Electromagnetic Performance Analysis of Variable Flux Memory Machines with Series-magnetic-circuit and Different Rotor Topologies

In this paper,the electromagnetic performance of variable flux memory(VFM)machines with series-magnetic-circuit is investigated and compared for different rotor topologies.Based on a V-type VFM machine,five topologies with different interior permanent magnet(IPM)arrangements are evolved and optimized under same constrains.Based on two-dimensional(2-D)finite element(FE)method,their electromagnetic performance at magnetization and demagnetization states is evaluated.It reveals that the iron bridge and rotor lamination region between constant PM(CPM)and variable PM(VPM)play an important role in torque density and flux regulation(FR)capabilities.Besides,the global efficiency can be improved in VFM machines by adjusting magnetization state(MS)under different operating conditions.

Winding Function Theory Based Thrust Calculation on Nested-loop Secondary Linear Machine Adapted to Linear Metro

With advantages of strong drive capability,nested-loop secondary linear machine(NLS-LM)has great potentiality in linear metro.For its secondary structure with multiple loops,it is difficult to calculate the electromagnetic thrust of NLS-LM reasonably.Hence,in this paper,one thrust calculation method is proposed considering variable loop inductance and transient loop current.Firstly,to establish the secondary winding function,the modeling domain is confined to a limited range,and the equivalent loop span is employed by analyzing the coupling relationship between primary and secondary.Then,in order to obtain the secondary flux density,the transient secondary current is solved based on the loop impedance and induced voltage.Finally,the electromagnetic thrust can be calculated reasonably by the given primary current sheet and the calculated secondary flux density.Comprehensive simulations and experiments have demonstrated the effectiveness of the proposed method.

Multi-layer Quasi Three-dimensional Equivalent Model of Axial-Flux Permanent Magnet Synchronous Machine

Axial-flux permanent magnet synchronous machine(AFPMSM)enjoys the merits of high torque density and high efficiency,which make it one good candidate in the direct-drive application.The AFPMSM is usually analyzed based on the three-dimensional finite element method(3D FEM)due to its three-dimensional magnetic field distribution.However,the 3D FEM suffers large amount of calculation,time-consuming and is not suitable for the optimization of AFPMSM.Addressing this issue,a multi-layer quasi three-dimensional equivalent model of the AFPMSM is investigated in this paper,which could take the end leakage into consideration.Firstly,the multi-layer quasi three-dimensional equivalent model of the AFPMSM with single stator and single rotor is derived in details,including the equivalent processes and conversions of structure dimensions,motion conditions and electromagnetic parameters.Then,to consider the influence of end leakage on the performance,a correction factor is introduced in the multi-layer quasi three-dimensional equivalent model.Finally,the proposed multi-layer quasi three-dimensional equivalent model is verified by the 3D FEM based on an AFPMSM under different structure parameters.It demonstrates that the errors of flux linkage and average torque obtained by the multi-layer quasi three-dimensional equivalent model and 3D FEM are only around 2%although the structure parameters of the AFPMSM are varied.Besides,the computation time of one case based on the multi-layer quasi three-dimensional equivalent model is only 6 min,which is much less than that of the 3D FEM,1.8 h,under the same conditions.Thus,the proposed multi-layer quasi three-dimensional equivalent model could be used to optimize the AFPMSM and much time could be saved by this method compared with the 3D FEM.

Driving Range Parametric Analysis of Electric Vehicles Driven by Interior Permanent Magnet Motors Considering Driving Cycles

This paper presents parametric analysis of driving range of electric vehicles driven by V-type interior permanent magnet motors aiming at maximum driving range,i.e.,minimal total energy consumption of the motors over a driving cycle.Influence of design parameters including tooth width,slot depth,split ratio(the ratio of inner diameter to outer diameter of the stator),and V-type magnet angle on the energy consumption of the motors and driving range of electric vehicles over a driving cycle is investigated in detail.The investigation is carried out for two typical driving cycles with different characteristics to represent different conditions:One is high-speed,low-torque cycle-Highway Fuel Economy Test and the other is low-speed,high-torque cycle-Artemis Urban Driving Cycle.It shows that for both driving cycles,the same parameters may have different influence on the energy consumption of the motors,as well as driving range of electric vehicles.

Performance Analysis of Nested-loop Secondary Linear Doubly-fed Machine Considering End Effects

Nested-loop secondary linear doubly-fed machine(NLS-LDFM) is a novel linear machine evolved from rotary brushless doubly-fed induction machine, which has a good application prospect in linear metro. In order to analyze the performance of NLS-LDFM, the mechanism and action rules of end effects are investigated in this paper. Firstly, the mechanism of static and dynamic end effects is analyzed in aspect of direct coupling, winding asymmetry and transient secondary current. Furthermore, based on the winding theory for short primary linear machines, the machine parameters are established qualitatively considering pulsating magnetic field of NLS-LDFM. Finally, the NLS-LDFM performance analysis is supplemented by the finite element algorithm(FEA) simulation and experiments under different operating conditions.

Fast Design Method of Variable Flux Reluctance Machines

In this paper,a fast design method is developed based on a combination of analytical and finite element(FE)methods for variable flux reluctance machines(VFRMs).Firstly,the feasibility of using analytical method in optimization under unsaturated condition is confirmed.Then,by applying the FE method,the influence of magnetic saturation is considered.Compared with the unsaturated case,the optimal split ratio for magnetically saturated case is increased by 1~1.2 times,the optimal rotor pole arc ratio varies within 0.33~0.44,and the stator pole arc ratio remains the same.Based on this,the optimal structural parameters can be initially set by analytical method and then refined by the FE method.Due to the fast speed of analytical method,less variable counts and narrowed variation ranges,the proposed method is significantly faster than the conventional pure FE based global optimization.Finally,the proposed method is used for optimizing the 6-stator-slots VFRMs having different numbers of rotor poles.The 6-stator-slot/7-rotor-pole(6s/7r)VFRM is found to have the highest torque density.It is prototyped and tested to verify the analyses.

An overview of bearing voltages and currents in rail transportation traction motors

In modern rail transportation,inverter drive systems have been extensively used due to their excellent speed control capabilities.However,in recent years,premature failure problems caused by bearing voltage and current phenomena have been frequently reported in electric motors,with electrical bearing failures making up a considerable percentage.The purpose of this review is to provide a comprehensive overview of facets relating to the electrical erosion of bearings in an electrical environment represented by railway vehicles.First,the origins of the phenomenon as well as typical bearing electrical failure modes are discussed.Next,we introduce the distinctive features of the electrical environment of railway traction motor bearings,including output voltages with high common-mode components and systems with complex grounding configurations.Then,we classify the fundamental mechanisms for generating bearing voltages/currents into four groups,and present their modeling processes,including equivalent circuit establishment and parameter determination methods.Furthermore,we summarize the strategies frequently used to protect bearings,and describe a typical solution to suppress electrical bearing failures in railway vehicles.Finally,we present a case example to illustrate a research procedure for systematic investigation of inverter-induced bearing currents in rail transportation.

Condition monitoring and fault diagnosis strategy of railway point machines using vibration signals

Condition monitoring of railway point machines is important for train operation safety and effectiveness.Referring to the fields of mechanical equipment fault detection,this paper proposes a fault detection and identification strategy of railway point machines via vibration signals.A comprehensive feature distilling approach by combining variational mode decomposition(VMD)energy entropy and time-and frequency-domain statistical features is presented,which is more effective than single type of feature.The optimal set of features was selected with ReliefF,which helps improve the diagnosis accuracy.Support vector machine(SVM),which is suitable for a small sample,is adopted to realize diagnosis.The diagnosis accuracy of the proposed method reaches 100%,and its effectiveness is verified by experiment comparisons.In this paper,vibration signals are creatively adopted for fault diagnosis of railway point machines.The presented method can help guide field maintenance staff and also provide reference for fault diagnosis of other equipment.

A novel MTPA and flux weakening method of stator flux oriented control of PMSM

Permanent magnet synchronous motor(PMSM)has the advantages of high efficiency,high power density and high reliability.It has been widely used in electric vehicles,rail transit,industrial transmission and other fields.Compared with the traditional PMSM control strategy,the Indirect stator-quantities control(ISC)of low torque ripple induction motor has high dynamic response performance in the whole speed range,with high stability and strong security.However,due to the inherent characteristics of PMSM,there are still some difficulties in applying ISC strategy,such as solving the load angle corresponding to the current torque,realizing the maximum torque per ampere(MTPA)control and flux weakening control method in the stator field oriented control algorithm of PMSM.In this paper,theoretical analysis and discussion are carried out for the above difficulties,and an indirect stator vector control(ISC)method for PMSM is proposed.Finally,combined with the electric drive application platform of electric vehicle,the simulation and experimental results verify that the proposed ISC control strategy of PMSM also has good dynamic and steady-state performance in the whole speed range.

