Performance Comparison of Phase Shifted PWM and Sorting Method for Modular Multilevel Converters Marcos Rejas 1 , Laszlo Mathe 1 , Paul Dan Burlacu 1 , Heverton Pereira 2 , Ariya Sangwongwanich 1 , Massimo Bongiorno 3 and Remus Teodorescu 1 Abstract Modular Multilevel Converters (MMC) are the solution of preference in HVDC applications due to modularity, scalability, low losses and low filtering requirement. Carrier-based (PWM) and carrier-less (nearest level control) modulation can be applied. By using advanced sorting methods focusing on keeping the capacitor voltage ripple under some limit, unnecessary switching events are eliminated leading to reduced switching losses. This paper presents a comparison between the steady-state performances in terms of output voltage THD and equivalent switching frequency of the Phase Shifted Carrier PWM and NLC plus sorting methods. I Introduction Modular Multilevel Converter (MMC) topology is a very promising solution for high power applications such as High Voltage Direct Current (HVDC), high-power STATCOM or high voltage drives. Due to their low switching frequency leads to high efficiency and the high number of output voltage levels requires a minimal grid side filter. Another advantage is that the large number of modules present in the topology ensures fault tolerant operation [1]. In Fig. 1 (a) the structure of MMC is presented, where each leg has an upper and lower arm which together supplies the phase currents (i a, i b, i c ). Each arm consist of n series connected sub-modules (SMs) together with an arm inductor (L arm ) and resistance (R arm ). The simplest construction for the SMs is the so called Half Bridge (HB) topology, through which a capacitor can be inserted or bypassed [2]. Thus, the number of the inserted capacitor voltages from a leg results the phase voltage of the converter. Similarly, the output current is resulted from the difference between the upper and lower arm current. Beside the output current of the MMC a circulating current is present in the converter, which circulates between legs and the DC link. However, the circulating current has no direct impact on the output current it is important to control it in order to maintain high efficiency of the converter [3]. From control point of view the system becomes complex as it is schemed in Fig. 2, several outer loops, such as current voltage control, has to be ensured. Additionally, in case of MMC, especially when large number of SMs are employed, internal control has to be established which ensures balance between the capacitor voltages and controls the circulating current. Several modulation strategies have been proposed in order to control the SM switches, they can be divided in two main classes: carrier based and sorting based algorithms (also called as carrier- less) [3]. From the carrier based modulation techniques, such as: Carrier Disposition (CD) and Phase Shifted Carrier (PSC) Pulse Width Modulation (PWM), PSC-PWM is the most promising due to its independent controllability in the SM [3-5]. Due to the different advantages/disadvantages of the carrier based and sorting method it is difficult to choose the suitable algorithm. In this paper a comparison between PSC-PWM and module sorting methods is presented. In the next section a small overview of the PSC-PWM and carrier-less methods are presented. In the third section two case scenarios are simulated: first when low 1 Aalborg University Aalborg, Denmark marcosrejas@gmail.com lam@et.aau.dk pdb@et.aau.dk ars@et.aau.dk ret@et.aau.dk 2 Federal University of Viçosa Viçosa, Brazil hevertonaugusto@yahoo.com.br 3 Chalmers University Goteborg, Sweden massimo.bongiorno@chalmers.se Performance Comparison of Phase Shifted PWM and Sorting Method for Modular Multilevel Converters REJAS Marcos EPE'15 ECCE Europe ISBN: 9789075815238 and CFP15850-USB P.1 © assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE)