Permanent Magnet Assisted Synchronous Reluctance Motor Research Articles

Fault Operation Analysis of a Triple-Redundant Three-Phase PMA-SynRM for EV Application

Due to the uninterrupted operation capability in the fault conditions, fault-tolerant machine drives are being favored by the safety-critical applications, such as the electric vehicles (EVs). Understanding the machine drive fault behavior is of key importance to facilitate the fault diagnosis, control law design, and avoid further damage. In this article, the fault operation behavior of a triple-redundant three-phase permanent magnet-assisted synchronous reluctance machine (PMA-SynRM) is analyzed in detail. The mutual-coupling mechanism of different three-phase modules is explained by analyzing the magnetomotive force (MMF) distribution. It is found that the three-phase set module affects each other via an MMF offset component, causing second harmonics in the dq -axis currents, voltages, and torque. Both the open- and short-circuit fault operation behaviors are investigated. The correctness of the analysis is validated by finite element (FE) simulations and experimental tests in different fault modes. It indicates that the machine drive requires an advanced control technique to enhance the current tracking capability in postfault operation conditions.

Design and Optimization of a Fault Tolerant Modular Permanent Magnet Assisted Synchronous Reluctance Motor With Torque Ripple Minimization

This article proposes a new asymmetric modular permanent magnet assisted synchronous reluctance motor (PMaSynRM) to offer low torque ripple and high reliability. First, the stator is segmented into three modules without magnetic coupling. The influence of flux gaps between modules is investigated on torque performance. For the torque improvements, the multilevel optimization strategy is conducted, which simultaneously enhances the fault-tolerant capability. Besides, the torque ripple reduction methods are proposed with the asymmetric rotor and shifted end-slots. The analytical formulae of asymmetric flux barrier angle are derived. Then, the asymmetric flux barrier is designed to reduce the 12th harmonic, and the end-slots are shifted to minimize the additional 2nd harmonic component caused by flux gaps. Finally, the enhanced fault-tolerant capability of the proposed modular PMaSynRM is also evaluated. The effectiveness of the proposed approach is verified by both simulation and experiment.

Electromagnetic and Thermal Behavior of a Triple Redundant 9-Phase PMASynRM With Insulation Deterioration Fault

This article analyzes the electromagnetic and thermal behavior when insulation deteriorates, leading to short-circuit (SC) faults in a triple redundant 9-phase permanent magnet-assisted synchronous reluctance machine. It defines a critical insulation resistance at which the temperature in the faulted insulation region reaches the cut-through temperature of the insulation material and determines the minimum and maximum bounds of the critical resistance for all possible faulty insulation volumes by three-dimensional thermal analysis. It suggests insulation resistance thresholds for fault detection and mitigation action in order to prevent complete insulation failure with serious consequences. Moreover, an example is given to show that the insulation deterioration process may begin from large insulation resistance and is accelerated when the insulation material resistivity decreases with increase in temperature. Finally, tests on a prototype machine drive are performed to validate the predicted electromagnetic behavior under turn-to-turn insulation deterioration leading to SC faults.

Torque Calculation of Stator Modular PMa-SynRM With Asymmetric Design for Electric Vehicles

This article proposes a modular asymmetrical permanent magnet-assisted synchronous reluctance machine (PMa-SynRM) combining segmented stator and distributed winding. Meanwhile, an analytical model is investigated for the modular PMa-SynRM, considering the effects of stator slots and flux gaps (FGs). First, the rotor magnetomotive force (MMF) generated by permanent magnets and stator MMF are analyzed by combining the magnetic equivalent circuit (MEC) and conformal mapping. Moreover, an armature reaction magnetic field model is presented considering the influence of the shifted end slots on the winding factor. Besides, the torque of the modular PMa-SynRM is calculated under asymmetrical rotor poles. Finally, a modular PMa-SynRM prototype is manufactured, and the comparison conclusion is validated by the finite-element method (FEM) and experimental results.

