A DER Based Single-Phase Asymmetrical 27 Level Inverter Topology

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1 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: A ER Based SinglePhase Asymmetrical 7 Leel Inerter Topology V. Gopi Latha, K. Ratna Raju ( PG Scholar, epartment of EEE, NCET, JNTUK, Jangareddy Gudem,AP,INIA ( HO,epartment of EEE, NCET, JNTUK, Jangareddy Gudem,AP,INIA ABSTRACT :This paper deals single phase 7leel multileel inerter topology for ER sbased C/AC conersion system. This work mainly focuses on cascaded MLI using three unequal dc sources in order to produce twenty seenleel output. In this study, a high stepup conerter is introduced as a frontend stage to improe the conersion efficiency of conentional boost conerters and to stabilize the output dc oltage of ERs such as photooltaic modules for use with the simplified MLI. A conentional 7leel cascade multileel inerter requires a combination of 3 Hbridge (singlephase fullbridge) inerter modules but the present topology, 7 leel multileel inerter is obtained by using only 3 Hbridge inerter modules with different dc oltage sources This MLI offers strong adances such as improed output waeforms, smaller filter size, low TH, reduced olume and cost, and lower electromagnetic interference. The need of seeral sources on the C side of the conerter makes multileel technology attractie for many photooltaic applications. This paper proides an oeriew of ER based 7leel multileel inerter topology and inestigates their suitability for singlephase. A simulation model based on MATLAB/SIMULINK(ersion 7.) is deeloped. Keywords: Cascaded H Bridge inerter, High stepup conerter, PV Array, TH. I. INTROUCTION Conentional energy systems and highenergy Factories located in the geographical locations suitable for the production of the majority of Power, which is then transported to the consumption of large Longdistance transmission lines to the center. System Control centers monitor and control the system continuously to ensure the quality of the power. For deliering premium electric power in terms of high efficiency, reliability, and power quality, integrating interface conerters of ERs such as photooltaic (PV), wind power, micro turbines, and fuel cells into the micro grid system has become a critical issue in recent years[][4]. In such systems, most ERs usually supply a dc oltage that aries in a wide range according to Various load conditions. In light of public concern about global warming and climate change, much effort has been focused on the deelopment of enironmentally friendly distributed energy resources (ERs). Thus, a dc/ac power processing interface is required and is compliable with residential, industrial, and utility grid standards Multileel inerters can be diided into three presentable topologies; diodeclamped, flyingcapacitor, and cascaded H bridge cell [5][9]. Among them, cascaded Hbridge multileel inerters hae been receied a great attention because of their merits such as minimum number of components, reliability, and modularity. In the iewpoint of obtaining a sinusoidal output oltage multileel inerters may increase the number of output oltage leels. Howeer, it will need more components resulted in complexity and cost increase. To minimize these drawbacks, multileel inerters employing cascaded transformers hae been studied Owing to the trinary characteristic of output oltage, they can synthesize high quality output oltage near to sinusoidal waes. By using a cascaded transformer, they obtain galanic isolation between source and loads. Howeer, the transformer may decrease the power conersion efficiency, and olume and cost will be increased. To alleiate these problems, propose a cascaded H bridge multileel inerter using trinary dc input source without transformers [0]. In the case of photooltaic (PV) systems, the grid connection of many small (less than 50 kw) specifically designed inerters can be anticipated. These generators will ineitably hae some impact on the oltage waeform at the point of common coupling, and thus on the network power quality. When powerelectronic sources are operated in parallel, two particular effects are apparent which affect harmonic generation: attenuation and cancellation (see [8] and [9]). Attenuation occurs since the generated currents cause oltage ariations that in turn affect the other sources; the impact is such as to reduce the currents causing the disturbance. Cancellation is the result of the harmonic current components of the different sources being to some extent out of phase, resulting of course in a reduction in that particular harmonic for the aggregate. The specific case of cancellation of the switching harmonics for multiple inerters, which can generally be taken to be of statistically independent phase, has been dealt with in recently published work, [0]. The objectie of this