Review of flux-weakening algorithms to extend the speed range in electric vehicle applications with permanent magnet synchronous machines

This article reviews Flux-Weakening (FW) algorithms for Permanent Magnet Synchronous Machines (PMSMs), focusing on the automotive sector, especially in electric and hybrid electric vehicles. In the past few years, the spread of Electric Vehicles (EVs) has improved the technology of electric machines and their control to achieve more compact and competitive solutions. PMSMs are the most widespread electric machines used in EVs thanks to their high-power density and potential operation at constant power range during high speed. Such high speed implies a high electromotive force. An FW technique is mandatory to reduce the electromagnetic flux generated by the electric machine due to the voltage limits of the traction inverter and the energy source. This article classifies and analyses the state-of-the-art FW control strategies by comparing their main advantages and drawbacks. The Vector Current Control (VCC) method that regulates the modulus of the applied voltage is the most common one in the literature thanks to i) its robustness to parameter modification and model unsureness, ii) low computational complexity, and iii) high dynamic response and control stability.Peer ReviewedPostprint (published version

Multi-level-objective design optimization of permanent magnet synchronous wind generator and solar photovoltaic system for an urban environment application

This Ph.D. thesis illustrates a novel study on the analytical and numerical design optimization of radial-flux permanent magnet synchronous wind generators (PMSGs) for small power generation in an urban area, in which an outer rotor topology with a closed-slot stator is employed. The electromagnetic advantages of a double-layer fractional concentration non-overlapping winding configuration are discussed. The analytical behavior of a PMSG is studied in detail; especially for magnetic flux density distribution, time and space harmonics, flux linkages, back-EMF, cogging torque, torque, output power, efficiency, and iron losses computation. The electromagnetic behavior of PMSGs are evaluated when a number of various Halbach array magnetization topologies are presented to maximize the generator’s performance. In addition, the thermal behavior of the PMSG is improved using an innovative natural air-cooling system for rated speed and higher to decrease the machine’s heat mainly at the stator teeth. The analytical investigation is verified via 2-D and 3-D finite element analysis along with a good experimental agreement. Design optimization of electrical machines plays the deterministic role in performance improvements such as the magnetization pattern, output power, and efficiency maximization, as well as losses and material cost minimization. This dissertation proposes a novel multi-objective design optimization technique using a dual-level response surface methodology (D-RSM) and Booth’s algorithm (coupled to a memetic algorithm known as simulated annealing) to maximize the output power and minimize material cost through sizing optimization. Additionally, the efficiency maximization by D-RSM is investigated while the PMSG and drive system are on duty as the whole. It is shown that a better fit is available when utilizing modern design functions such as mixed-resolution central composite (MR-CCD) and mixed-resolution robust (MR-RD), due to controllable and uncontrollable design treatments, and also a Window-Zoom-in approach. The proposed design optimization was verified by an experimental investigation. Additionally, there are several novel studies on vibro-acoustic design optimization of the PMSGs with considering variable speed analysis and natural frequencies using two techniques to minimize the magnetic noise and vibrations. Photovoltaic system design optimization considered of 3-D modeling of an innovative application-oriented urban environment structure, a smart tree for small power generation. The horizon shading is modeled as a broken line superimposed onto the sun path diagram, which can hold any number of height/azimuth points in this original study. The horizon profile is designed for a specific location on the Barcelona coast in Spain and the meteorological data regarding the location of the project was also considered. Furthermore, the input weather data is observed and stored for the whole year (in 2016). These data include, ambient temperature, module’s temperature (open and closed circuits tests), and shading average rate. A novel Pareto-based 3-D analysis was used to identify complete and partial shading of the photovoltaic system. A significant parameter for a photovoltaic (PV) module operation is the nominal operating cell temperature (NOCT). In this research, a glass/glass module has been referenced to the environment based on IEC61215 via a closed-circuit and a resistive load to ensure the module operates at the maximum power point. The proposed technique in this comparative study attempts to minimize the losses in a certain area with improved output energy without compromising the overall efficiency of the system. A Maximum Power Point Track (MPPT) controller is enhanced by utilizing an advanced perturb & observe (P&O) algorithm to maintain the PV operating point at its maximum output under different temperatures and insolation. The most cost-effective design of the PV module is achieved via optimizing installation parameters such as tilt angle, pitch, and shading to improve the energy yield. The variation of un-replicated factorials using a Window-Zoom-in approach is examined to determine the parameter settings and to check the suitability of the design. An experimental