Control And Experiment For Bearingless PMSMs

A bearingless permanent magnet synchronous motor(PMSM)is a high performance PMSM adopting bearingless technology,and has high power factor,efficiency and power density of PMSMs and magnetic bearing’s excellent characteristics of no mechanical friction,needless lubrication and little maintenance.It can operate under high speed or hypervelocity,and has potential prospects for applications in the hi-tech fields of chemistry & chemical engineering, life sciences,energy transportation,aerospace,robot,etc.Under the susports of National Natural Science Foundation of China(50275067)and National Hi-Tech Research and Development Plan of China(2007AA04Z213),the theory and experiment research around the control of bearingless PMSMs is developed in the dissertation.The main work is as followings.1.Bearingless PMSM has two kinds of stator windings,which are motor windings and suspension windings.With analyzing the flux intersection between the two kinds of windings,a method of converting mechanical coordination to electrical one is adopted,and based on this method,flux and voltage equations of the two sets of windings are derived.Based on analyses of each Lorentz force’s role,the electromagnetic torque equation of bearingless PMSM is given. After analyzing each radial force’s mathematical expression,the complete form of bearingless PMSM radial suspension force equation is given.This mathematical model provides theoretical basis for the simulation study,experiment waveform analysis and structure design of bearingless PMSMs.2.Bearingless PMSM mainly use rotor permanent magnet to excite its flux,thus,it has the advantage of small starting current,but its starting is difficult.Based on PMSM torque producing principle,the starting process of bearingless PMSM without adding suspension subsystem is studied,and the necessary and sufficient condition to precise rotor initial orientation and optimizing orientation sequence are put forward.On base of rotary encoder,the method of reliably detecting rotor position is given,and then,the starting of motor with rotor flux oriented control is implemented.The results indicate that,adopting this starting strategy,bearingless PMSM implements rapid and reliable starting and then enter steady running state,the starting current is very small,and it has advantage in safety and reliability.3.Bearingless PMSM has torque ripples induced by multiple factors,and the current tracking performance is bad as it runs with no load or light load.After optimal speed calculation formula is given,with analyses of PMSM mathematical model and consideration of load effect in bearingless motor,a strategy of controlling bearingless PMSM speed by means of combining flux enhancing control with voltage regulation is proposed,and its optimal realization method is also given.The experiment results indicate that,after adopting the strategy,the motor windings’ current ripples in bearingless PMSM are weaken,the speed is stable with high control accuracy, and the suspending performance can also be improved.The strategy is simple and effective for bearingless PMSM speed control.4.The decoupling control of torque and radial suspension force is the difficult problem and key technology for bearingless motors’ stable suspending operation.Based on the concept of flux equivalent virtual winding currents,a simple,reliable and accurate analysis method for bearingless motors’ radial suspension force is given.Adopting this analysis method,the bearingless motors’ suspending operation condition that the difference is one between motor windings pole pairs and suspension windings pairs is quoted,and the relative motion between suspension windings air-gap flux and radial force and the necessary condition to generating a stable radial force in a single direction are derived.On this basis,the strategy of bearingless motors’ radial suspension force control is presented.The results show that,the experimental result corresponds with the theoretical analysis one based on this strategy,and a stable and reliable radial suspension force is obtained,by which the validity and feasibility of this strategy is confirmed.5.Bearingless PMSM control system has a large number of control variables but a relatively small amount of data,and thus,adopting optimal coding scheme is demanded in its human-computer interaction.Based on analysis of data format in serial port communication and data types of control variables,an optimal scheme of data resolution and combination and a coding one are given.A software synchronization strategy is proposed for keeping data integrity. A decoding vectors table of linear pointer array structure and a sending descriptors table of single list structure are introduced to accelerate decoding process and implement dynamic adjustment of sending contents respectively.With this human-computer interaction strategy,code extension is easily realized and has no effect on the efficiency of program.The results show that stable bearingless PMSM operation is preserved,smooth communication,data integrity,convenient code extension and simple maintenance are obtained with this human-computer interaction strategy,which lays a foundation for the commissioning and control ofbearingless PMSM.