Determination of PM Flux Linkage Based on Minimum Saliency Tracking for PM-SyR Machines Without Rotor Movement

Permanent magnet assisted synchronous reluctance (PM-SyR) motors often present relevant magnetic saturation, especially if overload capability is exploited. The knowledge of current-to-flux relationship is mandatory for proper motor control, and it becomes even more critical in the case of sensorless applications. Reliable standstill self-commissioning tests have been recently developed for synchronous reluctance (SyR) motors without producing rotor movement. This procedure can be extended to PM-SyR motors, but being at standstill, it does not retrieve the flux contribution related to the permanent magnets (PMs). This article integrates the identification of the flux characteristics including a novel test for estimating the PM flux linkage, obtaining the complete magnetic characteristic of the PM-SyR motor. The identification session is performed at standstill and without a position transducer, independently of the mechanical load being connected or not. Such conditions are considered the most demanding for self-commissioning tests. The machine is first excited with a proper sequence of bipolar high voltage pulses to determine its current-dependent flux components. Then, the estimate of PM flux linkage is retrieved at standstill by evaluating the local saliency along the negative q -axis. The proposed method is supported by detailed finite element analysis and experimentally verified on two PM-SyR motor prototypes, confirming the accuracy of the PM flux linkage estimate.

Analytical design, electromagnetic field analysis and parametric sensitivity analysis of an external rotor permanent magnet-assisted synchronous reluctance motor

This paper deals with analytical design, electromagnetic field analysis and parametric sensitivity analysis of an external rotor permanent magnet-assisted synchronous reluctance motor (PMASynRM). In this work, parametric sensitivity analysis of rotor geometry is performed to obtaining the minimum torque ripple and maximum electromagnetic torque with employing numerical analysis based on two-dimensional finite element method (FEM). In order to determine the optimum operation effect of geometry parameters like the q axis insulation ratio and the flux barrier arm angle for the proposed machine with three barriers is investigated and sensitivity of structure for rotor geometrical variation is presented. The studied machine in this work is a three phase, six pole, external rotor PMASynRM, which is designed by analytical approach and analyzed to obtain the maximum torque and minimum torque ripple based on a parametric sensitivity analysis approach. The obtained results from the FEM-based sensitive analysis and electromagnetic field analysis confirm the analytical design procedure for the proposed PMASynRM.

Transient 3-D Lumped Parameter and 3-D FE Thermal Models of a PMASynRM Under Fault Conditions With Asymmetric Temperature Distribution

This article proposes a novel transient 3-D lumped-parameter (LP) thermal model and a 3-D finite-element (FE) thermal model of a triple redundant nine-phase permanent magnet-assisted synchronous reluctance machine to predict the asymmetric temperature distribution under various fault conditions. First, the predicted transient and steady-state temperatures are compared between the 3-D LP and the 3-D FE thermal models under fault conditions with uneven loss distribution. Also, the temperatures predicted by the LP and FE thermal models, which account a number of practical issues are comprehensively compared with the test results under healthy and short-circuit fault conditions. The relative merits of the two thermal models are discussed. It is shown that both models have reasonable accuracy in predicting the machine's thermal behavior under fault conditions and can be chosen according to the requirements.

Comparative study on performance characteristics of PM and reluctance machines equipped with overlapping, semi‐overlapping, and non‐overlapping windings

In this study, the compatibleness/effectiveness of the proposed novel semi-overlapping winding (NSW) topology has been investigated by implementing into different synchronous machine technologies, namely interior permanent-magnet machine, synchronous reluctance machine (SynRM), permanent-magnet assisted SynRM, and double-salient reluctance machine. All considered machines have also been designed with different winding topologies; i.e. integer-slot distributed winding, fractional-slot concentrated winding (FSCW) in order to reveal the merits/demerits of the proposed NSWs. A comprehensive electromagnetic performance comparison has been presented. It has been validated that the proposed winding topology promises significant advantages; such as improved efficiency with substantially reduced total axial length, low eddy permanent magnet (PM) loss and low risk of irreversible magnet demagnetisation over conventional winding topologies. It has also been revealed that the implementation of proposed NSWs into the reluctance machines results with higher torque and power output than that of FSCWs.

