Survey Grid Connected PV

2012 - International Conference on Emerging Trends in Science, Engineering and Technology

404

ISBN : 978-1-4673-5144-7/12/$31.00 2012 IEEE

A Survey of Single Phase Grid Connected Photovoltaic System

M.Venkatesan Karpagam University

Coimbatore Tamilnadu,India

R.Rajeswari Govt. College of Technology

Coimbatore Tamilnadu,India

K.Keerthivasan Karpgam University

Coimbatore Tamilnadu, India

AbstractThisreview focuses on inverter topologies for Photo

Voltaic (PV) modules, which are connected with single phase grid systems. Various inverter topologies for PV modules such as (i) Centralized inverter (ii) String inverter (iii) Multi-string inverter and their recommended standards, trends, Principle of integration issues connecting with grid systems are presented in this review. The centralized and string PV systems have drawbacks such as losses due to mismatching of PV module, high voltage DC cables between PV modules and the inverter, limited power rating of converter unit and additional power losses due to the string diodes. The solutions for the above stated problems are overcome by multi string inverter. The different Pulse Width Modulation (PWM) technique for PV inverter modules is being presented in this review.

IndexTermsPhotovoltaic module, Inverter topology, Grid connected system, PWM technique.

I. INTRODUCTION As the world is focusing with fossil-fuel exhaustion and

environment problems caused by conventional power generation, renewable energy is the very popular for the last two decades. Photovoltaic has been used many in todays life for many applications because, they have advancing of being maintained and pollution free [1]. Solar energy demand has grown constantly by 20-25% per annum, which is mainly due to decrease in price. The price of the PV module was major contribution to make system in the past. The cost of the grid connected inverter is therefore becoming more visible in the total system price. The cost reduction per watt is therefore important to make PV generated power more attractive [2]. This paper mainly focuses on the basic concepts of multilevel inverter topologies, PV inverter topologies, photovoltaic modules, recommended standards, and their characteristics.

II. RECOMMENDED STANDARDS, ENERGY FEATURE A. Principle of Integration Issue

If the inverter is connected to the grid, user must follow the standards given by companies. In particular present standards of PV module are EN61000 and IEC61727 and the US National Electrical code (NEC) 690 are considered. These standards deal with issues, like power quality problems, detection of islanding operation, grounding, etc. Draft IEC

62116 standards that describing international test for inverter anti islanding are developed in the International Electro Technical Commission Technical committee 82-Solar photovoltaic energy systems [4-5]. NEC (National Electrical Code) standards demands that the PV modules shall be the system grounded and monitored for ground faults [5-6]. The current trend across developed economics tips the scale in favor of renewable energy. For the last three years, the continents of North America and Europe have embraced more renewable power capacity as compared to conventional power capacity. Renewables accounted for 60% of the newly installed power capacity in Europe in 2009 and nearly 20% of the annual power production [7]. Wind and biomass occupy a major share of the current renewable energy consumption. Recent advancements in solar photovoltaic technology and constant incubation of projects in countries like Germany and Spain have brought around tremendous growth in the solar PV market as well, which is projected to surpass other renewable energy sources in the future. By 2009, more than 85 countries had some policy target to achieve a predetermined share of their power capacity through renewables. This was an increase from around 45 countries in 2005. Most of the targets are also very ambitious, landing in the range of 30-90% share of national production through renewables [7]. Remarkable policies are the European Unions target of achieving 20% of total energy through renewables by 2020 and Indias Jawaharlal Nehru Solar Mission, through which India plans to produce 20GW solar energy by the year 2022. It is shown in table 1. B. Photovoltaic Module

A model of a PV cell is shown in Fig. 1 and its complete electrical characteristics of solar cell is illustrated in Fig. 2

Fig. 1 Equivalent circuit of PV solar cell


405

ISBN : 978-1-4673-5144-7/12/$31.00 2012 IEEE

Fig. 2 V-I Characteristics of PV cell

TABLE I. ENERGY SOURCES

SI.No. Energy sources

1 Fossil fuel 78%

2 Nuclear 2.8%

3 Renewable Energy Power generation 19%

I Wind / Solar/ Biomass/Geo thermal power generation

0.7%

Ii Bio fuels 0.6%

Iii Traditional Biomass 13.1%

Iv Biomass/Solar/Geothermal /heating 1.4%

V Hydro power 3.2%

Nowadays PV technologies are the mono crystalline and

the multi crystalline silicon modules, which are based on traditional and expensive microelectronics manufacturing processes. The voltage range from these PV modules is from 23V to 38V at a power generation approximately 160 Watts and their open circuit voltage is less than 45V. Thin larger silicon, amorphous silicon and photo electrical chemical (PEC) are in new developments [1], [10]. These types of PV modules can be made arbitrarily large by an inexpensive roll-on-roll-off process. The voltage range for these modules is ground 0.5~1.0 V at several hundred amperes per square meter cell [8-10]. The basic voltage current equation (V-I) characteristic of PV model is described by the following equation:

