Leakage Current Elimination using Non-Isolated Photovoltaic Grid Connected Inverters

Transcription

1 Journal of Recent Research in Enineerin and Technoloy 3(5), 2016, pp 18 Article I J51601 IN (Online): , IN (Print): Bonfay Publications, 2016 Research Article Leakae Current Elimination usin NonIsolated Photooltaic Grid Connected Inerters Gowri Manohari. R 1, Janaki. N 2, owmiya.n 3 1Assistant Professor, epartment of Electrical & Electronics, Vels Uniersity, Chennai, Tamil Nadu 2Assistant Professor, epartment of Electrical & Electronics, Vels Uniersity, Chennai, Tamil Nadu 3PG cholar, epartment of Electrical & Electronics, Vels Uniersity, Chennai, Tamil Nadu Receied 15 April 2016; Accepted 20 May 2016 Abstract olar inerters which are transformer less possess hih efficiency when compared to that of an isolation link. A major issue with this is the leakae current issue. In this paper we propose a sinle phase with six switch transformer less inerter topoloies alon with an ac bypass circuit. With the help of these circuits the two unidirectional freewheelin current units are embedded in the midpoint of a full bride inerter. This is done to attain a freewheelin current path, to separate the solar panels from the rid in the freewheelin state. The adantae of freewheelin is that it consists of ery few deices and aoids the poor performance body diodes which lead to hiher efficiency. It is also not required to add a oltae balancin control system as that of a half bride inerter. In this paper, simulations are also added in order to alidate the proposed topoloies. Keywords: olar panel, inle phase sixswitch transformerless inerter, Leakae current, Grid connected inerter. I. INTROUCTION In present years, demand for enery is increasinly hihly due to which there tremendous deelopment in the alternatie power sources. ome of them to be named are the photooltaic (PV) modules, wind turbines and fuel cells. In specific PV modules are in much of attraction as they belon to the renewable sources. Other attributes of PV modules are, small in size, easy installation, noiseless operation, it is possible to install them closer to the user. When it comes to the PV (photooltaic) power systems, transformer less inerters are of reat uses in terms of efficiency, structure, reliability, cost and many more. But these nonisolated inerters do hae their own faultier sides like round leakae or commonmode oltae issue between the rid and the PV system [1]. It is strictly restricted if the leakae current to round is reater than 300mA, in that case the disconnection has to happen within 0.3s[2]. 1

2 Journal of Recent Research in Enineerin and Technoloy Gowri Manohari et al, This paed way for many researches to take place on leakae current issue in nonisolated ridconnected PV inerters. Based on the full bride structure, an auxiliary circuit is introduced to diert the direction of flow of freewheel current and hence helpin the leakae current problem to be resoled. Based on this new proposed method the solar panel is separated from the rid in the freewheel stae. Based on the aboe proposed alteration, many structures are been proposed. A H5 inerter is also introduced by MA solar Technoloy AG [3]. As few deices are used in this structure it reatly reduces the cost. Howeer, freewheel diodes hae the problem of reerse recoery. This makes it difficult to work on improin the efficiency of the structure. Hence it is required to hae a full bride inerter with dc bypass circuit, this is to produce low current ripple in the ac and reduce the chances of conerter loss. The connected inerters are in the form of national standards. Let s consider German standard IN VE , transformer less PV inerters are connected to the rid. A oltae balance control will be necessary because of the midpoint by oltae diidin of the dc link capacitor. unidirectional freewheel cells are bein embedded in between the midpoints of the full bride inerter to produce a result of freewheel path. This separates the solar panel from the rid in the freewheel stae. This structure contains few deices and also aoids the poorperformance of the body diodes in the freewheelin path. This helps in obtainin a hih efficiency. Hence remoin the oltae balance control from the system. Verification and results of the proposed method are discussed in other sections of the paper. olar PV: olar enery is the enery that we receie from the sun. The enery that we receie is radiated from the sun. The sun can enerate tremendous amount of enery just in a second. This enery is enerated within the sun. The sun is just like other stars which are made up of as like hydroen and helium. The enery is produced due to a process called the nuclear fusion. The study around the results or influence of this control is not been analyzed in this paper. It is obsered that the difficulty of the control is increased. The commonmode (CM) oltae and leakae current are bein restrained usin the bipolar modulation scheme. This results in unipolar modulation effect. The topoloy considered in this paper work has body diodes in the current path which has limitation in performance. Hence a H6 inerter topoloies with ac bypass circuit with two urin this chemical process in the sun, hih pressure and hot temperature makes the hydroen atoms to fuse or combine the nuclei. urin this process some of the matter is lost 2