investigation was carried out to verify the 3-D shading analysis and NOCT technique for an open-circuit and grid-connected PV module.Esta tesis muestra un novedoso estudio referente al diseño optimizado de forma analítica y numérica de un generador síncrono de imanes permanentes (PMSGs) para una aplicación de microgeneración eólica en un entorno urbano, donde se ha escogido una topología de rotor exterior con un estator de ranuras cerradas. Las ventajas electromagnéticas de los arrollamientos fraccionarios de doble capa, con bobinas concentradas se discuten ampliamente en la parte inicial del diseño del mismo, así como las características de distribución de la inducción, los armónicos espaciales y temporales, la fem generada, el par de cogging así como las características de salida (par, potencia generada, la eficiencia y la distribución y cálculo de las pérdidas en el hierro que son analizadas detalladamente) Posteriormente se evalúan diferentes configuraciones de estructuras de imanes con magnetización Halbach con el fin de maximizar las prestaciones del generador. Adicionalmente se analiza la distribución de temperaturas y su mejora mediante el uso de un novedoso diseño mediante el uso de ventilación natural para velocidades próximas a la nominal y superiores con el fin de disminuir la temperatura de la máquina, principalmente en el diente estatórico. El cálculo analítico se completa mediante simulaciones 2D y 3D utilizando el método de los elementos finitos así como mediante diversas experiencias que validan los modelos y aproximaciones realizadas. Posteriormente se desarrollan algoritmos de optimización aplicados a variables tales como el tipo de magnetización, la potencia de salida, la eficiencia así como la minimización de las pérdidas y el coste de los materiales empleados. En la tesis se proponen un nuevo diseño optimizado basado en una metodología multinivel usando la metodología de superficie de respuesta (D-RSM) y un algoritmo de Booth (maximizando la potencia de salida y minimizando el coste de material empleado) Adicionalmente se investiga la maximización de la eficiencia del generador trabajando conjuntamente con el circuito de salida acoplado. El algoritmo utilizado queda validado mediante la experimentación desarrollada conjuntamente con el mismo. Adicionalmente, se han realizado diversos estudios vibroacústicos trabajando a velocidad variable usando dos técnicas diferentes para reducir el ruido generado y las vibraciones producidas. Posteriormente se considera un sistema fotovoltaico orientado a aplicaciones urbanas que hemos llamado “Smart tree for small power generation” y que consiste en un poste con un generador eólico en la parte superior juntamente con uno o más paneles fotovoltaicos. Este sistema se ha modelado usando metodologías en 3D. Se ha considerado el efecto de las sombras proyectadas por los diversos elementos usando datos meteorológicos y de irradiación solar de la propia ciudad de Barcelona. Usando una metodología basada en un análisis 3D y Pareto se consigue identificar completamente el sistema fotovoltaico; para este sistema se considera la temperatura de la célula fotovoltaica y la carga conectada con el fin de generar un algoritmo de control que permita obtener el punto de trabajo de máxima potencia (MPPT) comprobándose posteriormente el funcionamiento del algoritmo para diversas situaciones de funcionamiento del sistemaLa tesis desenvolupa un nou estudi per al disseny optimitzat, analític i numèric, d’un generador síncron d’imants permanents (PMSGs) per a una aplicació de microgeneració eòlica en aplicacions urbanes, on s’ha escollit una configuració amb rotor exterior i estator amb ranures tancades. Es discuteixen de forma extensa els avantatges electromagnètics dels bobinats fraccionaris de doble capa així com les característiques resultats vers la distribució de les induccions, els harmònics espacials i temporals, la fem generada, el parell de cogging i les característiques de sortida (parell, potencia, eficiència i pèrdues) Tanmateix s’afegeix l’estudi de diferents estructures Halbach per als imants permanents a fi i efecte de maximitzar les característiques del generador. Tot seguit s’analitza la distribució de temperatures i la seva reducció mitjançant la utilització d’una nova metodologia basada en la ventilació natural. Els càlculs analítics es complementen mitjançant anàlisi en 2 i 3 dimensions utilitzant elements finits i diverses experiències que validen els models i aproximacions emprades. Una vegada fixada la geometria inicial es desenvolupen algoritmes d’optimització per a diverses variables (tipus de magnetització dels imants, potencia de sortida, eficiència, minimització de pèrdues i cost dels materials) La tesi planteja una optimització multinivell emprant la metodologia de superfície de resposta i un algoritme de Booth; a més, es realitza la optimització considerant el circuit de sortida. L’algoritme resta validat per la experimentació realitzada. Finalment, s’han considerat diversos estudis vibroacústic treballant a velocitat variable, emprant dues tècniques diferents per a reduir el soroll i les vibracions desenvolupades. Per a finalitzar l’estudi es considera un sistema format per una turbina eòlica instal·lada sobre un pal de llum autònom, els panells fotovoltaics corresponents i el sistema de càrrega. Per a modelitzar l’efecte de l’ombrejat s’ha emprat un model en 3D i les dades del temps i d’irradiació solar de la ciutat de Barcelona. El model s’ha identificat completament i s’ha generat un algoritme de control que considera, a més, l’efecte de la temperatura de la cèl·lula fotovoltaica y la càrrega connectada al sistema per tal d’aconseguir el seguiment del punt de màxima potenciaPostprint (published version

