Research On Starting Method Of Sensorless Brushless DC Motor Based On IVMS

Position sensorless brushless DC motors have been gradually applied in aerospace,electric vehicles and intelligent robots etc.but in the startup process,there are several problems such as inaccurate initial rotor position and large commutation error during acceleration.These problems will lead to instability,jitter,and reversal when the motor started with load.Therefore,it is valuable to find a starting method with high reliability and strong anti-interference in both theoretical research and practical application.The main work of this paper is as follows:Firstly,several mature startup methods such as the traditional three-stage startup method,the up-conversion boost startup method,and the pulse injection startup method has been analyzed.It is found that these starting methods are open-loop structures in the acceleration phase.It is difficult to ensure that the motor accurately acquires the real-time rotor position during the starting process,which will resulting in low anti-interference capability and unstable operation of the motor.Secondly,in view of above problems,this paper proposes a composite startup method based on IVMS(induced voltage induced by magnetic saturation).This method mainly includes the following three stages:(1)injecting pulse to determines the initial rotor position;(2)comparing the detected IVMS with the threshold voltage Vsh to determines the closed-loop acceleration stage of the commutation point;(3)switching to the self-synchronization stage which realize commutation by dectecting the back-EMF zero-crossing point of the unexcited phase.In the stage of determining the initial rotor position,injecting a set of switching voltage vectors in both forward and reverse directions to the stator winding of the motor,and then determine the rotor angle within 180° electrical angle range by comparing its response current.On this basis,injecting two additional switching voltage vectors in this I180°electrical angle range,and then determine the rotor angle within 60° electrical angle range.By repeating this step,we can finally limit the rotor angle to 30° electrical angle range.Since the three-phase stator windings are spatially coupled to each other,when two-phase conduction mode is employed,two excited phase windings would inevitably generate IVMS on the non-conducting phase winding.After modeling and analyzing the IVMS,it is found that the established objective function has the same type of waveform as the back-EMF.Using this feature,in the closed-loop acceleration stage,by compared the IVMS with the threshold voltage and then control commutated directly,which can avoid the commutation error caused by delaying the 30° electrical angle,and ensure accurate commutation during the closed-loop acceleration of the motor.When the motor speed reaches a certain value,it is smoothly switched to the self-synchronous operation mode by using the average method.Finally,the simulation model of the position sensorless brushless DC motor control system has been built in Matlab/Simulink,and the simulation research of each sub-module and the whole model has been completed.The simulation results show that the simulation results are basically consistent with the theoretical analysis results,which reduced the jitter phenomenon of the motor during the startup process,decreased the commutation error during the acceleration stage,and ensured the effective startup of the position sensorless brushless DC motor.