The 2014 International Power Electronics Conference DC-Voltage Regulation of a Five Levels Neutral Point Clamped Cascaded Converter for Wind Energy Conversion System Farid Merahi l , 2 , Saad Mekhilef 2 I Automatic Laboratory of Setif (LAS), Department of Electrical Engineering, F. Abbas University, Setif. Algeria 2 Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, 50603 Kuala Lumpur Malaysia. merahif@gmail.com, saad@um.edu.my Abstract- Multilevel converters are widely recognized as a suitable solution for directly interfacing different types of power sources and energy storage systems to the medium voltage grids, due to their ability in high-voltage and high-power applications. The DC-voltage regulation of a fve-level neutral-point clamped (NPC) in closed loop is presented. It consists to regulate the average value of the DC-voltage by using one loop instead of four loops. The modeling and the control of the different components of the wind energy conversion system are presented. The wind turbine is controlled using the maximum power point tracking algorithm (MPPT) based on the wind speed estimation. The vector control of active and reactive power is used to control the doubly fed induction generator (DFIG) through the rotor. The dynamic behavior of the global system is simulated in MATLAB/Simulink interface programming. The results are shown to validate the effectiveness of the proposed system. Keywords-NPCmultilevel converters, DC voltage regulation; windenerg;DFIG. I. INTRODUCTION Multilevel converters are characterized by the ability to supply staircase-like voltage waveforms. Their applications become very interesting, especially with the insertion of the new renewable sources which is originally random into the electrical grid [1]. This new type of great power converters can contribute to the improvement of the quality of energy produced by attenuating the fuctuations which can occur. This feature enables converters with a high number of levels to reduce voltage and current total harmonic distortion (THD), and their architecture enables high-voltage high-current operation [2], [3], [4]. The fndamental principle of the multilevel conversion techniques is essentially based on an association series/parallel of the electronic power switches. They allowing bypassing the problem involved in maximum limit of the blocking voltage of the principal power semiconductors. These structures allow increasing in voltage beyond the limits of the semiconductors with a very good resolution of the output voltage [5], [6], [7]. The DC-voltages balancing in the DC-link is the main concer in the NPC 978-1-4799-2705-0/14/$31.00 ©2014 IEEE 560 El Madjid Berkouk 3 3 Process Control Laboratory (LCP), High Polytechnic National School. Hassan Badi Street, BP 182, Algiers, 16000-Algeria emberkouk@yahoo.f multilevel converter topology. The active NPC control approach [8], passive NP controls approach [9], dual curent controller approach [ 10] has been proposed as solution to regulate the DC-voltage. However, these approaches suffer fom constraints in high modulation, the system delivered unbalanced currents to the grid under unbalanced voltage dips and the systems required a linearization method for their implementation This paper proposes the regulation of the DC-voltage of fve-level NPC cascaded converters in closed loop. One closed loop is used instead of four loops, and the details of the control principal are theoretically explained. The wind energy conversion system description based on fve-level NPC cascaded converters is shown in Fig. 1. II. MODELING OF THE WI GENERATOR A. Modeling a/the Wind Turbine and the Gearbox The aerodynamic power P a e r , which is converted by a wind turbine, is dependent on the power coefcient C p' It is given by [ 1 1]: 1 () 2 3 P a e r = - C A p1R v 2 p (1) Where p is the air density, R is the blade length and v the wind velocity. The turbine torque is the ratio of the output power to the shaf speed. It is given by: P (2) a e r The turbine is normally coupled to the generator shaf through a gearbox. Neglecting the transmission losses, the torque and shaf speed of the wind turbine, referred to the generator side of the gearbox, are given by [12]: T T = .. ! . g G (3)