A Comprehensive Approach to Flexible LVRT Strategies for Inverter-Based PPMs Enhancing Voltage-Support, Overcurrent Protection, and DC-Link Voltage Quality

Abstract

This paper focuses on enhancing the resilience of Power Park Modules (PPMs) connected to the grid via power electronic units under asymmetrical voltage sag conditions. We particularly address three interconnected constraints crucial for Low-Voltage Ride-Through (LVRT) capability of PPMs: grid voltage support, overcurrent protection and the DC-link voltage quality. Existing literature often overlooks the holistic consideration of these factors, prompting this study to introduce and compare three flexible LVRT strategies compliant with German grid codes. The proposed strategies use distinct approaches to reinforce the LVRT capability of the PPMs. Strategy A adopts a simple approach, utilizing static gain factors associated to the reactive current positive and negative sequences and the active current negative sequence (ACNS) injected into the grid. In contrast, Strategy B employs flexible gain factors to determine the appropriate reactive current. Moreover, an additional focus on minimizing the DC-bus voltage ripple is addressed via the injection of NSAC that completely eliminate the real power oscillations. Similarly, Strategy C calculates flexible gain factors associated to the injected reactive currents. In addition, it adopts an alternative approach to improve the DC-bus voltage quality by eliminating the ACNS limiting partially real and imaginary power oscillations. The three strategies are tested on an inverter-based PPM with 400 kW PV modules and a 200A storage system. The obtained results demonstrate the superior performance of Strategy C. Through the introduced approaches, authors feels that this research work is useful for developing the grid codes and improving the safety and reliability of grid-connected Power Systems.