waveforms are obtained, The motor speed curve is obtained by processing the speed data. The results of analysis indicate that the designed control system based on non-position sensor not only run stably, but also has a better control effect than the control system based on position sensor.