3 Gowri Manohari et al, Journal of Recent Research in Enineerin and Technoloy into the space as radiant enery. The enery from the sun's core to reach the solar surface takes around millions of years. After which it takes eiht minutes to trael the 93 million miles to earth. This solar enery traels at a speed of 186,000 miles per second, the speed of liht to trael to the earth. The enery that we receie in earth is just a small portion of the enery radiated by the sun into space that is one part in two billion. till we find that this is a hue amount of enery receied by earth. Eeryday enouh enery strikes the earth where in United tates this solar enery supplies the countries need for one and a half year. 15 percent of sun's enery is reflected back to the space. 30 percent is bein used in the process of eaporation which causes rainfall. Land, plants and the oceans absorb solar enery and the rest is used by human beins to supply our daily needs. Photooltaic (PV) is the technoloy that deals with conertin sun enery (sunliht, ultra iolet radiation) into electricity. The rowin demand for solar enery and other clean sources of enery has put a hih demand on the manufacturers of solar cells and photooltaic arrays to expand dramatically. This hih demand has doubled the production of solar enery eery year with an increase of 48% each year since 2002 and hence it is the hihest rowin enery technoloy. In the lobal, PV installation reached 15,200 meawatts in the end of Around 90% of these PV installations are rid tied electrical systems. Most of the installations are roundmounted (like farmin and razin) or een built on the roof or walls of buildins which is known as Buildin Interated Photooltaic or BIPV in short. Financial incenties and net meterin like preferential feedin tariffs for solar electricity has increased the solar PV installations in countries like Germany, Japan, Australia, and Israel and in the U. inle stae Grid connected PV system The rid connected photooltaic (GPV) installations consists of CAC power processin system and PV panels. The most required are of research when it comes to GPV system is the way the elements of the GPV inerter are arraned (PV panels and the power conerter stae or staes). The efficiency of the PV module can ary accordin to the desin of the arranement of these deices. Let s consider an example of the most commonly used "central inerter". In this confiuration all the deices are series parallel connected to the input of a sinle fullbride power inerter. In this kind of approach the cost of the complete system is comparatiely less as only one power conditionin module is required. Also the central inerter confiuration needs a minimum of passie filter elements. The ease of this structure and the flexibility to easily add other power conerter staes, we are considerin this power conditionin structure in the present work. There are a few points to be adhered to attain efficient enery transfer. The below control objecties are to be adhered by the control stratey of the power inerter that interfaces the PV array with the utility rid. The conersion of C input power into an AC output current should be proper and injected to the rid. 3

4 Journal of Recent Research in Enineerin and Technoloy Gowri Manohari et al, This output current injected to the rid should be of low harmonic contents and in phase with the rid oltae to attain power transfer as unity power factor. The maximum power extraction depends on the PV array and the solar panels maximum power point (MPP) which aries with the solar irradiance and the PV panels' temperature. The aboe mentioned requirements can be met by a stratey based on two cascaded control loops with the help of pulsewidth modulation (PWM) scheme as seen in Fiure 2.2. The inner control loop handles the duty ratio for the production of sinusoidal output current which is in phase with the rid oltae. maximum power and hence ensurin power transfer to the rid. ystem Block iaram H6 inerter topoloy with bypass circuit is also bein used based on the full bride structure. This proposed structure has unipolar PWM output waeforms and also eliminates the hih frequency pulsates of the CM oltae. This leads to ariation of low frequency of the CM oltae which only has low leel leakae current and that can be nelected. Other existin methods used for minimizin leakae current uses the body diodes in the current path which is eliminated in the proposed method. Voltae balance control and oltae diidin capacitors are also not required in our new method. These adantaes help in improin the conersion efficiency and reliability of the proposed system. The experimental results and the simulations hae practically proed that the proposed structure shows ood performance. It minimizes leakae current and has hihquality output oltae waeforms for the rid. Hih conersion efficiency is also obtained. Fiure 2.1: GridConnected Photooltaic The outer control loop helps to settle the PV array operatin point at its maximum power alue for any temperature and irradiance ariation. This is done with the help of maximum power point trackin (MPPT) alorithms like the Perturb and Obserer or other adanced ones. The outer loop proides the inner control loop the current reference amplitude correspondin to the PV array Existin system: In the existin system full bride structure is used and auxiliary circuit is used to sole the leakae current problem by forcin the freewheelin current to chane its flowin path. This helps to separate the solar panel from the rid in the freewheelin stae. 4

