Analysis of Low-Cost BTB-DC Electric Spring in DC Microgrid Considering Impedance Ratio Impact

Dc electric spring (ES) is an emerging and feasible method to stabilize the fluctuating critical loads (CL) voltage caused by renewable energy. However, conventional single dc electric springs (S-dc-ES) require high costs and have poor voltage and system adaptability. Its poor voltage adaptability may result in the noncritical load (NCL) unintentionally going <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>-grid, while poor system adaptability may cause S-dc-ES to fail in maintaining CL voltage stability when the proportion of NCL capacity in dc microgrid system is small. To address these issues, a back-to-back dc ES (BTB-dc-ES) and its corresponding control are proposed in this article. The power can be diverted between NCL and CL controllably through BTB-dc-ES. Thus, the additional energy storage device can be removed, and the total power rating and output voltage of the converters can be reduced significantly, leading to a significant reduction in costs. Besides, the results from the numerical case study confirm that BTB-dc-ES can maintain stable CL voltage with smaller NCL voltage adjustment. This allows more NCLs with narrow voltage thresholds to participate in load demand response. The impedance ratio impact analysis reveals that BTB-dc-ES ensures stable CL voltage performance, regardless of whether the NCL capacity ratio is greater or smaller than that of the CL in dc microgrid system. This enables it to adapt to more types of dc microgrid scenarios. Finally, simulation and hardware-in-the-loop experiment results are provided to verify that BTB-dc-ES can effectively guarantee CL voltage stability and show excellent voltage and system adaptability.