Torque Of Machine Research Articles

A Distributed Winding Wound Field Pole-Changing Vernier Machine for Variable Speed Application

This paper proposes a distributed winding wound field pole-changing vernier machine for variable speed application. The proposed machine uses a wound field rotor with two sets of windings. The direction of current in one set of the field windings is reversed to change the number of poles of the machine. Hence, the machine can run in two modes: a vernier mode and a wound field synchronous machine (WFSM) mode. The electromagnetic characteristics of the machine are thoroughly investigated at base speed initially. Then, the two modes of the machine are combined for variable speed operation. The 2-D finite-element analysis shows that the machine provides the advantages of high torque and high power of a vernier machine until the base speed is reached. After the base speed, the advantages of the WFSM mode are utilized, enabling wide speed range operation and restraining the efficiency of the machine from decreasing abruptly during variable speed operation.

Efficiency Improvement by the Intermittent Control for Switched Reluctance Machine in Automotive Application

In this paper, the intermittent control is proposed for switched reluctance machine (SRM) drive to both increase the efficiency and decrease the cost of the traction system for low-cost electric vehicles. With the purpose of maintaining the average machine torque required by the load, the intermittent control imposes a higher phase torque during a shorter time. The simulation and experimental results achieved with three different SRMs show that the intermittent control increases the system efficiency by reducing the converter losses and the core losses. Additionally, three different strategies of the control have been proposed to analyze their impact automotive application based on the criteria of efficiency, machine vibration, and torque pulsation. It can also be easily applied for any SRMs using average-torque-control-based methods.

Fast Iron Loss and Thermal Prediction Method for Power Density and Efficiency Improvement in Switched Reluctance Machines

To effectively find an optimal solution in the development process of electrical machines, it is essential to predict machine iron loss and thermal behavior in the predesign stage. Most existing publications only consider thermal behavior by roughly limiting the maximum current density. However, especially for high-speed application, iron loss can also be an essential part in thermal-behavior estimation. This paper proposes a simplified model to efficiently calculate iron loss and thermal behavior in the design procedure of switched reluctance machines. For this purpose, a maximum coenergy loop control method is implemented to facilitate the estimation of flux waveform and machine torque. Three different iron loss calculation methods are compared in terms of accuracy and time. Besides, a simplified lumped parameter thermal network is applied for machine sizing. Furthermore, the impact of number of turns and peak magnetomotive force on the losses and machine sizing is discussed. The efficiency and power density of various machine geometries are comparatively analyzed. Finally, the accuracy of the simplified model is verified by comparison with finite element simulations and experiment results.

Rotor Resistance Estimation for Induction Machines Using Carrier Signal Injection With Minimized Torque Ripple

This paper presents a technique for estimating the rotor resistance of an induction machine over the machine's entire speed and torque range. This technique is based on injecting a relatively low-frequency carrier signal into the reference of the rotor flux linkage magnitude and extracting the induction machine's response to the carrier signal, which is then used in a model reference adaptive system. This paper also presents a technique to minimize the torque ripple generated by the carrier signal. This technique utilizes the rotor flux linkage reference in conjunction with a proportional-integral-resonant feedback plus feedforward control to generate references for the direct and quadrature axis stator currents. This paper also improves tracking of the torque and rotor flux linkage in direct field-oriented control of the induction machine through employing electromotive force and resistive compensation methods for tracking q-axis and d-axis reference stator currents, respectively. Simulation and experimental results demonstrate the effectiveness of the technique over the entire operating range.

Influence of static and dynamic rotor/stator misalignments in axial flux magnetically geared machines

Here, static and dynamic (rotating) misalignments between the low-speed rotor (LSR) and the stator of axial flux magnetically geared machines are studied with the aid of 3-D finite element analysis (FEA). The influence of rotor/stator axis misalignments on machine performance in terms of cogging torque, air-gap flux density, and back-EMF is investigated with reference to the fully healthy condition. The results show that the LSR and HSR cogging torques are significantly affected by such misalignments due to distorted air-gap flux density. However, the amplitude and the harmonics of the back-EMF are only slightly changed. Furthermore, the influence of the misalignments on the machine torque performance is investigated. It is shown that the machine torque is significantly reduced when the LSR axis is misaligned with the axis of the stator. Thus, it is concluded that the torque performance of axial flux magnetically geared machines significantly deteriorates under static and dynamic axis misalignments. In addition, the two types of misalignments have similar effects on machine performance.

