A Novel Grid Forming Control Scheme Revealing a True Inertia Principle

This article proposes an unconventional strategy for a grid forming converter, based on a phase restoring control concept by which a constant steady state frequency is achieved. This control scheme is inherently without a phase-locked loop (PLL) and keeps the power system frequency at its nominal value. Under disturbance, the control response mimics infinite virtual inertia since the power system frequency always returns to its nominal value. Therefore, this control presents a physical equivalence to a power system response with substantial inertia provided by synchronous machines. The understanding of frequency drift as a local phenomenon and power system frequency as a global aspect is briefly introduced. Further, the inherent discretization of a converter control as part of the feedback loop over the continuous network system is also considered. The concept has been mathematically investigated in a realistic test bench and global stability of the control is displayed based on the necessary boundary conditions. Simulation results supporting the mathematical hypothesis and visualizing the controller actions are presented. As a beneficial coincidence of these ideas, the control structure ensures similar responses in both electromagnetic transients (EMT) and root mean square (RMS) simulations.