Classification Method to Define Synchronization Capability Limits of Line-Start Permanent-Magnet Motor Using Mesh-Based Magnetic Equivalent Circuit Computation Results

High-efficiency motors are being gradually introduced in many industrial applications because of their positive impacts on the environment by reducing energy consumption and CO2 emission. In this respect, line start permanent magnet synchronous motors (LS-PMSMs) have been introduced recently. Due to their unique configuration, LS-PMSMs allow the obtaining of super premium efficiency levels, accompanied with a high torque and power factor. However, since the use of LS-PMSMs in the industry is in its infancy, no efficient scheme has yet been reported for broken rotor bar (BRB) fault detection in this type of motor. Accordingly, the main aim of this research is to investigate the fault-related feature for BRB faults on LS-PMSMs. In this regard, a simulation model and experimental setup for the investigation of BRB in LS-PMSM are implemented. The detection strategy for BRB in LS-PMSM proposed here is based on the monitoring of the start-up current signal and discrete wavelet transform. The entropy features are used as fault-related features for BRB faults. Finally, the ability of these features is validated for the detection of BRB in LS-PMSM through statistical analysis. In this research, the importance of the starting load is also considered for BRB detection in LS-PMSMs.

Free-piston machines are widely used in refrigeration compressors, cryocoolers, expanders, and combustion engines. Without crank mechanism, the free-piston machines are more efficient. However, the piston position of free-piston machines needs to be accurately detected with cost-effective methods. This article proposes a novel sensorless stroke detection technique using a low-cost inductive coil wound around main core for resonant free-piston machines. The flux linkage based sensorless technique was implemented in a moving-magnet-type linear compressor. A magnetic equivalent circuit (MEC) model and a finite-element analysis (FEA) model are presented to form the theoretical basis. The flux linkage in each core varies linearly with the piston displacement and a good agreement is shown between the MEC and the FEA models. Experiments are conducted in the linear compressor at resonance to prove the sensorless concept and to validate the two models. The flux linkage difference at two zero-current crossing points is shown to be a linear function of the piston stroke. The average percentage error between the measurements and the MEC model is about 12%. The proposed low-cost sensorless stroke detection technique can achieve an error of only 4%. The adoption of this novel technique is crucial to the commercialization of free-piston machines for high efficiency.

This paper investigates the use of moving coil linear machines (MCLM) in the internal combustion linear generator (ICLG), which is a novel solution for series hybrid electric vehicles, distributed generation, and emergency power supply. According to the analysis of the basic structure of MCLM, an improved tubular MCLM equipped with quasi-Halbach magnetized magnets is suggested and analyzed with a proposed equivalent magnetic circuit (EMC) model. Measurements on a 4-kN prototype show good agreement with the results from the EMC model. Compared with the reported moving magnet linear machines (MMLM) for the same application, the proposed machine has the merit of less moving mass, faster response, and better controllability.

Purpose. Analysis of the rotor configuration of line start permanent magnet synchronous motor (LSPMSM) when using 3-bar magnet structure with two cases: one with a separating magnetic steel bridge and one without it. Research results allow selecting the appropriate rotor configuration to obtain the best starting characteristics, current, torque, and performance. Thereby, it is possible to replace high efficiency LSPMSM with low efficiency induction motors used in ventilation and water pumping loads to improve the efficiency of electricity use in mining. Methodology. The article uses analytical methods and simulation methods on Ansys/Maxwell software and conducts a laboratory test evaluation to determine the effect of rotor configuration on the starting characteristics, working current, torque ripple, and working efficiency of an LSPMSM for mining applications. Findings. An LSPMSM model was built based on a 15 kW–3,000 rpm induction motor with two rotor configurations: one with a separating magnetic steel bridge and one without it. The results of the study show that when a rotor configuration has no separating magnetic steel bridge, the LSPMSM reaches its maximum speed in 0.45 seconds, a synchronous speed of 3,000 rpm in around 0.75 seconds, a torque ripple of 23.1 %, a current total harmonic distortion of 14.3 %, and a performance of 93.3 %. In contrast, when a rotor structure has a separating magnetic steel bridge, starting the motor is more difficult, taking 1.14 seconds to reach synchronous speed and having a lower starting torque, a current total harmonic distortion of 16.1 %, and a performance of 92.5 %. Originality. Research rotor configurations of LSPMSM based on the 15 kW–3,000 rpm induction motor with and without a separating magnetic steel bridge. The research results allow choosing the appropriate rotor configuration to obtain the best starting characteristics, current, operating torque and performance efficiency. Practical value. The research results are important scientific guidance in the design and manufacture of LSPMSM for application in underground mining to improve the efficiency of electricity use in mining.

