A Homothetic Scaling Criteria for Synchronous Reluctance Machines Design

This paper proposes a concept for homothetic scaling of Synchronous Reluctance (SynRel) machines with the aim to generate a design for a wide range of power ratings. A generalized modeling approach, based on the saliency ratio, is presented in detail to analytically evaluate the magnetic behavior of the scaled SynRel machines. The analytical model has been applied to a wide range of machines and validated through finite element analysis. General scaling functions are derived to size and evaluate the performance of the scaled machines using the data resulting from the analytical model. The accuracy of the proposed functions is validated, for a range of operating conditions, comparing the results with the experimental measurement carried out on two 4-poles SynRel prototypes. These have been designed using the homothetic method proposed, which has been proven to be a quick and accurate preliminary sizing tool for SynRel motors

Novel sizing and modeling techniques for synchronous reluctance machines

In recent years, there is a growing interest for high efficiency electric motors without, or with reduce content of, permanent magnets (PMs) for industrial applications. The Synchronous Reluctance (SynRel) machine is one of the most promising candidates that can meet the requirements of efficient and low cost drive [1]. The key benefits of this technology are a rotor structure made of flux barriers and iron parts, without excitation coils or PMs, like in induction motors (IM) and PM machines, respectively [2]. This leads to a cost effective structure that is using the reluctance principle to generate torque. The reluctance machine topology was introduced in 1920s, however has not been utilised at high industrial volumes yet due to superiority of the alternative technologies. IMs are considered as an industry “work horse”, which dominates the electrical machines market in applications such as industrial fans, pumps and mill type loads, as it is known to be the cheapest and the most reliable machine topology. On the other hand, PMs are mostly used in high performance applications, where the power-density is of the priority. Whereas, the interest in SynRel is mainly driven by lack of magnets or any other field excitation, as well as high efficiency [3], [4], [5]. The rare-earth permanent magnets began to commercialize for electrical motors in early 1980s. Various types of applications such as electric vehicles, wind turbines, actuators, started utilization of the PM synchronous machines [6], [7], [8]. Neodymium-iron-boron (NdFeB) permanent magnets are the common type for the high-performance applications due to their superior magnetic properties. In comparison the remanent flux density Br and coercivity Hc values of NdFeB are higher than any other type of magnets i.e. samarium-cobalt (SM2Co17), which was the major breakthrough in 1970s [9], and it is still extensively used when operating temperatures are very high. The main downfall of the NdFeB is the cost. The prices of the Neodymium had a huge spike in the mid-2011, as it was increased by factor of 25 compared to the beginning of 2010 [10], [11]. After hitting its peak, the price dropped rapidly and settled at its pre-bubble price [12]. Such price instability had a huge financial effect on PM machine manufacturers. Hence, as of 2019, there is a high research 4 emphasis on electrical machines with low volume of rare earth permanent magnet material [13], [14]. There is also a growing interest in very high efficiency, or super-premium efficiency electrical machines for the industrial sector [2], [15], [16]. This is driven by new requirements of the local governments for the industrial sector, as well as the world trend towards the reduction of the energy consumption and greenhouse gas emissions [17], [18]. Currently world leading manufacturers and R&D institutions are constantly investigating the possibility of increasing the efficiency using inexpensivee solutions. SynRel is a promising technology, which has features that are aligned with both research streams – high efficiency as well as lack of magnets [10], [12]. Leading manufacturing companies such as ABB (“Asea Brown Boveri”), KSB ("Klein, Schanzlin & Becker") and Siemens already started the serial production of the high efficiency SynRel. However, despite its advantages, there are still number of problems that are being investigated. From the machine design perspective, the main challenges of the topology come from the complex anisotropic structure of the rotor. Torque ripple, power factor and other secondary effects such as rotor iron losses, vibration and noise, are the main issues in SynRel [19], [20]. These issues mainly addressed using comprehensive analysis and optimization using FE. The proposed ideas and innovative techniques that are described in this thesis could significantly reduce time and effort required to design the SynRel machines. In some cases, it was shown that the time-consuming design optimization by means of FE can be bypassed. This is achieved by applying new dimensioning techniques, hence leading to a quick and effective design tools that is applicable for the wide power range machines

