Fault-tolerant Permanent-magnet Machine Research Articles

A Multi-Mode High-Efficiency Fault-Tolerant Permanent Magnet Machine

This article proposes a new multi-mode high-efficiency fault-tolerant permanent magnet machine with an inner stator to place AC field windings. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current in the field windings enables the proposed machine to be driven individually or together with the armature windings. On the other hand, the flux can be regulated by applying the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current to the field windings. As a result, multiple operation modes are realized. The proposed machine can run in different modes at different torque and speed operating conditions, implementing the multi-zone high-efficiency operation. Meanwhile, a new fault-tolerant control method can be applied in the proposed machine by combining the mode switching and compensation current in the healthy windings, thus improving the efficiency under fault-tolerant operation. Moreover, the multi-zone high-efficiency regions of the proposed and conventional machines are investigated. The proposed and traditional fault-tolerant methods for the proposed machine are compared. The results reveal that the proposed machine offers a larger high-efficiency region and is capable of stronger fault tolerance. Furthermore, since the double stators in the proposed machine need to operate individually, a swallow-shaped rotor with auxiliary salient poles is adopted to reduce outer torque ripple and inner torque ripple. Finally, the experiments are performed to verify the predicted performances.

A Hybrid-Slot Radial-Flux Dual-Stator Permanent-Magnet Machine With Fault-Tolerant Consideration

In this article, a hybrid-slot radial-flux dual-stator permanent-magnet machine (HS-RDPM) with fault-tolerant consideration is presented. On the one hand, the torque density of this structure is improved compared with conventional fault-tolerant permanent-magnet machines (FTPMs). On the other hand, both large torque ripple and weak phase isolation coming from dual stators are optimized. First, radial-flux dual stators with higher torque density are extended to FTPMs innovatively. Second, to decrease torque ripple, dual-layer fractional-slot concentrated winding (DFCW) is used, while optimized rotor and staggered stators are proposed. Finally, the hybrid slots that are composed of deep and narrow notches (DNNs) and large-opening slots are raised to enhance phase isolation; meanwhile, the deflection teeth are proposed to increase slots’ utilization. The comparisons between HS-RDPM with conventional and intermediate structures are made. The higher torque density and smaller torque ripple are testified by back-EMFs and torques. The greater phase isolation is proven jointly by flux just with single-phase current, inductance performances, and back-EMFs varieties after a short circuit. In addition, the loss distributions are studied, while the winding temperatures indicate that the security of the machine under a short circuit can be guaranteed if the current is limited. A prototype is manufactured, and the experimental results verify the correctness of simulations.

Analysis of a Fault-Tolerant Module-Combined Stator Permanent Magnet Synchronous Machine

To solve the problems of large-size machining and complex control of fault-tolerant permanent magnet machines, a module-combined stator permanent magnet synchronous machine is proposed in this paper. The winding of the module-combined stator has two forms: large and small spans. The independent power supply of each module is adopted to decouple the electricity between each module, which enhances the manufacturing flexibility and the fault-tolerant ability of the motor. A mathematical model of the module-combined stator permanent magnet synchronous machine is established, and the design method of the machine is summarized. Then the analytical formula of the radial force acting on the stator under asymmetric operation is deduced. In addition, the torque-angle characteristics of the machine and the factors affecting the radial force are studied. Finally, the machine is prototyped, and both simulation and experiment are used verify the rationality of the proposed design.

Design of a New Fault-Tolerant Permanent Magnet Machine With Optimized Salient Ratio and Reluctance Torque Ratio

This article proposes a new fault-tolerant permanent magnet (FTPM) machine with the improved salient ratio and reluctance torque ratio. The key of the proposed machine is the new slot-pole combination (20-slot/14-pole), which breaks the traditional rule which stipulates that the difference between slot number and pole number in FTPM machines is equal to 2. After the selection of slot-pole combination, the influence of the ratio of armature diameter to length and the injected current on salient ratio and reluctance torque ratio is evaluated, indicating that the relationship between the salient ratio and the reluctance torque ratio is contradictory in the FTPM machine. Therefore, the multiobjective method is employed to obtain optimal rotor parameters. In order to confirm the superiority and the uniqueness of the proposed FTPM machine, the comparison between the proposed FTPM machine and the two traditional FTPM machines (20-slot/18-pole) is analyzed. From the finite-element method and experimental results, it clearly depicts that the designed 20-slot/14-pole FTPM machine exhibits good fault-tolerant capacity, the improved salient ratio and reluctance torque ratio.