Comparative Research for a Novel Dual-Stator Synchronous Machine With Permanent Magnet-Reluctance Composite Rotor

This paper presents the research work for a novel dual-stator composite-rotor synchronous machine (DSCRSM) with ferrite magnets. Compared with the conventional permanent magnet-assisted synchronous reluctance machine (PMASynRM), the proposed DSCRSM is capable to provide a higher output torque when the same amount of ferrite magnets consumed. The superiority of the DSCRSM is obtained by the utilization of a composite rotor that is capable of full use of torque components, as both magnetic and reluctance torques can reach their maximum values near or at the same current phase angle. To evaluate the contribution, the torque performance of the proposed DSCRSM is compared with a conventional PMASynRM, which consuming the same amount of ferrite magnets. A higher torque production is found by the proposed machine. Moreover, more machine performances, including torque ripple and efficiency, are also further researched and compared for the two machines.

Magnet temperature estimation based on a novel frequency determination algorithm for the five‐phase PMa‐SynRM

This study presents a novel frequency determination algorithm for the magnet temperature estimation of a five-phase permanent magnet assisted synchronous reluctance motor (PMa-SynRM) using the signal injection method. The signal injection method is a convenient and non-invasive approach to determine the magnet temperature in permanent magnet motors by exploiting the temperature dependency of magnet resistance. However, its implementation as a magnet temperature estimation tool warrants an adaptive frequency determination method in order to ensure its effective employability under more pragmatic dynamic operations. The proposed method in this study proposes an analysis of the frequency spectrum to isolate the fundamental and fault frequencies and their respective harmonics to determine a range of available frequencies that may be employed in this method. The available frequencies are further concentrated based on the signal-to-noise ratio constraints. As an additional part of the contribution of this study, an innovative rotating hardware set-up is developed which would transmit the magnet temperature data wirelessly to verify the accuracy of the proposed temperature estimation algorithm.

Effective Turn Fault Mitigation by Creating Zero Sequence Current Path for a Triple Redundant 3 × 3-Phase PMA SynRM

Effective mitigation of excessive stator turn fault current is crucial for fault tolerant machine drives. In this paper, a simple and effective method is proposed for a triple redundant 3 × 3-phase permanent magnet-assisted synchronous reluctance machine by using three 3-phase 4-leg inverters. The fourth leg creates a zero sequence current path when a terminal short circuit is applied in an event of a turn fault in a 3-phase winding set. Consequently, the zero sequence flux linkages are reduced by the resultant zero sequence current. This leads to lower residual flux linkage and decreased fault current. The machine drive can therefore have larger safety margin or can be designed for improved torque density and efficiency. The proposed approach is verified by both finite element (FE) simulations and experimental tests in a wide operation range. It shows that the fault current is reduced by ∼40% and the output torque is not affected.

Electromagnetic-Thermal Coupled Simulation Under Various Fault Conditions of a Triple Redundant 9-phase PMASynRM

This article performs electromagnetic (EM) and thermal coupled simulation based on two-dimensional (2-D) transient electromagnetic and 3-D thermal model of a triple redundant nine-phase permanent magnet-assisted synchronous reluctance motor under various fault conditions at different speeds. The coupled simulation process is controlled by a scripting file. The resultant temperatures under EM-thermal coupled simulation will be comprehensively compared with those under thermal-only simulation. The predicted current waveforms under fault conditions by the 2-D EM model and predicted temperatures by the 3-D thermal model will be compared with the test results for validation. The outcomes of the study not only gives a better understanding of the thermal behavior, but also provides a guidance to the necessity of the EM-thermal coupled simulation under different fault conditions as well as to determination of the maximum permissible fault detection time before permanent damage due to the fault may occur.

Performance Analysis of Synchronous Reluctance Motor with Limited Amount of Permanent Magnet

This paper analyzes the performance of a synchronous reluctance motor (SynRM) equipped with a limited amount of a permanent magnet (PM). This is conventionally implemented by inserting PMs in rotor flux barriers, and this is often called the PM-assisted SynRM (PMa-SynRM). However, common PMa-SynRMs could be vulnerable to irreversible demagnetization. Therefore, motor performance and PM demagnetization should be simultaneously considered, and this would require the PM to be properly arranged. In this paper, various rotor configurations are carefully studied and compared in order to maximize the motor performance, avoid irreversible demagnetization and achieve higher PM utilization. Moreover, the field weakening capability is investigated and improved by regulating armature excitation. A particular rotor type with flux intensification was found to possess higher PM utilization, lower demagnetization possibility with fairly high performance. Thus, suitable rotor configurations are recommended for certain applications.