I=IL IO ( -1) (1)

Where:

I is the PV cell current in Ampere IL is the current generated by light in Ampere Io is the saturation current of diode Q is the charge of electron K is the Boltzman constant T is the temperature of the cell Rs, Rsh are the series and shunt resistance of the cell respectively V is the output voltage in volts

The PV inverter industry has been influenced by the developments in the PV module industry where size and peak power rating of PV module have continuously increased over the past years. This reduces cost of PV system. The PV topologies is classified as PV inverter with DC-DC converter, the configuration of this type of DC-DC converter may be with isolation or without isolation and PV inverter without DC-DC converter this may be with isolation or without isolation. The isolation used in both categories can be made through transformers that can be placed on either the grid (or) low frequency side, high frequency side. Line frequency transformers are important in the system but main consideration is the size, weight, and cost. HF transformers are more useful but it requires some special attention.

III. MULTILEVEL INVERTER TOPOLOGIES The multilevel inverters have tremendous interest in the

power industry. They present a new set of feature that is well suited for use in reactive power compensation. It may be easier to produce a high power and high voltage inverter with the multilevel structure because of the way in which devices voltage stress are controlled in the structure. Increasing number of voltage levels in the inverter without requiring higher ratings individual devices can increase power rating. The unique feature structure of multilevel voltage source inverter allows them to reach high voltages with low harmonics without the use of transformers or series connected synchronized switching devices. As the number of voltage level increases, the harmonics content of the output voltage waveform decreases significantly.Basically multilevel inverter topologies are divided into three types (i) Diode clamped multilevel inverter (ii) Flying capacitor multilevel inverter (iii) Cascade multilevel inverter. Diode clamped multilevel inverter three levels neutral point clamped (NPC) inverter is shown in Fig. 3.

Fig. 3 Diode clamped inverter topology

NPC topology was proposed by Nabae et al. [11]. It was the first widely popular multilevel topology, and it continues to be mostly used in industrial applications. Afterwards, the NPC inverter was generalized for a greater number of levels, using the same concept ofdiode clamped voltage levels, which resulted in the current designation of a diode clamped


406

ISBN : 978-1-4673-5144-7/12/$31.00 2012 IEEE

converter [12]. The three levelNPC inverter uses capacitors to generate an intermediate voltage level, and the voltages across the switches are only half of the dc input voltage. Applications of diode clamped topology is limited because of capacitor voltage balancing issues, requiring more number of clamping diode to make the structure, it will produce the more losses. Practical diode clamped inverters have been mostly limited to the original three level structure.

Fig. 4 Flying capacitor inverter topology

The three level flying capacitor topology, as shown in Fig. 4 can overcome by the drawbacks of diode clamped multilevel inverter [13], In this topology, additional levels and voltage clamping are achieved by means of capacitors that float with respect to the dc source reference. It does not require additional clamping diodes and provides redundant switch states that can be used to control the capacitor charge even under loads with the dc level. Nevertheless, larger structures require a relatively high number of capacitors, and additional circuits are also required to initialize the capacitor charge. Hybrid multilevel inverter topology is to be made of several H-bridge converters in cascade connection. Fig. 5 shows a two cell inverter. The cascade topology allows the use of dc sources with different voltage values, and high resolution multilevel waveforms can be achieved with a relatively low number of components [13] In addition, dc sources can be added or subtracted which can increase the number of output levels. Although the original cascaded topology requires several isolated dc sources, in some systems, they may be available through batteries or PV panels; thus, it has been used to implement high efficiency transformerless inverters [14].

Fig. 5 Hybrid inverter topology

IV. PV INVERTER TECHNOLOGIES In PV converter topologies, three designs of inverter

families are defined central, module oriented and string inverter. The central converter connects in parallel and/or in series on the DC side. One converter is used for entire PV plant. Configuration of multi-string inverter topology is shown in Fig. 6.

