Citation: Rashid, G.; Ali, M.H. FRT Capability Enhancement of Offshore Wind Farm by DC Chopper. Energies 2023, 16, 2129. https://doi.org/ 10.3390/en16052129 Academic Editor: Tek Tjing Lie Received: 24 November 2022 Revised: 11 February 2023 Accepted: 13 February 2023 Published: 22 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article FRT Capability Enhancement of Offshore Wind Farm by DC Chopper Gilmanur Rashid 1 and Mohd Hasan Ali 2, * 1 Renesas Electronics America, Durham, NC 27703, USA 2 Department of Electrical and Computer Engineering, The University of Memphis, Memphis, TN 38152, USA * Correspondence: mhali@memphis.edu Abstract: Offshore wind farms (OWF) are establishing their position to be the next strategy to expand the growth horizon of wind power production. For proper integration of OWFs into the existing grid, the voltage source converter (VSC)-based high voltage direct current (HVDC) transmission is being vastly utilized. For the stable operation of the existing grid, these VSC-HVDC-connected OWFs need to abide by the fault ride through (FRT) grid codes. Though there are many proposed solutions to tackle the FRT problem of the onshore wind farms, all of them cannot be applied to the OWFs. The OWFs cannot respond to the onshore faults depending solely on local measurements. Additionally, there are very few techniques available for FRT capability enhancement of the doubly fed induction generator (DFIG)-based OWFs. One notable solution is the use of the DC chopper resistor across the HVDC line. No intelligent controller is yet to be reported for better control of the DC chopper resistor. To enhance the performance of the DC chopper resistor in enhancing the FRT capability of the DFIG-based OWF, a particle swarm optimization (PSO)-based nonlinear controller is proposed. Simulations carried out in the Matlab/Simulink environment reveal that the PSO-optimized nonlinear controller-based DC chopper is very effective in maintaining the FRT of the DFIG-based OWF systems. Additionally, the proposed method provides better FRT performance than that of the conventional controller-based DC chopper. Keywords: DC chopper; doubly fed induction generator (DFIG); fault ride through (FRT); nonlinear controller (NC); offshore wind farms (OWF); particle swarm optimization (PSO) 1. Introduction Perpetual increase in electricity demand and heightened concern for carbon neutral sustainable development with environmental protection led to intense interest in the generation of electric power from the renewable energy sources. The wind energy stepped up to be one of the most prominent renewable energy sources. Its’ boom was initiated in the onshore locations and continued until recent scarcity of good wind flow locations, dispute over land ownership, difficulty to move logistics, and lower wind power utilization due to nonuniform wind speed [1]. Thus, offshore wind farms (OWF) turned out to be the next solution to facilitate the growth of wind power production with better utilization of wind power, less legal concern, and higher power production capacity by individual wind farms. In the US, the offshore wind pipeline grew 13.5% in 2022 (compared to 2021) due to falling offshore wind prices, federal action, and state-level commitments. The National Renewable Energy Laboratory estimates that the offshore wind technical potential is more than 2000 GW of capacity, which is 7200 terawatt-hours per year of generation [2]. Transmitting bulk power from the OWFs and successful and feasible integration of OWFs into the existing grid is very challenging. The voltage source converter (VSC)- based high voltage DC (HVDC) transmission is being widely adopted and the VSCs help overcome these challenges [3]. However, controlling a VSC is very challenging ensuring the system capability is subjected to variations and transients in the AC system or the Energies 2023, 16, 2129. https://doi.org/10.3390/en16052129 https://www.mdpi.com/journal/energies