paper is to study a newly constructed transformer less 7leel Multistring inerter topology for ERs. In this work, proposed inerter is reduced to multileel inerter topology that requires only twele actie switches instead of the fiftytwo required in the conentional cascaded Hbridge (CCHB) multileel inerter []. In addition, among them, two actie switches are operated at the line frequency. The input to the proposed prototype is obtained from PV modules. In order to improe the conersion efficiency of conentional boost conerters, a high stepup conerter is also introduced as a frontend stage to stabilize the output dc oltage of each ER (PV) modules for use with the simplified multileel. II. PV ARRAY PHOTOVOLTAIC (PV) power supplied to the utility grid is gaining more and more isibility, while the world s power demand is increasing []. Not many PV systems hae so far been placed into the grid due to the relatiely high cost, compared with more traditional energy sources such as oil, gas, coal, nuclear, hydro, and wind. Solidstate 30 Page

2 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: inerters hae been shown to be the enabling technology for putting PV systems into the grid. Photons of light with energy higher than the bandgap energy of PV material can make electrons in the material break free from atoms that hold them and create hole electron pairs. These electrons howeer, will soon fall back into holes causing charge carriers to disappear. If a nearby electric field is proided, those in the conduction band can be continuously swept away from holes toward a metallic contact where they will emerge as an electric current. The electric field with in the semiconductor itself at the junction between two regions of crystals of different type, called a pn junction. The PV cell has electrical contacts on its top and bottom to capture the electrons. When the PV cell deliers power to the load, the electrons flow out of the nside into the connecting wire, through the load, and back to the pside where they recombine with holes [8]. Note that conentional current flows in the opposite direction from electrons.. emands efined by the Photooltaic Cell(s) A model of a PV cell is sketched in Figure. (a) and its electrical characteristic is illustrated in Figure. (b). The most common PV technologies nowadays are the mono crystalline and the multi crystallinesilicon modules, which are based on traditional, and expensie, microelectronic manufacturing processes []. The MPP oltage range for these PV modules is normally defined in the range from 3 to 38 V at a power generation of approximate 60 W, and their opencircuit oltage is below 45 V. Howeer, new technologies like thinlayer silicon, amorphoussilicon, and photo Electro Chemical (PEC) are in deelopment [], []. These types of PV modules can be made arbitrarily large by an inexpensie rollon rolloff process. Figure.. Model and characteristics of a PV cell. (a) Electrical model with current and oltages defined. (b) Electrical characteristic of the PV cell, exposed to a gien amount of light at a gien temperature. As indicated, ripple at the PV module s terminals results in a somewhat lower power generation, compared with the case where no ripple is present at the terminals. This means that new modules with only one cell may see the light in the future. The oltage range for these cells/modules is located around 0.5,.0 V at seeral hundred amperes per square meter cell [3] [5]. The inerters must guarantee that the PV module(s) is operated at the MPP, which is the operating condition where the most energy is captured. This is accomplished with an MPP tracker (MPPT). It also inoles the ripple at the terminals of the PV module(s) being sufficiently small, in order to operate around the MPP without too much fluctuation. Analyses of the circuit in Figure. (a) shows that there is a relationship between the amplitude of the oltage ripple and the utilization ratio [6].A solar cell basically is a pn semiconductor junction. When exposed to light, a current proportional to solar irradiance is generated. The circuit model of PV cell is illustrated in Figure. (a). Standard simulation tools utilize the approximate diode equialent circuit shown in Figure. (a) in order to simulate all electric circuits that contain diodes.. Theoretical Mathematical Model The equation [] & [] that are used to sole the mathematical model of the solar cell based on simple equialent circuit shown in Figure., are gien below; I = I O [e q(v+irs ) KT ]. () I = I L I O [e q(v+irs ) KT ] V+IRs Rsh. () Where: I is the cell current in (A). q is the charge of electron =.6x09 (coul). K is the Boltzmann constant (j/k). T is the cell temperature (K). IL is the light generated current (A). I o is the diode saturation current. Rs, Rsh are cell series and shunt resistance (ohms). V is the cell output oltage (V). Fig (a) Equation () was used in computer simulation to obtain the output characteristics of a solar cell, as shown in the Figure(b). This cure clearly shows that the output characteristics of a solar cell are non linear and are crucially influenced by solar radiation, temperature and load condition..3. Variation in Aailable Energy ue To Sun s Incident Angle: PV cell output with respect to sun s angle of incidence is approximated by a cosines function at sun angles from 0 to 50.Beyond the incident angle of 50 the aailable solar energy falls of rapidly as shown in the Figure. Therefore it is conenient and sufficient within the normal operating range to model the fluctuations in photocurrent (I ph ) erses incident angle is gien by Equation (3) Fig (b) 3 Page

3 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: Power Vs Voltage Characteristics: Figure shows the typical Power ersus Voltage cure of the PV array. In this Figure, P is the power extracted from PV array and V is the oltage across the terminals of the PV array. The characteristics hae different slopes at arious points. When maximum power is extracted from PV array the system is operating at MPP where slope is zero. The PV cure aries according to the current insulation and temperature. When insulation increases, the power aailable from PV array increases whereas when temperature increases, the power aailable from PV Array decreases. Vpri = Vin. ( )... (4) where V in represents each the lowoltage C energy input sources, and oltage of the secondary winding is Vsec = Ns Ns. Vpri =. Vin..(5) Np Np ( ) Similar to that of the Boost conerter, the oltage of the chargepump capacitor C pump and clamp capacitor Cc can be expressed as Vcp = Vcc = Vin. (6) ( ) I ph = I max cos θ. (3) Figure : Power Vs Voltage The graph shown in Figure.3 is used to find the maximum power extracted from the sun when the PV arrays are inclined a different angles. From the Figure we obsere that Max power is obtained when the slope of the PV array is equal to zero. Hence, the oltage conersion ratio of the high stepup conerter, named input oltage to bus oltage ratio, can be deried as Vsi Ns = ( +. ).. (7) Vin Np IV. NEW MULTILEVEL INVERTER The new hybrid multileel inerter consists of full bridge modules which hae the relationship of, 3, 9,..3s V for dc link Voltage The output waeform has 7 leels, ± 3 V dc, ± V dc, ± V dc, ±0 V dc, ± 9 V dc, ±8 V dc, ±7 V dc, ±6 V dc, ± 5 V dc, ±4 V dc, ±3 V dc, ± V dc, ± V dc, and 0.The inerter generates 3s different oltage leels (e.g.an inerter with S =3 cells can generate 3 3 =7 different oltage leel).the basic hybrid multileel inerter structure for single phase is illustrated in Figure 4.This multileel inerter is made up of a set of series connected cells. Each cell consists of a 4switch Hbridge oltage source inerter. The output inerter oltage is obtained by summing the cell contributions. In conentional method, low leel inerter is used. Better sinusoidal output was not obtained which is the drawback of the conentional system and the harmonics was high. So increase the leels of the inerter to get high resolution, hence the output wae form is mostly sinusoidal wae form. The common function of multileel inerter is to synthesize a desired oltage from seeral separate C sources []. Each source is connected to a single phase full bridge inerter. Each inerter is capable of generating three different output oltages, +V dc, 0 and V dc. Figure. 3: Variation In Aailable Energy ue Sun s Incident Angle Variation. III. HIGH STEPUP CONVERTER STAGE In this study, high stepup conerter topology in [3] is introduced to boost and stabilize the output dc oltage of arious ERs such as PV cell modules for employment of the proposed simplified multileel inerter. The architecture of a high stepup conerter initially introduced from depicted in Figure4, and is composed of different conerter topologies: boost, fly back, and a charge circuit. The coupled inductor of the high stepup conerter can be modeled as an ideal transformer, a magnetizing inductor and leaky inductor. According to the oltage seconds balance condition of the magnetizing inductor, the oltage of the primary winding can be deried as 4. Modeling Of New Multileel Inerter: For each full bridge inerter the output oltage is gien by V 0i = V dc (S i S i ) And the input dc current is I dci = I a (S i S i ) i =,, 3 (Number of full bridge inerters employed). I a is the output current of the new inerter. S i and S i is the upper switch of each full bridge inerter. Now the output oltage of each phase of the new multileel inerter is gien by Von = n i= V0i V. NEW THREE HBRIGE 7LEVEL MULTILEVEL INVERTER The topology of the proposed c Ac Hbridge multileel inerter is shown in Figure.4. The inerter uses a standard threeleg and an H bridge with its dc source in series with each phase leg. In the proposed method of the inerter, there are three input stages. All the modules are connected as new hybrid with each module haing power switches. The power 3 Page

