0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2016.2642891, IEEE Transactions on Industry Applications Analysis of Direct-On-Line Synchronous Reluctance Machine Start-up Using a Magnetic Field Decomposition Juha Tampio, Tero Känsäkangas, Student Member, IEEE, Saku Suuriniemi, Jere Kolehmainen Member, IEEE, Lauri Kettunen, and Jouni Ikäheimo Member, IEEE Abstract—Direct-on-line synchronous reluctance machines combine the characteristics of induction machines and syn- chronous reluctance machines. Saturation of core materials, the eddy currents, and the asymmetry of the rotor core and cage make it difficult to predict to which kind of loads a machine can synchronize. In this paper, the start-up of a direct-on-line synchronous reluctance machine is analyzed with a magnetic field decomposition that makes it possible to quantify and isolate forces between any two distinct parts of an electric machine using a transient time-stepping finite element field solution. The results show explicitly, which portion of the torque is produced by the rotor core and which by the rotor cage. Compared to conventional average torque analyses (also known as pseudo-constant-speed or quasi-steady state analyses) used to distinguish between the torque on the rotor core and cage, the proposed method makes no assumptions on the state of the machine. This results in a more detailed view of the starting transient. Index Terms—direct-on-line (DOL) start, eddy currents, finite element analysis (FEA), magnetic cores, magnetic fields, magnetic forces, magnetization, synchronous reluctance ma- chine (SynRM), synchronization, torque I. I NTRODUCTION T HE requirements for high efficiency IE4 (and possibly upcoming IE5) class electric machines are difficult to meet with traditional induction machines (IM) [2]. The technologies satisfying the high efficiency requirements are usually synchronous machines with variable speed drive (VSD), but there are high efficiency direct-on-line (DOL) J. Tampio is a Doctoral Student at the Department of Electrical Engineer- ing, Electromagnetics, Tampere University of Technology, Tampere, 33720 Finland (e-mail: juha.tampio@tut.fi). T. Känsäkangas is a Doctoral Student at the Department of Electrical Engineering, University of Vaasa, Vaasa, 65200 Finland and is working as a R&D engineer at ABB, Motors and Generators, Vaasa, 65320 Finland (e-mail: tero.kansakangas@fi.abb.com). S. Suuriniemi is an independent researcher and previously with the Tampere University of Technology, Tampere, 33720 Finland (e-mail: saku.suuriniemi@iki.fi). J. Kolehmainen is an Adjunct Professor of Rotating Electrical Ma- chines at the University of Vaasa, Vaasa, 65200 Finland, and is work- ing at ABB Motors and Generators, Vaasa, 65320 Finland (e-mail: jere.kolehmainen@fi.abb.com). L. Kettunen is a Professor of Computational Science at the Department of Mathematical Information Technology, University of Jyväskylä, FI-40014 Jyväskylä, Finland (e-mail: layrolke@jyu.fi). J. Ikäheimo is a Manager of Future Technologies at ABB, Motors and Generators, Vaasa, 65320 Finland (e-mail: jouni.ikaheimo@fi.abb.com). capable machines as well [2]. While most of the research interest in the field is focused on line-starting permanent magnet (LSPM) machines [3]–[5], it is evident that the direct- on-line synchronous reluctance machines (DOLSynRM), that do not require expensive rare earth metal magnets, are given more interest. There have been attempts to create line-starting SynRMs before [6]. The designs were heavily based on IM with flux barriers carved into the rotor while retaining the IM cage design. A new angle to design line-start SynRMs is to start from a traditional SynRM rotor, and fill-in the flux barriers fully with aluminium [7]. This design improves the steady state performance of the machine, but leads to weaker start-up properties. The direct-on-line start and synchronization capability of synchronous machines has been studied extensively [3]–[5], [7]–[11]. Apart from [4], [11], each of these publications divide the machine torque into asynchronous torque and bipolarly pulsating synchronous torque using the so-called average torque analysis (also known as pseudo-constant speed and quasi steady state analysis). Publications [4], [11] do not divide the torque into components. The average torque analysis assumes steady state operation at each rotor speed, respectively. This assumption rules out the possibility that electrical and mechanical transients can have an effect on the asynchronous and synchronous torque. One consequence of this is that asynchronous torque is constant at a given rotor speed. In this publication, the torque produced by a DOLSynRM during a start-up transient is analyzed using a magnetic field decomposition [12], [13]. It makes it possible to study forces between any two distinct parts of an electromechanical device in the time domain, while taking into account motion, mag- netic saturation and eddy currents. The presented decompo- sition is founded on the basic electromagnetic theory, which makes it a reliable and application independent analysis tool. When applied to DOLSynRM, the method makes explicit the contributions of the rotor core and cage to the torque regardless of the state of the operation of the machine. With this new information, a machine designer can better understand the DOLSynRM operation, and adjust the design to better satisfy the design goals. In this paper, Section II reviews the magnetic field and torque decomposition. Section III introduces the DOLSynRM simulation model. Moreover, the results of a successful and