Line Start Permanent Magnet Synchronous Motor (LSPMSM) has been proved as an economically feasible, high efficiency alternative to an induction motor where constant speed is desirable. These motors are having the properties of an induction motor during starting and synchronous motor during steady state period. The need of line starting, calls for a cage winding in addition to permanent magnets in the rotor, which increases the complications in rotor design, and restricts the choice of rotor geometries. There is always conflict in the rotor design of this machine. This conflict is in between synchronous and asynchronous performance of the machine which in turn is a conflict between cage and magnet placement in the rotor. This paper reports an attempt in the direction of removing this conflict and optimizes both synchronous and asynchronous performances of the machine. A new two-part rotor geometry is suggested and analyzed using the dynamic model of LSPMSM prepared in Simulink.

In electric machine drive systems, hardware-in-the-loop (HIL) emulation provides accurate testing of actual control system prototypes and protection devices interfaced with the electric machine model on a real-time simulator in a non-destructive environment particularly when faults are studied. A compromise between the model accuracy and computational burden makes the magnetic equivalent circuit (MEC) model ideal for real-time simulation of electric machines. However, satisfying the timing constraints of real-time simulation to accommodate internal machine faults is still challenging due to the nonlinearity and rotation of electric machines. In this paper, the transmission line modeling (TLM) method is utilized to keep the MEC coefficient matrix unchanged during nonlinear iterations. Afterward, for the first time, the entire potential of the TLM method for pre-calculation is exploited by proposing an efficient matrix re-ordering combined with the left-looking Gilbert–Peierls algorithm to minimize the computational burden of the sparse MEC matrix LU decomposition required in each time-step due to rotation. Furthermore, the massive hardware architecture of the field programmable gate array is used as the platform for implementation to fully exploit parallelism. With the proposed MEC-based real-time TLM method, the minimum time-step as low as 500 $\mu \text{s}$ can be achieved and the results validation with two-dimensional finite element model (FEM) of the commercial Jmag-Designer software shows the accuracy and efficiency of the proposed methodology.

Starting phase of a motor in general is a very complicated period. Motors draw a large amount of current, several times the normal full-load current when first energized. In starting period of Line Start Permanent Magnet Synchronous Motors (LSPMSM), high current causes saturation in stator and rotor. The effect of saturation on the “q-axis” synchronous inductance, L mq , of LSPMSM is studied in this paper. The paper will proposes a method to calculate the L mq using the Lumped Parameter Method. Comparative results will be carried on using finite element method. Good agreement between results is justified.

The paper presents a 2D field-circuit model of coupled electromagnetic thermal and mechanical phenomena in a line start permanent magnet synchronous motor (LSPMSM). The nonlinearity of the magnetic circuit, the influence of temperature on magnetic properties of the permanent magnets as well as on electric and thermal properties of the materials have been taken into account. The elaborated on the basis of this model algorithm as well as a developed computer program have been used to analyze the influence of temperature and armature reaction on the magnet stabilization during the starting process of the considered motor. The selected results of simulations have been presented and discussed.

Basic Transverse flux permanent magnet generators (TFPMs) are considered for direct drive wind turbine applications because of having high value of torque density. However, the presence of cogging torque in TFPMs is troublesome in wind turbine applications. This paper implements step skewing technique to eliminate the cogging torque of the TFPM. The analytical approach is presented to formulize the optimum skew angle validated by both finite element method (FEM) and magnetic equivalent circuit (MEC) method. The design algorithm of the TFPM based on MEC modeling is presented including the step skew and iron saturation effects. The MEC results are compared by FEM in terms of accuracy and time consumptions. The MEC method is ten times faster than FEM and it also shows acceptable accuracy. In order to achieve the optimum design, Taguchi design of experiments is used to optimize the TFPM torque characteristics.

An axial-flux permanent-magnet (PM)-assisted claw-pole generator (APCG) is designed based on an equivalent magnetic circuit model (EMCM). It is designed for generating power in vehicle with the merits of high power density, no brush, and wide airgap flux density modulation range. This paper mainly focuses on establishing the EMCM of the APCG and designing a set of optimal structure parameters. First, the topology and operation principle of the APCG are introduced in detail, including material, fabrication, and magnetic flux distribution. Second, the magnetic circuits in claw poles are simplified and the relationships among the key parameters are discussed. Finally, based on the simplified model and the relationships among the key parameters, the EMCMs of current and PM excitation are established, respectively. According to the EMCM, a scheme of a 4 kW APCG is carried out. Comprehensive investigations demonstrate that the EMCM is time-saving and relatively accurate when compared with a finite element method.

