A Systematic Review of Grid Following, Grid Forming and Mode Switching Control in MVDC Distribution Networks

ABSTRACT With the remarkably increased integration of DC loads and renewable energies, such as solar power generation, into distribution networks, these networks are facing many operational challenges, such as random power flows and large‐scale voltage violations, owing to the intermittent characteristics of inverter‐based resources (IBRs). Medium‐voltage direct current (MVDC) technology is expected to be a promising solution to address the above issues due to its independent control of active and reactive power. In most operations and planning of MVDC projects in distribution networks, the control of MVDC can be classified into two categories: grid‐following control (GFL) and grid‐forming control (GFM). The MVDC adopting GFL can provide accurate active and reactive power control, but it faces stability challenges in weak grids. The MVDC adopting GFM performs better under weak grid operating conditions, but it may suffer from limited power regulation under strong grid conditions. To ensure the continuous, stable operation of MVDC, researchers have developed numerous switching controls for GFL and GFM to further expand MVDC applications in distribution networks. This paper reviews the common GFL and GFM control principles, technical characteristics, and the limitations of their MVDC applications. In addition, typical switching strategies for GFL and GFM are introduced and analysed. Finally, the applications of MVDC adopting GFL, MVDC adopting GFM, and MVDC configured with GFL/GFM switching control are compared and discussed.