An Enhanced Voltage Control Method for Multilevel-Converter-Based Electric Spring at the Distribution Voltage Level

Static compensators (Statcoms) are traditionally used to control the grid voltage and such approach provides excellent performance if the transmission lines have high reactance to resistance (X/R) ratio. Recently, medium-voltage electric springs (ESs) are proposed to regulate the grid voltage by injecting reactive power into the distribution network that has a much lower X/R ratio (about 1) than that of the transmission network. The reactive-power-based voltage compensation performance would be adversely affected by this low X/R ratio. To address this issue, this paper presents an improved droop voltage control method for a multilevel converter (MLC)-based ES connected at the distribution voltage level. The control method would provide both active and reactive power compensation according to the grid voltage. It does not require any communication and huge modification of the original ES control loop. Therefore, it can be installed in all electric springs used at distributed level to enhance both the dynamic and steady-state compensation performance in the ac grid.