Novel sizing and modeling techniques for synchronous reluctance machines

In recent years, there is a growing interest for high efficiency electric motors without, or with reduce content of, permanent magnets (PMs) for industrial applications. The Synchronous Reluctance (SynRel) machine is one of the most promising candidates that can meet the requirements of efficient and low cost drive [1]. The key benefits of this technology are a rotor structure made of flux barriers and iron parts, without excitation coils or PMs, like in induction motors (IM) and PM machines, respectively [2]. This leads to a cost effective structure that is using the reluctance principle to generate torque. The reluctance machine topology was introduced in 1920s, however has not been utilised at high industrial volumes yet due to superiority of the alternative technologies. IMs are considered as an industry “work horse”, which dominates the electrical machines market in applications such as industrial fans, pumps and mill type loads, as it is known to be the cheapest and the most reliable machine topology. On the other hand, PMs are mostly used in high performance applications, where the power-density is of the priority. Whereas, the interest in SynRel is mainly driven by lack of magnets or any other field excitation, as well as high efficiency [3], [4], [5]. The rare-earth permanent magnets began to commercialize for electrical motors in early 1980s. Various types of applications such as electric vehicles, wind turbines, actuators, started utilization of the PM synchronous machines [6], [7], [8]. Neodymium-iron-boron (NdFeB) permanent magnets are the common type for the high-performance applications due to their superior magnetic properties. In comparison the remanent flux density Br and coercivity Hc values of NdFeB are higher than any other type of magnets i.e. samarium-cobalt (SM2Co17), which was the major breakthrough in 1970s [9], and it is still extensively used when operating temperatures are very high. The main downfall of the NdFeB is the cost. The prices of the Neodymium had a huge spike in the mid-2011, as it was increased by factor of 25 compared to the beginning of 2010 [10], [11]. After hitting its peak, the price dropped rapidly and settled at its pre-bubble price [12]. Such price instability had a huge financial effect on PM machine manufacturers. Hence, as of 2019, there is a high research 4 emphasis on electrical machines with low volume of rare earth permanent magnet material [13], [14]. There is also a growing interest in very high efficiency, or super-premium efficiency electrical machines for the industrial sector [2], [15], [16]. This is driven by new requirements of the local governments for the industrial sector, as well as the world trend towards the reduction of the energy consumption and greenhouse gas emissions [17], [18]. Currently world leading manufacturers and R&D institutions are constantly investigating the possibility of increasing the efficiency using inexpensivee solutions. SynRel is a promising technology, which has features that are aligned with both research streams – high efficiency as well as lack of magnets [10], [12]. Leading manufacturing companies such as ABB (“Asea Brown Boveri”), KSB ("Klein, Schanzlin & Becker") and Siemens already started the serial production of the high efficiency SynRel. However, despite its advantages, there are still number of problems that are being investigated. From the machine design perspective, the main challenges of the topology come from the complex anisotropic structure of the rotor. Torque ripple, power factor and other secondary effects such as rotor iron losses, vibration and noise, are the main issues in SynRel [19], [20]. These issues mainly addressed using comprehensive analysis and optimization using FE. The proposed ideas and innovative techniques that are described in this thesis could significantly reduce time and effort required to design the SynRel machines. In some cases, it was shown that the time-consuming design optimization by means of FE can be bypassed. This is achieved by applying new dimensioning techniques, hence leading to a quick and effective design tools that is applicable for the wide power range machines

Homothetic Design in Synchronous Reluctance Machines and Effects on Torque Ripple

This paper presents a novel design concept for Synchronous Reluctance (SynRel) machines aimed at reducing the torque ripple. Two general sizing approaches based on the homothetic scaling principle are defined and compared. An in depth analysis on the torque ripple, for a wide range of scaled geometries, evaluated by finite element, has been carried out at different operating conditions. A further analysis is performed on 4 scaled geometries that have been optimized starting from 4 different rotor geometries. It is shown that the main rotor geometrical variables converge to similar values for all scaled machines. The accuracy of the proposed model is then validated by comparing the FE simulated torque ripple waveforms with the experimental data carried out, for a range of operating conditions, on a machine prototype. The outcome of this work is a fast and accurate scaling technique for the preliminary design of SynRel machines with reduced torque ripple

Synchronous Reluctance Machines: A Comprehensive Review and Technology Comparison

In the last decade, the trend toward higher efficiency and higher torque density electrical machines (EMs) without permanent magnets (PMs) for the industrial sector has rapidly increased. This work discusses the latest research and industrial advancements in synchronous reluctance machines (SynRMs), being the emergent motor topology gaining wide acceptance by many industries. This article presents an extensive literature review covering the background and evolvement of SynRM, including the most recent developments. Nowadays, SynRM has found its niche in the EM market, and the reasons for that are highlighted in this work together with its advantages and disadvantages. The key journal publications in SynRM topics are discussed presenting the biggest challenges and the latest advancements with particular regards to the design methodology. This article aims to provide a thorough overview to the research community and industry about SynRM. There is a clear potential for SynRM to take over a significant portion of the EM market in the near future to meet efficiency standards in industrial applications without the use of rare-Earth PM technology

Hybrid Method for Optimization of Permanent Magnet Synchronous Machine (PMSM) Rotation using FA-ANFIS