Fig. 6 Multi-string inverter configuration of PV system

The nominal power of this topology is upto megawatts. The module oriented converters with several modules usually connected in series on the DC-side and in parallel on the AC side. The nominal power rating of PV power plant varies upto several megawatts. It also requires supervision and produce lower efficiency than string inverter. The power handling capacity of the string inverter is low; it is approximately limited to 2kW. Due to limited voltage capacity of PV modules it is not suitable to extend the rated power of single string. General structure of multi-string inverter configuration is shown in Fig. 6. The solution for the above stated problem is overcome by multi-string inverter. The attractive features of the multi-string inverter are the rated power of converter unit is not limited, reduction the installation and better efficiency.

A. Centralized Inverter The centralized inverter technology that interfaced a

large number of PV module were divided into series connections [16]. These series connections were connected in parallel with the help of string diodes. The series connections made a high voltage to avoid further amplification and parallel combinations of PV modules to achieve high power level. Today, central inverters are available upto a power level between 1MW and 2 MW. However this development trend towards larger and larger inverter is driving higher external costs. It is shown in Fig. 7. Centralized inverter has some limitations such as mismatching problem that occur between the PV modules additional losses due to the presence of string diodes and power losses due to a centralized MPPT. The grid connected stage was involving thyristors devices. A basic characteristic of thyristor devices is commutated by neutral communication, due to presence of thyristors to introduced


407

ISBN : 978-1-4673-5144-7/12/$31.00 2012 IEEE

current harmonics and power quality problems. These problems are eliminated by string inverter topology.

Fig. 7 Centralized inverter topology

B. String Inverter The string inverters are an attractive alternate to central

inverter in PV systems [16]. String topology consists of the string inverter module. The string topology is an advanced method of centralized inverter. The input voltage of this topology may be high enough to avoid voltage amplification [15]. The basic structure of the string inverter topology is represented in Fig. 8. The main feature of the string topology is that there is no losses and individual MPPT can be applied to the each string which increases the overall system efficiency and limited price rating due to absence of string diodes. String inverters of today offer the major advantages of central inverters such as high DC system voltage range and three-phased output while maintaining the high efficiencies.

Fig. 8 String inverter topology

This leads to reduced losses inboth AC and DC cabling assuring higher yield. A large number of maximumpower point trackers ensure that more power from the panels is utilized. Additionally, string combiners and external string monitoring are not required thus making simple cabling possible.

C Multi-String Inverter The Multi-string inverter is the further development string

inverter [7], where several strings are in interfaced with their own DC-DC converter to a common DC-AC inverter. The multi-string inverter concept [15], [17] has been developed to combine the advantage of higher energy yield of a string inverter with the lower cost of a central inverter. In this topology shown Fig. 9 every string can be controlled individually. To expand the system within a certain power range only a new string with a DC/DC converter has to be included. All DC/DC converters are connected via a DC bus through a central inverter to the grid.

Fig. 9 Multi string inverter topology

The central inverter is a PWM inverter based on the well-known and cheap GIFT technology already used in drive systems and includes all supervisory and protection functions. Depending on the size of the string the input voltage ranges from 125 to 750 V. The inverter has a maximum power rating of 5 kW and become available in 2002. Further developments are easily achieved since a new string with DC-DC converter can be plugged into existing platform. It is easily designed with higher operating efficiency can be achieved.

V. MODULATION TECHNIQUES FOR MULTILEVEL INVERTER

Many pulse width modulation techniques are adapted to the multilevel inverter topologies. These techniques are most effective way of controlling for photovoltaic applications. In order to control the inverter, multi carrier PWM techniques are presented in [12]. In general, the phase displacement between any two of adjacent triangular carrier is free, hence number of combinations can be considered as follows: The carrier signals are alternatively in opposition All carrier signals above the zero value reference are

in phase but in opposition with those below. All carrier signals are in phase. The multilevel phase opposition multicarrier disposition

method was used to generate the switch gate signals for the multilevel inverter is presented [12]. The modulation index Ma for a five level inverter is presented [20]


408

ISBN : 978-1-4673-5144-7/12/$31.00 2012 IEEE

(2)

Where: Ac is the (Pu) carrier peak to peak value Am the peak value of the modulating signal.

A novel PWM control scheme for the PV application is recently presented by J.Selvarj [1]. This control scheme has two references signal which are identical to each other with an offset equivalent to the amplitude of carrier signal are used to generate PWM signals for switches and three reference signals compare with offset value is possible in feature. Furthermore, several modulation and control strategies have been developed or adapted for multilevel inverters, including multilevel sinusoidal PWM, selective harmonics elimination, and space vector modulation. [5] In a novel isolated single phase inverter with generalized zero vector modulation scheme was first presented by C.T. Pan and W.C Tu, nevertheless, this circuit can still only operate in a limited voltage for real time applications and also reduces overall efficiency of the boost converter at front end. Solution for the above stated problem is overcome by newly constructed transformer less five level multi string inverter topologies for DERs has been presented in [19].

