Fault-Tolerant Control of a Flux-switching Permanent Magnet Synchronous Machine

Je jasné, že nejúspěšnější konstrukce zahrnuje postup vícefázového řízení, ve kterém každá fáze může být považována za samostatný modul. Provoz kterékoliv z jednotek musí mít minimální vliv na ostatní, a to tak, že v případě selhání jedné jednotky ostatní mohou být v provozu neovlivněny. Modulární řešení vyžaduje minimální elektrické, magnetické a tepelné ovlivnění mezi fázemi řízení (měniče). Synchronní stroje s pulzním tokem a permanentními magnety se jeví jako atraktivní typ stroje, jejíž přednostmi jsou vysoký kroutící moment, jednoduchá a robustní konstrukce rotoru a skutečnost, že permanentní magnety i cívky jsou umístěny společně na statoru. FS-PMSM jsou poměrně nové typy střídavého stroje stator-permanentní magnet, které představují významné přednosti na rozdíl od konvenčních rotorů - velký kroutící moment, vysoký točivý moment, v podstatě sinusové zpětné EMF křivky, zároveň kompaktní a robustní konstrukce díky umístění magnetů a vinutí kotvy na statoru. Srovnání výsledků mezi FS-PMSM a klasickými motory na povrchu upevněnými PM (SPM) se stejnými parametry ukazuje, že FS-PMSM vykazuje větší vzduchové mezery hustoty toku, vyšší točivý moment na ztráty v mědi, ale také vyšší pulzaci díky reluktančnímu momentu. Pro stroje buzené permanentními magnety se jedná o tradiční rozpor mezi požadavkem na vysoký kroutící moment pod základní rychlostí (oblast konstantního momentu) a provozem nad základní rychlostí (oblast konstantního výkonu), zejména pro aplikace v hybridních vozidlech. Je předložena nová topologie synchronního stroje s permanentními magnety a spínaným tokem odolného proti poruchám, která je schopná provozu během vinutí naprázdno a zkratovaného vinutí i poruchách měniče. Schéma je založeno na dvojitě vinutém motoru napájeném ze dvou oddělených vektorově řízených napěťových zdrojů. Vinutí jsou uspořádána takovým způsobem, aby tvořila dvě nezávislé a oddělené sady. Simulace a experimentální výzkum zpřesní výkon během obou scénářů jak za normálního provozu, tak za poruch včetně zkratových závad a ukáží robustnost pohonu za těchto podmínek. Tato práce byla publikována v deseti konferenčních příspěvcích, dvou časopisech a knižní kapitole, kde byly představeny jak topologie pohonu a aplikovaná řídící schémata, tak analýzy jeho schopnosti odolávat poruchám.It has become clear that the most successful design approach involves a multiple phase drive in which each phase may be regarded as a single-module. The operation of any one module must have minimal impact upon the others, so that in the event of that module failing the others can continue to operate unaffected. The modular approach requires that there should be minimal electrical, magnetic and thermal interaction between phases of the drive. Flux-Switching permanent magnet synchronous machines (FS-PMSM) have recently emerged as an attractive machine type virtue of their high torque densities, simple and robust rotor structure and the fact that permanent magnets and coils are both located on the stator. Flux-switching permanent magnet (FS-PMSM) synchronous machines are a relatively new topology of stator PM brushless machine. They exhibit attractive merits including the large torque capability and high torque (power) density, essentially sinusoidal back-EMF waveforms, as well as having a compact and robust structure due to both the location of magnets and armature windings in the stator instead of the rotor as those in the conventional rotor-PM machines. The comparative results between a FS-PMSM and a traditional surface-mounted PM (SPM) motor having the same specifications reveal that FS-PMSM exhibits larger air-gap flux density, higher torque per copper loss, but also a higher torque ripple due to cogging -torque. However, for solely permanent magnets excited machines, it is a traditional contradiction between the requests of high torque capability under the base-speed (constant torque region) and wide speed operation above the base speed (constant power region) especially for hybrid vehicle applications. A novel fault-tolerant FS-PMSM drive topology is presented, which is able to operate during open- and short-circuit winding and converter faults. The scheme is based on a dual winding motor supplied from two separate vector-controlled voltage-sourced inverter drives. The windings are arranged in a way so as to form two independent and isolated sets. Simulation and experimental work will detail the driver’s performance during both healthy- and faulty- scenarios including short-circuit faults and will show the drive robustness to operate in these conditions. The work has been published in ten conference papers, two journal papers and a book chapter, presenting both the topology of the drive and the applied control schemes, as well as analysing the fault-tolerant capabilities of the drive.

