100% Renewable Power Systems

Massive integration of inverter-based renewable energy systems has been displacing conventional generating units (mainly synchronous generators) and causing a reduction in power system inertia. This emerging grid is often known as low-inertia power systems. Renewable energy systems are integrated into power systems through power electronics (PE) inverters. These can be generally categorized as (i) grid-following (GFL) and (ii) grid-forming (GFM). The GFL is currently the most commonly used technology and synchronizes with the grid and follows the grid's voltage and frequency. On the other hand, the GFM is a promising emerging technology that generates it's own voltage signal and has the capability to regulate the frequency and voltage at the point of interconnection, independent of the grid conditions. The GFM is gaining more attention given that as we move towards a low to no inertia grid, frequency regulation becomes challenging. It is presently well taken care of by the synchronous machines in hydro and thermal power plants. The cutting edge is to understand what happens when we move towards a power grid that is dominated by power electronics-based generation and to develop technologies that would mitigate the subsequent challenges and enable this transition. This changing landscape of the power grid causes a broad range of challenges for system modelling, planning, stability, and control. We are working on a range of problems in this area including high-fidelity modelling of GFM and GFL, their parallel operation and control, low inertia systems small-signal and large-signal stability analysis, and developing analytical and computational tools for low inertia systems planning and operation. Our work in this area recently published in Nature Communications (https://doi.org/10.1038/s41467-022-30164-3) challenges the notion that inertia is needs to be replaced. The fast active power response that can be provided by GFMs acts as damping in the system and suggests that we are moving toward a new power system stability paradigm.