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Power Electronics andControl Research Group
A STANDA STAND--ALONE PHOTOVOLTAIC SYSTEM ALONE PHOTOVOLTAIC SYSTEM BASED ON DCBASED ON DC--DC CONVERTERS IN A MULTIDC CONVERTERS IN A MULTI--
STRING CONFIGURATIONSTRING CONFIGURATION
J. Imhoff, G. F. Rodrigues, A. R. Bülow, R. Gules, J. R. Pinheiro and H. L. Hey
Power Electronics andControl Research Group
OutlineOutline
• Introduction;Motivation;
• Photovoltaic Systems (PV systems);Centralized Photovoltaic Systems;Decentralized Photovoltaic Systems;
• MPPT Technique Choice;• Simulation Results;• Summary;• Next Steps.
Power Electronics andControl Research Group
IntroductionIntroduction: : MotivationMotivation
• 12 million Brazilians remain without electricity (~80% in rural areas);
• Brazil is among the countries that present the highest incidence solar energy.
Source: ANEEL - Atlas de Energia Elétrica do Brasil
Power Electronics andControl Research Group
IntroductionIntroduction : : MotivationMotivation
Photos Credit: Harin Ullal (NREL PIX)
© Minister of Natural Resources Canada 2001 – 2004.
• 100% natural, free and inexhaustible;• Locally generated energy;• Modular, silent and reliable.
•• Irregular energy supplied;• Low efficiency;• Expensive technology.
BenefitsBenefits:
DrawbacksDrawbacks::
Power Electronics andControl Research Group
IntroductionIntroduction: : MotivationMotivation
• Shortage of fossil fuels;• Crescent reduction in the costs of PV Systems;• Increase in the acceptance of PV Systems.
Source: Development of the PV industry in Europe," Sustainable Energy 2005 (EPIA)Source: Department of Energy/ US
Power Electronics andControl Research Group
Photovoltaic SystemsPhotovoltaic Systems
•• PV systems can be classified as:PV systems can be classified as:Grid-connected systems;Stand-alone systems;
Centralized Based Concept Topology;Decentralized Based Concept Topology.
Power Electronics andControl Research Group
Centralized Photovoltaic SystemCentralized Photovoltaic System
Centralized MPPT;Low utilization of the generated
energy;Battery bank is placed in the power
path;Reduced life cycle of the batteries.
Features:
Single array of PV panels (series and/or parallel connection);Single DC-DC converter to realize the MPPT.
• The most widely spread stand-alone PV system.
Power Electronics andControl Research Group
Proposed SystemProposed System
As an alternative to centralized configuration,As an alternative to centralized configuration,a standa stand--alone photovoltaic systemalone photovoltaic system
with distributed energy processing is proposedwith distributed energy processing is proposed..
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Decentralized Photovoltaic SystemDecentralized Photovoltaic System
Features:
Division of the PV array in strings;Each string has its own non-isolated DC-DC boost converter to
perform the MPPT;DC-DC boost converters are connected in series;Integrated buck and boost converters, with bi-directional power flow
control, dedicated to the battery bank.
Power Electronics andControl Research Group
Decentralized Photovoltaic SystemDecentralized Photovoltaic System
Features:Individualized MPPT;Modularity;PV strings can be installed at different orientations;Smaller individual converter power ratings;The battery bank is out of main power path;Longer life cycle of the batteries.
Power Electronics andControl Research Group
MPPT Technique ChoiceMPPT Technique Choice
•• Constant Voltage (CV);Constant Voltage (CV);•• Perturbation and Observation (PO);Perturbation and Observation (PO);•• Incremental Conductance (Incremental Conductance (IncCondIncCond).).
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Power Electronics andControl Research Group
Incremental Conductance TechniqueIncremental Conductance Technique
• This technique presents good steady state and dynamic response results;
• The Power x Voltage curve of the array of PV panels is employed to track the MPP.
0dPdV
=
( ) 0dP d IV dII VdV dV dV
= = + =
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Power Electronics andControl Research Group
Input Stage Simulation ResultsInput Stage Simulation Results
• It is presented the simulation results for the input stage of both: the centralized stand-alone PV system and the proposed decentralized stand-alone PV system for the following conditions:
1) For both system the panels are under the same radiation;
2) Some of the PV panels are submitted to a decreased radiation, characterizing shading/failure/aging of such panels.
Power Electronics andControl Research Group
Centralized PV System
Proposed PV System
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20
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Simulation Results: Case 1Simulation Results: Case 1
~480 W
~480 W
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Centralized PV System
Proposed PV System
Simulation Results: Case 2Simulation Results: Case 2
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20
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Pow
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) ~404 W
~343 W
Power Electronics andControl Research Group
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• In the case studied, the Proposed Topology delivered up to 17% more energy to the DC bus, when compared to the centralized system.
Centralized vs. Proposed SystemCentralized vs. Proposed System
Gain 17%
Power Electronics andControl Research Group
SummarySummary
• Stand-alone photovoltaic systems are traditionally based on centralized structures;
• The work introduced a stand-alone photovoltaic system topology, based on decentralized structures;
• In the case studied the proposed topology delivered up to 17% more energy to the DC bus, when compared to centralized systems..
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Next StepsNext Steps
•• System implementation;System implementation;•• New design methodology; New design methodology;
Efficiency optimization;PV panels cost reduction.
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AcknowledgementAcknowledgement
PPGEEPrograma de Pós-Graduaçãoem Engenharia Elétrica - UFSM
C A P E S
CNPqConselho Nacional de Desenvolvimento
Científico e Tecnológico