Improving fault tolerant drives for aerospace applications

D EngThe aerospace industry is moving towards the more electric aeroplane where traditional hydraulic systems are being replaced with electrical systems. Electrical technology offers some strong advantages compared to hydraulic technology including; cost, efficiency, power on demand and relative ease of maintenance. As with most new technologies, a major disadvantage is its limited reliability history. A lot of research in the aerospace field therefore focuses on improving fault tolerant electrical systems. Work done in this thesis builds on an existing fault tolerant drive, developed by Newcastle University and Goodrich Actuation Systems as part of the ELGEAR (Electrical Landing Gear) project. The purpose of this work is to continue improving the drive’s fault tolerant features; especially in areas where the drive is most vulnerable. The first part of this thesis focuses on improving the overall system reliability by monitoring the health of the dc-link capacitors in the fault tolerant drive. The implemented estimation technique makes use of voltage and current sensors which are already in place for protection and control purposes. The novel aspect of the proposed technique relates to monitoring capacitors in real time whilst the motor is operational. No external interferences, such as injected signals or special operation of the drive, are required. The condition monitoring system is independent of torque and speed, and hence independent of a variation in load. The work was validated using analytical methods, simulation, low voltage experimentation and high voltage implementation on the ELGEAR drive. The second part of this thesis focuses on single shorted turn faults, in fault tolerant permanent magnet (PM) motors. Despite the motor being able to withstand a wide range of faults, the single shorted turn fault remains a difficult fault to detect and handle. The problem arises from the magnets on the spinning rotor that cannot be ‘turned off’ at will. This thesis investigates the severity of the faulted current in a shorted turn and how it varies depending on the turn’s location in the stator slot. The severity of the fault is studied using 2D finite element analysis and practical implementation on the ELGEAR rig. Finally, recommendations are proposed for improving the ELGEAR motor for future fault tolerant designs.EPRSC and Goodrich Aerospace (now United Technologies

Analysis of vertical strip wound fault-tolerant permanent magnet synchronous machines

This paper investigates the behavior of a vector- controlled, fault-tolerant, permanent magnet motor drive system adopting a vertically placed strip winding (VSW) which can limit inter-turn short-circuit (SC) fault current to its rated value regardless of the position in the slot containing the shorted turns. The drives’ dynamic behavior is simulated using a per-phase equivalent circuit model with the winding inductances and resistances analytical calculated based on the machine geometry and fault location. A simplified thermal model is also grafted into the system model to effectively simulate the dynamic behavior of the machine during healthy, inter-turn SC fault and post-fault controlled scenarios. The SC fault current limiting capability, the additional losses and thermal behavior of the winding are studied and compared with conventional winding adopting round conductors winding (RCW). The proposed winding design is verified with Finite Element (FE) analysis and then validated experimentally. Results show that the VSW inherently limits the SC current, reduces its dependence on the position of the fault within the slot but results in an increase in AC losses

Multiphase induction motor drives - a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio

A Fault Tolerant Machine Drive Based on Permanent Magnet Assisted Synchronous Reluctance Machine

A fault tolerant machine drive based on permanent magnet assisted synchronous reluctance machine (PMA SynRM) is proposed and investigated for applications where reliability and safety are crucial. In order to achieve enhanced fault tolerant capability, the risk of permanent magnet field that cannot be turned off under fault conditions is minimized without compromise in torque density and efficiency. This is achieved by employing a synchronous reluctance rotor topology with embedded permanent magnets. Three independent, segregated 3-phase windings are configured to ensure isolation and non-overlapping between the three 3-phase winding sets. Each 3-phase winding set is driven by a standard 3-phase inverter to facilitate fast integration and cost reduction. The machine behavior under various fault conditions has been evaluated by finite element (FE) simulations. A 40kW prototype was designed, constructed and tested. The test results demonstrate the performance and excellent fault tolerant capability of the proposed drive system under various faults, including open circuit and short circuit conditions