High efficiency sensorless fault tolerant control of permanent magnet assisted synchronous reluctance motor

In the last decades, the development trends of high efficiency and compact electric drives on the motor side focused on Permanent Magnet Synchronous Machines (PMSMs) equipped with magnets based on the rare-earth elements. The permanent magnet components, however, dramatically impact the overall bill of materials of motor construction. This aspect has become even more critical due to the price instability of the rare-earth elements. This is why the Permanent Magnet Assisted Synchronous Reluctance Motor (PMaSynRM) concept was brought to the spotlight as it gives comparable torque density and similar efficiencies as PMSM although at a lower price accredited for the use of magnets built with ferrite composites. Despite these advantages, PMaSynRM drive design is much more challenging because of nonlinear inductances resulting from deep cross saturation effects. It is also true for multi-phase PMSM motors that have gained a lot of attention as they proportionally split power by the increased number of phases. Furthermore, they offer fault-tolerant operation while one or more phases are down due to machine, inverter, or sensor fault. The number of phases further increases the overall complexity for modeling and control design. It is clear then that a combination of multi-phase with PMaSynRM concept brings potential benefits but confronts standard modeling methods and drive development techniques. This Thesis consists of detailed modeling, control design, and implementation of a five-phase PMaSynRM drive for normal healthy and open phase fault-tolerant applications. Special emphasis is put on motor modeling that comprises saturation and space harmonics together with axial asymmetry introduced by rotor skewing. Control strategies focused on high efficiency are developed and the position estimation based on the observer technique is derived. The proposed models are validated through Finite Element Analysis (FEA) and experimental campaign. The results show the effectiveness of the elaborated algorithms and methods that are viable for further industrialization in PMaSynRM drives with fault-tolerant capabilities.En últimas décadas, las tendencias de desarrollo de accionamientos eléctricos compactos y de alta eficiencia en el lado del motor se centraron en las maquinas síncronas de imanes permanentes (PMSM) equipadas con imanes basados en elementos de tierras raras. Sin embargo, los componentes de imán permanente impactan dramáticamente en el coste de construcción del motor. Este aspecto se ha vuelto aún más crítico debido a la inestabilidad de precios de los elementos de tierras raras. Esta es la razón por la que el concepto de motor de reluctancia síncrona asistido por imán permanente (PMaSynRM) se ha tomado en consideración, ya que ofrece una densidad de par comparable y eficiencias similares a las de PMSM, aunque a un precio más bajo acreditado para el uso de imanes construidos con compuestos de ferritas. A pesar de drive PMaSynRM resulta muy complejo debido a las inductancias no lineales que resultan de los efectos de saturación cruzada profunda. Esto también es cierto para los motores PMSM polifásicos que han ganado mucha atención en los últimos años, en los que se divide proporcionalmente la potencia por el mayor número de fases. Además, ofrecen operación tolerante a fallas mientras una o más fases están inactivas debido a fallas en la máquina, el inversor o el sensor. Sin embargo, el número de fases aumenta aún más la complejidad general del diseño de modelado y control. Está claro entonces que una combinación de multifase con el concepto PMaSynRM tiene beneficios potenciales, pero dificulta los métodos de modelado estándar y las técnicas de desarrollo del sistema de accionamiento. Esta tesis consiste en el modelado detallado, el diseño de control y la implementación de un drive PMaSynRM de cinco fases para aplicaciones normales en buen estado y tolerantes a fallas de fase abierta. Se pone especial énfasis en el modelado del motor que comprende la saturación y los armónicos espaciales junto con la asimetría axial introducida por la inclinación del rotor. Se desarrollan estrategias de control enfocadas a la alta eficiencia y se deriva la estimación de posición basada en la técnica del observador. Los modelos propuestos se validan mediante Análisis de Elementos Finitos (FEA) y resultados experimentales. Los resultados muestran la efectividad de los algoritmos y métodos elaborados, que resultan viables para la industrialización de unidades PMaSynRM con capacidades tolerantes a fallas.Postprint (published version

