مطالعه در مبدل DC-DC کاسکد برای استفاده در فتوولتائیک ساختمان یکپارچه Study on a cascaded DC-DC converter for use in Building-Integrated Photovoltaics

I. Introduction The Strategic Energy Technology (SET) Plan [1] of the European Commision (EC) aims to reduce the emissions of carbon by encouraging the use of alternative energy sources. Specific implementation of the SET-Plan in the building sector has lead to a new legislation for buildings. By the end of 2018, all new buildings of public authorities need to be near-Zero-Energy-Buildings (nZEB), while by the end of 2020 all new buildings need to be nZEB. NearZero-Energy-Buildings are constructed in a way that their energy consumption is very low compared to traditional buildings, and the required energy is mainly produced locally via renewable sources [2]. Building Integrated PhotoVoltaics (BIPV), applied in the fa¸cade of the building seem to be a very attractive solution to enable the required targets and is also stimulated by the EC. This technology tries to integrate the PV panels inside other building elements such that multiple functions can be combined. In this specific case, a fa¸cade, offering protection against external influences is combined with an energy-generating device. Due to the non-ideal orientation of the PV panels to the sun and the possibility of partial shading due to other buildings or entities near the building, a module-level converter is often set forward as a better solution compared to the more traditional string inverter where arrays of PV panels are connected in series or in parallel [3]. To further enhance the full potential of BIPV, integrating it into a DC microgrid offers several advantages compared to AC microgrids. The first one being that less copper is required to transfer the same amount of power in a DC grid. A second advantage is that less conversion steps are required to convert the DC power produced by the panels. This leads to higher overall system efficiency, higher reliability and simplifies the control. A third advantage is that the interchanging power with other DC appliances, such as energy storage devices, is also more efficient which can lead to significant energy savings in commercial and residential buildings [4]. The system of interest is shown in Fig. 1. Three parts can be distinguished: the PV panel, the DC grid and the module-level converter connecting both aformentioned parts. Notice that the module-level converter is an integrated part of the BIPV module and leads to an additional feature, which is the conditioning of the uncontrolled PVgenerated power. The module-level converter only injects power to the DC grid and does not control this voltage level. This is usually done in a centralized AC/DC converter as described in [5]. This paper is constitued as follows: In section II, the specific challenges for BIPV converters are discussed. From these requirements, section III proposes a circuit topology that covers these aspects and section IV describes the chosen component values. Section V describes the dynamics of this converter and shows the simulation results. Section VI discusses the experimental prototypes and section VII presents the conclusion.