1、参考文献及翻译A grid-connected photovoltaic power conversion system with single-phase multilevel inverterErsoy Beser , Birol Arifoglu , Sabri Camur , Esra Kandemir Beser, Department of Electrical Engineering, Kocaeli University, Umuttepe Campus, 41380 Kocaeli, TurkeyReceived 7 May 2010. Revised 26 Septembe
2、r 2010. Accepted 28 September 2010. Available online 20 October 2010.Communicated by: Associate Editor Nicola Romeo. http:/dx.doi.org/10.1016/j.solener.2010.09.011, How to Cite or Link Using DOICited by in Scopus (4)Permissions & ReprintsAbstractThis paper presents a grid-connected photovoltaic (PV)
3、 power conversion system based on a single-phase multilevel inverter. The proposed system fundamentally consists of PV arrays and a single-phase multilevel inverter structure. First, configuration and structural parts of the PV assisted inverter system are introduced in detail. To produce reference
4、output voltage waves, a simple switching strategy based on calculating switching angles is improved. By calculated switching angles, the reference signal is produced as a multilevel shaped output voltage wave. The control algorithm and operational principles of the proposed system are explained. Ope
5、rating PV arrays in the same load condition is a considerable point; therefore a simulation study is performed to arrange the PV arrays. After determining the number and connection types of the PV arrays, the system is configured through the arrangement of the PV arrays. The validity of the proposed
6、 system is verified through simulations and experimental study. The results demonstrate that the system can achieve lower total harmonic distortion (THD) on the output voltage and load current, and it is capable of operating synchronous and transferring power values having different characteristic t
7、o the grid. Hence, it is suitable to use the proposed configuration as a PV power conversion system in various applications.KeywordsPhotovoltaic; Photovoltaic power conversion; Grid-connected; Single-phase multilevel inverterNomenclatureCk capacity of the kth capacitor group (F)f grid frequency (Hz)
8、I inverter current (A)IPM maximum power current value (A)Ls inductance of the self inductor (H)m number of the level modulesn output level numberPLMk power of the kth level module (W)Pref reference real power (W)P0 system output power (W)Qk(t) the kth switching signalQref reference reactive power (V
9、Ar)Rs resistance of the self inductor ()S sum of the energy ratiost instantaneous time value (s)tmax maximum value of the sample time (s)tsample value of the sample time (s)Vb voltage of the base level module (V)Vbus bus voltage (V)Vbusref the reference bus voltage (V)VCk voltage of the kth capacito
10、r group (V)Vg grid voltage (V)Vmax maximum value of the required voltage (V)VPM maximum power voltage value (V)Vref reference voltage (V)Vz voltage of the self inductor (V)V0 output voltage (V)WCk energy of the kth capacitor group (J)WLMk energy of the kth level module (J)XLs reactance of the self i
11、nductor ()Zs impedance of the self inductor ()t time between ti and ti+1 (s) angle between V0 and Vg ()ref reference angle between Vref and Vg () the angle between Rs and XLs () power angle () angular speed (rad s1)1. IntroductionRecently, renewable energy resources have been becoming popular due to
12、 the decrease of fuel sources and their damages to the environment. As a result of the negative effects of global warming and climate changes, the interest of renewable resources has been increased gradually.Solar energy is one of these alternative energy resources. It is converted to the electrical
13、 energy by photovoltaic (PV) arrays. PV arrays do not generate any toxic or harmful substances that pollute the environment ( Kang et al., 2005aandKang et al., 2005b). Another considerable feature of them is the requirement of low maintenance. Depending on the development in photovoltaic technologie
14、s, the efficiency of the PV arrays has been improved. Therefore, studies on PV systems have increased gradually.PV systems are occasionally operated in stand-alone mode and they feed fixed loads by stand-alone PV inverters ( Myrzik, 2001, Kang et al., 2005a, Kang et al., 2005b, Daher et al., 2008, L
15、alouni et al., 2009andSaravana Ilango et al., 2010). PV systems are also interconnected to the grid. Interconnecting a PV system to the grid has been the popular design trend and grid-connection types of PV inverters have been proposed ( Calais et al., 1999, Myrzik, 2001, Kuo et al., 2001, Alonso et
16、 al., 2003, Yu et al., 2005, Wu et al., 2005, Patcharaprakiti et al., 2005, Lee et al., 2008, Hassaine et al., 2009andRahim et al., 2010). Therefore various power electronics technologies are improved to convert the dc to ac power for PV applications.In addition, it is important to operate PV energy
