Magnetomotive Force Research Articles

Comparative Analysis of Noise and Vibration for Dual Three-Phase IPMSM Under Healthy and Multi-Phase Open-Circuit Fault Operations

The dual three-phase interior permanent magnet synchronous machines (IPMSMs) exhibit excellent fault-tolerant capabilities due to their multi-phase winding configurations. Under certain winding failure circumstances, by using the fault tolerant control (FTC) to reconstruct the normal rotating magnetomotive force, the machine can still provide the expected comparable torque as the healthy mode does. However, in the existing literature, limited attention was paid to the noise and vibration (NV) problems targeting the dual three-phase IPMSMs in FTC operation. To fill this knowledge gap, this paper conducts a quantitative comparison on the NV performance of a dual three-phase IPMSM under healthy and multi-phase open-circuit fault conditions under FTC. The comparative studies involve radial electromagnetic force, acceleration distribution, sound pressure level as well as machine housing deformation, which are analyzed under healthy and multi-phase open-circuit fault operations. Based on our exclusive findings, after applying the FTC, even though the machine can deliver the desired electromagnetic performance, the maximum deformation and sound pressure level of the IPMSM can be mitigated by 12.9% and 16.9%, respectively, compared to the ones under the faulty condition without FTC.

Novel Dual Inverter Sub-Harmonic Synchronous Machines

Sub-harmonic synchronous machines are a relatively new bread of brushless wound field synchronous machines considered alternatives to many electric machines in transportation electrification applications. This paper presents two dual inverter sub-harmonic synchronous machines having unique two-layer and three-layer stator winding topologies. The two inverters provide the stator windings with two sets of balanced three-phase currents. These two and three-layer windings are arranged in such a way that they can generate both fundamental and sub-harmonic magnetomotive force. Furthermore, the fundamental MMF component of this machine is four times the sub-harmonic MMF component used for the brushless operation. In contrast, the sub-harmonic magnetomotive force is used for field excitation, which leads to brushless operation. Two 8-pole, 48-slot, 2-inverter, 2-layer and 3-layer sub-harmonic machines are designed to validate the concept through a 2-D finite element analysis of these new topologies, showing a better overall torque profile and performance as compared with the other sub-harmonic and brushless wound field synchronous machines.

Modelling and Analysis of Salient-Pole Rotor Interior Permanent Magnet Synchronous Motor for Oil and Gas Pump Applications

This paper presents the design and dynamic simulation of a line-start, three-phase Interior Permanent Magnet Synchronous Motor (IPMSM) intended for pump applications in the oil and gas industry. The problem addressed in this paper pertains to the replacement of an existing induction motor (IM) in an oil and gas pump station with a more efficient and controllable solution, the IPMSM since IMs are known to be less efficient and IPMSM is easier to control. The chosen motor type employs a traditional salient-pole rotor with cage windings, known for its line-start capability, making it a feasible choice for constant-speed and pump applications. The dynamic simulation of the proposed IPMSM is carried out using MATLAB/Simulink, focusing on fundamental harmonic analysis in direct-phase variables. The results demonstrate rapid startup to synchronous speed with minor deviations effectively dampened by the rotor's damper windings. Torque characteristics exhibit some pulsations caused by magneto-motive force (MMF) harmonics; a phenomenon captured by Finite Element Analysis (FEA). The performance results show that the proposed IPMSM with a salient-pole rotor is viable and a promising replacement for induction motors in oil and gas pump stations.

THE CHOICE OF THE TYPE OF MAGNETIC CIRCUITS IN INDUCTION DEVICES
 DIRECT CONVERSION OF MECHANICAL ENERGY INTO THERMAL ENERGY

As the technical characteristics of permanent magnets manufactured by the industry improved, they began
 to be used more often in the generation of electricity, as well as in induction devices for direct conversion of mechanical
 energy into thermal energy. To increase the efficiency of the latter, it is necessary either to increase the frequency
 of interruptions of magnetic fluxes, or to increase their intensity. In this paper, a comparative analysis
 of unbranched magnetic circuits with sources of magnetomotive force (MDS) in the form of a permanent magnet
 and in the form of a coil with a current (electromagnet) is carried out in order to quantify the effect of air gaps on
 the change of magnetic fluxes in these circuits. The results of this comparative analysis make it possible to optimize
 the choice of the type of magnetic circuits in induction devices for direct conversion of mechanical energy into
 thermal energy.