Reduction of Torque Ripple in Consequent-Pole Permanent Magnet Machines Using Staggered Rotor

Consequent-pole permanent magnet (CPM) machines have considerable potential for low-cost applications because they can improve the permanent magnet (PM) utilization ratio. However, the phase back electromotive force (EMF) of CPM machines with Ns /( mt ) = odd ( t is the greatest common divisor of the stator slot number Ns and the rotor pole-pair number p , and m is the phase number) is asymmetric, i.e., the phase back EMF has even-order harmonics, which will increase torque ripples. This paper utilized the staggered rotor to eliminate the even-order harmonics and reduce the cogging torque of CPM machines, thereby potentially decreasing torque ripples considerably. The axial flux barrier in the middle of the rotor was used and optimized using three-dimensional finite element (FE) analysis to reduce the axial leakage flux of the CPM machine with the proposed staggered rotor. Furthermore, the axial magnetized PM was embedded in the flux barrier, which improved the flux density of the airgap above the iron-pole and, consequently, further increased the output torque. The electromagnetic performance of the proposed machine, including the open-circuit airgap flux density, back EMF, average torque, torque ripples, and PM utilization, was compared with that of the conventional CPM machine. Results showed that the proposed machine obtained a similar torque and PM utilization ratio but a much lower torque ripple compared with the conventional one.

A Noninvasive External Flux Based Method for In-Service Induction Motors Torque Estimation

This paper presents a novel method to determine the electromagnetic torque of grid-powered induction machines (IM). The torque determination constitutes a key point for the energy diagnosis and for choosing the well adapted motor in industrial processes. The proposed method is noninvasive as it is based on the measurement of the current and the magnetic external flux around induction machines. The torque estimation protocol is explained and experimental validations are made with an 11 kW IM. The impact of supply voltage variations on the accuracy of the proposed method is also analyzed.

Flux-Density Harmonics Analysis of Switched-Flux Permanent Magnet Machines

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.

Permanent magnet flux switching motor technology as a solution for high torque clean electric vehicle drive

<span lang="EN-US">A breakthrough in this century has been the development of electric vehicle which is propelled by electric motor powered by electricity. Already, many electric motors have been used for electric vehicle application but performances are low. In this paper, a permanent magnet motor technology using unconventional segmented rotor for high torque application is presented. Unlike conventional motors, this design, flux switching motor (FSM) is an advance form of synchronous machine with double rotating frequency. It accommodates both armature winding and flux source on the stator while the rotor is a simple passive laminated sheet steel. Conventionally, rotor of the maiden FSM and many emerging designs have focused on the salient pole, this design employs segmented rotor. Segmented rotor has advantages of short flux path more than salient rotor pole resulting in high flux linkage. Geometric topology of the proposed motor is introduced. It consists of 24Stator-14Pole using PM flux source with alternate stator tooth armature winding. The 2D-FEA model utilized JMAG Tool Solver to design and analyze motor’s performance in terms of torque with average torque output of 470Nm. The suitability of segmented outer-rotor FS motor as a high torque machine, using permanent magnet technology is a reliable candidate for electric vehicle.</span>

Torque Distributed Control Strategy for the Dual Three-Phase PMSM in Hybrid Energy Storage System Application

This paper proposes a torque distributed control strategy for the multiphase machines in the hybrid energy storage system application. Different with the conventional energy current regulation method, the system energy management is researched by the machine torque distribution in different sets of windings. The load power is then afforded by the energy storage devices connected with the windings through the inverters. The principle of the distributed torque operation is explored with a dual three-phase permanent-magnet synchronous machine model and the asymmetrical windings operation is explained with the flux vector diagram. The windings decoupling compensation, flux observer, and parameter identification methods are presented. Based on the proposed strategy, a power frequency dividing coordinated regulation is achieved. The hybrid energy storage devices can directly respond to the average or instantaneous parts in the load torque and power fluctuation. Simulation and experiments are demonstrated with different operation cases.

