160 IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, VOL. 5, NO. 1, JANUARY 2014 Stability Enhancement of Large-Scale Integration of Wind, Solar, and Marine-Current Power Generation Fed to an SG-Based Power System Through an LCC-HVDC Link Li Wang, Senior Member, IEEE, and Mi Sa-Nguyen Thi Abstract—The integration of the renewable-energy power sources including solar, wind, and marine current with high penetration levels can have a negative impact on system stability. This paper presents an effective control scheme using a line-com- mutated high-voltage direct-current (LCC-HVDC) link joined with a damping controller based on adaptive-network-based fuzzy inference system (ANFIS) to achieve damping improvement of an integration of wind, solar, and marine-current power systems fed to a synchronous generator (SG)-based power system. The proposed ANFIS is an adaptive, robustness controller by com- bining the advantages of artificial neural network and fuzzy logic controller to face different operating conditions of the studied system. A time-domain scheme based on a nonlinear-system model subject to a three-phase short-circuit fault at the infinite bus is utilized to examine the effectiveness of the proposed control schemes. Comparative simulation results show that the designed ANFIS damping controller is shown to be superior for improving the stability of the studied system subject to a severe disturbance. Index Terms—Adaptive-network-based fuzzy inference system (ANFIS) damping controller, high-voltage direct-current (HVDC) link, marine-current power generation, proportional-inte- gral-derivative (PID) damping controller, solar power generation, wind power generation. NOMENCLATURE A. General and Abbreviation ANFIS Adaptive-network-based fuzzy inference system. ANN Artificial neural network. FLC Fuzzy logic controller. GB Gear box. HVDC High-voltage direct current. ICR Inverter-current regulator. Manuscript received October 20, 2012; revised February 12, 2013 and May 28, 2013; accepted July 17, 2013. Date of publication September 20, 2013; date of current version December 12, 2013. This work was supported by the National Science Council of Taiwan under Grant NSC 102-3113-P-006-009. L. Wang is with the Department of Electrical Engineering National Cheng Kung University, Tainan City 70101, Taiwan, and also with the Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan City 70101, Taiwan (e-mail: liwang@mail.ncku.edu.tw). M. S.-N. Thi is with the Department of Electrical Engineering, Na- tional Cheng Kung University, Tainan City 70101, Taiwan (e-mail: dalat1984@yahoo.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TSTE.2013.2275939 Proportional gain of PID controller. Integral gain of PID controller. Derivative gain of PID controller. LCC Line-commutated converter. MCF Marine-current farm. MCT Marine-current turbine. MF Membership function. OWF Offshore wind farm. PID Proportional-integral-derivative. PMSG Permanent-magnet synchronous generator. PV Photovoltaic. SCIG Squirrel-cage induction generator. SG Synchronous generator. VSC Voltage-source converter. VSWT Variable-speed wind turbine. WT Wind turbine. , PU quantities of ac, dc current. Differential operator with respect to . pu Per unit. , PU quantities of resistance and reactance. Washout-term time constant of PID controller. , PU quantities of ac and dc voltages. , Wind speed and marine-current speed. PU quantities of rotor speed. Extinction angle of inverter of LCC-HVDC link. Eigenvalue. B. Subscripts , Quantities of - and -axis. , Quantities of maximum and minimum. Quantities of marine-current farm. Quantities of reference. , Quantities of stator and rotor windings. Quantities of offshore wind farm. 1949-3029 © 2013 IEEE