Research On Control Strategy Of The Switched Reluctance Motor For The Alternating Load

Switched reluctance motors(SRMs)have the advantages of high efficiency,low cost,high starting torque,low starting current,wide speed range,torque control,etc.They are widely used in the industrial field.The power factors of the traditional motors are very different under the condition of no-load and full load,while the power factor of the SRM is very high.When the rotor speed and load torque change greatly,SRM systems can operate stably at a high level.Therefore,the application of the SRM under the alternating load circumstances can improve the operating efficiency and realize the energy-saving operation of the equipment.The double saliency structure and magnetic saturation characteristics of the SRM make it difficult to obtain the accurate analytical model,and the impulse power supply mode also brings obvious torque ripples.Aiming at the nonlinear modeling of SRMs,miN mizing of the instantaneous torque ripples,control of bus voltage under alternating load and the controller designing,the main research works in this paper mainly include four aspects as follows:Firstly,the four-link geometry mechanism and motion form of pumping unit are analyzed by the vector analysis method.The torque mathematical model of pumping unit is established,and the periodic alternating load characteristics of beam pumping unit are analyzed,which provides a basis for the study of instantaneous torque ripples suppression,energy saving and torque characteristic matching in the alternating load circumstance of SRM.Secondly,a fuzzy logic system is proposed to solve the precise flux linkage model of SRMs.It solves the problem of accurate flux linkage modeling of SRMs based on torque-balanced measurement method with few rotor flux linkage information.At the same time,the advantages of the torque-balanced method are kept.The proposed method obtains the flux linkage characteristics at four specific rotor positions according to the symmetrical structure of the SRM,performs fuzzy set division,extracts the fuzzy rules from the flux linkage samples,and applies the centroid method to solve the whole flux linkage characteristics of the SRM.The flux linkage characteristics of the proposed method are compared with those measured by the rotor clamping method,and good agreements can be obtained.The model of the SRM based on fuzzy system proposed in this paper has high precision and can be used in the structure design,controller design and algorithm verification.Thirdly,aiming at the problem that the double saliency structure of SRMs and the impulse power supply mode lead to torque ripple,especially when the torque ripples are too large in alternating load,a predictive direct instantaneous torque control(PDITC)method based on torque-sharing is proposed.According to the static electromagnetic characteristics of the SRM,the proposed algorithm establishes the discrete prediction model of the SRM,and uses the torque sharing function(TSF)to assign the reference value of total torque to each phase as the reference value of phase torque,By implementing the discrete prediction model and the sampling values of each phase winding,the phase torque of the next moment is predicted online by traversing all possible switching states of the phase power converter.the Torque error and the switching times of the power converter are evaluated by the index evaluation function synthetically,and the switching states with the minimum comprehensive evaluation indexes are determined.The proposed PDITC algorithm does not need complex hysteresis rules,and can consider multiple performance indexes synthetically through the performance evaluation function.Fourth,aiming at reducing consumption and reducing vibration in the alternating load situation,a control method of variable bus voltage of the SRM is proposed.Under the same torque and rotor speed,the optimal bus voltage is obtained to change the waveforms of phase current to minimize the phase current area of energy conversion and reduce the invalid areas of phase current.The proposed method can not only improve the efficiency,but also can reduce the loss consumption and the vibration.Then,a fast and accurate controllable bus voltage rectification method is proposed,which applies the finite control set model predictive control(FCS-MPC)in the neutral point clamped active-front-end converters(NPC-AFEs).The optimized model predictive direct power control(MP-DPC)algorithm is proposed,which can obtain the required bus voltage value quickly and accurately,and can also meet the requirements of variable bus voltage control of the SRM.