Abstract Renewable energy sources (RES) like wind and PV are dependent on weather conditions and geographic location and as results their stochastic behavior can significantly influence power systems performance. These effects will be more relevant in case of large-scale penetration of RES. Therefore, modern power plants based on RES should both deliver power as conventional generators and contribute to support the grid services by providing ancillary services and in this way applications of advanced technology are very important to reach this goal. Active power and frequency controls are known as essential ancillary services that should be provided by generation units in large power plants. Therefore, controlling this type of grid interactive power plants is critical issue to achieve large-scale integration of RES in distributed power systems. In consequence, it is necessary to take advantages of new technologies and advanced control concepts in order to configure more intelligent and flexible generation systems, which should be able to improve the performance and stability of grid. A brief review on conventional active power/frequency control issues and complete investigation on adapted scenarios of active power/frequency control considering liberalized markets, high penetration of RES and coexistence of AC and DC networks will be explained in this chapter.
Keywords Active power · Frequency control · Automatic generation control · Advanced optimal control · Deregulated power market
Energy is a very important issue all around the world and during the last few decades, energy demands increased rapidly. Beside all problems related to coal energy, the new trends in the world are to increase the application of renewable energy sources to provide more green electrical energy. The concept of deregu- lation and competition in power market of energy is another important issue that forced the scientists to think more about the challenges related to modification of conventional large-scale power system .
Solar power is a type of energy with great future potential. As reported by EPIA (European Photovoltaic Industry Association), the world cumulative installed solar energy capacity was 22,900 MW in 2009, a change of 46.9 % compared to 2008. Renewable type electricity will be faced with a remarkable growth by 2030 [2, 3]. This suggests RE could participate in several ancillary services like frequency support and play important roles in transition to a sustainable energy economy. However, in order to have more DGs systems as a major source of energy, advanced development of technologies are very important.
These days we are facing with growth and extension of AC systems and as result with more complexity and more stability problems. In new scenarios of modern power system with high penetration of renewable energy sources (RES), the role of advanced technologies will be so important. For example, HVDC can essentially improve the reliability of complex interconnected systems. Further- more, HVDC is a kind of firewall against cascading disturbances and in this way, it prevents blackouts. For these reasons, in some parts of the world, HVDC or hybrid interconnections, consisting of AC and DC interconnections, became already the preferred solution. The first commercial application of HVDC was between the Swedish mainland and the island of Gotland in 1954 . Since then, there has been a huge increase in the application of HVDC transmission.
Based on this brief introduction, that is clear the future power system is a very challenging issue with high penetration of RES, DC transmission, and high complexity. Scientists and engineers have intensified their research efforts during the last decade to change such pessimistic electrical scenario. Technological advances, such as the use of modern power processing systems, energy storage and control techniques in high-power systems, as well as some last decade socioeconomic factors, such as the large-scale penetration of renewable energy sources, the generalized liberalization of electrical markets and the strategic importance dispensed to the security in supply, have led to a reformulation of the conventional power systems, moving toward a more flexible distributed generation scheme.
The organization of the chapter is as follows: Section 2 presents the conventional story for frequency/active power control with a complete model of automatic generation control (AGC) for active power control and Sect. 3 presents adapted scenarios considering market environment for adapting the conventional model of AGC model in the deregulated environment of power system. Detailed model of AGC considering the effects of renewable resources like PV and also the effects of adding the HVDC links on the active power responses will be discussed and presented. Then new applications of advanced control concepts for active power and frequency control issues will be presented in Sect. 4. It should be noted that to have a better understanding for each concept of this chapter; several simulation examples with different scenarios are presented. Finally, Sect. 5 closes the chapter with the main conclusions and possible solutions for modern future power system.