Design Methods for Surface-Mounted Permanent Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSMs) provide several advantages compared with induction machine, such as higher power and torque density, and better dynamic response. Among PMSMs, Surface-mounted permanent magnet (SPM) machine has simple rotor configuration and easy control strategy due to its isotropic characteristics. Plenty of publications have illustrated the fundamentals and the design methods of SPM machines. Based on these, this dissertation presents new design methods for SPM machines. Both design methods are comprehensively illustrated. The presented design methods are embedded into a machine design platform available online. One of the new methods is an automatic design procedure using multi objective optimization method, whose principle is to combine multi objective differential evolution (MODE) optimization with finite element analysis (FEA) to obtain the machine with the best trade-off among the targeted objectives, like maximum torque, minimum torque ripple, good flux weakening capability, etc. Two cases are reported by using such automatic design method, one for a SPM machine with concentrated winding (CW-SPM) and the other with distributed windings (DW-SPM), respectively. The CW-SPM machine is designed for traction application. In this case, design equations, magnetic FEA, multi objective optimization, simplified structural and thermal co-design are presented. Torque and power profiles of the designed machine are reported. The losses and efficiency map are also presented. The DW-SPM machine is capable of low cogging torque thanks to the automatic design procedure. Dependent on demagnetization limit and optimal magnet span calculation, the magnet bounds in optimization process are obtained. The cogging torque and maximum torque waveforms of three different machines on Pareto front are shown, which are obtained by MODE optimization and FEA simulations. One optimum machine is selected as the best trade-off machine among PM volume, torque and cogging torque behaviors. Besides the automatic design process, the other design method called parametric design for SPM machines is reported. The parametric design provides a very effective and concise solution for SPM machine design without losing precision on the machine performance calculation. Three steps of parametric design development are reported. For each step, design flowcharts and examples are presented. Firstly, a parametric design plane was established based on rotor split ratio x and per unit magnetic loading b. All the sizing equations, torque and power factor calculation are functions of x and b. An example for designing a CW-SPM for traction application is reported. Later the parametric design plane was modified into the x and l_m⁄g plane, the latter parameter being the magnet-airgap length ratio. The design process of DW-SPM machines using the parametric plane is described. A prototype 一s built and verified the validity of the design process. Then, a general design approach based on accurate steel loading for both DW and CW SPM machines is proposed. By using subdomain model during the design process, the stator sizing equations are improved by considering the only one most loaded slot pitch rather than the entire pole pitch. Five different cases of SPM machines are analyzed to get the precise flux quantities passing through the most loaded teeth in one slot. A comprehensive parametric design flowchart for SPM machines is addressed. By using the parametric method, machine models are built according to each sizing situation. The steel loadings on both each tooth and yoke are measured by FEA and compared with target steel loading B_fe at open load condition, which shows good agreements with analytical cases. Finally, the designs are also tested at the respective rated currents. The presented methods give insightful and effective means in SPM machine desig

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

Modelling and Detecting Faults of Permanent Magnet Synchronous Motors in Dynamic Operations

Paper VI is excluded from the dissertation until the article will be published.Permanent magnet synchronous motors (PMSMs) have played a key role in commercial and industrial applications, i.e. electric vehicles and wind turbines. They are popular due to their high efficiency, control simplification and large torque-to-size ratio although they are expensive. A fault will eventually occur in an operating PMSM, either by improper maintenance or wear from thermal and mechanical stresses. The most frequent PMSM faults are bearing faults, short-circuit and eccentricity. PMSM may also suffer from demagnetisation, which is unique in permanent magnet machines. Condition monitoring or fault diagnosis schemes are necessary for detecting and identifying these faults early in their incipient state, e.g. partial demagnetisation and inter-turn short circuit. Successful fault classification will ensure safe operations, speed up the maintenance process and decrease unexpected downtime and cost. The research in recent years is drawn towards fault analysis under dynamic operating conditions, i.e. variable load and speed. Most of these techniques have focused on the use of voltage, current and torque, while magnetic flux density in the air-gap or the proximity of the motor has not yet been fully capitalised. This dissertation focuses on two main research topics in modelling and diagnosis of faulty PMSM in dynamic operations. The first problem is to decrease the computational burden of modelling and analysis techniques. The first contributions are new and faster methods for computing the permeance network model and quadratic time-frequency distributions. Reducing their computational burden makes them more attractive in analysis or fault diagnosis. The second contribution is to expand the model description of a simpler model. This can be achieved through a field reconstruction model with a magnet library and a description of both magnet defects and inter-turn short circuits. The second research topic is to simplify the installation and complexity of fault diagnosis schemes in PMSM. The aim is to reduce required sensors of fault diagnosis schemes, regardless of operation profiles. Conventional methods often rely on either steady-state or predefined operation profiles, e.g. start-up. A fault diagnosis scheme robust to any speed changes is desirable since a fault can be detected regardless of operations. The final contribution is the implementation of reinforcement learning in an active learning scheme to address the imbalance dataset problem. Samples from a faulty PMSM are often initially unavailable and expensive to acquire. Reinforcement learning with a weighted reward function might balance the dataset to enhance the trained fault classifier’s performance.publishedVersio

Modelling and design methodology of an improved performance photovoltaic pumping system employing ferrite magnet synchronous reluctance motors

