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3. FUNDAMENTALS <strong>OF</strong> DVR Mustafa İNCİ phase itself further worsens the severity of the sag. Additionally, these schemes cannot provide phase correction, as sags are generally accompanied by phase jumps (Subramanian et al., 2010). 3.2.3. Energy Storage Energy storage is required to provide real power to the load when large voltage sags take place. Examples of energy storage are lead-acid batteries, flywheel, superconducting magnetic energy storage (SMES), etc. For SMES, batteries and capacitors, which are dc devices, solid-state inverters are used in the power conversion system to accept and deliver power. For flywheels, which have rotating components, ac-to-ac conversion is performed. The energy storage devices used for this study are lead-acid batteries. Batteries provide rapid response for either charge or discharge, but the discharge rate is limited by chemical reaction rates so that the available energy depends on the discharge rate. Generally, the DVR has several operating states (Zhan et al., 2001). 1) When a voltage sag/swell occurs on the line, the DVR responds by injecting three single-phase voltages in synchronism with the network voltages. Each phase of the injected voltages can be controlled independently or together in magnitude and phase. The DVR draws active power from batteries and supplies this together with reactive power to the load (Zhan et al., 2001). 2) When the voltage supply is operating under normal conditions, the DVR operates in a standby mode if the battery is fully charged; or the DVR operates in the self-charging control mode if the batteries need to be recharged (Zhan et al., 2001). 3) In the event of a fault or short circuit downstream, the DVR (specifically, the VSI) must be protected against overcurrent flowing through the power semiconductor switches. The rating of the DVR inverters is the limiting factor for normal load current seen in the primary windings and reflected in the secondary windings of the series insertion transformer. For line currents exceeding the inverter rating, a bypass scheme is incorporated to protect the power electronics (Zhan et al., 2001). 23
3. FUNDAMENTALS <strong>OF</strong> DVR Mustafa İNCİ 3.2.4. Injection Transformer The main purpose of the injection transformer is to boost the voltage supplied by the filtered VSC output to the desired level while isolating the Series Compensator circuit from the distribution network (Perera et al., 2006). The injection transformers not only reduce the voltage requirement of the inverters, but also provide isolation (Ghosh et al., 2002). In addition, the injection transformer is a special purpose transformer that has the ability to limit the coupling of noise and transient energy from the primary side to the secondary side (Zhan et al., 2001). The MVA rating is determined by using power calculation equation by (3.1) and (3.2). VDVR is the primary voltage of the injection transformer and V DVR, max is the voltage rating of injection transformer. DVR = V VA, rating dvrIload (3.1) V DVR VA, rating dvr, max = (3.2) Iload By using (3.1) and (3.2), the depth of voltage sag which can be compensated is calculated in (3.3) V V dvr,max sag, pu = 0 ≤ sag, pu ≤ 1 Vsource V (3.3) During a voltage sag compensation, the load voltage is maintained at 1 p.u. The maximum DVR injected voltage (defined by the DVR VA rating) is V DVRVA, rating 0.4 = = 0. pu (3.4) I 0.1 DVR, max = 4 load 24
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 ................
Page 9 and 10: VII
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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