Research Of Sensorless Control System And Commutation For Brushless DC Motor

The brushless DC motor(BLDC), with the electrical circuit to replace the mechanical brush and the commutator, is one of the most high effective motor currently for combining the advantages of both AC motor and DC motor. The introduction of sensorless control technology not only surmounts the deficiency of sensor's precision and installation but also impulses the application realm of BLDC. Nowadays, sensorless control technology has been the major direction of BLDC control strategies.In recent decades, most institutes focuses on the issues– detection of rotor position without position sensor, the problems on motor starting, the ripple of torque etc. However, the sensorless control technology has many problems, and the very important one is the leading or delaying commutation caused by unavoidable errors in both sensor and sensorless control strategies. These errors may cause the vibration, noise, and low efficiency, high current impulse even lead to failure commutation and out of step. By introducing and comparing the mainstream sensorless control methods, the zero cross detection of Back Electromotive Force is adopted and presented specifically in the paper. And also the paper gives the qualitative analysis of the rotor position detection error.Then the paper deeply analyzes the BLDC commutation with three-phase Y-connected windings in six-state operate mode, and discusses specifically on the three situation: commutation correcting, leading and delaying. The phase current analytical expressions in three situations are deduced. It can lay a foundation of the online transient current optimized control when the motor works at commutation failure. The paper focuses on some key points and proposes the corresponding control scheme.The simulation model of BLDC sensorless system based on the zero cross detection of Back Electromotive Force is established in the Saber simulation platform. Based on the model, the operation of the current close-loop control system and under the different commutations are analyzed specifically.Then the paper presents the experiment platform which is based on the DSP TMS320LF2407A and the Intelligent Power Modules and presents the hardware and software design.Finally, based on the experiment platform, the issues on BLDC operation and commutation are discussed. The paper obtains the coherent results with theory simulation and analysis.