Research On Predictive Torque Control For Permanent Magnet Synchronous Motor Drive System

The predictive torque control(PTC)for permanent magnet synchronous motor(PMSM)has a lot of merits such as fast response,flexible application and so on,so PTC can be regarded as an advanced control strategy compared with DTC and FOC.However,it still has some disadvantages such as the complex tuning of weighting factor and the useless duty cycle modulation.Aim at these disadvantages,two new PTC approaches are studied in this paper.In this paper,Equal Torque Effect(ET-Effect)is discovered,which means that the same torque can be obtained by applying different voltage vectors whose terminals locate on a special curve called the Equal Torque Curve(ET-Curve).By means of ET-Effect,an improved Predictive Torque Control without weighting factor is proposed.Firstly,to obtain the volt-sec vectors whose terminals locate on the ET-Curve,the proposed PTC calculates the duty cycles of all the voltage vectors intersected with the ET-Curve,and then establishes Finite Control Set(FCS)by accumulating those volt-sec vectors.Secondly,a cost function that includes only the flux error is defined to select the optimal volt-sec vector,and thus to avoid weighting factor adjustment since the torque error no longer exists in the cost function.Because of the two-step optimization of torque and flux,the proposed PTC can avoid the problem that the duty cycle can't be fully utilized in standard PTC.As a result,the proposed PTC achieves better performance of torque and flux than standard PTC and PTC with duty cycle.We obtain the two optimal operating time of vector separately through the analysis of the stator voltage and flux linkage equations.By means of the two optimal operating time,an improved Predictive Torque Control without weighting factor is proposed.The proposed method uses the two optimal operating time to measure the influence on torque and flux modulus of one vector separately,and replaces the torque and flux modulus errors in the cost function with the two optimal operating time.Therefore,the proposed method gets rid of the weighting factor because the cost function only contains one dimension time.Meanwhile,the new cost function can avoid the situation that the duty cycle doesn't work in the traditional PTC.The proposed method combines duty cycle modulation with virtual vectors and optimizesthe finite control set.As a result,the new method not only has fewer alternative vectors,but also obtains better performance.The proposed methods are tested in one two-level VSI fed PMSM experimental platform.The contrast experiments have been carried out.The experimental results prove that the proposed methods can solve the two problems and get better torque and flux performance.