High-speed Synchronous Reluctance Machines Research Articles

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 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 70 krpm). 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 5 kW-50 krpm SyR prototype.

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

This paper 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 non-linearities, 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 multi-physics 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 a 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 6.5kW, 80krpm SyR machine prototype.

Analytical Power Limits Curves of High-Speed Synchronous Reluctance Machines

The aim of this paper is to tackle the design of synchronous reluctance machines with transverse laminated rotor for high-speed applications by means of an analytical model. In high-speed applications, the mechanical design greatly affects the motor performance in terms of torque density and power factor. In fact, as the rated speed increases, the radial ribs thicknesses increase as well to ensure the rotor structural integrity against the centrifugal force. This increases the quadrature flux and, therefore, the rotor anisotropy gets worse. Hence, the optimal rotor design is the result of a compromise between mechanical and magnetic aspects. The purpose of this paper is twofold: First, to develop an analytical model that links the maximum average torque to the rated speed, and second, to determine the maximum power that can be generated by a specific rotor geometry. The analytical approach allows a fast motor design and analysis so that a rapid extrapolation of the results to different machine size is possible. Finite element analysis is used only to validate the final results.

Synchronous Reluctance Machine Optimization for High-Speed Applications

The synchronous reluctance machines with transversally laminated rotor and multi flux barriers per pole reach a high torque density, so that they are proposed as a valid alternative to permanent magnet machines. Such machines have been analyzed for different applications, mainly home appliance, industrial tool, traction, up to low-speed high-power generators. On the contrary, the use of synchronous reluctance machines for high-speed applications remains almost unexplored yet. The aim of this paper is to investigate the potential of a high-speed synchronous reluctance machine. An optimization is carried out so as to maximize the machine performance (high power, proper power factor, low vibration) at a given speed. The machine size is fixed and the focus is on the rotor geometry, with the purpose of maximizing the electromagnetic torque, according to the necessary thickness of the ribs. It is shown that, even if the ribs are thick, it is possible to reach a proper torque density. It is shown that different solutions exist, which allow to reach high torque and minimum torque ripple. However, the optimal solutions are quite sensitive to the geometrical variations, so that a particular care is required in the manufacturing of the machine. Finally, the power limit of the synchronous reluctance motor with barrier rotor is found.

Design methodology for high‐speed synchronous reluctance machines

This study presents two design methodologies for high-speed synchronous reluctance (REL) machines. The interest for high-speed drives comes from the request for compactness and high efficiency. The synchronous REL motors have been widely studied for several applications, but a coherent design procedure for high speed has not been proposed in the literature. The study proposes some analytical procedures to get an initial design. Then the rotor geometry optimisation through a differential evolution algorithm is described. Finally, a design example is given and thoroughly analysed using these two approaches.

Design Optimization of a High-Speed Synchronous Reluctance Machine

Synchronous reluctance machines, including the permanent-magnet-assisted variants, are competitive motor topologies if the application requires high efficiency and a cost-effective solution with a high flux-weakening capability. However, increasing operating speeds incur challenging design and development decisions, mainly in order to find design solutions that ensure the machine's structural integrity without compromising the overall performance. In this paper, a comprehensive design procedure for high-speed synchronous reluctance machines is presented. In order to validate the procedure, a 5-kW 80 000-r/min machine is considered. The proposed strategy consists of a two-step procedure in which the electromagnetic and structural designs have been properly decoupled, dividing the design space in two subsets. Each subset mainly affects the electromagnetic or the structural performances. Several structural design optimizations have been then performed with the aim of finding the optimal tradeoff between the rotor geometrical complexity (that defines the required computational resources) and the electromagnetic performance. The reported experimental tests of the prototyped machine validate the proposed design strategy, which can be used as general guidelines on the structural design of synchronous reluctance machines.

Robust Control of High-Speed Synchronous Reluctance Machines

High-speed regimes allow an increase in the power density of electrical drives, which is a necessary characteristic in aeronautical applications. In such a context, together with the typical nonlinearities of low-speed drives, i.e., core saturation, phenomena related to high fundamental to sampling frequency ratios appear increasingly significant. This paper applies methodologies based on modern robust control to high-speed synchronous reluctance machines. The proposed method is based on a reformulation of the motor model as a linear parameter varying system. This allows transforming the current controller design in a multivariable optimization problem, which is solved with efficient numeric tools. The mathematical formulation of a robust digital controller directly designed in the discrete time domain is proposed. The controller performance are experimentally compared to of its counterpart designed in the continuous-time domain, and subsequently, discretized, as proposed in a previous work by the same authors, to have agreement a more standard decoupled current control using proportional-integral regulators. Results demonstrate the effectiveness of the proposed controller structure in current regulation, especially at high-speed regimes.

Design of a 50.000-r/min Synchronous Reluctance Machine for an Aeronautic Diesel Engine Compressor

This paper describes the design procedure followed to realize a high-speed synchronous reluctance machine for aeronautical application. The attention is mainly focused on the rotor design that is the most critical part of any synchronous reluctance machine; in particular for high-speed applications. After a preliminary optimization of the rotor geometry, a multiphysical design that considered mechanical, thermal, and electromagnetic properties was developed. The main steps of the design procedure together with an extensive analysis of the final design are presented here. Two prototypes have been realized using different rotor lamination materials in order to validate the design procedure.

A magneto-thermal study of a high-speed synchronous reluctance machine

The paper presents a magneto-thermal model of a high-speed synchronous reluctance machine (SRM). Both magnetic and thermal aspects are described using two-dimensional and three-dimensional finite-element method for machine modeling. Additional current harmonics losses, friction losses, and convective exchange coefficients at high speed are estimated. Finally, test results on a 20kW, 20 000rpm SRM are reported and compared with the simulation results.

Nonlinear modeling and robust control of synchronous reluctance motors

High speed synchronous reluctance machines can be used in electric drives and power generation systems. This paper develops nonlinear mathematical models for synchronous reluctance motors using the machine ( abc) variables as well as the quadrature, direct and zero ( qd0) variables. Kirchhoff’s and Newton’s laws are used to derive the differential equations that describe the circuitry and torsional–mechanical dynamics. The Park transformation is applied in the model developments to derive the nonlinear differential equations in the rotor reference frame. As complete, highly coupled, nonlinear mathematical models are found, synchronous reluctance motors should be controlled to attain the desired performances in the full torque-speed operating envelope. Hence, controllers must be designed. A robust controller with nonlinear error and state feedback mappings is designed to guarantee robust tracking and to ensure stability, as well as to attain disturbance rejection. The reported straightforward and computationally efficient synthesis procedure is based on the well understood nonlinear feedback mappings and Lyapunov stability theory. Innovative results in modeling, simulation analysis and design are applied to control electric drives driven by three phase synchronous reluctance motors.

High-speed synchronous reluctance machine with minimized rotor losses

This paper presents a refined design of a high-speed synchronous reluctance machine with minimized eddy-current losses in the rotor. Design criteria are high power capability, ability of the rotor to withstand high speeds, ability to operate in vacuum, negligible zero-torque spinning losses, high reliability, high efficiency, and low manufacturing cost. The rotor of the synchronous reluctance machine consists of bonded sections of ferromagnetic and nonmagnetic steels. A finite element code, incorporating rotor rotation, has been developed in MATLAB that calculates steady-state motionally-induced eddy currents (and losses) in the rotor. A stator iron and stator winding have been designed to minimize rotor losses, and two such prototype machines have been fabricated. Experimental results show an efficiency of 91% at a 10 kW, 10000 rpm operating point, and negligible rotor heating.