The Flexible Multi-Mode Power Plant Solution : Addressing Energy Transition Challenges and Improving Frequency Stability in Low-Inertia Systems

Abstract

The primary goal behind the global energy transition is to reduce greenhouse gas emissions by shifting the source of energy generation from fossil fuels to renewables such as wind and solar. This transition brings many changes to power systems; however, this thesis focuses on three key aspects: renewable energy integration, structural changes in modern power systems, and changes on the demand side. Due to the intermittent, variable, and low-inertia nature of renewable energy sources, the global energy transition also creates challenges in power systems, such as the increasing need for flexibility, stability, controllability of the generation-load balance, and reliability. To address these challenges, solutions are being explored worldwide. This thesis proposes a solution concept, “The Flexible Multi-Mode Power Plant Solution,” which is particularly beneficial for microgrids (both islanded and grid-connected) and power networks with high renewable penetration. The solution concept is in the form of a hybrid power plant and consists of internal combustion engine generating sets, synchronous condensers, and battery energy storage systems. As the name implies, the solution concept relies on operating the power plant in different modes, created by the inclusion or exclusion of its components. Moreover, to validate the power plant solution concept, frequency stability simulation studies are conducted employing DIgSILENT PowerFactory, one of the leading power system analysis software programs. To create simulation models, the IEEE 14-Bus system is used as a template, representing an islanded microgrid. There are four voltage levels in the simulation models: 0.63 kV (battery energy storage system bus voltage), 0.69 kV (wind and solar plant bus voltage), 11 kV (internal combustion engine generating set bus voltage), and 33 kV (grid voltage). The frequency of the system is 50 Hz, and the total active power of loads is chosen as 100 MW. In the simulation models, the Wärtsilä internal combustion engine generating set model is used to represent synchronous generation. The synchronous condenser model is created based on the Wärtsilä internal combustion engine generating set model. For the battery energy storage system, a model from one of the leading inverter manufacturers is used. Lastly, for renewable generation, WECC models of wind and solar power plants from the DIgSILENT PowerFactory library are used. Different study cases are created to assess how the solution concept improves frequency stability under different modes. According to the results of the simulation studies, it is observed that the power plant solution concept significantly improves frequency stability, particularly in low-inertia power systems. Specifically, in one case, the maximum frequency deviation and RoCoF are reduced by 79.2% and 74.6%, respectively. Overall, “The Flexible Multi-Mode Power Plant Solution” concept offers a promising approach to achieving cleaner, more flexible, and more stable power systems.