Fault ride-through of wind farms using series dynamic braking resistors

Abstract

Wind power is one of the world's fastest growing industries. The resulting penetration of wind power has led to substantial changes in requirements for large wind farms. Fault Ride-Through (FRT) was an important new requirement for wind farms to remain connected and actively contribute to system stability during a wide range of network faults. The wind industry responded with several approaches to FRT compliance including dynamic Reactive Power Compensation (dRPC) and pitch control. New requirements, combined with the reduced cost and increased efficiency of power electronic converters has led to the increasing dominance of Variable Speed Wind Turbines (VSWTs). Recent research has therefore focused on VSWTs. This Thesis presents a new technology, invented and developed during my PhD project, which provides a rearguard opportunity for Fixed Speed Wind Turbines (FSWTs) to comply with FRT requirementsu sing a series Dynamic Braking Resistor (sDBR). sDBR contributes directly to the balance of active power during a fault by inserting a series resistor into the generation circuit, increasing generator terminal voltage. The aim of the analysis, simulation and experimental work in this Thesis is to demonstrate the potential and scope of sDBR to contribute to FRT compliance of FSWTs. sDBR is shown to be a simple and effective means of displacing expensive dRPC to achieve full compliance with Great Britain's FRT requirements. It is also shown to be capable of contributing to compliance with the more onerous FRT requirements in conjunction with other technologies. Detailed transient simulations of sDBR were confirmed by experimental results using a 7.5kW test-rig. Although the FSWT market is severely weakened, opportunities remain in niche markets for new and existing wind farms. Continued research into high-speed switching, variable resistance and integrated control could further improve basic sDBR performance. Further research into new applications with distribution networks,s mall wind turbines and doubly-fed induction generators could also extend its application in new markets with longer horizons.