This paper describes a novel surface-mounted permanent magnet synchronous generator with hybrid excitation to solve the magnetic field adjustment and voltage stabilization. The machine structure and hybrid excitation principle are explained. Then equivalent magnetic circuit (EMC) models at different excitation modes are built. By means of EMC, voltage regulating under flux enhancing operation and magnetic circuit coupling in the hybrid mode could be obtained rapidly, which is in agreement with the results of 2D FEM. Thus the EMC model could provide reference for parameter setting quickly and accurately in the initial structural design stage.

Harmonic magnetic gears (HMGs) have the advantage of lubrication‐free, high speed ratio and high torque density, which make it an attractive solution for safety critical applications. Due to eccentricity caused by machining and assembly, HMG suffers from dynamic eccentricity (DE) in operation, however, its effect on HMG performance is still unknown. Transmission characteristic of HMG under DE is studied. First, a magnetic equivalent circuit (MEC) model of HMG is proposed to build the magnetic coupling torque analytically, and the geometry of air gap is analysed parametrically to derive its equivalent reluctances. Flux density and coupling torque can be acquired by solving MEC equations. The accuracy of the MEC model is verified by finite element method. To study the transmission characteristic, an electromechanical coupling simulation framework for HMG is constructed, motion trajectories of rotors are investigated in case of DE, the output torque in locked‐rotor condition and speed response in continuous operation can be derived by simulation. It is found that torque ripples that have the same frequency with input rotor are induced by DE; the results are then verified in the experiment. This paper provides a theoretical guidance for the design and condition monitoring of HMG.

This paper focuses on the development of a magnetic equivalent circuit (MEC) of an exciter machine with an armature rotating interior to a wound field. The machine is intended as part of an excitation system for a wound rotor synchronous machine (WRSM) serving as a motor or generator. The MEC model is structured to enable multi-objective optimization of the exciter as a standalone system or as part of a system-level design in which the exciter (machine, diode rectifier, control) and WRSM are designed together within a system-level optimization. Validation of the exciter model is evaluated by comparing with hardware for a standalone open-circuit experiment and when used to supply field current to a WRSM under transient load application.

Magnetic equivalent circuit (MEC) models are increasingly valuable for analysis and design of electromechanical devices, particularly electrical machines, because of their moderate computational effort and reasonable accuracy. Force and torque calculations in prior MEC implementations are almost exclusively based on the virtual work method (VWM) adapted to the specific device model. But VWM does not easily extend to a general MEC modeling approach. In this paper, the more direct Maxwell stress tensor (MST) method is applied to a general 3-D MEC modeling framework. MST theory and implementation are presented. Its application is discussed with the example of an electromagnet. Results are compared to both measurements and analytical and finite-element models.

This article proposes a novel high-precision nonlinear semi-analytical model for the magnetic fields and the electromagnetic performance calculation of three-dimensional magnetic circuit permanent magnet motor (3DMCPMM) in aircraft electric propulsion applications, which can take the effects of the magnetic saturation nonlinearity and the permanent magnet (PM) end-leakage flux into account. The high torque density 3DMCPMM topology is firstly proposed, which can improve the output torque per unit weight via the three-dimensional magnetic circuit coupling. In order to simplify the computation, the three-dimensional magnetic circuit equivalent decoupling method is proposed for the 3DMCPMM, which can convert the three-dimensional magnetic circuit into dual two-dimensional magnetic circuits. The 3DMCPMM analytic model is then proposed based on the harmonic subdomain approach, which can accurately predict the magnetic field distribution and the electromagnetic performance. Furthermore, by using the equivalent magnetic circuit (EMC) model, the PM end leakage flux coefficient is proposed for the 3DMCPMM analytic model, which can eliminate the calculation error due to the PM end-leakage flux effect. The nonlinear iteration based magnetic permeability is proposed for the 3DMCPMM analytic model, which can improve the analytic calculation accuracy by considering the magnetic saturation nonlinearity. A 630 N·m 3DMCPMM is designed and manufactured with the torque density of 25.37 N·m/kg. Simulation and experimental results show that the proposed semi-analytic model has the excellent electromagnetic prediction performance with the maximum calculation error of 4.62%, which can achieve the analytic calculation of three-dimensional magnetic circuit motor. The 3DMCPMM semi-analytical model is proposed for the first time, which lays the foundation for the 3DMCPMM rapid design and iterative optimization.