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CU-Boulder ECEN 4517 - Miniaturised “Low Profile” Module Integrated Converter

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Miniaturised “Low Profile” Module Integrated Converter for Photovoltaic Amlications with Integrated Magnetic Components Mike Meinhardt, Terence O’Donnell, Henning Schneider, John Flannery, Cian 6 Mathuna PE1 Technologies, National Microelectronics Research Centre, Lee Maltings, Cork, Ireland, Email: [email protected] Phone: +353 21 90 42 41, Fax: +353 21 270 271 Abstract This paper deals with reliability aspects of Module Integrated Converters (MIC) for grid connected photovoltaic applications. The presented “Low Profile Design” of a MIC has almost twice the power density and a 70% longer lifetime than commercially available MICs. In order to miniaturise and increase the reliability of the MIC all magnetic components have been realised using planar cores and windings integrated into PCB. Additionally the converter’s resonant inductor has been integrated into the transformer by using the leakage inductance as the inductor. The leakage inductance of planar transformers with integrated windings can be adjusted very precisely. 1 INTRODUCTION The use of renewable energy sources and rational use of energy are fundamental pillars of a responsible energy policy for the future. Because of their sustainable character, renewable energy sources almost exclusively based on solar energy are capable of preserving resources and providing energy services virtually without any environmental impact. Therefore, intensive research and development in solar energy technologies are justified and necessary. Grid connected Photovoltaic (PV) systems distinguish themselves Figure 1: Cross-section of a MIC mounted to the frame of a solar module Peter Zacharias, Thomas Krieger Institut fuer Solare Energiesysteme e.V. Koenigstor 59,341 19 Kassel, Germany Email: pzacharias @iset.uni-kassel.de Phone: +49 561 7294 -0, Fax: +49 561 7294 -100 through the lack of a need for energy storage devices such as batteries. Grid connected Ehotovoltaic (PV) systems include in general a solar module transforming sunlight into electrical energy and a converter connecting the solar module to the grid. As shown in Figure 1 a (solar) Module Integrated Converter (MIC) for PV applications is mounted directly to the frame of a solar module The combination of MIC and solar module - often called “AC Solar Module” - allows a direct connection of the solar modules to the grid by converting the module DC voltage to a 230 V AC voltage. Recent investigations have shown that - Module Integrated Converters for Photovoltaic applications have some important advantages over string orientated or central inverter concepts such as: - Increased energy yield in case of systems suffering from shading effects. - Reduced danger of arcs due to replacing the DC installation by an AC installation. - Simplified configuration of PV systems due to standardised interface (220 V-). Nevertheless in the future central inverter concepts will still be used especially in very large-scale PV systems. Depending on the PV system’s site and properties of installation string oriented systems are likely to be used in the medium power range. Reliability is the issue Since the MIC is part of the solar module, the electronic elements of the MIC are exposed to extreme environmental conditions (e.g. temperature, humidity and lightning). This high thermomechanical stress determines the lifetime of the MIC, which should exceed 15 years in order to approach the lifetime of the solar modules themselves. Miniaturisation and cost reduction are required. These aspects are conflicting and lead to a need for advanced power packaging solutions to find a compromise between cost, miniaturisation and reliability requirements. 0-7803-5160-6/99/$10.00 0 1999 IEEE. 3052 WORLD MARKET FOR MODULE INTEGRATED CONVERTERS Figure2 shows the results of a survey of different predictions of the development of the PV market. Even considering the two most pessimistic forecasts published in 1993 the PV market in 2005 will be about 300 ... 400 MW, world wide. If one third of PV production is used for grid connected or similar application in 2005 the potential market for AC modules would be 100.. .130MWp. Assuming that at this time two thirds of this market volume will be occupied by other converter concepts (in kW range) a more or less realistic market expectation for Module Integrated Converters (MIC) could be 55 ... 65MWp per year. Considering the rated power of one MIC in a range of 100 ... 300Wp this market volume corresponds to 160,000 ... 500,000 pieces per year in 2005. 3500 I I SU (ACC) 92 I I SU (ACC) 92 I c 2000c .I 4 1995 2000 2005 2010 Year Figure 2: World wide PV market increase [ 11 3 MODULE INTEGRATED CONVERTER 3.1 The block diagram shown in Figure 3 illustrates the different components of the MIC. Structure and Mode of Operation Solar I I ,p kHZ Hz I I Grid 1 1 I I I I Control (5) (incl. voltage, current and temp. sensors) Module Integrated Converter (ME) MIC.dem~AI Figure 3: Schematic of the Module Integrated Converter The solar module on the left generates a maximum power of 110 W at a voltage between 26 V and 37 V. The MIC transforms the DC-power into grid conformant AC power (50/60Hz). The basic structure of a MIC is similar to conventional Switch-Mode-ACIDC-Power-Supplies. The main magnetic components are a resonant inductor, transformer and line inductors. In order to increase the efficiency and decrease the required size of the converter the resonant inductance is integrated in the transformer. This topic will be dealt in detail in section 4. 3.2 Although the back of the solar module gives a relatively large area for mounting a MIC and therefore there is no direct need for miniaturisation of the entire MIC, it is proposed to target a “low profile” MIC design with a high power density for the following reasons: - A much simplified thermal model [2] shows that a decreased height of a MIC leads to reduced component temperatures and consequently to a higher reliability of the MIC. The MIC can easily be mounted to the frame of the solar module and due to the reduced weight the mechanical connection is more reliable and cheaper. The power density of power supplies is commonly used as a general measure of technical advancement. A


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CU-Boulder ECEN 4517 - Miniaturised “Low Profile” Module Integrated Converter

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