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This article presents an online method to acquire the stator inductance and flux linkage for inverter-fed surface-mounted permanent magnet synchronous motors (SPMSMs) using switching state functions instead of average models. Given the switching state functions when different voltage vectors are applied to the motors, the information of inductance and flux linkage is revealed. Based on the dc bus voltage and current derivatives obtained from either hardware methods like Rogowski coil and differential circuit, or software methods such as tracking differentiator, stator inductance, and flux linkage are able to be figured out directly using the redundant or more practical methods with the help of recursive least square (RLS). Simulations and experiments are carried out to prove the effectiveness of the proposed methods, besides, dc voltage and operating speed variation as well as the impact of resistance are taken into account. Finally, compared with the conventional parameter identification based on the average models either in α–β or d–q coordinate, the proposed methods with switching state functions have remarkable advantages especially when the rotor position error exists. What needs further effort is the challenging case at very low speed, e.g., it is hard to identify flux linkage due to the small back electromotive force (EMF). [ABSTRACT FROM AUTHOR]

This paper proposed a hybrid subdomain model (HSM) for calculating the magnetic field distribution of interior permanent-magnet (IPM) machine accounting for slotting effect, rotor saliency, and iron nonlinearity. In the constant permeability region, i.e., slots, slot-opening, and air-gap, three subdomains are introduced to represent their magnetic field. By applying the subdomains interface conditions and nonlinear boundary conditions, the analytical air-gap field solution can be obtained based on the governing Laplace and Poisson equation. For the iron region, the magnetic reluctance network (MRN) is proposed to account for rotor saliency iron and nonlinearity. The magnetic voltage source is introduced to represent the permanent-magnet (PM) while the air-gap flux source is used to replace the air-gap reluctance network, which is the key to guarantee the computational efficiency and high accuracy. The electromagnetic performances of both flat-shaped and V-shaped IPM machines are investigated to show the advantages of different IPM machine topologies analytically. The HSM predictions for both IPM machines are validated by finite-element (FE) analysis and experimental results. [ABSTRACT FROM AUTHOR]

In this article, we developed an improved hybrid field model (IHFM) to predict the on-load performance of the interior permanent-magnet (IPM) motors considering both iron saturation and slotting effect. It combines the airgap analytical model based on the modified conformal mapping with the reluctance mesh method for stator and rotor. The reluctance mesh method can accurately predict the rotor saturation and tooth-tip saturation even their field distribution is complicated due to the armature reaction. Besides, IHFM will significantly accelerate computation speed using the analytical model for airgap region while keeping high accuracy. The finite-element analysis and experimental results of the flat-type and V-type IPM motors are demonstrated to verify the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

This article proposed a nonlinear analytical model (NAM) for external rotor permanent magnet synchronous motor (ER-PMSM) considering both rotor and stator saturation. The improved magnetic equivalent circuit (IMEC) is introduced to accurately describe the saturation effect of rotor and stator. The air gap reluctance is replaced by magnetic flux source, and, therefore, the size of IMEC can be reduced while keeping high accuracy. For the air gap field calculation, the analytical solution will be obtained based on the modified boundary condition from the IMEC. The complex permeance function is extended to represent the slotting effect of ER-PMSM. Hence, the NAM will be numerically solved from the combination of IMEC and analytical air gap solution. Both finite-element analysis (FEA) and experiment demonstrate that the proposed model has high accuracy and requires little time. [ABSTRACT FROM AUTHOR]

This article proposes a novel doubly fed flux reversal machine (DF-FRM) with two sets of armature windings wound on both stator and rotor teeth. The proposed DF-FRM can provide much higher torque density than conventional FRM due to better utilization of rotor space. Moreover, the DF-FRM exhibits higher fault tolerance and it can still offer almost the desired output torque of FRM during fault operation, albeit one set of armature windings is malfunctioning. The machine topology as well as operation principles of a 12-stator-slot/14-rotor-slot DF-FRM is introduced and explained. Furthermore, the electromagnetic performances of FRM and DF-FRM with optimized structure aiming at maximum torque density are analyzed and compared using finite element (FE) method. The results show that DF-FRM can yield 60% higher torque density than the conventional FRM. Finally, a prototype is manufactured and tested to validate the FE results. [ABSTRACT FROM AUTHOR]

