A Variable Speed Wind Turbine Control Strategy to Meet Wind Farm Grid Code Requirements

TLDR

Fixed‑speed wind generators struggle to meet new wind‑farm grid‑code requirements due to their heavy reliance on reactive power, and while FACTS devices can address this, they add significant cost. The study proposes a new operational strategy for a small‑scale wind farm that combines fixed‑speed WTGSs with variable‑speed VSWT‑PMSG units and develops a control strategy for the multilevel frequency converter. The authors employ a VSWT‑PMSG with a fully controlled frequency converter, analyze its LVRT behavior under a real grid code, and evaluate dynamic performance using actual wind‑speed data. Simulations demonstrate that the proposed topology improves LVRT compliance and reduces voltage fluctuations in both fixed‑ and variable‑speed WTGSs while being cost effective.

Abstract

This paper presents a new operational strategy for a small scale wind farm which is composed of both fixed and variable speed wind turbine generator systems (WTGS). Fixed speed wind generators suffer greatly from meeting the requirements of new wind farm grid code, because they are largely dependent on reactive power. Integration of flexible ac transmission systems (FACTS) devices is a solution to overcome that problem, though it definitely increases the overall cost. Therefore, in this paper, we focuses on a new wind farm topology, where series or parallel connected fixed speed WTGSs are installed with variable speed wind turbine (VSWT) driven permanent magnet synchronous generators (PMSG). VSWT-PMSG uses a fully controlled frequency converter for grid interfacing and it has abilities to control its reactive power as well as to provide maximum power to the grid. Suitable control strategy is developed in this paper for the multilevel frequency converter of VSWT-PMSG. A real grid code defined in the power system is considered to analyze the low voltage ride through (LVRT) characteristic of both fixed and variable speed WTGSs. Moreover, dynamic performance of the system is also evaluated using real wind speed data. Simulation results clearly show that the proposed topology can be a cost effective solution to augment the LVRT requirement as well as to minimize voltage fluctuation of both fixed and variable speed WTGSs.