Current Ripple Reduction Employing the Reactor of DC–DC Converter to Have Variable Inductance through Magnetic Saturation

When DC distribution grids with different voltage levels are connected, harmonic currents flow into the grid under light load conditions, which is a significant cause of grid instability. In this paper, we proposed a method to reduce the current ripple at light load by designing a bidirectional DC–DC converter reactor to have an inductance variable according to the load power capacity. The inductance is varied using magnetic saturation and implemented in three ways: two magnetic circuits in one magnetomotive force (MMF) circuit, a single magnetic circuit in one MMF circuit, and two magnetic components with different magnetic permeability in one MMF circuit. The feasibility is verified through simulation and experiments targeting the 750 and 380 V DC grid connection. The operating characteristics and efficiency are compared and analyzed by applying the existing and proposed variable reactor to a bidirectional DC–DC converter.

Antisaturation and Power Decoupling Control of Multiwinding Energy Harvester Based on Magnetomotive Force Compensation

With the rapid development of smart grids, numerous monitoring sensors have been widely used for the state inspection of power lines. To ensure reliable operation of these sensors, the problem of their power source needs to be solved urgently. In particular, non-invasive inductive energy harvesters clamped over the lines are suitable as power sources for the monitoring sensors. This paper presents the multiwinding energy harvester (MWEH), equipped with multiple energy output channels. To improve the anti-saturation ability of the magnetic core and eliminate power cross effects between the windings simultaneously, an auxiliary winding is introduced to regulate the magnetomotive force. The method of maintaining the unsaturated working state of the magnetic core and the power decoupling control strategy between the windings are proposed. Hence, the global power fluctuation can be eliminated with a constant unsaturated state when the load and turns of any winding change. The experimental results suggest that regulating the energy harvesting factor of the auxiliary winding can desaturate the magnetic core. Furthermore, based on the linear operation of the MWEH, the problem of power linkage of the windings can also be solved, which stabilizes the output power of one or more windings.

Torque Generation Mechanism of Dual-Permanent-Magnet-Excited Vernier Machine by Air-Gap Field Modulation Theory

The dual-permanent-magnet-excited vernier (DPMEV) machine has attracted increasing interest for its high torque density. However, it is difficult to analyze due to the complex structure. In this article, the torque generation mechanism of DPMEV machines is analyzed from the perspective of magnetic field modulation. First, based on air-gap field modulation theory, the stator and rotor modulation factor models as well as armature and permanent magnet magnetomotive force (MMF) models are established, respectively. Considering the bidirectional field modulation effect of the DPMEV machine, the modulation process of MMF is derived. Then, by analyzing the modulated armature and permanent magnetic field, the torque generation mechanism is investigated. In addition, a machine with stator flux gap structure is proposed and the reasons for its torque increase are explained. Finally, a prototype of DPMEV machine is manufactured and tested to verify the effectiveness of the analytical results.

Sub-harmonic-based Cost-effective Brushless Wound Rotor Synchronous Machine Topology

This paper proposes a sub-harmonic-based brushless wound rotor synchronous machine (WRSM) topology. The proposed topology involves two three-phase stator windings with a different number of turns. Both windings are linked in parallel and are provided with current from a single inverter. One of these windings is a four-pole winding while the second winding is a two-pole winding. This arrangement generates a magneto-motive force (MMF) in the air-gap of the machine comprising of two components: a regular fundamental MMF and a sub-harmonic MMF. The fundamental component produces the main stator field whereas the sub-harmonic component generates a sub-harmonic field that is utilized to produce a harmonic current in a two-pole rotor harmonic winding. The induced harmonic current is rectified to inject direct current (DC) to the field winding and produce a four-pole rotor magnetic field. The four-pole rotor magnetic field when magnetically interacts with the same number of the main stator field poles producing torque. Finite element analysis (FEA) is carried out to confirm the operation and achieve the electromagnetic behavior of theproposed topology.

