Analysis andevaluation of brush-DCequivalent controlled multiphase cage induction machine drive

[摘要] ENGLISH ABSTRACT: The multiphase induction machine drive has been under investigation for the last half century.Although it offers several attractive advantages over the conventional three-phase induction machinedrive, it is restricted to highly specialised applications. One aspect of the multiphase inductionmachine drive is the complexity of the control algorithm for decoupled flux and torque control. Thecomplexity, arising from the required coordinate transformations, increases with increase in thenumber of phases of the machine. Recently, a method that allows the control of a six-phase inductionmachine drive without any coordinate transformations was developed and tested. This new controltechnique allows the control of the machine to be similar to that of dc machines through the use ofspecial trapezoidal-shaped stator current waveforms. These stator phase current waveforms consist offield (flux) and torque current components, with flat-topped amplitudes allowing a stator phase to actalternately in time as either a flux or a torque producing phase. The idea is to have a number of statorphases acting as flux producing phases, whilst the remaining phases act as torque producing phases ateach time instance. This dissertation takes a further step in the research on this particular controltechnique. As the control method relates directly to the brush-dc machine operation, in thisdissertation, the control method is defined as a 'brush-dc equivalent (BDCE) control method.First, in this dissertation, a simple analytical method is developed to determine a defined optimalratio of the number of field to the number of torque phases of a multiphase induction machine thatutilises trapezoidal stator current waveforms. The method is applied to induction machines with up tofifteen stator phases. Finite element analysis is used to verify the validity of the developed criterionand to verify the square-like air gap flux density.Secondly, in this dissertation, an analytical method for predicting and evaluating the rotor barcurrent waveform of a cage multiphase induction machine is proposed. The method is based on theFourier transform and the winding function theory under linear condition assumptions. The methodalso allows for the calculation of the electromagnetic torque and rotor bar losses. Skin effect isconsidered in the calculation of the rotor bar resistance of the machine. Again, finite element analysisis used to verify the analytically calculated results. The developed method can be expanded and usedto evaluate the rotor current waveform of any multiphase induction machine supplied with any statorcurrent waveforms.The BDCE control method is implemented on a prototype nine-phase cage-rotor induction machinedrive. A nine-phase inverter and control system are developed for supplying the nine-phase inductionmachine with the trapezoidal stator current waveforms. Rotor current waveform measurements aretaken on a specially designed rotor to verify the analytically predicted waveform. The linearrelationship of the developed torque and torque current of the proposed BDCE control method isverified through measurements. Through the comparison of analytical calculated results with finiteelement calculated and measured results, it is shown in this dissertation that the developed analyticaltechniques can be used in the design and performance analysis of multiphase induction machines.Also, from the results, it is clear that the new control technique works remarkably well even in the fluxweakening region. However, outstanding aspects, such as efficiency and generated torque quality ofthe proposed drive still need to be investigated further.

[发布机构] Stellenbosch University