A Hardware-in-the-Loop Realization of Speed Sensorless Control of PMa-SynRM With Steady-State and Transient Performances Enhancement

This paper presents the design and implementation of a novel low-cost speed sensorless control technique for a permanent magnet assisted synchronous reluctance motor (PMa-SynRM). A robust adaptive speed (RAS) observer is designed for estimating the rotor speed and position, respectively. The RAS observer estimates the PMa-SynRM speed and position from the back electromotive force space-vector determination without voltage sensors by using the reference voltages issued from the current controllers instead of the actual ones. The novelty of the proposed RAS estimation technique is the adaptation of the feedback error of the actual values. Thus, the proposed observer structure promises a higher degree of robustness against PMa-SynRM parameter changes in the sensitivity analysis presented in this paper. The dynamic model and experimental realizations of the proposed control technique are introduced. A 6-kW PMa-SynRM drive test setup is constructed including a dSPACE 1104 board as the control heart of the proposed system. The hardware-in-the-loop Typhoon HIL 402 device is used to experimentally emulate the PMa-SynRM and the inverter connected to a dSPACE MicroLabBox. The proposed RAS observer robustness is evaluated using a HIL model and experimental results under different conditions. A comparative experimental analysis between the proposed RAS and Luenberger observers has been performed.

Design and Analysis of a Novel PM-Assisted Synchronous Reluctance Machine Topology With AlNiCo Magnets

The absence of field excitation on the rotor of the synchronous reluctance machine, results in poor power factor and low power density when compared to permanent magnet synchronous machines. To mitigate these problems, permanent magnet-assisted synchronous reluctance machines were introduced. The inserted permanent magnet boosts the machine's power factor and enhances its power density. In this paper, a new topology for permanent magnet-assisted synchronous reluctance machines using low cost AlNiCo magnets is proposed. The results of the proposed design with various magnet dimensions using AlNiCo magnets are compared with a previously designed and prototyped synchronous reluctance machine. Simulations for the same magnet dimensions are also carried out using a rare earth magnet material to study the effect of magnet type on the machine's performance. A final design using AlNiCo magnets is chosen based on the gain in the power density, manufacturing cost, torque ripple, and the power factor improvement. A rotor prototype is manufactured based on the selected topology and tested under various operating conditions.

PM-Assisted Synchronous Reluctance Machine Drive System for Micro-Hybrid Application

The demand for increased power and improved fuel economy are driving changes in alternator technology for automotive applications. To meet these demands requires a drive system with capabilities of torque assist, regenerative braking and power generation to supply vehicle loads while keeping the battery charged. Furthermore, to minimize add-on cost, the system must be air-cooled with minimal changes to the vehicle hardware and operate at 12 V with the same or smaller packaging footprint of the current alternator. In this paper, a low cost 12 V, 4 kW air-cooled permanent magnet-assisted synchronous reluctance machine drive system for a micro-hybrid vehicle is presented. The design and analysis in terms of machine, inverter, controller, and control algorithm are discussed in detail. Thermal performance of the system under different operating conditions, which is another key aspect for the harsh environment application, is also studied. Fuel economy analysis of the proposed low-cost micro-hybrid system for a Segment B vehicle shows significant reduction in fuel consumption resulting in a direct benefit to the customer. Finally, a prototype drive system was built and tested and found to meet the cost, performance, and packaging requirements.

Comprehensive Design Procedure and Manufacturing of Permanent Magnet Assisted Synchronous Reluctance Motor

Combining the main advantages of the permanent magnet synchronous motors and pure synchronous reluctance motors (SynRM), permanent magnet assisted synchronous reluctance motor (PMaSynRM) has been considered as a promising alternative to the conventional induction motors. In this paper, utilizing a macroscopic design parameter, called insulation ratio along the q-axis, and based on the magnetic reluctance concept, a simple and fast design procedure of synchronous reluctance motor is introduced. Then, the performance improvement of the machine by inserting the permanent magnets into the rotor body is investigated. After calculating the width of the magnetic flux barriers two dimensions Finite Element Method (FEM) analysis simulation of the designed motor is presented. Additionally, the performance characteristics of the designed motor such as torque producing capability and torque ripple are discussed. Furthermore, thermal analysis is conducted to determine the temperature distribution in the designed motor. Consequently, the prototype motor is fabricated and the experimental results are compared to the simulation results which validate the usefulness of the design method.

