Power System Inertia

System inertia is the instantaneous power reserve that stabilizes power systems after large-scale disturbances. It declines with increasing renewable generation, causing an increased risk of black-out unless action is taken. Providing additional inertia will be necessary to maintain security of supply at a reasonable level. To solve the problem of reduced inertia in a reliable and cost-efficient way, this thesis first systematically describes requirements on system level, as basis for the following evaluation of different technological solutions and control schemes. System-level studies of the system split scenario are conducted to derive requirements for inertia. Different technologies, i.e. battery storage, wind turbines and synchronous condensers are compared with respect to their costs, and inertia from wind turbines is evaluated in detail. Two distinct inverter control schemes that provide emulated inertia are designed and extensively compared: extended current control and virtual synchronous machine. Detailed inverter models are described and applied for a robust control design that considers the frequency range from synchronization dynamics up to the filter resonance. Providing additional inertia with wind turbine rotors or from additional battery storage modules is potentially competitive with synchronous condensers. Cost for the inertia reserve are estimated to be between 86 million € per year and 2 billion € per year for Germany, depending on robustness requirements and with technological uncertainty. The detailed analysis of control schemes reveals that the carefully designed extended current control is grid-forming. However, it involves contradictory design aspects, which cause high effort for obtaining robustness. Virtual synchronous machine control has superior transient performance and is straightforward to design. Both control schemes can stabilize a system with 100% renewable generation after the most severe system split events. For the investigated technological options, potentially attractive directions for cost optimization are described. For example, the DC-coupled additional battery storage in renewable power plants is an attractive solution: At potentially competitive cost, it facilitates renewable-only generation situations and integrates seamlessly into the existing system. Offering additional services should be considered to generate further revenue.