4 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: switches may be IGBT, MOSFET or any other power deices. The MOSFET s are used in this system. The power switches are operated in switching mode such that any two switches are in operating conditions at a time and other two remain in open condition. The switching is as S =S 3 and S = S 4. This method is adopted to protect the circuit from short circuiting. The number of leels is increased by connecting maximum number of modules. Figure 4: Single phase dc ac three Hbridge 7 leels multi leel inerter. 5. New Multileel Inerter Switching: Table. New Multi Inerter Switching Sequence Output oltages and switching states for the new hybrid inerter, S=3 V dc dc 3 dc 9 dc Vo ut N O P N O P N O P N O P N O P N O P N O P N O P N O P N N N O O O P P P N N N O O O P P P N N N O O O P P P N N N N N N N N N O O O O O O O O O P P P P P P P P P VI. PROPOSE CONCEPT The proposed prototype consists of three stages of operation as shown in figure 5.First stage deals with ERs such as PV modules supply dc oltage that aries in a wide range according to arious load conditions. In this paper three indiidual dc oltages 30V, 90V, 70V are obtained from three indiidual PV modules and then they are boosted to 00V, 300V, 900V respectiely by using boost conerter in the second stage of operation. In the third stage, boosted dc sources are applied as inputs to the proposed asymmetrical 7leel multileel topology. The proposed inerter topology requires only actie switches instead of the 5 required in the conentional cascaded Hbridge []. In order to improe the conersion efficiency of conentional boost conerters, a high stepup conerter is introduced as a frontend stage to stabilize the output dc oltage of each ER modules for use with the simplified multileel inerter. Finally a Twenty Seenleel output is obsered by giing three supply oltages to the multileel inerter. To deelop the model of hybrid multileel inerter, a simulation is done based on MATLAB/SIMULINK (ersion 7.) is used. Figure 5: Configuration of ER Based SinglePhase Asymmetrical 7 Leel Inerter Topology VII. SIMULATIONS RESULTS To erify the feasibility of the ER based singlephase asymmetrical 7leel inerter, a widely used software program MATLABSimulink is applied to simulate the circuit according to the preiously mentioned operation principle. Input sources, the output oltages of each p array are 30, 90,70 respectiely are connected is as shown in fig 6 to the inerter followed a linear resistie load through the high stepup dc/dc conerters. High stepup conerter topology in used to boost and stabilize the 33 Page

5 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: output dc oltage of ER such as arious PV arrays for employment of the proposed simplified multileel inerter The three input oltage sources feeding from the high stepup conerter is controlled at V dc = 00, Vdc = 3 V dc, Vdc3 = 9 V dc.the proposed prototype of 7 leel inerter is shown in fig 7 and corresponding lower inerter generates a fundamental output oltage of 80V using three indiidual C sources. The harmonic spectrum is as shown fig 9. Based on the simulation results, the proposed multileel inerter was tested by a prototype. Components comparison between conentional inerters and the proposed approach appearing 7 output leels is gien in Table. It is compared with the conentional multileel inerters, i.e., diodeclamped, flying capacitor, cascaded H bridge, and cascaded transformer based multileel inerter. In the case of diodeclamped, a large number of clamping diodes are a seere drawback. And a lot of balancing capacitors is a disadantage of the flying capacitor method. Among them, the isolated CML looks ery effectie to synthesize output oltage leels. It only needs a single dc input source. Howeer, it shows low. Efficiency because of adopting a cascaded transformer. And it will be suffered from large size and heay weight. Moreoer, this method is not desirable for the motor dries employing VF (ariable frequency) control scheme because of the saturation of transformer. Figure 8: Twenty Seen leel output Figure 9: FFT Analysis of Twenty Seen leel output Figure 6: Simulation of P Array No of leel S = 3 Input C Voltage Cascade Hybrid Proposed Prototype S+, 7 S+, 5 3 s,7 leel leel leel V dc, V dc S V dc, 4 V dc 3 S V dc, 9 V dc Table. Comparison of different Topologies From the comparison, it is clear that the most outstanding adantage of the proposed multileel inerter scheme is the elimination of transformer in the main power stage. Howeer, each cell of the proposed multileel inerter requires its own isolated power supply. The proision of these isolated supplies is the main limitation in the power electronic circuit design. So the proposed multileel inerter is suitable for photooltaic power generating systems equipped with distributed power sources. Figure 7: Simulation of Main Circuit VIII. CONCLUSION In this Paper much effort has been focused on the deelopment of enironmentally friendly distributed energy resources (ERs) along with cascaded Hbridge multileel inerter employing trinary dc sources to obtain a large number of output oltage leels with minimum deices. 34 Page