Irreversible Demagnetization Analysis for Multilayer Magnets of Permanent Magnet-Assisted Synchronous Reluctance Machines Considering Current Phase Angle

This paper investigates the demagnetization problem of permanent magnets for permanent magnet-assisted synchronous reluctance motors (PMa-SynRM) and applies “demagnetization ratio” as an index to evaluate demagnetization of permanent magnet (PM). The PMa-SynRM is often designed with multilayer flux barriers to improve saliency and reluctance torque in the rotor. Weaker or less PM (than that for interior PM motors) is embedded into the rotor which could be demagnetized in high-performance operation. PM demagnetization involves temperature, current magnitude, current phase angle, designed PM operating point, or combined effect of the above factors. This work investigates the demagnetization risk for PMs in all the layers of PMa-SynRM rotor considering these factors. In particular, the current phase angle for flux weakening operation is often omitted in demagnetization analysis. First, the motor performance to satisfy the operation condition over a wide speed range is analyzed and the proportion of motor torque components, i.e., reluctance torque and electromagnetic torque, considering temperature is investigated. Then, the flux density distributions on PMs at each position/layer are studied and the PM operating points are obtained based on the variation of excitation current, current phase angle, and temperature in order to evaluate the demagnetization risk. The analysis suggests that the high current phase angle combining the effect of high temperature is the major cause of irreversible demagnetization. Finally, a method incorporating the index “demagnetization ratio” is proposed to redesign the PMa-SynRM to avoid demagnetization. Experiments are conducted to validate the simulation.

Torque Enhancement for a Novel Flux Intensifying PMa-SynRM Using Surface-Inset Permanent Magnet

This paper proposes a flux-intensifying permanent magnet-assisted synchronous reluctance motor (FI-PMa-SynRM) using surface-inset permanent magnet (PM) instead of embedded PM in the rotor. The proposed FI-PMa-SynRM employs a small amount of PM that is inset on the rotor surface facing $d$ -axis instead of facing $q$ -axis as in common PMa-SynRMs. It also differs from conventional flux-intensifying interior PM motor, where the PM is embedded inside the rotor. The proposed motor enables making use of the arrangements of two types of flux barriers (FBs): the cutoff FB and the magnet FB, collectively referred to the outer FBs, to enhance the torque output and reduce the torque ripple. The first objective in this paper is to explain the principles of the proposed FI-PMa-SynRM, and the second is to analyze the proposed technique for enhancement of the torque output with small PM volume while keeping the lowest possible torque ripple. The finite-element analysis is employed to validate the proposed motor and analyses, and the results demonstrate their advantages and effectiveness.

Hybrid Adopted Materials in Permanent Magnet-Assisted Synchronous Reluctance Motor With Rotating Losses Computation

This paper presents an optimized design in the permanent magnet-assisted synchronous reluctance motor (PMa-SynRM) rotor structure design with hybrid adopted materials for enhancing the motor characteristics and operation. Two types of permanent magnet (PM) materials are embraced in the PMa-SynRM rotor of rare-earth and ferrite PMs. The optimized design for the PMa-SynRM rotor structure considers the motor magnetic equivalent circuit for reducing the reluctance of the hybrid PMs to improve the motor performance. Moreover, the irreversible demagnetization of the ferrite PM which occurs due to the reversing of the magnetic field of the rare-earth PM is presented. The analytical rotating losses computation with the hybrid adopted materials at the design process is introduced. The rotating losses of the PMa-SynRM are investigated as core, magnet, proximity, ohmic, and friction losses. The core loss in the PMa-SynRM occurs due to the altering of the flux densities in numerous fragments of the iron structures. The loss measurements can be accomplished by measuring the electric parameters of the PMa-SynRM at a defined operating point. The magnetic modeling of the improved 6 KW PMa-SynRM manufactured prototype structure is derived and rotational losses are computed, validated, and compared with the finite element analysis (FEA).