17、 conversion systems near the maximum power point to increase the output efficiency of PV arrays ( Kuo et al., 2001, Alonso et al., 2003, Yuvarajan et al., 2004, Yu et al., 2005, Patcharaprakiti et al., 2005andLee et al., 2008). Thus, power electronics inverters are required for maximum power point t
18、racking (MPPT) algorithm, which provides maximum PV power. They are also needed for transferring the PV power to a load or to the grid.Multilevel inverters are suitable choices for realizing this objective. Various multilevel inverter topologies have been introduced and studied in the literature. Th
19、e most considerable of these types are the diode clamped, the flying capacitor, the cascaded H-Bridge, the magnetic coupled and the full bridge with cascaded transformers inverters. The remarkable feature of these inverters is generating less harmonic components on both output voltage and load curre
20、nt. By increasing the number of output levels, the quality of the output voltage and load current is increased step by step ( Calais et al., 1999, Rodriguez et al., 2002, Kang et al., 2005a, Kang et al., 2005b, Daher et al., 2008, Rahim et al., 2010andBeser et al., 2010). Due to the production of le
21、ss harmonic components, the PV power is transferred to the load or to the grid in a high-quality form by multilevel inverter structures.Related to these developments, this study presents a PV assisted multilevel inverter system for the conversion of PV power to the electrical power. The proposed str
22、ucture of the inverter system is quite suitable for the use of PV arrays. Owing to the use of a multilevel inverter structure, more sinusoidal shaped output voltage waves are obtained. Therefore, the THD of the output voltage is considerably reduced. Placement of the PV arrays in the system is the s
23、ignificant point of the study because of loading the arrays in the same condition. To accomplish this, a simulation study is performed and the number and connection types of the PV arrays in the system are determined. According to the order of the PV arrays a configuration is formed for the PV assis
24、ted inverter system. The system is simulated while operating synchronous and transferring various power values having different characteristics to the grid. The validity of the proposed system is also verified through an experimental study. The measured THD values of the output voltage and current a
25、re quite low. The system provides good performance as a PV energy conversion system.2. Proposed PV assisted single-phase multilevel inverter system2.1. Configuration and structural parts of the proposed systemFig. 1 shows the base configuration of the proposed PV assisted multilevel inverter. It con
26、sists of PV modules, level modules (LM) and a conventional H-Bridge module. The base configuration of the multilevel inverter generates a 7-level shaped output voltage wave. However, the proposed system can be easily expanded and the number of output voltage levels is increased by adding level modul
27、es to the system (Beser et al., 2010).Fig. 1.Configuration of the proposed PV assisted single-phase multilevel inverter system.View thumbnail imagesThe proposed inverter structure provides an advantage in point of switching element number compared to some inverter types in the literature. A switch n
28、umber comparison related to output level number (n) is made between different inverter types in Table 1.Table 1. Switch number comparison related to output level number (n).Inverter typeSwitch numberDiode clamped2(n1)Flying capacitor2(n1)Cascaded H-Bridge2(n1)Magnetic coupled4log3(n)Full-bridge with
29、 cascaded transformer4log3(n2)+4Proposed2log2(n+1)+2Full-size tableIt can be seen from Table 1 that 60 switches are used in diode clamped, flying capacitor and cascaded H-Bridge inverters to obtain 31-level output voltage. The magnetic coupled inverter type uses 12 switches and shapes 27-level volta
30、ge wave. The full bridge with cascaded transformer inverter type uses 16 switches and forms 29-level shaped output voltage. However, the proposed inverter achieves 31-level output voltage by using only 12 switches.Another considerable feature of the proposed inverter is that the system configuration
31、 allows operating regenerative. So this feature provides to transfer both active and reactive power to the grid.2.1.1. PV moduleFig. 2 shows the configuration of the PV module. It can be seen from Fig. 2 that it consists of PV arrays and a capacitor group.Fig. 2.Configuration of the PV module.View t
32、humbnail imagesDepending on the increase of the output level number, PV arrays are suitably connected serially and PV module is expanded according to the number of level modules. The configuration of the expanded PV module is shown in Fig. 3.Fig. 3.Configuration of the serially connected PV arrays in the PV mo