Multiparameter Control of Energy Characteristics of Waveguide-Cavity Resonator-Slot Radiators

The problem of connecting three electrodynamic volumes with ideally conducting walls through electrically narrow rectilinear connecting slots and a radiating slot is solved by the generalized method of induced magnetomotive forces (MMF). The solution is obtained in an analytical form, taking into account the finite thickness of the walls of the connected volumes. The volumes are an infinite rectangular waveguide excited by a fundamental wave, a rectangular cavity resonator, and a half-space above an infinite plane. The energy characteristics of this system have been comprehensively studied depending on the geometric parameters of the constituent elements of the structure under consideration.

Electromagnetic Characteristics Analysis and Torque Ripple Reduction for Doubly Salient PM Machine

In this paper, the air-gap field modulation analysis and torque ripple reduction method for doubly salient permanent magnet motor (DSPMM) are presented. Based on the flux linkage distributions in the motor, the equivalent magnetic circuit models for permanent magnet (PM) and armature winding excitations are built, respectively. The air-gap magnetomotive forces (MMFs) caused by PM MMF and armature MMF can be obtained by combining the air-gap permeance and equivalent magnetic circuit models. The electromagnetic properties of the DSPMM are investigated from the perspective of air-gap field modulation principle. It is revealed that multiple field harmonics contribute to torque generation, and the torque ripples of the DSPMM are mainly caused by the cogging torque. To reduce the torque ripples, the 5th or 7th harmonic currents can be injected into the armature winding to compensate the cogging torque, and their analytical formulas will also be given. The finite element simulations and experiments are carried out to verify the results of theoretical analysis and the effectiveness of the proposed control method.

Exact THD Calculations Applied to Minimize Space Harmonic Content of Winding and Rotor Magnetic Fields

As a metric for measuring the combined space harmonic content of electric machine winding magnetomotive force (MMF), the winding total harmonic distortion (THD) is defined with an infinite series. Without truncation, the exact THD can be evaluated via a “family grouping” facilitated by a “family sum” over the fewest possible winding factors. Uniformly applicable to distributed windings and fractional-slot concentrated windings (FSCWs), this procedure also explains the inherent difference in harmonic content between both winding categories. Furthermore, the minimal THD (mTHD) that can be achieved by optimizing a winding is revealed with a closed-form expression. While intended for windings, the mTHD concept also benefits the design of low harmonic content rotor magnetic fields. Examples of both winding and rotor mTHD designs are provided.

Enhanced Fault Tolerance of Dual Three-Phase Permanent Magnet Motor With Three-Redundancy Control

This article proposes a novel three-redundancy control for the dual three-phase permanent magnet (DTP-PM) motor to enhance the open-phase fault tolerance. Three redundancies can be operated individually or synergistically. Hence, the faulty redundancy can be disconnected from the system to address the open-phase fault. The fault tolerance can be significantly enhanced. Primarily, the structure of the DTP-PM motor is analyzed. Six phases of the DTP-PM motor are separated into three sets of orthogonal phases and considered three two-phase motors. Therefore, three redundancies can be established. Since orthogonal phases provide a balanced structure, the magnetomotive force of each redundancy can be well controlled. Then, a DTP-PM motor control system with three redundancies is established, and a potential topology for the proposed strategy is also illustrated. Furthermore, the basic voltage vectors for each redundancy are investigated. The reference voltage vectors can be modulated expediently. Finally, some simulations and experiments are carried out, validating the feasibility and effectiveness of the proposed strategy.

Speed and Axial Position Control for a Linear-Rotary Switched Reluctance Motor With Two Radial Windings

For 6/4 Linear-Rotary Switched Reluctance Motors (LRSRMs), the magnetic-flux paths of the two windings are coupled in the radial direction, thus it is difficult to design the two-winding current algorithm for the linear and rotary control simultaneously. To solve this problem and achieve linear motion and rotation at the same time, speed and axial position control method is proposed through employing the equal magnetomotive force of two windings to calculate the given currents. This control method has advantages of simple principle, easy implementation and can realize the coordinated control of rotation and linear motion. In addition, the mathematical model of LRSRM is established to facilitate the design of current algorithm. Simulation and various experiments are completed to verify the demonstrated performance of the proposed control method.