Investigation of novel multi-layer spoke-type ferrite interior permanent magnet machines

The permanent magnet synchronous machines have been attracting more and more attention due to the advantages of high torque density, outstanding efficiency and maturing technologies. Under the urges of mandatory energy efficiency requirements, they are considered as the most potential candidates to replace the comparatively low-efficient induction machines which dominate the industrial market. However, most of the high performance permanent magnet machines are based on high cost rare-earth materials. Thus, there will be huge demands for low-cost high-performance permanent magnet machines. Ferrite magnet is inexpensive and abundant in supply, and is considered as the most promising alternative to achieve the goal of low cost and high performance. In consideration of the low magnetic energy, this thesis explored the recent developments and possible ideas of ferrite machines, and proposed a novel multi-layer spoke-type interior permanent magnet configuration combining the advantages of flux focusing technique and multi-layer structure. With comparable material cost to induction machines, the proposed ferrite magnet design could deliver 27% higher power with 2-4% higher efficiency with exactly the same frame size. Based on the data base of International Energy Agency (IEA), electricity consumed by electric machines reached 7.1PWh in 2006 [1]. Considering that induction machines take up 90% of the overall industrial installation, the potential energy savings is enormous. This thesis contributes in five key aspects towards the investigation and design of low-cost high-performance ferrite permanent magnet machines. Firstly, accurate analytical models for the multi-layer configurations were developed with the consideration of spatial harmonics, and provided effective yet simple way for preliminary design. Secondly, the influence of key design parameters on performance of the multi-layer ferrite machines were comprehensively investigated, and optimal design could be carried out based on the insightful knowledge revealed. Thirdly, systematic investigation of the demagnetization mechanism was carried out, focusing on the three key factors: armature MMF, intrinsic coercivity and working temperature. Anti-demagnetization designs were presented accordingly to reduce the risk of performance degradation and guarantee the safe operation under various loading conditions. Then, comparative study was carried out with a commercial induction machine for verification of the superior performance of the proposed ferrite machine. Without loss of generality, the two machines had identical stator cores, same rotor diameter and stacking length. Under the operating condition of same stator copper loss, the results confirmed the superior performance of the ferrite machine in terms of torque density, power factor and efficiency. Lastly, mechanical design was discussed to reduce the cost of mass production, and the experimental effort on the prototype machine validates the advantageous performance as well as the analytical and FEA predictions

