The Main Configurations of Solar Electrical Systems and Photovoltaic Invertors Topologies.pdf

7/30/2019 The Main Configurations of Solar Electrical Systems and Photovoltaic Invertors Topologies.pdf

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THE MAIN CONFIGURATIONS OF SOLAR ELECTRICAL SYSTEMS AND

PHOTOVOLTAIC INVERTERS TOPOLOGIES

TIMOFTE Daniel*, UNGUREANU Marius-George*

*Naval Academy Mircea cel Btrn, Constana, Romnia

1. IntroductionThe number of classical energy sources (thermal power stations, atomic plants) could be

substantially reduced by using nonconventional energy conversion systems as solar panels, wind

turbines, wave energy converters(WEC) etc., having as benefits a lower pollution, a renewal of

local resources and the creation of a modern energetical industry with major economy impact.[1]By converting solar energy, the global installed power between 1992 and 2004 had an

exponential growth to 2.5GW by a total of 3.7GW. By 2020s, the cost of the solar panels is

estimated to decrease to half and the global installed power will have gained 1GW.[5]

Solar energy conversion is realized by Photovoltaic (PV) Systems, using solar panels to

transform sun radiation to electrical energy. The PV System operates by concentrating sunrays from

a large surface to a smaller one (1cm2); this way, water cooled PV cells are capable to reach high

temperatures and a 38-40% eficiency.[3]

PV Systems come in various shapes, dimensions and powers(e.g. 25kW 850W/m2) and may

work individually or as a part of a grid.[6] In practice are used by satellites, race cars and houses.

2. The main configurations of PV SystemsThe solar panels are connected serial or parallel to a monophasic or triphasic inverter, which

converts the DC produced by panels to AC, on photovoltaic effect basis. The cells are connected

serial in a panel, one cell being capable of producing 1-4W.

Fig. 1. Various

configurations of solar

systems


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On high power systems (10 - 250kW), the panels are connected parallel to a triphasic central

inverter. This configuration is defined by high efficiency, low costs and a lack of safety and

reliability.

A second solution, designed for medium powes(1.5 - 5kW) is to provide each row of panels with

an individual inverter. This way, the system works with maximum eficiency, no matter how the row

is orientated; for powers smaller than 5kW triphasic inverters are required.

The third configuration contain small power modul inverters(50180W) for each panel and isdefined by having a pretty high cost, a difficult maintenance and low efficiency.[4]

3. Various converters topologies for PV invertersA large variety of converters tolpologies is dedicated to PV Systems, generally depending on

power and galvanic separation requirements.

Two quadrant PV inverters are mostly used in residential applications, having an installed power

up to 4.5kW. Configurations which lack transformers for galvanic separation are more attractive,

mainly because of the high efficiency.[3]

Fig. 2. The main components of a PV inverter

As shown in fig. 2, a PV inverter may contain a DC-DC converter (for boosting the voltage) and

a transformer for galvanic isolation.[1] The need of using coverters comes from the fact that the

continuous voltage is much lower than the grids one.[3]

3.1.

PV inverters with DC-DC converters and isolation transformers

Fig. 3 illustrates the block diagram of a PV inverter wich contains a DC-DC converter. The

differebce between the two configurations is the transformers emplacement: on the low frequency

LF side (3.a) or on the high frequency HF side (3.b).


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Fig. 3. Block diagram of a PV inverter with DC-DC converter

The solution presented in fig. 3.b is a more compact one but has a more complex design. A

classical detailed circuit of a PV inverter is shown in fig. 4; the inverter has a full bridge

configuration, activated by pulse width modulation(PWM). This topology is generally used for

powers bigger than 750W, with low continuous input voltage. The benefits are: a good efficiency of

the HF transformer, amall losses and high performance; the dimension and the complexity are some

of the drawbacks.

Fig. 4. PV inverter with bridge configuration

3.2. PV inverters with DC-DC converters, withut isolation transformersThis type of inverters is gaining more and more popularity due to high frequency, especially in

Japan and Germany where the galvanic isolation isnt necessary.

The solution has the benefits of a >96% efficiency(due to the lack of the transformer) and a

compact design, but requires an aditional diode.[2]


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Fig. 5. The block diagram(a) and the detailed diagram(b) of a PV inverter w/o trafo

3.3. PV inverters without DC-DC converterAre used on a small scale, particulary on low input voltage applications. The classical solution

encapsules a full bridge inverter, with (Fig. 6.a) or without(Fig. 6.b) isolation transformer.

Fig. 6. The solution (a) has the drawback of a large volume, due to the transformer.


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4. ConclusionSolar energy is a promising source with a huge potential. Due to high pollution, high costs and

exhausting resources, the replacement of classical energy sources by renewable ones has become a

necessity. More than anything, we need to change our perspective and look forward to invest....ETC

ETC

References:

1.

F. Blaabjerg, Z. Chen and S.B. Kjaer,Power electronics as efficient interface in dispersedpower generation systems, IEEE Transaction on Power Electronics, vol. 19, pp. 1189-1194, Sept.

2004.

2. J.M.A. Myrzikand M. Calais; String and Module Integrated Inverters for Sigle-PhaseGrid Connected Photovoltaic SystemsA Review; 2003 Bologna PowerTech Conference, 23-26

June, Bologna, Italy.

3. N. Mohan, T. Undeland, P.W. Robbins,Power Electronics. Converters, Applications andDesign, John Wiley & Sons, 2003, ISBN:0471226939.

4. ***www.iea-pvps.org, IEA Photovoltaic Power Systems Programme.5. ***www.enerdata.fr/enerdatauk/, World energy statistics databases, forecast and analyses.6. ***www.sunlight.gr, Systems Sunlight S.A.

Fig. 7. The detailed diagrams

of the two types of inverters

presented in Fig. 6

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The Main Configurations of Solar Electrical Systems and Photovoltaic Invertors Topologies.pdf