This article proposes a novel axially magnetized Vernier permanent-magnet (AMVPM) machine which has permanent magnets (PMs) clamped on both ends of the rotor with alternately magnetized directions. The topology improves the mechanical strength of the structure without weakening the electromagnetic performances. The detailed operating principles are described and the design parameters are optimized. The open-circuit back electromotive force (EMF) is calculated analytically by using the harmonic series expressions. Then, a comparison between the AMVPM machine and regular Vernier permanent-magnet (VPM) machine is analyzed by finite-element analysis (FEA) method. Finally, the machine prototype is manufactured and the electromagnetic performances are experimentally validated. [ABSTRACT FROM AUTHOR]

In railway traction applications, the six-step operation of traction inverters is frequently applied at high speed due to the limitation of switching frequency of the converter which is installed in very limited space on the train. Meanwhile, without hardware filters installed, fluctuation components of dc-link voltage will emerge due to the input power ripple introduced by the single-phase rectifier, and can cause significant current and torque ripple in the motor. In this article, a direct torque control scheme for permanent magnet synchronous motor in a six-step operation is proposed to suppress the dc-link voltage fluctuation-induced current and torque ripple without extra hardware. It adjusts the duration of voltage space vectors according to the predicted dc-link voltage waveform six times per fundamental cycle, and minimizes the error between output torque and reference torque at the end of each time. Experimental results on an interior permanent magnet synchronous motor demonstrate that the proposed control can more effectively suppress current and torque ripple than state-of-the-art controls and achieve torque control with high dynamics and accuracy. [ABSTRACT FROM AUTHOR]

The clamping bolts and bolt-holes can be employed to stack the steel laminations in permanent magnet machines. Their influence on the electromagnetic performance is analyzed in this paper, including the electromagnetic torque, open-circuit torque, phase back-EMFs, and circulating current loss. A restraining method of dummy bolt-hole is proposed to achieve both balanced phase back-EMFs and zero circulating currents in bolts. The ratio of bolt-hole edge thickness to bolt-hole radius is optimized to compensate the reduction of stator yoke caused by bolt-holes. Besides, a method of open bolt-hole edge is proposed to restrain the circulating currents. Furthermore, structure analyses are conducted to prove the reliability of the electromagnetic design. The proposed method is verified by experiments on a prototype machine. [ABSTRACT FROM AUTHOR]

A hybrid field model (HFM) based on the combination of magnetic equivalent circuit (MEC) and exact conformal mapping (ECM) is developed to calculate the open-circuit field of interior permanent-magnet (IPM) motor. In the proposed HFM, the IPM and iron saturations are transformed into equivalent current on the rotor surface and stator bore. ECM can calculate the air-gap field analytically using the equivalent current. Once the air-gap field is obtained, the MEC in the iron region can be solved and gives the new value of equivalent current, which forms a calculation loop. Hence, iterative solving process is required to determine the equivalent current and iron permeability in the rotor and stator. In order to verify the proposed model, both finite-element (FE) analysis and experiment are performed on IPM motors with V-type rotor and conventional “-” type rotor. Their results demonstrate the high accuracy of HFM. [ABSTRACT FROM AUTHOR]

In this paper, a novel hybrid permanent magnet variable flux memory machine using two-part rotor is proposed whose rotor comprises an AlNiCo part and a NdFeB part adjacent to each other on the same shaft. With the proposed topology, flexible flux controllability can be achieved since the magnetization state of AlNiCo can be adjusted by a temporary current pulse. The detailed operating principles are described, and the split ratio and some key design parameters are optimized. Then, the electromagnetic performance of the proposed machine with emphases on back electromotive force, flux density, flux-weakening performance, and torque characteristics is investigated. Finally, 3-D finite-element validation is implemented and a machine prototype has been manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

