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Title: Pulse width modulation control of dual-inverter supply for five-phase variable-speed drives
Author: Satiawan, I. Nyoman Wahyu
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2012
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Abstract:
Three-phase multi-level topologies have been drawing increased attention in the past two decades. The numerous advantages of multi-level supply include: good power quality (low voltage distortion and dv/dt), good electromagnetic compatibility, operation with a lower switching frequency (lower switching losses), high voltage capability, smaller common mode (CM) voltage (reducing the stress in the motor bearings). There are various topologies of multilevel converters. The main ones are the neutral point clamped (NPC), the flying capacitor (FC) and the cascaded converters. Another alternative is the dual two-level inverter configuration supplying an open-end winding machine. This topology has received growing attention due to its simple structure. The open-end topology has the advantages that the additional diodes used in the neutral- point-clamped (NPC) voltage source inverter (VSI) are not needed, leading to a saving in the overall number of components. Furthermore, the issue of proper capacitor voltage balancing does not exist if the supply is two-level at each winding side. Application of such a dual-inverter supply (with equal DC-links) enables drive operation with voltage waveform equivalent to the one obtainable with a three-level VSI. The advantages of multi-phase variable speed drives over the three-phase ones are numerous and include an increase of fault tolerance, the possibility to have several multi-phase machines connected in series and drive them independently with a single VSI and, when the machine is equipped with a concentrated winding, other, higher harmonics can also be used to increase the developed torque. This thesis explores the possibility of combining the multi-phase and open-end- winding multi-level topologies. In particular the five-phase open-end-winding topology is considered. General properties of the five-phase AC motor drives with sinusoidal winding distribution are at first reviewed, along with the previously developed two- level space-vector modulation algorithm for a five-phase two-level VSI. A mathematical model of the converter is developed and a detailed study of the available switching states and corresponding voltage space vectors is conducted. It is shown that, due to the large number of switching states available in the topology together with the additional requirements when driving a multi-phase machine, the design of a suitable modulation scheme is extremely challenging. Three different space-vector modulation methods are proposed in the thesis. The developed methods are relatively simple to implement since they consider each inverter individually hence breaking down the problem into one of simpler complexity. The three modulation methods and the performance of the five- phase drive are verified using simulations. Finally, a laboratory prototype is described, which utilises two two-level five- phase inverters connected across an open-end-winding five-phase induction machine. The three modulation schemes are implemented using a fast prototyping control system (dSP ACE) and the performance of the modulation techniques is compared. The motor is controlled in V/fmode, in open loop. It is demonstrated that two of the methods produce multi-level output waveforms and that one method offers superior performance, with reduced converter losses.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.585478  DOI: Not available
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