Design to Reduce Rotor Losses in Fault-Tolerant Permanent-Magnet Machines

This paper designs a new rotor topology of a fault-tolerant permanent-magnet (FTPM) machine with fractional-slot concentrated winding in order to reduce rotor losses, demagnetization risk, and temperature. The key is the appropriate flux barriers, which are designed in rotor yoke. First, the structure feature and losses of rotor are analyzed. An analytical expression is derived by the simplified permeance model to evaluate the armature reaction magnetic field of the newly designed FTPM machine. Second, both the newly designed and the original machines are optimized for a given set of specifications, and their performances are comparatively analyzed by using finite-element method. Finally, some experiments on the prototypes of both FTPM machines are carried out for validation.

Improvement of Reluctance Torque in Fault-Tolerant Permanent-Magnet Machines With Fractional-Slot Concentrated-Windings

Fault-tolerant permanent-magnet (FTPM) machines adopt fractional-slot concentrated-windings, thus reducing copper loss and improving fault tolerance. However, they usually suffer from insignificant reluctance torque. The novelty of this paper is to adopt some techniques to improve reluctance torque in FTPM machines, including rotor divisions between poles, two-layer interior magnets in oriented direction, and the specially designed flux barriers between two-layer magnets. The configuration of the newly designed FTPM machine is presented, and its inductance, electromagnetic torque, rotor losses, the flux-weakening capacity, and the speed range are analyzed by using the finite-element method. By using the new design, FTPM machines can offer high reluctance torque, low rotor losses, and good flux-weakening performance.

Eddy current loss analysis of open-slot fault-tolerant permanent-magnet machines based on conformal mapping method

This paper proposed an analytical method, based on conformal mapping (CM) method, for the accurate evaluation of magnetic field and eddy current (EC) loss in fault-tolerant permanent-magnet (FTPM) machines. The aim of modulation function, applied in CM method, is to change the open-slot structure into fully closed-slot structure, whose air-gap flux density is easy to calculate analytically. Therefore, with the help of Matlab Schwarz-Christoffel (SC) Toolbox, both the magnetic flux density and EC density of FTPM machine are obtained accurately. Finally, time-stepped transient finite-element method (FEM) is used to verify the theoretical analysis, showing that the proposed method is able to predict the magnetic flux density and EC loss precisely.

Impact of Slot/Pole Combination on Inter-Turn Short-Circuit Current in Fault-Tolerant Permanent Magnet Machines

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short-circuit (SC) current in fault-tolerant permanent magnet (FT-PM) machines. A 2-D sub-domain field computational model with multi-objective genetic algorithm is used for the design and performance prediction of the considered FT-PM machines. The electromagnetic losses of machines, including iron, magnet, and winding losses are systematically computed using analytical tools. During the postprocessing stage, a 1-D analysis is employed for turn–turn fault analysis. The method calculates self- and mutual inductances of both the faulty and healthy turns under an SC fault condition with respect to the fault locations, and thus SC fault current, considering its location. Eight FT-PM machines with different S/P combinations are analyzed. Both the performance of the machine during normal operation and induced currents during a turn–turn SC fault are investigated. To evaluate the thermal impact of each S/P combination under an inter-turn fault condition, a thermal analysis is performed using finite element computation. It is shown that low-rotor-pole-number machines have a better fault tolerance capability, while high-rotor-pole-number machines are lighter and provide higher efficiency. Results show that the influence of the S/P selection on inter-turn fault SC current needs to be considered during the design process to balance the efficiency and power density against fault-tolerant criteria of the application at hand.

