Voltage Support Capability Improvement for Grid-connected Converters under LVRT Conditions Considering Grid Impedance Variation

With the increasing employment of grid-connected converters (GCCs), the potential voltage support capability of the GCCs is expected to be fully utilized during the low voltage ride through (LVRT) condition. This study proposes a power reference adjustment strategy which improves the voltage support capability of the GCC. To be specific, a security-region-based analysis procedure is first introduced and then carried out considering the variation of the grid impedance and the depth of the voltage dip. Based on this, this study provides a theoretical upper limit of the voltage support capability under different depths of grid-side voltage collapse. Furthermore, a power reference adjustment strategy is proposed from the GCC’s perspective, which consists of a droop control and two power reference limiting steps. This strategy is applicable to the grid-following and the grid-forming control structures, and remains an explicit pattern for engineering applications. The simulation verifies the effectiveness of the proposed strategy and the dramatic improvements to the voltage support capability.