VI. CONCLUSION This survey paper has covered some of the recommended

standard of PV system, principle of integration issues, prices, world energy scenario and photovoltaic module with their V-I characteristics. The different multilevel structures such as (i) Diode clamped (ii) Flying capacitor (iii) Hybrid inverter have been discussed and also various type of inverter topologies for PV systems is reviewed. Furthermore various modulation schemes for grid connected PV system have been discussed in this review.

REFERENCES [1] N. A. Rahim and S. Michele, Implementation of three-phase grid

connected inverter for photovoltaic solar power generation system, in Proc.IEEE Power Con, Oct. 2002, vol. 1, pp. 570573.

[2] N. A. Rahim and jayarajselvaraj, multistring five- level inverter with novel PWM control scheme for PV application, IEEE transactions on industrial electronics, vol. 57, no.6, June 2010.

[3] IEC, Characterises of the utility interfaces for photo voltaic systems, IEC 61727CDV, 2002.

[4] IEEE standard for interconnecting distributed resources with electric power systems, IEEE std.1547, 2003.

[5] National electrical code, National fire protection association,inc., quincy, MA, 2002.

[6] Grid connection of PV generator: Technical and regulatory issues.

[7] REN 21 Renewables 2010 Global Status Report, 2010. [8] G. Carrara, S. Gardella, M. Marchesoni, R. Salutari, and G.

Sciutto, A new multilevel PWMmethod: A theoretical analysis, IEEE Trans. PowerElectron., vol. 7, no. 3, pp. 497505, Jul. 1992.

[9] R. Gonzalez, E. Gubia, J. Lopez, and L. Marroyo, Transformerlesssingle-phase multilevel-based photovoltaic inverter, IEEE Trans. Ind.Electron., vol. 55, no. 7, pp. 26942702, Jul. 2008.

[10] M. Calais, V. G. Agelidis, and M. S. Dymond, A cascaded inverter for transformerless single phase grid-connected photovoltaic systems, in Proc. IEEE 31st Annu. PESC, Jun. 1823, 2001, vol. 3, pp. 11731178.

[11] A. Nabae, I. Takahashi, and H. Akagi, A new neutral-point clamped PWM inverter, in Proc. IEEE Ind. Appl. Soc. Conf., 1980, pp. 761766.

[12] N. S. Choi, J. G. Cho, and G. H. Cho, A general circuit topology of multilevel inverter, in Proc. IEEE Power Electron, Specialists Conf., Cambridge, MA, 1991, pp. 96103.

[13] Sergio Daher, JurgenSchmid, and Fernando L. M. Antunes, Multilevel Inverter Topologies for Stand-Alone PV Systems, IEEE Transactions on industrial electronics, vol. 55, no. 7, July 2008

[14] O. Lpez, R. Teodorescu, and J. D. Gandoy, Multilevel transformerless topologies for single-phase grid-connected converters,inProc. IEEE Ind.Electron. Conf., Paris, France, 2006, pp. 51915196.

[15] B. Verhoevenetall Utility aspect of grid connected photo voltaic power systems, International energy agency photovoltaic power systems, IEA PVPS T5-01:1998.

[16] M. Calais, J, Myrzik, T. Spooner, and V. G. Agelidis,Inverter for single phase grid connected systems, An Overview in proc. IEEE PESC 02, vol. 2, 2002, pp. 1305-2000.

[17] M. Meinhard and G. Crammer, Past, present, future of grid connected photovoltaic systems and hybrid power systems, Inproc, IEEE,ISIE summer meeting, vol. 2, 2000, pp.1283-1288.

[18] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, A review of single-phase grid connected inverters for photovoltaic modules, IEEE Trans. Ind.Appl., vol. 41, no. 5, pp. 12921306, Sep./Oct. 2005.

[19] Yi- Hung Liao and Ching-ming Lai, Newly constructed simplified multistring multilevel topology for distributed energy resources, IEEE transaction on power electronics, July 2011.

[20] V. G. Agelidis, D. M. Baker, W. B. Lawrance, and C. V. Nayar, A multilevel PWM inverter topology for photovoltaic application, in Proc.IEEE ISIE, Guimaraes, Portugal, 1997, pp. 589594.

/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 200 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages false /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 400 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 600 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False

/CreateJDFFile false /Description >>> setdistillerparams> setpagedevice

Survey Grid Connected PV

Documents

Transcript of Survey Grid Connected PV