By developing a simple permeance-magnetomotive force (MMF) model of switched-flux permanent magnet (SFPM) machines, the air-gap flux density produced by both PMs and armature current can be derived, in which harmonics with the same order and rotational speed are called an effective harmonic pair (EHP). By investigating the influences of armature current angle $\delta $ on both the phase and amplitude of each EHP, it is found that the amplitudes of both PM and armature reaction flux-density harmonics maintain fixed, whereas the space phase shift between them changes accordingly with armature current angle. Specifically, the PM and armature reaction flux-density harmonics are orthogonal in space if zero ${d}$ -axis current is fed. Therefore, the maximal torque is realized for each EHP. As the total torque of SFPM machines is the superposition of the contributions by each EHP, the zero ${d}$ -axis current control method turns out to be the optimum for maximal torque per ampere, thus verifying analytically that the ${d}$ - and ${q}$ -axes inductances are equal according to the general torque equation for the investigated machine topology. In addition, the torque adjustment mechanism of each EHP in SFPM machines has also been analytically demonstrated to be resemble that of the surface-mounted PM synchronous machine (PMSM). Finally, the finite-element analysis (FEA) has been performed to validate the previous analytical predictions. [ABSTRACT FROM AUTHOR]

In this paper, an outer rotor interior permanent magnet synchronous machine (IPMSM) with hybrid permanent magnet (PM) material is proposed. The key is to adopt the outer rotor structure with two-layer crescent barriers and hybrid PM material to maximize the output torque and reduce the usage of high-cost rare-earth PM. The ferrite PMs are filled in the middle of the crescent barriers with thicker thickness, while the rare-earth PMs are filled into the bilateral of the crescent barriers with thinner thickness. To verify the effectiveness of the proposed rotor structure, optimizations are first carried out among the conventional rotor structures with single kind of PM material and the proposed rotor structure with hybrid PMs. Then, detailed comparisons have been investigated. Results indicate that the proposed machine has higher torque density than the machine with only ferrite PM and can reduce almost half the usage of rare-earth PM in comparison to the machine with only rare-earth PM. Moreover, the proposed rotor structure is further optimized considering productivity. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear hybrid field model to predict the open-circuit magnetic field distribution in surface-mounted permanent-magnet machines. It combines the complex permeance model (CPM) with the magnetic equivalent circuit (MEC). The saturation effect is accounted for in the CPM by considering the magnetic potential distribution on the stator bore, which is calculated by the MEC and can be transformed to the virtual current on the slot. The proposed model significantly improves the calculation accuracy for saturated machines, which is verified by the finite-element analysis and the experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents an improved magnetic circuit (MC) model considering the leakage, cross coupling, and saturation effects for the performance analysis of an integrated 3 degrees of freedom magnetic bearing (3-DOF MB). Compared with the conventional MC model, this paper analyzes the permanent-magnet bias field, radial and axial control current fields together. By using this improved MC model, it reveals the cross-coupling effect between radial and axial directions in such an integrated 3-DOF MB. The stiffnesses of radial force are significantly influenced by the axial control current, while the stiffnesses of the axial force are independent of the radial control current. Its accuracy is verified by the 3-D finite-element method. [ABSTRACT FROM AUTHOR]

The current capacity of superconducting materials is far larger than that of copper. This paper utilizes MgB2 wires as stator armature windings to obtain a higher output power capacity and presents the electromagnetic design of a direct drive dual-stator superconducting permanent magnet (PM) wind power generator of several megawatts. Considering the irreversible demagnetization in PM materials caused by the huge stator current, several new rotor pole configurations are presented. The features of each configuration are discussed, and the finite element method results show that the output power capacity of the proposed generator can be raised by 8% because the stator current can be larger for the generator with new rotor configurations under the restriction of demagnetization. [ABSTRACT FROM AUTHOR]

