Mitigation of Frequency Issues in Grid Connected Renewable Energy Sources

The increasing penetration of variable-speed wind turbines in the electricity grid will result in a reduction of the number of connected conventional power plants. This will require changes in the way the grid frequency is controlled. Like conventional generators, wind turbines have a significant amount of kinetic energy stored in the rotating mass of their blades. In case of variable-speed wind turbines, this energy will not contribute to the inertia of the grid as the rotational speed is decoupled from the grid frequency by a power electronic converter. Frequency stability is the ability of the power system to maintain steady frequency following a severe system upset resulting in significant imbalance between generation and load. As a low inertia system is integrated to the grid, the rate of change frequency (ROCOF) changes. This paper studies the rate of change of frequency for a grid integrated with renewable energy sources. The remedies such as Virtual Inertia is used to overcome the frequency stability issue. Simulation results of implementation of ROCOF relay, droop characteristics and virtual inertia are discussed in this paper.