Analysis of a Dual-Winding Fault-Tolerant Permanent Magnet Machine Drive for Aerospace Applications

With the increasing development of aircraft and helicopter, new electric drive system for aerospace applications have attracted more and more attentions in the aviation sector [1]-[2]. The common hydraulic drive helicopter winch is replaced by the electric drive helicopter winch gradually, due to the fact that the electric drive system can not only improve the system efficiency and the flexibility of variable speed control, but also reduce the weight and volume of the system [2]-[3]. However, in the electric drive helicopter winch systems, where continuous operation must be ensured, high reliability and strong fault tolerance become a critical requirement [2]-[4]. The purpose of this paper is to propose a new electric drive helicopter winch system based on a six-phase ten-pole dual-winding fault-tolerant permanent magnet (DFPM) machine. The DFPM machine, which incorporates the merits of high power density and high efficiency of permanent magnet (PM) machine and high fault-tolerance of dual-winding machine, consists of optimal surface-mounted permanent magnet rotor and 12 slots stator with two sets of independent three-phase concentrated armature windings on alternate teeth. To achieve the fault-tolerant performance, the redundant fault-tolerant control strategy based on speed, current, voltage three-loop control is proposed and analyzed. Then, the electromagnetic performances of the DFPM machine drive with an open-circuit fault under load hoisting and dropping conditions have been verified by experiments. The research results showing the effectiveness of the proposed fault-tolerant control strategy and the high performance of the fault-tolerant characteristic of the proposed DFPM machine drive.

Fault Detection and Fault Tolerant Operation of a Five Phase PM Motor Drive Using Adaptive Model Identification Approach

Nowadays, the use of multiphase fault tolerant permanent magnet (PM) machines is a suitable solution for increasing the reliability of high-performance motion control applications. This solution requires fault detection, isolation, and control adaptation. For this reason, a new open switch fault detection scheme in voltage-source inverter supplying a PM motor is presented in this paper. The detection method is based on model identification of the motor phase currents. The detection scheme is fast, robust, general, and capable of detecting multiple faults. The control algorithm, detection method, isolation, and reconfiguration strategies are discussed. After that, the proposed method is implemented in the fault tolerant control of a five-phase brushless direct current (BLDC) motor drive. Simulation results in MATLAB/Simulink are shown to demonstrate the effectiveness of the proposed detection technique. Experimental results on a five-phase fault tolerant BLDC motor validate the theoretical developments.

High-Power-Density Fault-Tolerant PM Generator for Safety-Critical Applications

Many safety-critical applications particularly in aviation require high-power (mass)-density generators with high reliability. While permanent-magnet (PM) machines promise significant improvements in power density and reliability, the widespread use of PM generators has been hitherto limited by the potentially detrimental effect of internal machine faults caused by the lack of de-excitation capability during fault conditions. Although there are several publications addressing fault-tolerant PM machines, most of these target auxiliary systems. In this paper, the detailed analysis, design, and test results of a 175-kW main power fault-tolerant embedded PM generator for aerospace applications will be presented. The design tradeoffs and the novel aspects of this machine will be discussed in detail.

Winding Turn-to-Turn Faults Detection of Fault-Tolerant Permanent-Magnet Machines Based on a New Parametric Model

This paper proposes a parametric model for inter-turn fault detection in a fault- tolerant permanent-magnet (FTPM) machine, which can predict the effect of the short- circuit fault to various physical quantity of the machine. For different faulty operations, a new effective stator inter-turn fault detection method is proposed. Finally, simulations of vector-controlled FTPM machine drives are given to verify the feasibility of the proposed method, showing that even single-coil short-circuit fault could be exactly detected.

A Novel Multi-Tooth Fault-Tolerant Flux-Switching Machine

Fault tolerant flux-switching permanent magnet (FTFSPM) machine is a novel fault tolerant machine having magnet in the stator, which not only has the advantages such as excellent physical, mechanical and magnet insulation abilities, but also overcomes the disadvantages in conventional rotor-PM topology like magnets are subjected to centrifugal force and difficult to dispel heat. However, the ability to inhibit short circuit current of FTFSPM has a great impact on the machine torque (power) density. In this paper, a novel multi-tooth fault-tolerant flux-switching permanent magnet (MTFTFSPM) machine which has big self inductance is proposed. Finite element analyses (FEA) are employed to compare the electromagnetic performance of three types of fault-tolerant topology including flux-linkage, back-EMF, torque density and inductances. The results show that the MTFTFSPM machine can reach higher torque density than traditional FTFSPM due to the multi-tooth structure.