Electromagnetic interference modeling and suppression techniques in variable-frequency drive systems

Electromagnetic interference （EMI） causes electromechanical damage to the motors and degrades the reliability of variable-frequency drive （VFD） systems. Unlike fundamental frequency components in motor drive systems, high-frequency EMI noise, coupled with the parasitic parameters of the trough system, are difficult to analyze and reduce. In this article, EMI modeling techniques for different function units in a VFD system, including induction motors, motor bearings, and rectifierinverters, are reviewed and evaluated in terms of applied frequency range, model parameterization, and model accuracy. The EMI models for the motors are categorized based on modeling techniques and model topologies. Motor bearing and shaft models are also reviewed, and techniques that are used to eliminate bearing current are evaluated. Modeling techniques for conventional rectifierinverter systems are also summarized. EMI noise suppres- sion techniques, including passive filter, Wheatstone bridge balance, active filter, and optimized modulation, are reviewed and compared based on the VFD system models.

Solid-state transformer-based new traction drive system and control

A new type of traction drive system consisting of solid-state traction transformer （SSTT）, inverter unit, auxiliary inverter, traction motor and other key components is built in order to suit the demand of developing the next-generation electric traction system which will be efficient and lightweight, with high power density. For the purpose of reducing system volume and weight and improving efficiency and grid-side power quality, an efficient SSTT optimized topology combining highvoltage cascaded rectifiers with high-power high-frequency LLC resonant converter is proposed. On this basis, an integrated control strategy built upon synchronous rotating reference frame is presented to achieve unified control over fundamental active, reactive and harmonic components. The cartier-interleaving phase shift modulation strategy is proposed to improve the harmonic performance of cascaded rectifiers. In view of the secondary pulsating existing in a single-phase system, the mathematical model of secondary power transfer is built, and the mechanism of pulsating voltage resulting in beat frequency of LLC resonant converter is revealed, so as to design optimum matching of system parameters. Simulation and experimental results have verified that the traction system and control scheme mentioned in this paper are reasonable and superior and that they meet the future application requirements for rail transit.

Coupling real-time simulation of power supply,trains and dispatching for urban rail transit

In order to study the interaction among the traction power supply,the train group and the operation dispatching of urban rail transit,a coupling simulation system of power supply system,trains and dispatching management is constructed.In order to solve the problems of different timescales and difficult cooperation operation for related subsystems,a multi-bus distributed real-time network architecture based on hierarchical management of communication data is established,and simulation management software is developed to facilitate the free expansion of the simulation system.Meanwhile,the track line,train operation and other large timescale subsystems are realized by the pure digital simulation.And the time-sensitive subsystems,such as train traction system,braking system,auxiliary power supply system and network system etc.,are built by the semi-physical simulation.In this article,the system structure and the main implementation principle of each simulation subsystem are given in detail,and the system is tested and verified at the end.The results show that the simulation system can meet the expected requirements.

An Integrated Observer Framework Based Mechanical Parameters Identification for Adaptive Control of Permanent Magnet Synchronous Motor

An integrated observer framework based mechanical parameters identification approach for adaptive control of permanent magnet synchronous motors is proposed in this paper.Firstly,an integrated observer framework is established for mechanical parameters’estimation,which consists of an extended sliding mode observer(ESMO)and a Luenberger observer.Aiming at minimizing the influence of parameters coupling,the viscous friction and the moment of inertia are obtained by ESMO and the load torque is identified by Luenberger observer separately.After obtaining estimates of the mechanical parameters,the optimal proportional integral(PI)parameters of the speed-loop are determined according to third-order best design method.As a result,the controller can adjust the PI parameters in real time according to the parameter changes to realize the adaptive control of the system.Meanwhile,the disturbance is compensated according to the estimates.Finally,the experiments were carried out on simulation platform,and the experimental results validated the reliability of parameter identification and the efficiency of the adaptive control strategy presented in this paper.