The 9 th International Renewable Energy Congress (IREC 2018) An Improved Control for DC-Link Fluctuation during Voltage Dip based on DFIG Ibrahima Ngom 1 , Student Member, IEEE, Alioune Badara Mboup 2 , Lamine Thiaw 5 ESP- Uinversité Cheikh Anta Diop Dakar LR 5085 LER, B.P 5085 Dakar, Senegal 1 ibrahima11.ngom@ucad.edu.sn, 2 mboupbadara@yahoo.fr, 5 lamine.thiaw@ucad.edu.sn Sondes Skander-Mustapha 3 , Ilhem Slama Belkhodja 4 , Senior Member, IEEE ENIT-Université de Tunis El Manar LR 11 ES, LSE, B.P.37,1002 Tunis, Tunisia 3 sondes.skander@enit.utm.tn, 4 ilhem.slamabelkhodja@enit.utm.tn Abstract— The main purpose of this work is to limit the DC-link voltage fluctuation in doubly fed induction generator (DFIG) based wind turbine system to enhance low voltage ride through capability. Grid-side and rotor-side converters control has been addressed to avoid disconnection of turbine during fault conditions but these works, thoughts, often ignore dc-bus voltage ripples limitation during voltage dips, and fault ride through of DFIG may not be satisfactory without minimizing the DC-link voltage fluctuations within their acceptable ranges. In this work an improved control strategy to limit the DC-link voltage fluctuation under normal and fault conditions is implemented. A modified control scheme has been applied to the direct current loop of the grid-side controller. If the grid filter active current setting during the voltage dip is determined, the sum of instantaneous powers of the grid and the grid filter is nearly equal to the instantaneous output rotor power, the DC-link voltage will not change significantly and will remain nearly constant. Simulations performed by Matlab software demonstrate the performances of the proposed method in limiting DC-bus voltage fluctuation during severe voltage dip. Keywords— DC-bus voltage fluctuation; PI controller; voltage dips; back-to-back power electronic converter; DC-link voltage ripples; ride-through control; wind power generation I. INTRODUCTION Over the last years, there has been a strong penetration of renewable energy resources into the power supply network. Wind energy generation has played a very important role in this area. Doubly fed induction generators (DFIGs) are widely used in wind energy conversion system (WECS) because theirs voltage source converters only handles a fraction of the total output power under steady state conditions. Additionally, the active and reactive power can be easily controlled independently through the back to back power electronics converter [1]. The DC part of the back-to-back converter is composed of a capacitor in parallel with a high resistance value, and acts as a storage of DC power and filters out the variations of the DC voltage prior to further processing in the inverter section. The filtered DC power is then fed into the grid side converter, which will convert and process the stable DC voltage to produce AC power with the desired frequency and voltage Level [2] [3]. However, it is shown that the instantaneous power of power converters, connected to the grid has both DC and pulsating components. While the DC part of grid power is transferred to the load, pulsating part must be absorbed by an instantaneous power-matching element typically realized by bulk DC link capacitor [4][10]. Unfortunately, the process of absorbing the sum of pulsating power by the DC-link capacitance creates the DC-link voltage ripples [4][5]. These ripples must reside within predetermined limits, set by both grid-connected converter topology and DC link capacitor voltage rating. Then, we can avoid violating both power converters functionality and DC-link capacitor voltage rating [4]. In order to handle such issues, the DC-link control plays a key role to reduce the DC-bus voltage fluctuation. Some control methods have been reported in the literature. In [6] an enhanced state observer base controller is presented to control the DC- link voltage and it has high disturbance rejection but its design is very complicated. In [7], it is proposed a back-to-back neutral-point clamped converter to maintain the DC-link voltage constant during the grid voltage dip by storing the active power surplus of the inertia of the generator. In [8], the sliding mode controller is used to improve the DC-link voltage stability in the outer loop of the grid side converter, providing excellent transient response and steady-state behavior. In [11] a dynamic DC-Link reference design is proposed due to the fact that the performance of the traditional PI controller is not satisfactory because of integrator anti-wind up problem. And recently, the author in [12] used an anti-windup predictive current controller applied to a DFIG-based wind turbine to investigate the DC-link voltage and current transient overshoots and ripples. On the other hand, it is demonstrated in [13][14], that when voltage dips occur a large voltage and high current in the rotor windings are induced at the connection point of the DFIG to the grid which can damage the rotor-side converter and increase the DC-link voltage. In [12] [14] it is shown that the deactivation of the rotor-side converter consumes more reactive power, hence creating voltage instability. The wind turbines are desired 978-1-5386-0998-9/18/$31.00 ©2018 IEEE