Design of line-start permanent magnet synchronous machines using the Taguchi Method

Thesis (PhD)--Stellenbosch University, 2017.ENGLISH ABSTRACT: Future energy challenges and global environmental concerns urge the world to focus on energy efficiency programs more than ever. Energy efficiency improvement is an important way to address these challenges. Since motor-driven systems are responsible for approximately 40-50% of all electricity consumption in industry, a huge amount of energy saving can be realised by increasing electrical motor efficiency. Induction motors are still the most common electric machines used in industry. Although the performance of induction motors have been significantly improved over the years, the inherent limitation of induction motors such as relatively poor efficiency and power factor cannot be easily remedied. With the introduction of more stringent energy efficiency standard, electrical motor manufacturers worldwide increasingly focuses on alternative motor technologies. Amongst others, line start permanent magnet synchronous motor (LS PMSM) technology has received considerable attention. The distinct advantages of LS PMSMs such as self-start capability, high efficiency and power factor have made this type of motor very attractive. There has been extensive research work on LS PMSMs in literature, which mainly focused on the development of rotor topologies, improving the steady-state analytical model and the utilisation of transient time-step finite element method (FEM) for synchronisation analysis. Since an LS PMSM has a hybrid rotor containing both cage winding and PM arrays, the torque components for the transient start-up and steady state operation modes are different. To validate the synchronisation capability of an LS PMSM design, transient time-step FEM simulations are usually employed. However, this verification method is computationally expensive, thus limiting the possibility for designers to incorporate it into an optimisation procedure. There have been limited attempts to develop a design strategy which enabled machine designers to consider both transient and steady-states objectives. This study focuses on formulating a comprehensive design approach for LS PMSMs that can consider both steady-state and transient performance objectives in a multiobjective design optimisation procedure. This was achieved by incorporating the Taguchi method for robust design methodology in an iterative optimisation structure. The use of Taguchi method in electrical machine design is relatively new. The method differs from commonly used optimisation methods in that it analyses the results to locate a region where the performance objectives are most stable rather than searching for a definite point in the domain. Some key advantages of the Taguchi method are reduced sensitivity to initial conditions, lower parameter complexity and the relative ease in determining the subsequent conditions of the parameters in an iterative process. Traditionally, the Taguchi method is unsuitable for iterative and multi-objective design optimisation (MODO) problems. To address this limitation, an improved version of the regression rate methodology is incorporated into the Taguchi method for LS PMSM designs. It is shown that the proposed method can effectively take into account both steady-state and transient synchronisation performance in the design of LS PMSMs. The Taguchi based regression rate (TBRR) framework as presented in this thesis possesses the ability to simultaneous optimise both steady-state and transient performances of LS PMSMs. The MODO was solved by first establishing the competing relationship between the selected steady-state and transient performance objectives using a Pareto front solution, and then identifying the balanced design using the objective function for each topology. The successful implementation of the TBRR method using its robust design approach can be seen as the first use of this method to solve electrical machine related design problem. To validate the proposed method a prototype machine was designed, manufactured and experimentally evaluated. It shows that the proposed method can effectively take into account both steady-state and transient synchronisation performance in the design of LS PMSMs. The analytical calculation of the transient performance index shows good agreement with that of the measured one close to rated load conditions. It confirmed that the performance index of an LS PMSM could be used as a performance objective in design optimisation method. This thesis presented an alternative way of viewing machine design through the use of the Taguchi method for robust design. The unique attributes of this method and the effects it may have on machine design is still less known. The implementation capabilities of this method in various optimisation methods along with Dr Taguchi’s methodology is very promising. The TBRR method as presented in this thesis is just one of many possible design variants relying on the fundamentals of the Taguchi method to realise improved designs. The TBRR method as presented could find even