This paper proposes a novel photovoltaic water pumping system (PVWPS) with an improved performance and cost. This system doesn’t contain a DC-DC converter, batteries nor rare-earth motors. Removing the aforementioned components will reduce the whole cost and increase the reliability of the system. For enhancing the performance of the PVWPS, a ferrite magnet synchronous reluctance motor (FMSynRM) is employed. Besides, the motor inverter is utilized to drive the motor properly and to extract the maximum available power of the PV system. This is performed using a suggested control strategy that controls the motor inverter. Furthermore, to show the effectiveness of the proposed PVWPS, the performance of the proposed system is benchmarked with a PVWPS that is employing a pure SynRM. Moreover, the complete mathematical model of the system components and the control is reported. It is proved that the flow rate employing the proposed system is increased by about 29.5% at a low irradiation level (0.25 kW/m2) and 15% at a high irradiation level (1 kW/m2) compared to the conventional solar system using a pure synchronous reluctance motor (SynRM). An experimental laboratory test bench is built to validate the theoretical results presented in this research work. Good agreement between the theoretical and the experimental results is prove

Performance comparison of conventional synchronous reluctance machines and PM-assisted types with combined star-delta winding

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star-delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star-delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star-delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star-delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts

Self-sensing permanent magnet servo motors

The use of Permanent Magnet Synchronous Machines (PMSMs) has become widespread across numerous applications and industries. Their high power density, efficiency and accuracy of control make them excellent choices, leading them to become the industrial standard. Two issues concerning PMSMs use in recent years have been associated with the elevated cost of rare earth materials required for the Permanent Magnet (PM) rotor poles and the reliance on a direct rotor position sensor such as an encoder. PMSMs require an accurate rotor position feedback within the control scheme, traditionally provided by an encoder or resolver. These devices are excellent at providing the realtime rotor position accurately but have a negative impact on the machine as a whole. Their use increases the size, weight and cost of the electrical machine, while reducing reliability and often limiting use in extreme environments. This has created motivation for sensorless control of PMSMs, which removes the need for a position sensor. Sensorless control can be categorized into two distinctive aspects. The first is the control scheme and focuses on how position dependent properties can be used to estimate rotor position. The second, which has had less focus, is the machine design. This is focused on the ability of a machine to act as a position sensor with clear position dependent properties. Self-sensing machine design is the common term applied to this field since in essence the machine acts as its own position sensor. This thesis is concerned with self-sensing oriented design. The work presented is focused on PMSMs with inset rotor topologies. A methodology was developed to assess the position tracking capability of a machine and incorporated within a traditional machine design optimization routine. The conceptual design of the machine emphasized a generic geometrical topology, accounting for practical material selections and construction techniques. This ensured the design outcome had widespread implications, as opposed to a novel machine design with limited commercial relevance

Modeling, Analysis and Control of a Variable Flux Machine

Electric motors are the key elements in electric propulsion systems. The performance of Electric vehicles (EVs) significantly depends on the electric motors. Permanent magnet synchronous machines (PMSMs) with rare-earth magnets are widely used in EV applications because they fulfill most requirements of EV motors. However, low efficiency at high speed, limited resources and fluctuating prices of rare-earth permanent magnets (PMs) have forced industries to develop alternatives to rare-earth machine technologies. Recently, Variable-Flux PMSMs (VF-PMSMs) also known as memory motors have been introduced to overcome the drawbacks of PMSMs. This thesis focuses on the modeling, analysis and control of the Aluminum-Nickel-Cobalt (AlNiCo) magnet-based VF-PMSMs. This thesis presents the effect of different magnetization pulse widths and methods on the magnetization level, back-EMF and no-load losses of the VF-PMSM. The injection of the magnetization or de-magnetization current pulse will change the magnet flux linkage and back-EMF harmonics. An adaptive nonlinear filter is used to estimate the back-EMF during the motoring mode. The harmonics present in the machine back-EMF due to different magnetization and de-magnetization current pulse widths and magnetization methods are analyzed. Besides, the quality of the back-EMF for different speeds and machine no-load losses are presented for different magnetization states (MSs)

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

Low-cost, high-resolution, fault-robust position and speed estimation for PMSM drives operating in safety-critical systems

In this paper it is shown how to obtain a low-cost, high-resolution and fault-robust position sensing system for permanent magnet synchronous motor drives operating in safety-critical systems, by combining high-frequency signal injection with binary Hall-effect sensors. It is shown that the position error signal obtained via high-frequency signal injection can be merged easily into the quantization-harmonic-decoupling vector tracking observer used to process the Hall-effect sensor signals. The resulting algorithm provides accurate, high-resolution estimates of speed and position throughout the entire speed range; compared to state-of-the-art drives using Hall-effect sensors alone, the low speed performance is greatly improved in healthy conditions and also following position sensor faults. It is envisaged that such a sensing system can be successfully used in applications requiring IEC 61508 SIL 3 or ISO 26262 ASIL D compliance, due to its extremely high mean time to failure and to the very fast recovery of the drive following Hall-effect sensor faults at low speeds. Extensive simulation and experimental results are provided on a 3.7 kW permanent magnet drive

Permanent Magnet Assisted Synchronous Reluctance Machine (PMa-SynRM) Design and Performance Analysis for Fan and Pump Applications

One of the major industrial applications of electric machines is driving fans and pumps. According to the pump and fan affinity laws, decreasing the speed of the load can reduce the power consumption on the load significantly. Therefore, a variable speed drive offers reduction in energy consumption of the induction motor driving those types of loads. As an alternative, synchronous machines can be used for this application to get the benefit of higher efficiency. In this work, the performance of an optimized permanent magnet assisted synchronous reluctance machine (PMa-SynRM) with a NEMA standard stator has been studied for fan and pump applications. The effect of using different quantities of the permanent magnet in this machine is studied experimentally. In addition, the performance of the PMa-SynRM is compared with a standard general purpose induction machine for the same loading condition. This work presents the comparison of the energy consumption and performance of the machines under the fan and pump type loads operating on specific typical duty cycles