M. Mohanraj et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 2( Version 1), February 2014, pp.633-637 www.ijera.com 633 | Page Implementation of Inverter with Flexible Voltage Control for A DC Line in a System M. Mohanraj*, R. Lalitha** *(Department of Electrical and Electronics Engineering, Kumaraguru College of Technology, Coimbatore-46) ** (Department of Electrical and Electronics Engineering, Kumaraguru College of Technology, Coimbatore-46) ABSTRACT Due to raising demands in electric power it becomes more important to use the available energy sources efficiently and along with them the distributed generation comes into picture which means collection of energy from many small sources say RES. For distribute generation (DG) systems a challenging issue is to smartly integrate renewable-energy sources into the grid as it leads to power quality problems under fault conditions. Another approach for meeting the power demand is to implement TEP .This work proposes an method which uses a control algorithm for inverters for providing a flexible voltage control using reference current generation under grid faults. The controlled inverter designed is used for inversion processes at the receiving end in a HVDC line. A system with three sources is considered, their performances if the three lines connecting three sources are AC lines and if one line is replaced with a DC line is studied. Keywords – Distributed Generation, High Voltage DC Transmission, Renewable energy sources, Transmission Expansion Planning. I. Introduction The Transmission expansion planning exercise aims for improving the security and reliability of power systems without taking economics as primary concern. Network expansions can be carried out by AC as well as DC model each having their merits and demerits. Compared to ac transmission the high voltage DC transmission (HVDC) has certain advantages which are stated as minimized power losses for long transmission lines, capability of delivering bulk power etc. It is considerable that the DC transmission system is most suitable for delivering the non-conventional energy sources from sites to load centre. A DC transmission system consists of two and more converters. One end converters will be used as rectifiers and another converter will be used as inveter.The inverter used here will be provided with a control scheme which will provide different voltage support strategies for different voltage sags under grid fault conditions. A control algorithm for flexible voltage control using reference current generation under grid fault condition is discussed in this work. Nowadays DG penetration into the grid sources is rapidly increasing and so the control schemes with high performances are required. This ensures the proper operation of DG systems especially under grid fault conditions. The proposed work here gives an idea of using current mode three phase inverters to support the grid voltage, whereas the behaviour of inverter is commanded by a controller unit. These type converters finds applications in HVDC lines for implementing the DC model TEP.A comparison will transmitted power and the voltage sag compensation in an AC and DC lines will be made here. The work here is done by considering a simple three bus system with all the three buses connected by AC lines and also another three bus system where any one line is replaced by DC line which uses controlled invereter.The voltage sag compensation is studied using simulation and also comparison between the transferred power of two models is done here. FIG.1.Block diagram of Flexible voltage control II. Flexible voltage control For DG system to be smartly integrated into the grid, a very important issue is to provide voltage support flexibly according to various voltage sags that occurs under various grid fault conditions. If the grid is suffered from a balanced three phase fault, the inverter will be injecting reactive power to raise the voltage levels in all three phases. If the fault occurred is unbalanced (i.e.) if one or two phase fault occurs, RESEARCH ARTICLE OPEN ACCESS