PMSM uses the principle of Faraday's experiment by rotating a magnet in a coil by utilizing another energy source. When the magnet moves in the coil or vice versa. The rotation of the machine will change the flux of magnetic force on the coil and penetrate perpendicularly to the coil so that a potential difference arises between the ends of the coil. It is caused by a change in magnetic flux. The Firefly Algorithm (FA) method has been proven successful in overcoming system optimization problems. Modifying the FA is expected to improve its performance of the FA. To get the best control method, it is necessary to vary the speed control model. This study compares the PMSM speed control without a controller, PID Control, PID-FA, and PID-FA-ANFIS. The simulation results show that the best model on the PID-FA-ANFIS controller which is closest to the Speed Reff (2980 rpm) is that PID-FA-ANFIS obtains a rotation profile with the smallest undershot, the fastest steady state, the best output current profile, the best torque profile, and the best stress profile. The results of this study will be followed by other uses of artificial intelligence.    

Rapid Magnetic, Thermal and Structural Scaling of Synchronous Machines Based on Flux and Loss Maps

The paper introduces a rapid and accurate method for scaling Permanent Magnet Synchronous Machines using flux linkage and loss maps. The method enables the design and comprehensive characterization of scaled machines to meet new specifications for peak torque, power, maximum operating speed, voltage, and current requirements without the need for finite-element simulations. The efficiency map of the scaled machine can be computed with negligible computational effort. The analysis encompasses the scaling of the liquid cooling jacket setup and evaluates the continuous stall torque of the final machine. Furthermore, the method addresses scaling rules for demagnetization current limits, peak short-circuit currents and uncontrolled generator voltages, allowing the evaluation of the safest shut-down strategy against the different fault scenarios. The use of the stack length versus number of turns selection plane facilitates the visualization of the key performance figures and the minimization of the stack length while adhering to inverter voltage and current constraints. Overall, this scaling method offers a streamlined approach to the preliminary design of e-motors and facilitates system-level optimization studies. The method is showcased by scaling the e-motor of the BMW i3 to meet the specifications of the moto-generator 2 of the 4th generation Toyota Prius

Design and Control of Electrically Excited Synchronous Machines for Vehicle Applications

Electrically excited synchronous machines (EESMs) are becoming an alternative to permanent magnet synchronous machines (PMSMs) in electric vehicles (EVs). This mainly attributes to the zero usage of rare-earth materials, as well as the ability to achieve high starting torque, the effectiveness to do field weakening and the flexibility to adjust power factor provided by EESMs. Furthermore, in case of converter failure at high speed, safety can be improved by shutting down the field current in EESMs. The purpose of this study is to investigate the potential application of EESMs in EVs. To achieve this aim, several topics are covered in this study. These topics are studied to confront the challenges before EESMs could become prevalent and to maximumly use the advantages of EESMs for EV applications. In control strategies, the challenge is to properly adjust the combination of stator and field currents so that high power factor and minimum copper losses can be achieved. To tackle this, control strategies are proposed so that reactive power consumption and total copper losses are minimized. With the proposed strategies, the output power is maximized along the torque-speed envelope and high efficiency in field-weakening is achieved. In dynamic current control, due to the magnetic couplings between field winding and stator winding, a current rise in one winding would induce an electromagnetic force (EMF) in the other. This introduces disturbances in dynamic current control. In this study, a current control algorithm is proposed to cancel the induced EMF and the disturbances are mitigated. In machine design, high starting torque and effective field weakening are expected to be achieved in the same EESM design. To realize this, some criteria need to be satisfied. These criteria are derived and integrated into the design procedure including multi-objective optimizations. A 48\ua0V EESM is prototyped during the study. In experimental verification, a torque density of 10 N\ub7m/L is achieved including cooling jacket. In field excitation, a contactless excitation technology is adopted, which leads to inaccessibility of the field winding. To realize precise control of field current in a closed loop, an estimation method of field current is proposed. Based on the estimation, closed-loop field current control is established. The field current reference is tracked within an error of 2% in experimental verifications. The cost of an EESM drive increases because of the additional converter used for field excitation. A technique is proposed in which the switching harmonics are extracted for field excitation. With this technique, both stator and field windings can be powered using only one inverter. From all the challenges tackled in this study, it can be concluded that the application of EESMs in EVs is feasible

Synchronous Machines with High-Frequency Brushless Excitation for Vehicle Applications

