A Novel Concept of Ribless Synchronous Reluctance Motor for Enhanced Torque Capability

The rotor structure of synchronous reluctance machines (SynRel) is conventionally retained mechanically by iron ribs. In this paper a novel structure for high speed synchronous reluctance rotor is presented. The novelty of this work is the proof of a concept of SynRel machine without iron ribs. Structurally, the rotor iron lamination segments are embedded in an adhesive resin material with high temperature resistance and mechanical strength. Three four-pole SynRel machines have been designed with the target of improving motor torque, and compared for different ribs configuration. It has been shown that the proposed motor performs enhanced torque, power factor and efficiency with respect to conventional SynRel with iron ribs. An extensive sensitivity analysis of the ribless rotor geometry is carried out, followed by both mechanical analysis and experimental over speed test to guarantee its robustness above the operating speed range. The manufacturing procedure of this novel rotor is introduced. Finally, the experimental results on both SynRel prototypes are presented, showing the increase in torque, power factor and efficiency of the proposed solution. This work is a first step towards the definition of a viable and novel solution of SynRel machines with improved performance

Optimal rotor design of synchronous reluctance machines considering the effect of current angle

The torque density and efficiency of synchronous reluctance machines (SynRMs) are greatly affected by the geometry of the rotor. Hence, an optimal design of the SynRM rotor geometry is highly recommended to achieve optimal performance (i.e., torque density, efficiency, and power factor). This paper studies the impact of considering the current angle as a variable during the optimization process on the resulting optimal geometry of the SynRM rotor. Various cases are analyzed and compared for different ranges of current angles during the optimization process. The analysis is carried out using finite element magnetic simulation. The obtained optimal geometry is prototyped for validation purposes. It is observed that when considering the effect of the current angle during the optimization process, the output power of the optimal geometry is about 3.32% higher than that of a fixed current angle case. In addition, during the optimization process, the case which considers the current angle as a variable has reached the optimal rotor geometry faster than that of a fixed current angle case. Moreover, it is observed that for a fixed current angle case, the torque ripple is affected by the selected value of the current angle. The torque ripple is greatly decreased by about 34.20% with a current angle of 45 degrees compared to a current angle of 56.50 degrees, which was introduced in previous literature

Optimised Design of Permanent Magnet Assisted Synchronous Reluctance Machines for Household Appliances

This paper is focused on the design, optimisation and control of a permanent magnet assisted synchronous reluctance machine (PMaSynRel) for low cost high efficiency household appliances, in particular a motor for washing machine. The design and optimisation of the motor aims at maximising the torque produced and power factor, while minimise torque oscillations and the losses, thus improving the efficiency. A campaign of tests has been carried out on the prototype of the optimised machine, comparing finite element results and experimental measurements as a validation of the proposed design. In addition, torque ripple measurements are confirming that the solution proposed is meeting the optimisation design targets. The outcomes of this project are demonstrating that PMaSynRel drives are a suitable candidate for white goods sector, and that the proposed design is able to boost the performance and efficiency class with respect to the state-of-the-art solutions

A Digital Internal Model Current Controller for Salient Machines

The performance of anisotropic electrical machines is strongly dependent on the current loop characteristics. The problems for achieving robustness and fast response, without overshoot and oscillations, are mainly related to different values and behaviour of the direct and quadrature inductances (Ld, Lq), as well as to high output frequencies. In this paper, a novel current controller structure based on Internal Model Control (IMC) method is presented, taking into account the magnetic anisotropy (Ld != Lq). The model of salient machines is derived directly in the discrete domain and used to obtain a model-based controller. The controller derivation does not rely on transport-delay approximations, which enables improved decoupling of axes dynamics and the closed-loop robustness for very high output frequencies. The presented controller enables enhanced response for higher current loop bandwidth and output frequencies than the state-of-the-art methods. The experimental verification is performed on a 3-phase synchronous machine, using a standard industrial 3-phase inverter

Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine

Optimal performance of the electric machine/drive system is mandatory to improve the energy consumption and reliability. To achieve this goal, mathematical models of the electric machine/drive system are necessary. Hence, this motivated the editors to instigate the Special Issue “Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine”, aiming to collect novel publications that push the state-of-the art towards optimal performance for the electric machine/drive system. Seventeen papers have been published in this Special Issue. The published papers focus on several aspects of the electric machine/drive system with respect to the mathematical modelling. Novel optimization methods, control approaches, and comparative analysis for electric drive system based on various electric machines were discussed in the published papers

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