broader applications in electrical machine design.AFRIKAANSE OPSOMMING: Toekomstige energie-uitdagings en omgewingskwessies vra die wêreld om nou, meer as ooit tevore op energie-doeltreffendheidsprogramme te fokus. Verbetering van energiedoeltreffendheid is ’n belangrike manier om hierdie uitdagings aan te spreek. Aangesien motor-aangedrewe stelsels verantwoordelik is vir ongeveer 40-50% van alle elektrisiteitsverbruik, kan ’n groot hoeveelheid energiebesparing gerealiseer word deur die verhoging van elektriese motors se doeltreffendheid. Induksiemotors is steeds die mees algemene elektriese masjiene wat in industrie gebruik word. Alhoewel die effektiviteit van induksiemotors oor die jare aansienlik verbeter het, kan die inherente beperking van die motors soos relatief swak doeltreffendheid en arbeidsfaktor nie maklik verbeter word nie. Met die bekendstelling van strenger energie-doeltreffendheidstandaarde, fokus elektriese motorvervaardigers wêreldwyd toenemend op alternatiewe motor tegnologië. Die direk-aan-lyn permanente magneet sinchrone masjien (DAL-PMSM) tegnologie het onder andere aansienlike aandag geniet. Die duidelike voordele van DAL-PMSMs soos self-begin vermoë, hoë doeltreffendheid en hoë arbeidsfaktor maak hierdie tipe motor baie aantreklik. Literatuur toon aan dat daar reeds baie navorsing gedoen is op DAL-PMSM’s, wat hoofsaaklik gefokus het op die ontwikkeling van rotor topologieë, die verbetering van die bestendige analitiese model en die gebruik van die eindige-element-metode (EEM) vir sinchronisasie-analise. Aangesien ’n DAL-PMSM ’n hibriede rotor het, wat beide n kourotor en permanente magnete bevat, is die wringkragkomponente vir die oorgangsen bestendige toestande verskillend. Om die sinkronisasievermoë van ’n DAL-PMSMontwerp te bevestig, word oorgangstyd-EEM-simulasies gewoonlik gebruik. Hierdie verifikasie metode gebruik baie bewerkingstyd, wat die moontlikheid vir gebruik in optimaliseringsprosedure beprek. Daar was egter enkele pogings in die verlede om ontwerpstrategië te ontwikkel wat masjienontwerpers in staat stel om beide toestande se doelwitte te oorweeg. Hierdie studie fokus op die formulering van ’n omvattende ontwerpbenadering vir DALPMSMs wat beide bestendige en oorgangse prestasie doelwitte in ’n multi-objektiewe ontwerps optimaliseringsprosedure kan oorweeg. Dit is behaal deur die Taguchi-metode vir robuuste ontwerpmetodologie in ’n iteratiewe optimaliseringsstruktuur in te sluit. Die gebruik van Taguchi-metode in elektriese masjienontwerp is relatief nuut. Die metode verskil van algemeen gebruikte optimaliseringsmetodes, omdat dit die resultate ontleed om ’n area te vind waar die doelwitte die mees stabiel is, eerder as om ’n bepaalde punt in die domein te soek. Enkele belangrike voordele van die Taguchi-metode is die verminderde sensitiwiteit van aanvanklike toestande, laer parameterkompleksiteit en die relatiewe gemak met die bepaling van die daaropvolgende toestande van die parameters in ’n iteratiewe proses. Tradisioneel is die Taguchi-metode onvanpas vir iteratiewe en multiobjektiewe ontwerpoptimalisering (MOO) probleme. Om hierdie beperking aan te spreek, vir DAL-PMSM-ontwerpe. Daar word aangetoon dat die voorgestelde metode effektief beide toestande se doelwitte in die ontwerp van DAL-PMSMs in ag kan neem. Die Taguchi gebaseer regressie-tempo (TGRT) raamwerk wat in hierdie proefskrif aangebied word, beskik oor die vermoë om gelyktydig beide die bestadigde en oorgangse doelwitte van DAL-PMSMs te optimaliseer. Die MOO is opgelos deur eers die mededingende verhouding tussen die geselekteerde doelwitte te vestig deur gebruik te maak van ’n Paretofront oplossing. Die gebalanseerde ontwerp is daarna geidentifiseer deur die doelwit funksie vir elke topologie te gebruik. Die suksesvolle implementering van die TGRT-metode met behulp van ’n robuuste ontwerpbenadering is die eerste gebruik van hierdie metode om elektriese masjienverwante ontwerpprobleme op te los. Om die voorgestelde metode te valideer, is ’n prototipe masjien ontwerp, vervaardig en eksperimenteel geëvalueer. Dit toon dat die voorgestelde metode beide die arbiedsfaktor en sinkronisasieprestasie kan optimeer in die ontwerp van DAL-PMSMs. Die analitiese berekening van die sinkronisasieprestasie-indeks toon goeie ooreenkoms met die gemete resultate by die gegewe lasvoorwaardes. Dit het bevestig dat die prestasie-indeks van ’n DAL-PMSM gebruik kan word as ’n prestasiedoelwit in ontwerpoptimaliseringsmetodes. Hierdie proefskrif het ’n alternatiewe manier van masjienontwerp bekyk deur die gebruik van die Taguchi-metode vir robuuste ontwerp te gebruik. Die unieke eienskappe van hierdie metode en die impak wat dit op masjienontwerp kan hê, is nog minder bekend. Die implementeringsvermoë van hierdie metode in verskeie optimaliseringsmetodes saam met Dr Taguchi se metodologie is baie belowend. Die TGRT-metode wat in hierdie proefskrif aangebied word, is net een van die vele moontlike ontwerpvariante wat staatmaak op die beginsels van die Taguchi-metode om verbeterde ontwerpe te realiseer. Die TGRT-metode soos aangebied kan selfs groter masjienontwerp toepassings vind