Electrically excited synchronous machines (EESM) are becoming an alternative to permanent magnet synchronous machines (PMSM) in electric vehicle (EV) applications. This mainly attributes to the zero usage of rare-earth material as well as the capabilities of high starting torque and good field weakening provided by EESM. EESM also improves safety in case of converter failure at high speed. The prevalence of wireless power transfer (WPT) technologies enables the employment of high frequency brushless excitation in EESM. This reduces the friction loss and maintenance effort compared with traditional excitation through brushes and sliprings.Hence this study aims at investigating the potential of EESM with high frequency brushless excitation in EV applications. Modeling, design and control are the main aspects of interest in this study. Due to the varieties of different vehicle applications, this study covers the developments of three EESM drive systems, one for mild hybrid vehicles, one for electric passenger cars and one for heavy duty vehicles. To achieve a comprehensive understanding of the system, modeling is firstly studied. This includes the modeling of the machine as well as the modeling of the high frequency brushless excitation system. Nonlinear properties of magnetic material are taken into considerations. Based on the machine modeling, the vector loci of current, voltage, torque and power factor in dq-frame as well as the envelop in torque-speed map are derived analytically. One step further, algorithms to achieve unity power factor along with minimizations of copper loss or field current are studied. To achieve unity power factor at high speed, the field excitation needs to be stronger than the armature reaction.\ua0 The design of the system starts with profiling of the specifications for the three applications. The varieties in specifications lead to the differences in design strategies. This study adopts a general design procedure with interactions of FEM analysis and operation point iterations. Then the design strategies are established based on each set of design specifications to tune the parameters of the machine geometry accordingly. The design for mild hybrid vehicles emphasizes on widening the flux path. In terms of the design for electric passenger cars, a good balance is required between copper area and flux path. Comparisons between open-slot and closed-slot designs bring a trade-off of torque ripples and average torque. Adding ferrite to the top of rotor slots introduces a study of influence from the ferrite pieces to the field excitation. This includes a possible ease of local saturation in rotor and a reduction of copper losses etc. As for the machine design for heavy-duty vehicles, investigations show that, the adjustable field in EESM brings a significant benefit in field weakening operation.A 48 V EESM with high frequency brushless excitation for mild hybrid vehicles is prototyped. The experimental results of both machine and exciter are consistent with the FEM calculation results. This verifies the modeling and the methods that are applied in the design and analysis.One challenge for the prevalence of EESM is the difficulty to access the field winding after assembly. As a solution, an algorithm is developed to estimate the field winding current and temperature. The dc-link current is utilized as a feedback in the algorithm to correct the estimations. The current and temperature variations are tracked quite well. As one step further, a closed-loop field current control is established. The ability to track field current reference is experimental verified as well. This closed-loop field current control enables a complete dynamic closed-loop control of the EESM

MEMS Generator Study for an Embedded Energy Harvesting System

This work has been triggered by an industrial project targeting the development of a novel regulation system for a mechanical watch. Mechanical watches have been known for over a century as one of the finest example of energy autonomous devices, embodying an exceptional amount of human knowledge and high craftsmanship. Nevertheless, the accuracy of a mechanical timepiece keeps being significantly lower with respect to a quartz watch powered by a chemical battery. The aim of the study is thus filling such gap without compromising energy independence. The new regulation concept revolves around a small scale electromagnetic generator, the development of which is severely constrained at different levels. A major key point is miniaturization, which is needed in order allow the embedding of the generator in a watch movement. In fact, the overall size of the generator falls in the millimeter range, while some inner features might reach a micrometric critical dimension. A first important consequence is that not all the mathematical models that are used for conventional scale applications are suitable when it comes to the design of small scale devices. Another fundamental aspect concerns the technology associated to the fabrication of the device, which heavily affects the solutions that can actually be considered. In this sense, the adoption of the ensemble of the latest MEMS (acronym for Micro Electro Mechanical System) technologies plays a fundamental role. The research presented within this thesis aims to address such topics in the most comprehensive way as possible, with the ambition of providing scientific tools of general use. After a brief review of the state of art in the vast domain of microscale power generation, an electromechanical model for the time-dependent description of the dynamics of synchronous machines is derived. In this context, the main issues associated with size reduction are discussed in detail, with a particular emphasis on how the manufacturing technique affects the overall functionality of this class of devices. The model is then refined accordingly and used for the analysis of an existing MEMS machine. Then, the design of the MEMS generator for the watchmaking application is addressed. On the basis of the theoretical structure defined, an algorithm is conceived in order to perform the optimization of the device. The dissertation will then digress on the modeling and manufacturing of single layer planar coils. In this framework, two different fabrication processes, based on copper and aluminum respectively, are explored and the limits of each technology are compared. The experimental data resulting from this pilot study are then used for finalizing the design of the MEMS generator, in particular by determining the most suitable configuration among the ones identified by the optimization routine. The last part of the thesis will be dedicated to the fabrication and characterization of a functional prototype. In order to pursue this objective, the copper process that was already used for the single layer planar coils is upgraded for enabling the manufacturing of multilayer structures. Morphological and electrical measurements will be performed throughout all the fabrication process as well as on the final prototype