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3. FUNDAMENTALS <strong>OF</strong> DVR Mustafa İNCİ 3.2.2. Use of Converters in DVR Numerous circuit topologies which are used for different functions are available for the DVR. These are: inverters, rectifiers, AC-AC converters and DC- DC converters. 3.2.2.1. Inverters The most common inverter topologies are the two- or three-level three-phase converter where the dc-side capacitor(s) is connected alternately to all ac phases. The purpose of this capacitor is to mainly absorb harmonic ripple and, hence, it has a relatively small energy storage requirement, particularly when operating in balanced conditions. The size of this capacitor has to be increased, if needed, to provide voltage support in unbalanced conditions. Also, since the capacitor is shared between the three phases, sag on only one phase may cause a distortion in the injected current waveforms on the other phases (Al-Hadidi et al., 2008). Another popular converter topology is the H-bridge cascade inverter. A single phase of this converter is shown in Figure 3.3. Converters with this topology are suitable in power systems applications due to their ability to synthesize waveforms with reduced lower order harmonics and to attain higher voltages with a limited maximum device rating. The principal of operation for this topology is that each capacitor can be connected by means of the insulated-gate bipolar transistor (IGBT) switches so that its voltage contributes positively or negatively or not at all to the output waveform. This makes the control more complex in comparison with conventional two- or three-level converters. However, in contrast to such conventional topologies, the multilevel offers the following significant advantages (Al-Hadidi et al., 2008). 1) Modularized circuit layout and packaging are possible because each level has the same structure. Increasing or reducing the number of modules permits the converter to be designed for any arbitrary voltage level in a straightforward manner. 17
3. FUNDAMENTALS <strong>OF</strong> DVR Mustafa İNCİ This also allows for the removal of the series transformer, thereby reducing size and cost. 2) Each bridge can be controlled independently permitting efficient singlephase voltage compensation. 3) The aspect of particular interest in this paper is the inherent energy storage capability of the capacitors which makes this topology ideal for the transient injection of real power. It is true that the H-bridge cascade topology requires larger capacitors due to second harmonics ripple on the capacitors, which could be seen as a disadvantage in comparison with traditional two- or three-level three-phase converters. However, the larger capacitors also provide additional energy storage capability which, if exploited, could turn this disadvantage into an advantage. The principle contribution of this paper is to devise a new control method that exploits the inherent stored energy of the capacitors in the most efficient manner to prolong the duration over which large unbalanced sags can be compensated (Al-Hadidi et al., 2008). Figure 3.3. H-Bridge Inverter A multilevel converter was proposed to increase the converter operation voltage, avoiding the series connection of switching elements. However, the multilevel converter is complex to form the output voltage and requires too many back-connection diodes or flying capacitors (Han et al., 2006). For higher power applications, power-electronic devices are usually connected to the medium-voltage (MV) grid and the use of two-level voltage 18
Page 1 and 2: ÇUKUROVA UNIVERSITY INSTITUTE OF N
Page 3 and 4: ABSTRACT MSc THESIS MODELING AND AN
Page 5 and 6: ACKNOWLEDGEMENTS First and foremost
Page 7 and 8: 3.2.2.1. Inverters ................
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Page 12 and 13: LIST OF FIGURES PAGES Figure 1.1. D
Page 14 and 15: Figure 5.3. Injected voltages by us
Page 16 and 17: LIST OF SYMBOLS C : DC Link Capacit
Page 18 and 19: LIST OF ABBREVATIONS A AC APF ASD C
Page 20: 1. INTRODUCTION Mustafa İNCİ 1. I
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Page 25 and 26: 2. POWER QUALITY Mustafa İNCİ 2.1
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4. MODELING OF PROPOSED DVR Mustafa
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5. SIMULATION RESULTS AND CASE STUD
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6. CONCLUSION Mustafa İNCİ 6. CON
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6. CONCLUSION Mustafa İNCİ • En
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DELFINO, B., FORNARI, F., PROCOPIO,
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KARIMI-GHARTEMANI M., IRAVANI M.R.
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OĞUZ, G., 2004. Performance Of A D
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TESTA A., AKRAM M.F., BURCH R., CAR
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BIOGRAPHY Mustafa İNCİ was born i
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APPENDIX 123
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LIST OF PUBLICATIONS International
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