Magnet Temperature Estimation in Permanent Magnet Synchronous Machines Using the High Frequency Inductance

Permanent magnet synchronous machines (PMSMs) torque production capability depends on the permanent magnets (PMs) magnetization state, which can be affected by PMs’ temperature and by the current flowing throughout the stator windings; knowledge of the PMs’ temperature can be therefore of great importance both for control and monitoring purposes. PMs’ temperature can be measured or estimated; PM temperature measurement is not easy and is not normally implemented in commercial drives. PM temperature estimation methods can be divided into thermal models based, back electromotive force (BEMF)-based, and signal injection based methods. Existing high frequency (HF) signal injection methods estimate the PM temperature from the measured stator HF resistance. Unfortunately, the resistance is also affected by magnetoresistive effect, which can limit the accuracy of the estimates. This paper proposes the use of the stator d -axis HF inductance for PM temperature estimation. This makes temperature estimation insensitive to magnetoresistive effect. In addition, it allows the use of higher frequencies, reducing the adverse impact of the injected signal on machine performance.

Fast iron loss prediction method in the pre‐design stage of SRMs

To effectively find a valid solution in the development process of electrical machines, it is essential to predict machine iron loss in the pre-design stage. In guidance on the choice of the most suitable configuration of the switched reluctance machine (SRM) is given, but iron loss prediction is neglected. Based on the study of Burkhart et al., this study proposes a simplified model to efficiently calculate iron loss in the design procedure of SRMs. For this purpose, a maximum co-energy loop control method is implemented to facilitate the estimation of flux waveform and machine torque. Three different iron loss calculation methods are compared in terms of accuracy and time. The accuracy of the simplified model is verified by comparison with finite element simulation results. Furthermore, the impact of different parameters on the iron loss is discussed, and the iron loss of various machine geometries is comparatively analysed.

Novel control implementation for electric vehicles based on fuzzy -back stepping approach

The present paper deals with a real-time assessment of a fuzzy –backstepping based control applied to a battery-supercapacitor (SC) hybrid energy storage system (HESS). To properly emulate the behavior of an electric vehicle, the proposed topology is extended to a PMSM drive, that represents the traction part. The proposed control scheme is divided into two parts: The first part plans a fuzzy logic power management approach, to operate the system in a smart way: First, It ensures an optimal load power-sharing, focusing the operation of the involved sources in a safe mode. Second, a quite regulation of both the dc bus and the SC voltage without additional controllers. The second part proposes a back-stepping direct torque control (BS-DTC), associated to a space vector modulation (SVM) strategy, to ensure decoupled torque and flux control of the PMSM machine. The experimental results, conducted on a small-scale system, controlled via two dSPACE 1104 cards, prove the effectiveness of the proposed control techniques, with good performances in dynamic and steady state.

Phase voltage distortion of IPM and SPM machines with distributed windings in field weakening region

This study investigates the field-weakening capability of interior permanent magnet (IPM) and surface-mounted permanent magnet (SPM) machines with distributed windings by considering phase voltage distortion in field-weakening region. For analysis and comparison, the Nissan Leaf vehicle traction machine is studied as a reference benchmark machine and then a comparable SPM machine is designed within the main constraints of the benchmark machine. A finite element analysis model of the benchmark machine is developed and validated by published experimental measurement. Sinusoidal phase current is desired to enhance machine torque performance and power electronic converters employing vector control method are commonly used for traction machine supply. However, the machine terminal phase voltage distortion may introduce additional difficulties for machine control. Therefore, firstly, phase voltage distortions of IPM and SPM machines with distributed windings are compared and the mechanisms are discussed. Due to the voltage distortion, the peak value of phase voltage may be higher than the fundamental one. Therefore, the influences of IPM and SPM topologies on machine traction characteristics are investigated. The study indicates that SPM machines with distributed windings can be designed to achieve comparable torque and power performance and better field-weakening capability compared to IPM machines.

Application of Standard Three-Phase Stator Frames in Prime Phase Order Multiphase Machine Construction

The application of multiphase machines in high-power applications is now a recognized alternative, thanks to their higher fault-tolerance when compared with standard three-phase systems. Although multiphase machines with multiples of three-phase winding sets have been favored in many applications, literature has shown that machines with a prime number of phases, such as five-phase machines, generally outperform other phase orders, especially in terms of machine torque density. One of the major problems when dealing with a prime number of phases either in academic research or industrial applications is the special stator design. This paper provides a general technique to rewind standard off-the-shelf three-phase stator frames with any general prime phase order while preserving the same copper volume. The proposed winding layout is derived using the star of slots theory and the concept of stator winding shifting. Finite-element simulations are used to investigate examples with different phase orders, while experimental investigation is carried out to corroborate the proposed concept by rewinding a standard three-phase stator as a five-phase machine.