Control óptimo de par para máquinas SynRM aplicadas a vehículo eléctrico

Las máquinas de reluctancia síncrona asistidas por imanes están atrayendo un considerable interés como alternativa a las máquinas síncronas de imanes permanentes para su uso en sistemas de propulsión de vehículos eléctricos. El control óptimo de estas máquinas (incluyendo operación en debilitamiento de campo) puede resultar complejo, ya que estas son, por lo general, muy sensibles al fenómeno de la saturación magnética. En este artículo se trata su control, desde los reguladores hasta el precalculo de referencias de corriente óptimas para todo el rango de operación de la máquina. Finalmente, se muestran resultados experimentales obtenidos en una máquina de 51 kW.Postprint (published version

Modeling and Parameter Measurement of Special Electric Machines

Recent engineering applications such as electric and hybrid electric vehicles require higher performance electric machines. Accordingly, there have been a significant increase on research on performance improvement of electric machines for transportation applications. Opposed to the conventional machines, new and innovative traction machines have higher power density, higher efficiency, faster dynamic response, wider speed range and higher reliability. The modern simulation and manufacturing tools made it possible to obtain the desired performance requirements in the new and special designs at reasonable cost. Due to the special designs to improve a certain output variable subjected to several constraints, it is required to have advanced machine models for control and operation of these machines. Moreover, parameter measurement of these special electric machines are gaining a significant interest due to new and advanced motor drive testing systems such as power hardware in the loop emulation which use a look-up table based machine model for fast and accurate solution of machine dynamics. This PhD work develops a novel automated current control method to measure the parameters of special electric machines. In contrast to the existing parameter measurement method that applies a voltage pulse excitation to the test motor for flux linkage measurement, the current control method developed in this thesis uses a current pulse with closed loop control. While the voltage pulse method requires a higher sampling frequency for machines with lower time constants, the number of samples available during the transient for a fixed sampling rate can be modified by using a current pulse to measure the flux linkages. In addition, the use of a current pulse in closed loop makes it possible to measure the machine flux linkages at operating points unattainable with the voltage pulse method due to inverter dead time and device drops. This PhD work also develops a current controller design methodology for the developed parameter measurement method, which aids in the automation of the measurement process in a real time system. This PhD research also develops an experimental method to obtain the static torque angle curves and torque-ripple of synchronous reluctance machines (SynRM). The developed technique is used to study the performance of a SynRM using cold rolled grain oriented (CRGO) laminations against a regular SynRM using cold rolled non-grain oriented laminations. The SynRM using CRGO laminations are designed to have a higher saliency, and thus a higher torque per ampere and higher power factor. This thesis presents a comparative study of the torque performance of the CRGO and CRNGO SynRMs. This PhD work also develops the mathematical model of an interior permanent magnet synchronous machine (IPMSM) with aligned magnet and reluctance torques. It is a new class of IPMSM also called shifted IPMSM, which is designed to have higher torque for lower magnet volume. The torque characteristics of the shifted IPMSM is different from conventional IPMSMs. For the analysis and operation of this new class of machine, a suitable mathematical model is lacking in the literature. The PhD work develops the mathematical model of the novel shifted IPMSM, and validates it using the experimentally obtained inductance, torque angle and torque-speed curves. This thesis also develops a mathematical model of a novel hybrid variable flux machine (VFM) having rare-earth magnets in series with AlNiCo magnets for power hardware in the loop emulation applications. In order to emulate the VFM, emulation of the change in magnetization state is crucial. This thesis models the magnetization and demagnetization characteristics of the VFM as look-up tables. The current control method to measure the machine parameter proposed in this thesis is used to measure the flux linkage characteristics of the VFM, and a complete VFM model suitable for power hardware in the loop emulation is developed. The developed model is validated experimentally through the comparison of transient and steady state machine behavior. The works presented in chapters 2 and 3 are primarily useful in generating the flux-linkages, inductances and torque look-up tables for behavioral model special electric machine models. Such a model is used in advanced model based controls that would not be possible with basic two axis machine models. Moreover, the developed techniques are useful in validation of finite element analysis simulation of special electric machines. Within the thesis, Chapters 4 and 5 used the techniques developed in chapters 2 and 3 to develop and validate the machine models of shifted interior permanent magnet synchronous machine and hybrid variable flux machine. The developed models are useful in drive operations of these motors using advanced control algorithms

