Operation and Control of Power Systems with Low Synchronous Inertia

Power systems are facing some tremendous challenges for the next decades to come. While dealing with an ageing infrastructure and an ever increasing demand for electric power, the projected increase of electricity generation coming from renewable energy sources will put an even higher stress to the already highly loaded power systems. From a system perspective, renewable electricity generation behaves quite differently from traditional, centralized generation facilities equipped with synchronous generators. Contrary to these generators, most of the renewable energy units do not contribute to the total inertia perceived by the system. This inertia is often considered as one of the vital system parameters upon which the synchronized operation of current day power systems is based. It determines the frequency response with respect to inequalities in the overall power balance. The lower the inertia, the more nervous the grid frequency reacts on abrupt changes in generation and load patterns. As it can be expected that more and more conventional power plants will be replaced by renewable energy generation, such as photovoltaic installations and wind farms, the power system will evolve to a system that will have to be less dependent on this physical inertia. New approaches to control the grid and its components are therefore required. This work covers the complete transition from a traditional power system towards an inertialess, converter based system. The focus lies in understanding the role of synchronous inertia and to provide potential pathways to improve overall system behaviour. To this end, both the quantification and measurement of inertia, together with its impact on the different forms of power system stability, are assessed in detail. Furthermore, distinct control strategies for low inertia systems as a whole, as well as for the provision of so-called ‘virtual inertia’ by renewable energy sources, are presented and evaluated. By applying these advanced controllers to deliver virtual inertia, the use of the otherwise masked (kinetic) energy stored in converter connected units is facilitated in order to improve system stability. Finally, also future approaches for the operation and control of large-scale power systems with zero synchronous inertia are given.

Publication year:2017

Accessibility:Open