Fault tolerant motor drive system with redundancy for critical applications

Some of the recent research activities in the area of electric motor drives for critical applications (such as aerospace and nuclear power plants) are focused on looking at various motor and drive topologies. This paper presents a motor drive system, which provides an inverter topology for three-phase motors, and also proposes an increased redundancy. The paper develops a simulation model for the complete drive system including synthetic faults. In addition, the hardware details including the implementation of DSP based motor controller, inverter module, and brushless PM motor system are provided and some experimental results are presented.N. Ertugrul, W. Soong, G. Dostal and D. Saxo

On the reliability of electrical drives for safety-critical applications

The aim of this work is to present some issues related to fault tolerant electric drives,which are able to overcome different types of faults occurring in the sensors, in thepower converter and in the electrical machine, without compromising the overallfunctionality of the system. These features are of utmost importance in safety-criticalapplications. In this paper, the reliability of both commercial and innovative driveconfigurations, which use redundant hardware and suitable control algorithms, will beinvestigated for the most common types of fault: besides standard three phase motordrives, also multiphase topologies, open-end winding solutions, multi-machineconfigurations will be analyzed, applied to various electric motor technologies. Thecomplexity of hardware and control strategies will also be compared in this paper, sincethis has a tremendous impact on the investment costs

Detection and remediation of switch faults on a fault tolerant permanent magnet motor drive with reduncancy

Copyright © 2007 IEEE. All Rights Reserved.Fault-tolerant motor drives are becoming more important in safety critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have a fault-tolerant capability. This paper considers a dual motor drive system on a common shaft to introduce redundancy. The paper provides a systematic classification for the potential electrical faults which may occur in a real motor drive. In the paper, the switch and winding short circuit fault detection and identification methods are studied and experimental results are presented. In addition, the effects of switch faults on the phase currents and output torque are discussed, and remedial strategies for these faults are proposed. Furthermore, it was also demonstrated using simulation results that the proposed remedial strategies can compensate for the loss of torque due to the switch faults and can keep the peak-to-peak torque ripple factor comparable to healthy operation of the drive.Jingwei Zhu; Ertugrul, N.; Wen Liang Soon

Design optimization on conductor placement in the slot of permanent magnet machines to restrict turn-turn short-circuit fault current

In Permanent Magnet (PM) machines, a turn-turn Short-Circuit (SC) fault is the most critical fault to eradicate. The fault introduces high SC current in the shorted turn which may consequently lead to secondary faults unless the fault is appropriately controlled. This paper proposes feasible conductors’ placement in a slot of PM machine to minimize such turn-turn fault current. In order to minimize the fault current, the conductor arrangement in a slot is optimized using multi-objective Genetic Algorithm (GA) incorporating with both analytical and Finite Element (FE) numerical tool. The possible combinations of conductors’ placement are set as variables and optimized for a given machine which is designed for safety critical applications. It is shown that the fault current associated to a single turn fault can be significant for the random winding placement even though the remedial strategies are put in place. It is also shown that the fault current can be limited significantly by rearranging the winding placement in a way to share slot-leakage fluxes. This is confirmed via experiment on E-core. Influences of the winding arrangement on both frequency dependent resistances and windings capacitances are experimented. It is demonstrated that adopting the winding arrangement that shares the slot-leakage flux effectively benefits to minimize the AC losses in addition to improved fault tolerance. But it increases the turn-turn capacitances whose effect however can be neglected as the resonance frequency occurs beyond the operational frequency range of the machines of interes

Fault analysis and remedial strategies on a fault-tolerant motor drive with redundancy

Copyright © 2007 IEEEFault-tolerant motor drives are required in a range of safety-critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have an effective fault-tolerant capability. Although a single motor fault-tolerant drive system may be sufficient in many critical applications, a higher degree of fault tolerance requires redundancy in the motor system as considered in this paper. This is achieved by using a dual motor module on a common shaft. The simulation model of the entire drive system and the analysis of the various faults are presented in this paper. The effects of fault(s) on the phase current and output torque are provided. Three remedial operating modes are proposed and their features are compared. In addition, an experimental setup was introduced, which is based on dual electrically and magnetically isolated brushless AC motor modules, H-bridge inverters for individual phases and dsPICDEM MCU motor controller. © 2007 IEEE