Power systems have started to and will continue to go through radical changes which bring up new challenges for their secure operation, as well as opening up opportunities to tackle them using modern technologies, e.g. synchronised measurement technology. Frequency security is rising to be one of the main issues in the future power systems control. Replacing fossil fuel burning synchronous generation with asynchronous renewable generation not only reduces system inertia but also decreases the sources capable of providing primary frequency reserves. The faster larger frequency deviation following frequency events (disturbance) in low inertia systems can be limited by contracting larger volume of governor response, which imposes excessive cost on system operators. Alternatively, a new form of frequency control response supported by wide area monitoring systems can be deployed, which is capable of releasing additional active power faster than conventional primary response. Considering the heightened uncertainty of parameters in future power systems, being adaptive to as many parameters as possible in an online manner would be integral to the success of these fast frequency control services. The objective of the research presented in this thesis was to create online methods for fast estimation of parameters governing frequency behaviour following any frequency event, with the intent to contribute to the development of faster and more adaptive frequency control actions suitable for future power systems. The research presented in this thesis includes the creation of two novel methods for fast and simultaneous detection of disturbance, and estimation of its size and location using limited synchronised measurements. Furthermore, an online method for continuous frequency security assessment and evaluation of required fast frequency response based on identified simplified frequency response (SFR) model of the system has been proposed. Finally, a novel Adaptive Under Frequency Load Shedding Scheme as a form of fast frequency response is suggested, which manifests the benefits of adapting response necessity and size to the identified SFR and estimated disturbance size.