High Efficient Bidirectional Battery Converter for Residential PV Systems Cam Pham Department of Energy Technology Aalborg University Aalborg, Denmark cpham05@student.aau.dk Tamas Kerekes Department of Energy Technology Aalborg University Aalborg, Denmark tak@et.aau.dk Remus Teodorescu Department of Energy Technology Aalborg University Aalborg, Denmark ret@et.aau.dk Abstract— Photovoltaic (PV) installation is suited for the residential environment and the generation pattern follows the distribution of residential power consumption in daylight hours. In the cases of unbalance between generation and demand, the Smart PV with its battery storage can absorb or inject the power to balance it. High efficient bidirectional converter for the battery storage is required due high system cost and because the power is processed twice. A 1.5kW prototype is designed and built with CoolMOS and SiC diodes, >95% efficiency has been obtained with 200 kHz hard switching. Keywords - Split converter, Dual phase converter, bidirectional DC-DC converter, Smart PV converter, Battery converter, SiC, CoolMOS. I. INTRODUCTION To prevent the climate change caused by the human activities, worldwide governments work on a common goal – to reduce carbon dioxide emission. The Danish energy policy in year 2025 for power system is to have 50 percent of power production to be generated from renewable sources and to be independent of fossil fuels in year 2050 [1]. Compared to wind power, PV installation is more accepted in residential area and the generation follows the residential power consumption pattern during daylight hours. In cases of unbalance between generation and demand, the Smart PV with its battery can absorb or inject the power to balance it. Beside functionalities of an inverter with storage, the Smart PV can support with reactive power and communicate with the grid. Together they make Smart PV an essential component of grid infra structure. Sol-ion project took place between March 2008 and December 2011 and in this project industries and research institutes from France and Germany collaborated to develop an innovative and competitive PV energy system. The energy management system (EMS) of the Sol-ion project for self- consumption is depicted in Fig.1, where the batteries will be discharged when there is no or insufficient generation from the PV. In case of surplus generation, the energy is stored in batteries and feed in when the batteries is charged [2]. Back in 2009, the average unit price of electricity for residential householders in Denmark was nearly 0.236€/kWh, but only 25 % of the price is the electric energy [3]. In the long term, self generation is an economic benefit and with storage capability, the benefit can be maximised by trading electricity with Spot Price from Nordpool. The stored energy can either be supplied or sell to the grid, when the spot price swings up. The Sol-ion self-consumption system is illustrated in Fig. 2, where PV and battery are boosted to a common DC link voltage and an inverter is used for grid connection. For three phase systems, 700V DC link is required to generate 400Vac. A high efficient bidirectional DC-DC converter for battery storage is needed to reduce the payback time, because the energy price from PV generation is high due to the system cost and the energy is processed twice; charge and discharge. II. TOPOLOGIES Numerous references have been reported about bidirectional DC-DC converter. Basically it can be divided Fig.2 An overview of the Sol-ion system Fig.1 The EMS from Sol-ion project [2]