2014 Ninth International Conference on Ecological Vehicles and Renewable Energies (EVER) 4-Wire Matrix Converter Based Voltage Sag/Swell Generator to Test LVRT in Renewable Energy Systems Matias Diaz University of Chile Av. Tupper #2007 Santiago,PC 8370451 ,Chile Roberto Cardenas University of Chile Av. Tupper #2007 Gustavo Soto University of Santiago of Chile Av. Ecuador #3553 Santiafo,PC 8370400,Chile Email: gmatias.sotob@mail.com Santiago,PC 8370451,Chile Email: matias.diaz@ing.uchile.c1 Email: rcd@ieee.org Abstract- The incorporation of high power rate Wind Energy Conversion Systems (WECS) have signiicant inluence in the stability, power quality and reliability of the electrical grid. Therefore, strict grid codes have been developed during the last years in order to enhance overall stability of the systems. Thereby Low Voltage Ride Through (LVRT) requirements is a key issue for WECS. In order to test the response of WECS under grid-voltage sag conditions, a Voltage Sag Generator (VSG) is needed. This paper presents a novel Matrix Converter based VSG Prototype in order to study the fulilment of LVRT requirements. Voltage sags/swell of variable magnitude, duration and type can be generated for the proposed VSG without using complex modulation schemes. Keywords- Wind Energy Conversion Systems, Voltage sag Generator, Matrx Converter, Lo Voltage Ride Throgh. I. INTRODUTTON The huge penetration of WECS into the utility grid has a signiicant inluence in the stability, power quality and availability of conventional power systems. In order to avoid stability problems and to regulate the interconnection of WECS to generation and transmission systems, grid codes have been published in several countries, where renewable energies have a considerable impact into the grid. A detailed review of international grid code requirements can be found in [1] and [2]. Voltage sags are the most prevalent disturbances in electrical power system. Recent surveys indicate that 92% of all disturbances correspond to voltage sags [3]. Consequently, grid codes mainly set Low Voltage Ride Through capability, demanding WECS to remain connected in presence of grid-voltage sags, contributing to the grid-stability during the fault. During design and development of WECS, voltage-sag test -according to 978-1-4799-3787-5/14/$31.00 2014IEEE international standards- should be conducted to conirm the voltage-sag ride through capability of the systems. Hence, devices to generate grid-voltage sag (called voltage sag generators) are required. According with IEC 61400-4-11 and IEEE 1159 standards, VSG must provide voltage-sags between 0.5- 30 cycles and their depth can vary between 10-90% of the rated value. The main desirable feature in a VSG is the easy programmability of variable magnitude, duration and type of voltage-sags [4]. There are mainly four different types of voltage sag generators [5], [6]: shunt impedance based, transformer based, generator based and full converter based VSG. Commercially available VSG are usually full converter based, offered by a few international manufacturers to high prices. Plenty of university-built VSG have been reported [6]. [7], mainly using shunt impedance or transformer based VSG. Either commercially available or university built VSG are suitable for 3-phase 3-leg systems, but not attention have been paid to studied 3-phase 4-leg VSG. The last are important to study the behaviour of RES connected to distribution systems, as it occurs in microgrids. The full converter based VSG enables more precise control of all voltage-sag characteristics. It uses a Back to-Back converter to interface the grid and RES, therefore, to implement a 3-phase 4-leg VSG implies to use tridimensional SVM algorithms and control of positive and negative sequence at the point of voltage sag generation. Such coniguration is more complex and costly than regular 3-phase 3-leg full converter based VSG [8]. In this paper the design and testing of a new 3-phase 4-leg full converter based VSG is described. The proposed VSG is shown in Fig. 1. t uses a Matrix Converter (MC) instead traditional Back-to-Back