In-wheel motors for electric vehicles

PhD ThesisThe in-wheel motor technology as the source of traction for electric vehicles has been researched recently because it is compact and ease-to-integrate. The motor is housed in the wheel. Since the room for the motor is tightly defined by the size of the wheel and there is no gearing system, the motor must have a high torque density to drive the vehicle directly and a high efficiency to keep cool. The existing motor uses a surface-mounted magnet topology. To make it more cost-competitive, the magnet material needs to be reduced while maintaining the torque performance at the rated operating condition. It is the motive of this Ph.D. research. The thesis starts with a brief introduction on the background of the electric vehicle. Then the major challenges of the in-wheel motor technology are summarised. With the derived specifications, an induction machine and a switched reluctance machine are then simulated and analysed. Still, the permanent magnet synchronous machine is proved to have the highest torque density. Change from surface-mounted to interior topology, six new magnet topologies are investigated. The V-shaped interior magnet topology shows superior torque-to-magnet-mass ratio and is easy-to-manufacture. It gives 96% torque while using 56% of the magnet mass compared to the existing motor due to the assist from the additional reluctance torque and the lower magnetic circuit reluctance. The key to use less magnet mass while avoiding the demagnetisation is the front iron shielding effect. The analytical explanation on the better resistance to demagnetisation in the V-shaped motor is provided. The magnet loss mechanism is discussed for proper segmentation. Detailed design adjustments are made to compromise between the torque-to-magnet-mass ratio and the manufactural practicality. Issues regarding to lower mechanical rigidity occurred in initial assembly of the prototype and solutions are proposed. Followed by successful assembly, experimental tests were conducted and results show good agreement with the simulation. A specific form of torque ripple is found in the V-shaped motor and occurs generally in all fractional-slot concentrated-winding machines with saliency. It is explained by an analytical model. This model is also extended to explain the generally lower reluctance torque in vi fractional-slot concentrated-winding machines. Potential design improvements are suggested and simulated for future versions.Protean Electri

Control optimo de par para maquinas SynRM aplicadas a vehiculo electrico

Las maquinas de reluctancia sincrona asistidas por imanes estan atrayendo un considerable interes como alternativa a las maquinas sıncronas de imanes permanentes para su uso en sistemas de propulsion de vehıculos electricos. El control optimo de estas maquinas (incluyendo operacion en debilitamiento de campo) puede resultar complejo, ya que estas son, por lo general, muy sensibles al fenomeno de la saturacion magnetica. En este articulo se trata su control, desde los reguladores hasta el precalculo de referencias de corriente optimas para todo el rango de operacion de la maquina. Finalmente, se muestran resultados experimentales obtenidos en una maquina de 51 kW.El trabajo descrito en este articulo ha sido generado y patrocinado por el Departamento de Educacion, Politica Linguistica y Cultura del Gobierno Vasco en base a las ayudas para apoyar las actividades de grupos de investigacion del sistema universitario vasco IT978-16 y ha sido financiado por el Ministerio de Economia y Competitividad a traves del proyecto de investigacion DPI2014-53685-C2-2-R y los fondos FEDER, por el Gobierno Vasco a traves del proyecto de investigacion KT4TRANS del programa ELKARTEK (KK- 2015/00047 y KK-2016/00061) y por los proyectos DPI2013- 41224-P (Ministerio de Economia y Competitividad) y 2014 SGR 267 (AGAUR)