Novel Double Mode Dual-Stator Wound Rotor Synchronous Machine for Variable Speed Applications

This paper offers a novel dual-mode double stator wound rotor synchronous machine for variable speed applications. The proposed motor integrates the benefits of both the traditional wound rotor synchronous machine (WRSM) and brushless wound rotor synchronous machine (BL-WRSM). A constant torque can be attained in the maximum torque per ampere region by operating the proposed machine as a traditional WRSM in Mode I, and a constant power can be attained in the field-weakening region by operating it as a BL-WRSM in Mode II. Moreover, due to the dual-stator structure, the proposed machine exhibits improved performance in terms of high torque density as compared to the existing single stator BL-WRSM. By using a special stator winding arrangement to achieve the sub-harmonic component of the stator magnetomotive force, the brushless operation of the proposed machine is achieved. The additional sub-harmonic component induces a voltage in the harmonic winding placed on the rotor, which is then rectified and provided a DC current to field winding for brushless excitation. In order to validate the effectiveness of the proposed machine, a two-dimensional finite element analysis (FEA) is carried out.

AC Copper Loss Reduction in Planar Inductors With Magnetic Building Blocks-Based Gapless Parallel Symmetrical Magnetoresistance Structure

Fringing and proximity effects are the main reasons for serious ac copper loss in high-frequency planar inductors. In this article, a novel air-gapless core structure based on magnetic building blocks with magnetoresistance parallel and symmetrically distributed relative to the windings is proposed, in which two magnetic building blocks parallel to the PCB windings are made of metal soft magnetic material with low relative permeability and three magnetic building blocks perpendicular to windings are made of ferrite with high relative permeability. Equivalent magnetic circuit models and theoretical analysis for the proposed core structure reveal that even if the interleaved winding structure fails in the inductor, a better distribution of magnetomotive force can be obtained by optimizing the distribution of magnetoresistance. Compared with the conventional inductors using stand airgaps, both the fringing and proximity effects can be weakened by the designed parallel symmetrical magnetoresistance core structure, which has been verified in three-dimensional finite element analysis (FEA)-based simulations. The FEA calculated results show that the proposed optimized core structure can achieve a 46% reduction in ac resistance, and this advantage will extend with increasing frequency over a certain frequency range. The experimental validation includes converter efficiency test and inductor loss test on a high-frequency critical conduction mode Boost converter has been carried out, the maximum efficiency improvement was 1.4% and the inductor loss reduction is also verified.

Discontinuous PWM Strategy with Frequency Modulation for Vibration Reduction in Asynchronous Machines

The aim of this paper is to present our research into the reduction of vibrations in induction motors. The use of power inverters results in the generation of electrical harmonics, which increase the level of the mechanical vibrations of electrical machines. To reduce these harmonics, we present a discontinuous pulse-width modulation (PWM) control strategy based on carrier-wave modulation applied to multilevel inverters. Using the proposed modulation technique, the amplitude of the electrical harmonics is reduced, as compared to other conventional techniques. These current harmonics produce the MMF (magnetomotive force) harmonics in the air gap, which are one of the main sources of vibrations. The control strategy makes it possible to vary the electrical spectrum at the output of a multilevel inverter by modifying a control parameter of the carrier wave in the PWM, thus avoiding the natural frequencies of mechanical resonance. The proposed technique also has the feature of attenuating the total harmonics distortion of the voltage of the multilevel inverters, as well as the achievement of a higher RMS value of the output voltage for the same DC level. Laboratory results for an induction motor with different modulation strategies, applied in a multilevel inverter and compared to the strategy presented, are attached.

Claw‐pole magnetic levitation torque motor for 2D valve with automatic neutral adjustment

AbstractIn order to solve the problems of complex structure and the difficulty of neutral adjustment of the existing 2D valve electro‐mechanical converter, a kind of claw pole magnetic levitation torque motor (CPMLTM) was proposed, which automatically suspended the rotor in an axially and circumferentially neutral position by using the cogging torque and axial recovery forces between the stator claw pole and the rotor permanent magnet (PM). Compared with the conventional moving iron torque motor, it has positive magnetic stiffness, 1.54 times higher PM utilisation and 33.6% lower mass. A qualitative mathematical model of output torque is derived based on equivalent magnetic circuit model. Then, the response surface method was used to build the second‐order response surface model, and NSGA‐2 was used to optimise the design of five key structural parameters, and the non‐inferior solution sets satisfying the maximisation of the cogging torque, output torque and axial recovery force were obtained. The experimental prototype was developed, and static experiments were carried out on the experimental rigs. The results show that the relationship between the input current and the output angular displacement of the CPMLTM is linearly proportional when the magnetomotive force generated by the coil winding is from −50 to 50 A.

