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

[摘要] 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 importantway 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 stillthe 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 easilyremedied.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 receivedconsiderable 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 synchronisationanalysis. 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 modesare different. To validate the synchronisation capability of an LS PMSM design, transienttime-step FEM simulations are usually employed. However, this verification method iscomputationally expensive, thus limiting the possibility for designers to incorporate itinto 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 PMSMsthat can consider both steady-state and transient performance objectives in a multiobjectivedesign optimisation procedure. This was achieved by incorporating the Taguchimethod for robust design methodology in an iterative optimisation structure. The use ofTaguchi method in electrical machine design is relatively new. The method differs fromcommonly used optimisation methods in that it analyses the results to locate a regionwhere the performance objectives are most stable rather than searching for a definitepoint in the domain. Some key advantages of the Taguchi method are reduced sensitivityto initial conditions, lower parameter complexity and the relative ease in determining thesubsequent conditions of the parameters in an iterative process. Traditionally, the Taguchimethod 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 synchronisationperformance in the design of LS PMSMs.The Taguchi based regression rate (TBRR) framework as presented in this thesis possessesthe ability to simultaneous optimise both steady-state and transient performancesof LS PMSMs. The MODO was solved by first establishing the competing relationship betweenthe selected steady-state and transient performance objectives using a Pareto frontsolution, and then identifying the balanced design using the objective function for eachtopology. 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, manufacturedand experimentally evaluated. It shows that the proposed method can effectively takeinto account both steady-state and transient synchronisation performance in the designof LS PMSMs. The analytical calculation of the transient performance index shows goodagreement with that of the measured one close to rated load conditions. It confirmedthat 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 useof the Taguchi method for robust design. The unique attributes of this method and theeffects it may have on machine design is still less known. The implementation capabilitiesof this method in various optimisation methods along with Dr Taguchi's methodologyis very promising. The TBRR method as presented in this thesis is just one of manypossible 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.

[发布机构] Stellenbosch University