Enhancement of power systems dynamics in the presence of renewable energy sources using smart storage units

Renewable Energy Sources are now important parts of power systems. Penetration of these sources is increasing every year and it is projected that 20-30% of worldwide electricity demand would be supported by renewable sources by 2020. While this means less pollution and less dependability on fossil fuels, integration of renewable sources has its own issues which should be taken care of. Wind and solar energy - two of the main renewable sources and most promising ones - have intermittent nature. This leads to undesirable uncertainty in power system operation that cannot be tolerated in case of high penetration of renewable sources. The fluctuating nature of the output power of these sources results in deterioration of grid stability and power quality. On the other hand, storage systems are being developed rapidly with storage capability of hundreds of megawatt-hours and response time in range of milliseconds. These capabilities made modern storage systems a good choice to mitigate the fluctuations created by the renewable sources. Storage systems are now an inevitable part of the hybrid systems including intermittent renewable sources. However, this means an increase in overall cost of power system due to high installation and maintenance cost of storage units. While adding storage units to hybrid systems is inevitable and costly, they can create new opportunities to affect the entire grid, not only by smoothing the output power of the renewable sources but also by improving the dynamics of the entire grid. Several control strategies have been reported in the open literature for output power smoothing of wind generators connected to an infinite bus. However, the effects of these storage units on the dynamics of more practical multi-machine power systems with high penetration of renewable sources have not been studied thoroughly, yet. This dissertation studies enhancement of power systems dynamics with renewable sources through the use of storage units. By exchanging active and reactive power, storage units are controlled to improve the dynamics of the power system. For this purpose, modeling of wind, PV and storage systems, and their integration with the power system is presented. Improvement of system dynamics is pursued by choosing appropriate control strategies for the storage system. The effectiveness of these control strategies is demonstrated through the simulation of test power systems in MATLAB Simulink environment. The results show that when the penetration of renewable sources are high (from 20% to 50% in this study), ECS unit can effectively mitigate the negative effects of these sources on power system and enhance the system dynamics considerably. Also, using small signal analysis it is shown that ECS can increase the loadability of the entire system.