Influence of Rotor Tooth Shaping on Cogging Torque of Axial Flux-Switching Permanent Magnet Machine

This paper proposes a rotor tooth shaping method to reduce the cogging torque of an axial flux-switching permanent magnet machine. The rotor tooth is shaped in different configurations, including constant, trapezoidal, asymmetrical, extended, and square shapes to evaluate the effects on cogging torque ripple minimization. A three-dimensional (3-D) finite-element analysis (FEA) is performed to compare the proposed shapes of the rotor tooth. Peak-to-peak cogging torque, fundamental flux linkage, loaded torque, and the total weight of teeth are compared using various rotor tooth angles. The simulation results show that overall minimum cogging torque is achieved by the extended shape of the rotor tooth. 3-D FEA results are also verified with experimental results.

FOC Transformation for Single Open-Phase Faults in the Five-Phase Open-End Winding Topology

Many critical five-phase permanent-magnet synchronous machine drive systems require operation after a single open-phase fault. The single dc supply open-end winding inverter topology allows for the injection of four unbalanced phase currents to better optimize the postfault machine torque after this fault. However, all previously published field-oriented control schemes send varying current references to the proportional–integral (PI) current controllers when controlling four unbalanced phase currents. This makes the design of the PI controllers considerably difficult as each machine operating point will require a different gain to accurately track the varying reference with minimum ripple. Consequently, this paper proposes a new postfault transformation matrix that obtains constant current references for any given set of four unbalanced sinusoidal phase currents. This facilitates easy design of the PI current controllers as the steady-state error can be reduced to zero in a user-defined response time for all operating points. This current control technique is the first to be designed specifically for the case of an open-phase fault to a five-phase open-end winding system.

Considerations on Torque and Power Factor Characteristics of Synchronous Reluctance Machines Based on Their Magnetic Energy Properties

Considerations on Torque and Power Factor Characteristics of Synchronous Reluctance Machines Based on Their Magnetic Energy Properties

Extension of Virtual-Signal-Injection-Based MTPA Control for Five-Phase IPMSM Into Fault-Tolerant Operation

This paper introduces a novel fault-tolerant control for the maximum torque per ampere (MTPA) operation in five-phase interior permanent magnet synchronous machine (IPMSM), termed MTPA fault-tolerant control. The key of this fault-tolerant control is that the reluctance torque is considered and used by MTPA under open-circuit fault. Based on the decoupled model of five-phase IPMSM on synchronous frame and the computing method of d -axis and q -axis voltages under various open-circuit faults, the virtual signal injection control (VSIC) can be applied to realize the MTPA under the fault-tolerant operation by the postfault field-oriented control (FOC) and carrier-based PWM (CPWM). This method is parameter independent in tracking of the MTPA points under the fault-tolerant operation. Besides, it can effectively reduce the amplitude of the fundamental current and improve efficiency compared with traditional $i_{d} = {\text{0}}$ fault-tolerant control. Moreover, it is robust to current and voltage harmonics and machine torque disturbances under the postfault operation. The proposed method is verified by experiments under various postfault operating conditions on an IPMSM prototype drive system.

Permanent-Magnet Machine Flux and Torque Response Under the Influence of Turn Fault

This paper analyzes different stator windings configurations for permanent-magnet synchronous machines during the presence of a stator turn fault. Due to the inverter pulsewidth modulation, the fault commonly occurs in variable-frequency permanent-magnet machine drives. In this paper, two types of windings are compared to identify key machine topologies that can achieve the reduced influence of the turn fault. When the machine is operated in real time, the windings with separated neutral points reduce the torque ripple caused by fault-reflected flux harmonics. Analytical models based on equivalent circuits are developed to predict the machine flux and torque waveform during the presence of the turn fault. All developed analytical models are verified by the finite-element analysis and experimental results on a 750-W surface permanent-magnet machine prototype.