Comparison of Two Analytical Methods for Calculating Cogging Torque Based on Homopolar Inductor Machines

Cogging torque can cause the torque ripple and noise of machines and reduce the machine control accuracy. The analytical calculation method of cogging torque has always been a hot research topic in the field of machine. Conventional energy method is usually adopted to compute the cogging torque. Recently, a novel energy method is proposed. To reveal the fundamental difference and respective merits of these two energy methods, this paper first derives the analytical models of cogging torque in homopolar inductor machines (HIMs) considering the leakage fluxes of the stator slots by the two energy methods. Based on the derived analytical models, the cogging torque production mechanisms expressed by the two energy methods are analyzed and compared from the viewpoint of air-gap field modulation principle. The cogging torque computed by the two energy methods is all produced by the interactions of the air-gap magnetic fields modulated by the harmonics of the air-gap magnetomotive force (MMF) and air-gap permeance. However, due to the difference in the approaches of solving the air-gap magnetic field energy density, the novel energy method takes into account more harmonics of the air-gap MMF and air-gap permeance. Furthermore, the computational accuracy and complexity of the two energy methods are analyzed and compared based on the analytical calculations and three-dimensional (3-D) finite element analysis (FEA) for the cogging torque in a 48-slot/4-pole (48S4P) permanent magnet (PM) HIM and a 45-slot/6-pole (45S6P) field winding HIM. Compared with the conventional energy method, the novel energy method has higher accuracy, but is more complex. Finally, a prototype of the 48S4P PM HIM is manufactured. The results of analytical calculation, 3-D FEA and comparison are verified by experiments.

Investigation on Stator Shifting Technique for Permanent Magnet Vernier Machines With Two-Slot Pitch Winding

This paper investigates the stator shifting technique (SST) for permanent magnet vernier (PMV) machines equipped with two-slot pitch winding (TSPW). By employing SST, TSPWs can be generated from the combination of two sets of fractional-slot concentrated windings (FSCWs), with various shift angles. The effects of various shift angles on armature magnetomotive force (MMF) harmonic contents are explored. It shows that proper shift angles can be selected to preserve the working component while eliminating loss-producing harmonics. Besides, the implementation of various shift angles leads to uneven stator teeth structure, which affects field modulation. Therefore, the output torque capability, phase inductance, power factor, core losses, and fault-tolerance are affected by different shift angles. This paper aims to exploit the full potential of TSPW-PMV machines by SST, considering the synthetic effects on harmonic reduction and field modulation. Through the exemplification of 24- slot, 19-rotor pole pair, and 5-armature pole pair PMV machines, it indicates SST is a more general and flexible design method that can provide new design opportunities and improve various performance metrics by introducing shift angle as an additional design variable. Finally, a prototype of the double-layer TSPW-PMV machine with optimal shift angle is fabricated for concept validations.

Electromagnetic design and performance analysis of large-scale offshore wind generators with modular fractional-slot concentrated winding

Future offshore wind engineering raises demands on higher reliability, better power generating performance, as well as lower manufacturing and transportation cost. This paper presents a direct-driven permanent magnet generator (DDPMG) with modular fractional-slot concentrated winding (MFSCW), to meet the large-scale, low-cost and high-reliability requirements of offshore wind power applications. The corresponding pole–slot combination method and electromagnetic characteristics analysis for this novel generator are proposed and performed in detail, including the winding coefficient analysis, magnetomotive force (MMF) harmonic analysis, cogging torque analysis, finite element simulations and generator parameter optimization. After finite element simulations, a 3.3 MW prototype MFSCW-DDPMG is developed to validate the proposed scheme. The results provide a complete and feasible scheme of pole–slot​ combination and electromagnetic design for future MFSCW-DDPMG engineering applications.