An important barrier to the adoption and acceptance of synchronous reluctance (SyR) machines in different applications lies in their non-standardized design procedure. The conflicting requirements incurring at high speeds among electromagnetic torque and structural and thermal limitations can significantly influence the machine performance, leading to a real design challenge. Analytical models used for design purpose lack in accuracy and force the designer to heavily rely on finite element analysis (FEA), at least during the design refinement stage. This becomes even more computationally expensive as the speed increases, as the evaluation of the rotor structural behaviour is required. This work presents a computationally efficient hybrid analytical-FE design process able to consider all the main limiting design aspects of SyR machine incurring at high speed, namely structural and thermal. As a vessel to investigate the proposed design routine accuracy, several high speed SyR machines have been designed for a wide range of operational speeds (up to 70krpm). The thermal and mechanical factors limiting the high speed operation are deeply analyzed aiming at maximize the mechanical output power. The proposed design approach is then validated by comparison against experimental measurements on a 5kW-50krpm SyR prototype. Index Terms-Analytical design, finite element analysis, high speed, iron bridges, iron losses, structural rotor design, synchronous reluctance machines.
A general middle complexity model of electromagnetic devices is applied to a cage induction motor. Such modelling approach has been simplified and adapted in order to pursue a fair representation of the electrical machine. Particular attention was given to the rotor cage, proposing a simplified representation exploiting the symmetry of the cage itself. A comparative analysis vs the results provided by a finite element model is also presented for validation purposes aiming to assess the accuracy of the proposed method.
In many industrial applications the self-starting capability of electric motors is still an important requirement enabling to simplify the drive architecture and increase the system's reliability. The efficiency improvement of this motor topology has been targeted by various national and international regulatory authorities with ad-hoc policies. Indeed, a lower energy consumption leads to the twofold benefits of reducing the operational costs and the CO2 emissions. The adoption of a copper cage has been successfully proven to reduce the motor losses. However, this could affect other performance indexes, such as the starting torque. In this paper, the advantages and drawbacks of adopting a copper cage are analysed in depth by comparing the motors performance at different operating conditions, with respect to the more common aluminium cage. Starting from a set of induction machines optimized with an aluminium cage, the effect of the direct material cage substitution is analysed both in terms of electromagnetic and thermal aspects. The overall performance are also compared against machines specifically optimized with a copper cage. With the presented performance comparison exercise, general design guidelines are outlined aimed at improving the efficiency without deteriorating other performance metrics.
The rotor slot geometry of a squirrel cage induction motor plays the most important role in defining the torquespeed characteristic when the power supply is directly provided by the main grid. In this paper it is shown how the rotor slot geometry can be optimised to satisfy different electromechanical requirements, depending on specific applications. This work, the second of two companion papers, briefly recalls the novel systematic approach, proposed in Part I, to perform the optimization of squirrel cage induction motors. Here, the optimization results achieved satisfying a wide spectrum of requirements are analysed in depth. Furthermore, the trade-off among the several performance indexes and their correlation with the geometrical parameters is discussed. The possible advantages and disadvantages of adopting a copper cage is also quantified for all possible performance requirements. The influence of the motor thermal behaviour and harmonic losses on the overall performance are also discussed allowing to validate the proposed design optimization procedure and its results. The outcomes of this work are opening to new design approaches that enable to optimise the performance of one of the most popular electrical machines adopted in industry, the squirrel cage induction motor.
Nowadays the Finite Element Analysis (FEA) represents the most accurate tool available to investigate the electromagnetic operation of electric machines. However, when induced currents have to be calculated, such as in Squirrel-Cage Induction Machines (SCIM), a transient analysis may require a long elaboration time. Such issue is exacerbated when the machine features a skewed stator or rotor, since this requires at least a 2D multi-slice approximated analysis or even ultimately a full 3D model. In this paper, a general analytical method for modeling electromagnetic devices is applied to an industrial SCIM featuring a skewed rotor structure. The modeling approach is wisely implemented to pursue a fair balance between accuracy of the analysis and computational burden, taking advantage of all the symmetries existing in the structure of the machine to minimize the complexity of the model. The results provided by the model developed are compared with respect to the corresponding values provided both by FEA and by experimental tests carried out on the reference machine. Such comparison shows that the proposed model is actually able to achieve a pretty good balance between accuracy and computational efficiency.
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