6 Vol., Issue. 5, Sep.Oct. 0 pp3035 ISSN: The proposed inerter can synthesize high quality output oltage near to sinusoidal waes. The circuit configuration is simple and easy to control. The proposed prototype consists of three dc sources with the use of switches Valuable and presentable merits of the proposed approach are summarized as () Economical circuit configuration to produce multileel outputs by using trinary input sources, () Easy to increase of the output oltage leels and output power owing to modularity characteristic, (3) Little transition loss of switches due to low switching frequency and reduced EMI; it is suitable for high oltage applications. REFERENCES [] YiHung Liao, and ChingMing Lai, Newly Constructed Simplified SinglePhase Multistring Multileel Inerter Topology for istributed Energy Resources IEEE Transactions on Power Electronics, Vol. 6, No. 9, September 0 [] N. Hatziargyriou, H. Asano, R. Iraani, and C. Marnay, Microgrids, IEEE Power Energy Mag., ol. 5, no. 4, pp , Jul./Aug [3] F.Katiraei, R. Iraani,N.Hatziargyriou, anda.imeas, Microgridsmanagement, IEEE Power Energy Mag., ol. 6, no. 3, pp , May/Jun [4] C. L. Chen,Y.Wang, J. S. Lai,Y. S. Lee, and.martin, esign of parallel inerters for smooth mode transfer microgrid applications, IEEE Trans. Power Electron., ol. 5, no., pp. 6 5, Jan. 00. [5] L. G. Franquelo, J. Rodriguez, S. Kouro, R. Portillo, and M. A. M. Prats, The age of multileel conerter arries, IEEE Ind. Electron Magazine, pp. 839, 008. [6] J. Rodriguez, J. S. Lai, and F. Z. Peng, Multileel Inerters: A surey of topologies, controls, and applications, IEEE Trans. Ind. Electron., ol. 49, no. 4, pp , Aug. 00. [7] J. S. Lai, and F. Z. Peng, Multileel ConertersA New Breed of Power Conerters, IEEE Trans. Ind. Appl., ol. 3, no. 3, pp , May/June, 996. [8] M. H. Rashid, Power Electronics Handbook, Academic Press, 00, pp [9] L. M. Tolbert, F. Z. Peng, and T. G. Habetler, Multileel conerters for large electric dries, IEEE Trans. Ind. Electron., ol.35, pp.3644, 999. [0] F. S. Kang, S. J. Park, M. H. Lee, C. U. Kim, An efficient multileel synthesis approach and its application to a 7leel inerter, IEEE Trans. Ind. Electron., ol. 5, no. 6, pp , 005. instead of 5 switches for conentional H bridge inerter to get required 7 leel output oltage. The operational principle and key waeforms are illustrated and analyzed. [] J. P. Benner and L. Kazmerski, Photooltaics gaining greater isibility, IEEE Spectr., ol. 9, no. 9, pp. 34 4, Sep [] E. Bezzel, H. Lauritzen, and S. Wedel. (004) The photo electro chemical solar cell. PEC Solar Cell Project, anish Technological Institute. [Online]. [3] H. Wilk,. Ruoss, and P. Toggweiler. (00) Innoatie electrical concepts. International Energy Agency Photooltaic Power Systems, IEA PVPS 7 07:00. [Online]. Aailable: [4] M. Wuest, P. Toggweiler, and J. Riatsch, Single cell conerter system (SCCS), in Proc. st IEEE WCPEC, ol., 994, pp [5] J. Riatsch, H. Stemmler, and R. Schmidt, Single cell module integrated conerter system for photooltaic energy generation, in Proc. EPE 97, ol., Trondheim, Norway, 997, pp [6] S. B. Kjaer, esign and control of an inerter for photooltaic applications, Ph.. dissertation, Inst. Energy Technol., Aalborg Uniersity, Aalborg East, enmark, 004/005. [7] W. Yu, C. Hutchens, J. S. Lai, J. Zhang, G. Lisi, A. jabbari, G. Smith, and T. Hegarty, High efficiency conerter with charge pump and coupled inductor for wide input photooltaic AC module applications, in Proc. IEEE Energy Coners. Congr. Expo., 009, pp [8] A. Mansoor, W. M. Grady, P. T. Staats, R. S. Thallam, M. T. oyle, and M. J. Samotyj, Predicting the net harmonic currents produced by large numbers of distributed singlephase computer loads, Inst. Elect. Eng. Trans. Power ist., ol. 0, no. 4, pp , 995. [9] E. F. ElSaadany and M. M. A. Salama, Reduction of the net harmonic current by singlephase nonlinear loads due to attenuation and diersity effects, Int. J. Elec. Power Energy Syst., ol. 0, no. 4, pp , 998. [0]. G. Infield, Combined switching harmonics from multiple gridconnected singlephase inerters, Proc. Inst. Elect. Eng., Gen. Transm. ist., ol. 48, no. 5, pp , 00. [] S. Vazquez, J. I. Leon, J. M. Carrasco, L. G. Franquelo, E. Galan, M. Reyes, J. A. Sanchez, and E. ominguez, Analysis of the power balance in the cells of a multileel cascaded Hbridge conerter, IEEE Trans. Ind. Electron., ol. 57, no. 7, pp , Jul Page