Decentralized Control of DC Electric Springs for Storage Reduction in DC Microgrids

Series dc electric springs (series ESs) can tackle the intermittency of the renewable generations (RGs) with reduced storage capacity in dc microgrids (MGs). They can actively manipulate the power profiles of the serially connected noncritical loads (NCLs) to follow the fluctuating RG. In the process of regulating the dc bus voltages, the power rating of an NCL can affect the power of its corresponding series ES. If multiple series ESs with differently rated NCLs can be operated in a coordinative way, the total storage capacity of the series ESs can be potentially reduced. In this article, a decentralized controller is proposed to coordinate the operations of multiple series ESs such that the required storage capacity of the series ESs can be reduced. The conditions for achieving the minimum battery charging and discharging power are analytically derived. The stability analysis of the system as well as the design of the decentralized controller is provided. Experiment results on a 120-V dc grid confirmed that the proposed controller can effectively reduce the total storage capacity of the series ESs in dc MGs by $\text{7.5}\%$.