Instantaneous Torque Control Technology Of Brushless DC Motor Without D-Axis Armature Reaction

Due to the non-sinusoidal waveforms of main magnetic field distribution and back-EMF,there are large torque ripples in brushless DC motor(BLDCM)under the driving with square wave current.In order to suppress the torque ripple of the BLDCM and tap the potential of its operating performance,three strategies for suppressing the torque ripple of BLDCM without d-axis armature reaction are proposed in this paper.The first method is the rotor field-oriented control method based on global coordinate transformation,this method is an inheritance and imitation of the Clarke,Park transformation and permanent magnet synchronous motor rotor field-oriented control.The innovation of this method is that the rotation angle in the Park transformation matrix is changed,so that the q-axis rotor flux linkage is zero.Firstly,through the comparative analysis of the rotor flux waveform under different rotor field distributions,it is concluded that the 3s/2r transformation with the rotor position as rotation angle cannot achieve rotor field-orientation when rotor field distribution is non-sinusoidal;Secondly,by changing rotation angle in the 3s/2r transformation matrix,the rotor flux has no d-axis component after the transformation,thereby establishing a non-sinusoidal rotor field orientation coordinate system and obtaining a dynamic mathematical model under it.Finally,the dand q-axis currents under reference torque without d-axis armature reaction is deduced theoretically,and based on it,rotor field-oriented control system without d-axis armature reaction of BLDCM is constructed.The second method is the rotor field-oriented control method based on phase-by-phase coordinate transformation.Compared with the first method,The innovation of this method is a new transformation which based on the d-axis armature reaction and the torque is unchanged.The transformation method can realize the decoupling of the d-and q-axis currents,so that the electromagnetic torque is only related to the q-axis current,which simplifies the mathematical model.This method can realize the decoupling of the d-and q-axis currents.Firstly,by analyzing the equivalent model for BLDCM rotor permanent magnet field orientation under d-q synchronous rotating coordinate system,it is shown that the armature reaction of d-axis and electromagnetic torque are determined by the current of d-axis and q-axis,respectively.Secondly,a new winding transformation method is given.Finally,the three-phase currents from the required d-axis and q-axis currents are obtained.These currents are regulated in closed loop form.The third method is the instantaneous torque control method based on harmonic decomposition.Compared with the previous two methods,this method is based on the analysis of the harmonic back-EMF vector and the current space vector in the two-phase rotating coordinate system,which has a more in-depth discussion on the characteristics of BLDCM.Its innovation lies in that different control performances can be selected under the premise of suppressing torque ripple.Firstly,in order to avoid the adverse effects caused by higher harmonic currents,this method only injects the fundamental wave and the 5th and 7th harmonic currents.Under the premise of no large torque ripple,it is concluded that the sum of the 5th and 7th current amplitudes remains unchanged;Secondly,by selecting different performance parameters to change the ratio of the 5th and7 th harmonic currents,and then under the premise of suppressing torque ripple,different performances can be selected,such as no d-axis armature reaction and copper loss minimization.It is possible to consider a variety of control performance for joint control.These three methods range from simple imitation of Clarke and Park transformation,to a new coordinate transformation method that is more suitable for non-sinusoidal characteristics,and then to the analysis of the harmonic back-EMF and the harmonic current through the space vector diagram,the research on the high-performance of BLDCM is gradually deepened.In addition,the feasibility and effectiveness of these three methods have been verified by MATLAB simulation and DSP experiment,which can not only suppress torque ripple without the detection of commutation zone,but also solves the problems of magnetization and demagnetization caused by d-axis armature reaction.