Transferring the driveshaft inertia to the grid via the DC-link in MV drive systems

This paper investigates a control approach that renders the driveshaft inertia completely available on the grid side and enhances the fault ride-through behavior of medium-voltage (MV) drive systems. Two main contributions are presented. First, we show how the rotational inertia of the driveline shaft can be synchronously coupled to the grid through a modification of the speed control reference signal and through an adapted DC-link control strategy. For the latter, we pursue two alternatives: one based on conventional cascaded control and another based on synchronous machine (SM) model matching. Second, we demonstrate that both the standard phase-locked loop (PLL) and the matching control approach can be interpreted, via the ray-circle complementarity, as feedback optimization schemes with distinct steady-state maps. This perspective allows us to revisit matching control, reveal its embedded PLL, highlight its current-limiting and tracking capabilities, and provide an extensive simulation study.