System-Level Low-Voltage Ride-Through Control for the Renewable Power Plant Connecting to Weak Grid

Abstract

This study focuses on the low-voltage ride-through (LVRT) control in large-scale renewable power plants (RPPs) connected to weak grids, where grids fail to offer adequate reactive power, resulting in voltage fluctuations and necessitating additional reactive support from RPPs. However, in weak grids, the impact of system-side responses on LVRT control—especially transformer connections (TCs)—becomes increasingly significant. The existing research overlooks this factor as its negligible effects in strong grid scenarios. However, in weak grids, this oversight becomes critical, as it can lead to voltage overruns at certain voltage levels, posing risks to system safety. Given this, a system-level LVRT control is proposed, focusing on safety constraints from system-side responses. This work introduces a novel voltage boundary vector trajectory model that captures the geometric relationships of the system-side response, allowing for a more accurate determination of voltage controllable boundaries. To compute optimal commands in the constructed boundaries, a discrete and clustering matrix-based calculation algorithm is proposed. Based on the hardware-in-loop experimental platform, comparisons are made with both the latest literature and widely adopted engineering practices. It is proven that voltage overruns can easily occur with the short circuit ratio (SCR) of less than 3, which can be up to 14%. This study effectively solves this security problem and simultaneously increases reactive power support by at least 30% when the voltage sag is not below 0.3 p.u.