16 th International Middle- East Power Systems Conference -MEPCON'2014 Ain Shams University, Cairo, Egypt, December 23 - 25, 2014 A proposed technique for bidirectional grid connected PV system G.El-Saady, El-Nobi A.Ibrahim, Mohamed EL-Hendawi Electrical Engineering Department, Faculty of Engineering, Assiut University Abstract - The present paper proposes a novel technique for bidirectional grid connected PV system. The analysis and implementation of a series connected PV system for grid- connection are developed. The objective of the gateway DC-AC conversion system is to develop a low-cost conversion system for clean residential electricity. The proposed grid connected PV system prototype has a combination of DC-DC, DC-AC and/or AC-DC converters for the flexible and uninterruptible energy utilization. A buck converter is used for the maximum power point tracking (MPPT) implementation and also it presents the functions of battery charger and step-down converter. Further the DC-DC converter realizes phase shifting to control power flow through a transformer with a MOSFET full bridge on the low voltage side (LVS). In addition, a voltage doubler on the high voltage side (HVS) is installed to achieve enough high voltage to run the inverter. The inverter is connected to the utility grid through the LC filter. The inverter operates as a current- controlled source to generate an output current based on a reference current signal. The operation principle, theoretical analysis and simulation results are presented .The digital simulation results prove the effectiveness of the proposed PV system in terms of fast response ,high efficiency and best waveforms of output voltage and current. Index Terms - utility grid, current control, battery charger. I. INTRODUCTION Renewable energy sources become a more and more important contribution to the total energy consumed in the world. Because of their independence from limited fossil and nuclear fuels and their low impact on the environment will become the only crisis-proof and reliable energy supply within the next decades. In several countries including Australia, an increasing number of PV generation systems are connected to the distribution network as a result of strong government support [1]. The PV market is growing rapidly (30–40%), and its price is constantly decreasing. Many countries are trying to increase the penetration of renewable energy. The US plans to meet up to 20% of electricity demand with solar technologies by 2030. Australia also promises to achieve 20% power generation from renewable energy by 2020 [1]. Towards the end of the last millennium, the primary market for PV was in off-grid applications, such as rural electrification, water pumping, and telecommunications. However, now majority of the global market is for grid-connected applications where the power is fed into the electrical network. Furthermore, most of the new PV capacity has been installed in the distribution grid as distributed generation. Although PV energy has received considerable attention over the last few years, the high installation cost of PV systems and the low conversion efficiency of PV modules are the major obstacles to using this alternative energy source on a large scale. Therefore, many studies are being researched in order to minimize these disadvantages. In this paper, a simple but efficient PV system is presented. It investigates power electronic devices that significantly increase the system efficiency. At last, it presents PSIM simulations for grid connected system with MPPT. The power electronics interface is essential to connecting renewable energy sources to the grid. This interface has two main functions: extracting the maximum amount of power from the PV modules and conversion of DC power to an appropriate form of AC power for the grid connection [2]. There are a lot of strategies to connect PV systems to utility. A single stage PV system connects the PV panel to inverter directly as shown in Fig.1a [3], [4]. This system have high efficiency and cheaper than the two stage system. But it has a lot of disadvantage (1) There is no converter to increase or decrease the input voltage to the inverter .Or it is must to use large transformer. (2) There is no energy storage like batteries to store the energy if the utility is disconnected. The two stage system as shown in fig.1b is more efficient but it does not have batteries to store the energy if the utility is disconnected [5], [6]. II. DESCRIPTION OF THE PROPOSED GRID CONNECTED PV SYSTEM Fig. 2 shows the overall proposed grid connected PV system .The developed conversion system depicted in Fig. 2 provides energy to both DC and AC load from PV panels and ac grid together. The PV panels are connected via the DC input terminal; the utility AC grid is plugged in through the AC input. Besides, a 48V battery stack is paralleled with the DC output terminal on the purpose of energy storage. In order to extract the maximum power of the PV array, the implementation of MPPT in stand-alone/grid-connected systems is generally accomplished by the series connection of a