REMEDIAL STRATEGIES OF THE FAULTS IN THE DRIVE CIRCUIT OF AIRCRAFT FUEL PUMP

This paper is aimed at examining the performance of H-bridges supplying fault-tolerant Permanent magnet machine in the aircraft fuel pump under short circuit condition. A significant DC component flows in the windings with a subsequent of saturation and higher iron losses, which possibly deteriorates the performance of the fuel pump. Expressions are derived to predict the inverter current during the fault. Also, the paper discusses all the possible remedial actions and highlights the most suitable one.

Analytical Prediction of Short-Circuit Current in Fault-Tolerant Permanent Magnet Machines

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes an analytical technique that can be utilized to predict the short-circuit current in a fault-tolerant permanent-magnet machine under partial-turn short-circuit fault conditions. It has been shown that the current in partially short-circuited turns is dependent on their relative position in the slot where the phase winding is accommodated, and the slot-leakage flux associated with these turns has a significant influence on the short-circuit current when a remedial action has been applied. An analytical model that quantifies the variation of the slot-leakage flux as a function of the relative position of partially short-circuited turns has been developed. Both finite-element analysis and experimental results demonstrate the effectiveness of the proposed technique for predicting the short-circuit current. </para>

Enhanced Optimal Torque Control of Fault-Tolerant PM Machine Under Flux-Weakening Operation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes an enhanced optimal-torque-control strategy for fault-tolerant permanent-magnet (PM) machines under flux-weakening operations. By adjusting the degree of flux weakening according to estimated instantaneous-torque-control errors, the torque-control performance of the machine can be improved when operating above its base speed under either open- or short-circuit fault condition. Extensive simulations under both healthy and fault conditions have been undertaken in order to validate the effectiveness of the proposed control strategy. Experimental results have also been given based on the testing of a prototype five-phase fault-tolerant PM machine. </para>

Analytical Prediction of the Short-Circuit Current in Fault-Tolerant Permanent-Magnet Machines

This paper describes an analytical technique that can be utilized to predict the short-circuit current in a fault-tolerant permanent-magnet machine under partial-turn short-circuit fault conditions. It has been shown that the current in partially short-circuited turns is dependent on their relative position in the slot where the phase winding is accommodated, and the slot-leakage flux associated with these turns has a significant influence on the short-circuit current when a remedial action has been applied. An analytical model that quantifies the variation of the slot-leakage flux as a function of the relative position of partially short-circuited turns has been developed. Both finite-element analysis and experimental results demonstrate the effectiveness of the proposed technique for predicting the short-circuit current.

Implications of shorted turn faults in bar wound PM machines

The paper discusses the effect of single turn short-circuits in the windings of fault tolerant permanent magnet machines. It is shown that previously recognised methods for dealing with shorted turns do not work for larger bar-wound machines, and a new method for protecting the windings against single turn faults is therefore proposed. The new method depends on rapid detection of the fault and injection of a current (of appropriate magnitude and phase) into the faulted winding. The paper gives a theoretical analysis supported by finite element simulations of the fault conditions and illustrates these with a case study taken from the aerospace industry.

Favourable slot and pole number combinations for fault-tolerant PM machines

A new approach is described for selecting pole and slot numbers for fault-tolerant permanent-magnet machines so that there is inherently negligible coupling between phases (regardless of other design detail). The preferred slot and pole number combinations thereby help to ensure that a fault in one phase does not undesirably affect the remaining unfaulted phases. Other well-known criteria for fault-tolerant operation, including high phase inductance, also have to be met. It is demonstrated how particular slot and pole combinations can be used to eliminate low pole number armature MMF, thereby reducing the vibration and stray loss present during normal operation.

A comparative study of permanent magnet and switched reluctance motors for high-performance fault-tolerant applications

Switched reluctance machines (SRMs) have been extensively researched for high performance aerospace applications because of their inherent fault tolerance. Recent work by the authors suggests that with careful design a similar degree of fault tolerance may be achieved with a permanent magnet machine (PM) at a significantly higher torque density than its SRM counterpart. This latter suggestion is of crucial importance in high performance applications, such as aerospace, where a low mass is essential. This paper is concerned with reporting measured results from a fault tolerant PM machine, and using these results to examine the relative merits of SR and PM technology for this application.