High Speed Synchronous Reluctance Machines: Modeling, Design and Limits

An important barrier to the adoption and acceptance of synchronous reluctance (SyR) machines in different applications lies in its 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 computational expensive as the speed increases, as the evaluation of the rotor structural behaviour is required. This work presents a computational 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

High Speed Permanent Magnet Assisted Synchronous Reluctance Machines - Part I: A General Design Approach

The design of synchronous reluctance machines with and without permanent magnets assistance constitutes a challenging engineering task due to the numerous design variables and performance indexes to be considered. The design complexity increases even further when the application requires high speed operation, with consequent rotor structural constraints and and related effects on the electromagnetic performance. Structured as two-parts companion papers, this first part proposes a comprehensive design procedure able to consider all the non-linear aspects of the machine behaviour, greatly reducing the number of independent design variables, without worsening the computational burden. In particular, the non linear behaviour of the rotor iron ribs and the effect of the permanent magnets on the structural design are all taken into account with the proposed iterative design procedure targeting the achievement of a desired power factor. The proposed method will be then used to draw some preliminary design considerations highlighting the several trade-offs involved in the design of high speed permanent magnet assisted synchronous reluctance machine. Part I is setting the theoretical bricks that will be further expanded and experimentally validated in the companion paper Part II

High-Speed Synchronous Reluctance Machines: Materials Selection and Performance Boundaries

This article presents a comprehensive comparative design exercise of synchronous reluctance (SyR) machines considering different soft magnetic materials and a wide range of speeds. First, a general design methodology able to consider all the consequences of selecting different materials is presented. In fact, magnetic nonlinearities, rotor structural limitations, and the rise of both stator and rotor iron losses are all considered. The adopted design approach allows achieving optimal stator and rotor geometries balancing all these competitive multiphysics aspects and keeping constant the cooling system capability. Both silicon–iron (SiFe) and cobalt–iron (CoFe) alloys with optimized magnetic and mechanical performance are examined to assess the maximum capabilities achievable with an SyR machine technology. The adoption of CoFe alloys leads to machines that outperform the SiFe counterparts up to a certain speed, above which, machines with SiFe provide better performance. Indeed, in the lower speed range, the effect of the higher saturation flux density of the CoFe materials is dominant, while for higher design speeds, their higher iron losses and lower yield strength, with respect to the SiFe ones, make the latter more convenient. All the design considerations are finally validated by comparing the predicted performance with the experimental test results on a 6.5-kW, 80-kr/min SyR machine prototype

Permanent Magnet Assisted Synchronous Reluctance Machine Design for Light Traction Applications

This paper presents a systematic comparative design study of permanent magnet assisted synchronous reluctance (PMaSyR) machines for a light traction application aimed at considering an holistic approach for a given outer envelope and cooling system specification. Electromagnetic, structural and thermal aspects are all accurately considered in a computationally efficient manner using a hybrid analytical-finite element (FE) design approach. The SyR machine geometries providing the maximum torque with increasing number of poles are identified and their performance deeply investigated with full FE analysis. The study has been carried out considering several requirements in terms of base and maximum speeds with the aim of drawing general design considerations. Results reveal that the optimal pole number from a torque perspective depends on the considered maximum speed. The reasons behind this behavior are fully investigated as well as how and why the optimal geometries change. The optimal SyR machines are then compared also considering the insertion of permanent magnets within the rotor slots with the aim of maximizing the constant power speed range. The rationales behind the selection of the machine to manufacture are then outlined including aspects related to efficiency and demagnetization under the worst short circuit condition in the entire torque-speed range. The optimized machine (after a FE-based design refinement) has been manufactured and tested on an instrumented test bench validating the proposed design approach and the deduced design insights

Fast Torque Computation of Hysteresis Motors and Clutches Using Magneto-static Finite Element Simulation

Hysteresis motor and clutches have several advantages, such as constant torque from zero to synchronous speed, low torque ripple, and low fabrication cost. Low efficiency and power factor are the main features that have limited the application of this type of electrical machine to few applications. Being a niche argument, little literature has addressed the problem of analytical and finite element (FE) modelling of hysteresis electrical machines. This paper first describes the most important contributions of the literature on the analytical and FE modelling of hysteresis motors and clutches and then proposes a method for the fast computation of its performance. The proposed procedure consists of two steps: first, a magneto-static FE simulation is performed considering the normal magnetization curve of the hysteresis material; then, the average torque is computed by a post-processing analysis. The proposed method is used to analyze a hysteresis clutch and the obtained results are compared with those achieved using a commercial finite element software that implements a vector hysteresis model

Influence and compensation of the stator flux on the direct flux control sensorless technique for PMSMs

Abstract Several techniques exploiting machines anisotropies have been proposed in literature for sensorless control of synchronous machines. Among them, the direct flux control (DFC) technique allows estimating the electrical rotor position by exploiting the zero‐sequence voltage of the machine. This work aims at analysing the effects of magnetic saturation on the application of the DFC technique to permanent magnet synchronous machines. This effect is present when stator flux is controlled during machine operation, leading to an error in the estimation of the electrical rotor position. Starting from an analytical model of the machine phase inductances, a complete mathematical description of the DFC technique is derived and presented. The proposed mathematical model shows how the estimated electrical rotor position is biased when operating under load conditions. Moreover, the result of the analysis of the DFC technique allows to refine the obtained estimate and to reduce the electrical rotor estimation error. Experimental results on a test motor are provided in order to verify and support the proposed mathematical model and technique