In this paper, dynamic reluctance mesh model (DRM) combined with an improved iron losses prediction model are presented to provide fast and accurate way to evaluate the iron losses for permanent magnet (PM) motors with pulsewidth-modulated power supply. A DRM model for high-speed train PM traction motor is first built. The magnetic field distribution for one cycle is then obtained using the DRM method. An improved engineering model of iron losses prediction is applied. Finally, the simulation and testing results are presented to confirm that the proposed combined method is accurate and effective as the finite element method (FEM) model with much less time consumed. [ABSTRACT FROM AUTHOR]

In low-speed high-torque applications, gearboxes are widely used to amplify the output torque of electrical machines, which inevitably introduce side effects caused by mechanical contact. Consequently, a gear-free system has become increasingly interesting. Although a Vernier permanent-magnet machine has good torque capability, the low power factor is its weakness. This paper proposes a novel topology called the Vernier pseudo-direct-drive (VPDD) machine. A two-stepped design methodology is adopted by combining the subdomain analytical method and finite-element method (FEM). According to the results, the exact subdomain analytical model allows a quick pre-optimization of the structure, and the FEM can be used for further adjustment, dealing with the saturation effect and demagnetization. The optimized VPDD is capable of reaching a very high torque density of 91.8 Nm/L, and the torque ripple is negligible. Its power factor is 0.94. [ABSTRACT FROM AUTHOR]

The power converter control system has a great impact on the behavior of the high-speed permanent magnet generator system (HSPGS) due to the high operating frequency. In this paper, a 3-D modeling based on finite-element analysis directly coupled with a power converter control system is built in order to accurately evaluate generator performance. The influence of the control system current time harmonics on the 3-D flux distribution, the vector eddy current in rotor sleeve, and the iron loss of the machine are investigated. The analytical model is validated by experimental test results from a developed prototype of the HSPGS. The obtained results could provide a reference for the system-level design and investigation for the HSPGS in the further design. [ABSTRACT FROM AUTHOR]

This paper proposes a novel rotor structure for high-speed interior permanent magnet motors to overcome huge centrifugal forces under high-speed operation. Instead of the conventional axial stacking of silicon-steel laminations, the retaining shield rotor is inter-stacked by high-strength stainless-steel plates to enhance the rotor strength against the huge centrifugal force. Both mechanical characteristics and electromagnetic behaviors of the retaining shield rotor are analyzed using finite-element method in this paper. Prototypes and experimental results are demonstrated to evaluate the performance. The analysis and test results show that the proposed retaining shield rotor could effectively enhance the rotor strength without a significant impact on the electromagnetic performance, while some design constraints should be compromised. [ABSTRACT FROM PUBLISHER]

It is essential to experimentally determine the profile of flux linkage, current, and position of a switched reluctance motor (SRM) in both design verifications and high-performance control implementations. In this paper, a fast measurement method of the flux linkage profile is proposed. In the proposed method, the rotor is first rotated to the aligned position, and then, the voltage pulses are applied to all phases simultaneously. The dc voltage and phase current waveforms are recorded to estimate the flux linkage curves at three different positions. These curves are used to calculate the coefficients of a second-order Fourier series flux linkage model, which represents the entire flux linkage profile of an SRM. The feasibility and accuracy of the proposed method are verified by experimental study with an 8/6 SRM. The impacts of rotor misalignment and phase couplings are investigated. A comparative study with the well-recognized rotor clamping method is given to demonstrate the advantages of the proposed method. The proposed method eliminates the requirements on rotor clamping devices or position sensors; therefore, it is suitable for product test in massive production and fast field measurement. [ABSTRACT FROM PUBLISHER]

This paper describes a five-phase brushless dc (BLDC) motor designed for an electrohydrostatic actuation system (EHA) suited to the thin and optimized wings. The foundation of the design is a motor with fault tolerance and high reliability, compact structure, and low weight. The motor power rating is 12 kW at 12 000 rpm, and a “wet” form of construction is used where hydraulic oil is present in the motor to reduce the number of oil seals of the EHA for enhanced reliability and lifetime. The losses and thermal behavior are evaluated for an optimized design. Fault tolerance for BLDC motors is discussed. A five-phase motor has been manufactured, and test results are presented to validate the design. [ABSTRACT FROM AUTHOR]