INTERNATIONAL JOURNAL of RENEWABLE ENERGY RESEARCH I. Ouerdani et al., Vol.6, No.3, 2016 Harmonic Analysis of Pulse Width Modulation- Based Strategies for Modular Multilevel Converter Imen Ouerdani * ‡ , Afef Bennani Ben Abdelghani **, Ilhem Slama Belkhodja * * Université de Tunis El Manar, Ecole Nationale d'Ingénieurs de Tunis LR11ES15 Laboratoire des Systèmes Electriques, 1002, Tunis, Tunisie ; ** Université de Carthage, Institut national des sciences appliquées et de technologie, Tunis 1080, Tunisie (imen.wardani@gmail.com, afef.bennani@gmail.com, ilhem.slamabelkhodja@gmail.com) ‡ Corresponding Author; Imen Ouerdani, BP 37, Le Belvédère, 1002 Tunis, Tunisia, Tel: +21671874700 Fax: +21671872729. imen.wardani@gmail.com Received: 03.06.2016 Accepted:05.07.2016 Abstract- MMC converters are an interesting solution for HVDC applications and renewable energy transport. This paper presents a mathematical analysis of the impact of various Phase Disposition PWM strategies on the circulating current which is one of the important MMC converter issues. The considered strategies are: Phase Disposition PWM (PDPWM), Phase Opposition Disposition PWM (PODPWM) and Alternative Phase Opposition Disposition PWM (APODPWM). Depending on the adapted modulation strategy, the proposed analysis proves that the circulating current varies from a DC component to a high current with high frequency components and a dominance of the second order harmonics. It is also demonstrated that PODPWM and APODPWM modulation strategies satisfy the balanced operation condition where only N sub-modules among the 2N available sub-modules are inserted into the phase leg and consequently ensure (N+1) voltage levels in the output voltage. Simulation results of a 2.7 MVA MMC converter are presented to verify the validity of the proposed methodology and analysis. Keywords Modular Multilevel Converter; circulating current; THD; Pulse Width Modulation. 1. Introduction With the beginning of a new era of energy production based on distributed energy resources and the need to build a smarter grid [1,2], High Voltage Direct Current (HVDC) is expected to be the method of choice of power transmission [3,4]. HVDC is considered advantageous compared to ac transmission due to its stability when connecting asynchronous ac grids, the great ease of active power control in the DC link and the low power losses even over very long distances [5,6]. These advantages make the HVDC a perfect candidate for grid integration of renewable energy where resources are usually located far from their consumption centres. Along with the modifications made on conventional centralized electric grids, power conversion attracted major investigations. New topologies were proposed to fit specific applications according to the voltage and power rates [7,8]. The Modular Multilevel Converter (MMC) has emerged as one of the most promising topologies in high voltage high power applications [9,10,11]. The MMC offers various advantages such as low harmonic distortion of the output voltage, low switching frequency, fault tolerant operation, etc. The modularity and scalability of this topology allowed it to reach high voltage ranges with very high number of voltage levels by a simple series connection of conventional sub-modules. Due to this criterion, the MMC has become especially attractive for HVDC transmission and power systems applications [12,13]. Since its introduction by R. Marquardt in 2001[14], extensive researches have been performed to improve the converter’s performance regarding its different aspects. In fact, first investigations were dedicated to the topology modelling [15] and dedicated modulation schemes [9],[16]. In [17] and [18], the authors adopted the nearest level control (NLC) also known as the round method. It is especially interesting for MMC with large number of sub-modules [19]. Space Vector PWM (SVPWM) modulation was also applied