Kinetic energy recovery and control of wind turbine generators for grid frequency support

Abstract

The nominal frequency of the national grid is 50 Hz. A deviation around this nominal point indicates an imbalance between supply and demand. There is an acceptable range by which the frequency may deviate to protect the grid integrity and all the connected devices. Large synchronous generators provide an inherent inertial response to frequency deviations due to their large rotating mass that is coupled to the grid via an electro-mechanical interaction between the rotor and stator. Wind energy conversion systems (WECS) have become increasingly important as a contribution to grid frequency support, to maintain power at the nominal frequency and mitigate power failures or supply shortages against demand. However, variable speed wind turbine (VSWT) generators are decoupled from the network by power electronic converters and therefore do not respond naturally to a system frequency change. As the finite nature of non-renewable energy resources are realised and climate change concerns become more prevalent, the need to shift to more sustainable forms of energy such as the adoption of renewable energy has seen an increase. A systematic literature review methodology was used and aimed to investigate the control methods used by WECS, more specifically variable speed wind turbines (VSWT), in supporting grid frequency as well as, the limitations of such methods. The Emulated Inertial Response was the primary means of providing frequency support identified by literature within a period of 2015 – mid 2022. Following the systematic literature review, a mathematical model of a doubly-fed induction generator (DFIG) and a frequency support controller was developed to provide an emulated inertial response and modelled using MATLAB/Simulink. The results showed that the frequency support controller provided adequate frequency support by raising the frequency nadir following a disturbance, even in the cases of consecutive disturbances.