5 Gowri Manohari et al, Journal of Recent Research in Enineerin and Technoloy oltae diidin in the dc link capacitor. The results of this control are not bein analyzed. Fi.1. inle phase fullbride inerter. There are arious structures based on the aboe mentioned concept. A H5 inerter with few deices and minimum cost are used. But freewheelin diodes hae the problem of reerse recoery problem. ue to which it is a challene to work on the efficiency of the structure. In this method we use a full bride with dc bypass circuit, this shows low current ripple in the ac side and a reduced conerter loss. A oltae balance control is bein used and a Proposed ystem: In the proposed method, H6 inerter topoloy is used with an ac bypass circuit, two unidirectional freewheel cells are embedded between the midpoint of the full bride. This helps to separate the solar panel from the rid in the freewheelin stae. In this structure, few deices are used and no poor performance body diodes are inoled in the freewheelin path. Hence hih efficiency is bein obtained. In this method, oltae balance is not required. Hence the reliability and the conersion efficiency are achieed. The experimental results and simulations show ood performance of the proposed method. The proposed structure also minimizes the leakae current and has hih quality output oltae waeforms for the rid. Hih conersion efficiency is also obtained. Fi. 3.3 The proposed H6 inerter 5

6 Journal of Recent Research in Enineerin and Technoloy Gowri Manohari et al, imulation Results: Proposed imulation iaram: iscrete, Ts = 2e006 s. powerui i [IF] [A1] [A2] [IG] i i 2 4 LOA1 LOA 1 [A3] [A3] AC [A2] 6 [V] A V [A1] B 3 5 >= [A1] >= [A2] aturation1 [IG] s [V] 1/220 >= [A3] 0 Constant NOT [A4] Fi 4.complete simulation schematic of proposed rid Inerter Fi 4.2 Modulation scheme of proposed Topoloy 6

7 Gowri Manohari et al, Journal of Recent Research in Enineerin and Technoloy Fi 4.3 Capacitor oltae of proposed topoloy Fi 4.6 Leakae current of conentional Hbride inerter Fi 4.4 Capacitor oltae of conentional topoloy Fi 4.7 Grid current of proposed conerter Fi 4.5 Leakae current of proposed topoloy Fi 4.8 Grid current of conentional H bride inerter Conclusion: H6 inerter topoloy with bypass circuit is also bein used based on the full bride 7

8 Journal of Recent Research in Enineerin and Technoloy Gowri Manohari et al, structure. This proposed structure has unipolar PWM output waeforms and also eliminates the hih frequency pulsates of the CM oltae. This leads to ariation of low frequency of the CM oltae which only has low leel leakae current and that can be nelected. Other existin methods used for minimizin leakae current uses the body diodes in the current path which is eliminated in the proposed method. Voltae balance control and oltae diidin capacitors are also not required in our new method. These adantaes help in improin the conersion efficiency and reliability of the proposed system. The experimental results and the simulations hae practically proed that the proposed structure shows ood performance. It minimizes leakae current and has hihquality output oltae waeforms for the rid. Hih conersion efficiency is also obtained. Reference: [1] O. Lopez, R. Teosorescu, F. Freijedo, and J.oalGandoy, Leakae current ealuation of a sinle phase transformerless PV inerter connected to the rid, in Proc. IEEE APEC., pp , [2]. M. C. Caalcanti, A. M. Farias, K. C. de Olieira, F. A.. Nees, and J. L. Afonso, Eliminatin leakae currents in neutral point clamped inerters for photooltaic systems, IEEE Trans. Ind. Electron., Vol.59, No.1, pp , Jan [3].. Aeaujo, P. Zacharias, and R. Mallwitz, Hihly efficient sinlephase transformerless inerters for ridconnected photooltaic systems, IEEE Trans. Ind. Electron., Vol.57, No.9, pp , ep [4].T. Kerekes, R. Teodorescu, P. Rodriuez, G. Vazquez, and E. Aldabas, A new hihefficiency sinlephase transformerless PV inerter topoloy, IEEE Trans. Ind. Electron., Vol. 58, No. 1, pp , Jan [5] M. C. Caalcanti, K. C. de Olieira, A. M. de Farias, F. A.. Nees, G. M.. Azeedo, and F. C. Camboim, Modulation techniques to eliminate leakae currents in transformerless threephase photooltaic systems, IEEE Trans. Ind. Electron., Vol. 57, No. 4, pp , Apr [6] F. Bradaschia, M. C. Caalcanti, P. E. P. Ferraz, F. A.. Nees, E. C. dos antos, and J. H. G. M. da ila, Modulation for threephase transformerless Zsource inerter to reduce leakae currents in photooltaic systems, IEEE Trans. Ind. Electron., Vol. 58, No. 12, pp , ec [7] R. González, J. López, P. anchis, and L. Marroyo, Transformerless inerter for sinlephase photooltaic systems, IEEE Trans. Power. Electron., Vol. 22, No. 2, pp , Mar