Five-Leg Converter Topology for Wind Energy Conversion System with Doubly-Fed Induction Generator Mahmoud Shahbazi a, c , Philippe Poure b , Shahrokh Saadate a , Mohammad Reza Zolghadri c a Groupe de Recherche en Electrotechnique et Electronique de Nancy (GREEN), Nancy Université, Nancy, France b Laboratoire d’Instrumentation Electronique de Nancy (LIEN), Nancy Université, Nancy, France c Center of Excellence in Power System Management & Control (CEPSMC), Sharif University of Technology, Tehran, Iran Abstract— In this paper, application of a five-leg converter in Doubly Fed Induction Generator (DFIG) for Wind Energy Conversion Systems (WECS) is investigated. The five-leg structure and its PWM control are studied and performances are compared with the classical six-leg topology. The main drawback of five-leg converter with respect to the six-leg back-to-back converter is the need to increase the dc-link voltage for the same operation point, i.e. the same powers in case of WECS. So, different methods for the reduction of the required dc-link voltage in the five-leg case are studied. The five-leg converter is used to replace the conventional six-leg one, with the same ability. For the performance evaluation of this structure and its fully digital controller in a more realistic and experimental manner, Hardware in the Loop experiments are carried out. It is shown that efficient control of active and reactive powers and dc-link voltage is performed. Hardware in the Loop results demonstrate the high performance of the proposed fully digital control which is implemented on an Altera FPGA target. Keywords: Wind Energy Conversion System (WECS), Five-leg converter, Doubly-Fed Induction Generator (DFIG), Hardware in the Loop (HIL). 1. INTRODUCTION Wind energy is the fastest growing type of renewable energy. One can notice an average growth rate of about 30% for installed wind turbines in the past 10 years. At the end of 2020, the installed capacity of wind turbines is expected to be around 1900 GW [1]. For European wind energy association, the goal is to produce 26 to 34% of the electricity of Europe from wind in 2030 [2]. Global market of wind energy is clearly expanding steadily, and consequently the technologic competition in this area has been accelerated. The most widely used structure in currently installed wind turbine is the Doubly-Fed Induction Generator (DFIG) -based wind turbine. One of its major advantages over other variable- speed turbine structures with a series converter is the reduced rating of the power electronic converter. The maximum power that the power converter has to handle in steady state condition is reduced to a fraction (20-30%) of the output rated power [3]. On the one hand, repairing a Wind Energy Conversion Systems (WECS) is a very time consuming process [4], and actually, in most cases, the repairing is scheduled annually [5]. Therefore, continuity of service and reliability are mandatory for such applications. This is again more important for islanded smart or micro grids where wind power has a major role, and the higher reliability of the converter of wind turbine is highly recommended. On the other hand, five-leg converter topology has been proposed for drive applications such as independent control of two three-phase motors [6], fault tolerant reversible AC motor drive systems [7] and AC/AC supply of a three-phase induction machine [8]. It has been shown that this converter topology could give satisfactory results in such applications. Moreover, it has better performances over other component-minimized topologies like nine-switch converter [9] and half-bridge-based converters [7]. In [9], it is shown that in this topology, the switches rating and losses are lower compared to 9-switch converter. In [7] it is stated that in contrary to the half-bridge- based converters, there is no AC current flowing through dc link capacitors in the five-leg converter, and also the required dc-link voltage can be minimized. Finally, the use of a reduced number of power devices leads to higher converter reliability compared with the conventional back-to-back six-leg topology. However, as far as DFIG-based WECS is concerned, the application of a five-leg converter topology and the study of the suited control and dc-link voltage minimization has never been reported in the literature. We think that such a converter topology might be interesting and efficient for this purpose. In this paper, a five-leg converter-based structure as the back to back converter of a DFIG based wind turbine is studied. It is shown that it might have some benefits compared to conventional 6-leg “back to back” converters. In the next section, the overall system under study is explained. Moreover, control of the DFIG, the dc-bus voltage and the five-leg converter is developed. In the third section, a comparative study of five-leg and six-leg converter topologies in WECS with DFIG is presented. Also different schemes for the minimization of the required dc-link voltage in the five-leg converter for wind application are discussed. Two PWM