Energy Management System for DC Electric Spring with Parallel Topology

DC electric spring (DCES) maintains the voltage stability and improves the power quality in dc microgrid with the inclusion of renewable energy sources. A parallel DCES topology has been recently proposed; it consists of a dc-dc three-port converter and an energy storage system made up of a battery paralleled with the critical load (CL) through a bidirectional buck-boost converter. In this article, an effective energy management system (EMS) is proposed for the parallel DCES topology. After illustrating the DCES operating modes, three functional states are introduced, namely normal, specific time, and emergency, where the normal state refers to the DCES operation under dc microgrid power fluctuations, whereas the specific time and emergency states refer, respectively, to the environment conditions and battery contingent situations. The EMS decides the transitions between the DCES operating modes, changes the operating status of the battery, and realizes multiple charging and discharging mechanism. This gives DCES the capabilities of guaranteeing the voltage stability of CL while keeping the state of charge of the battery within a reasonable range, which extends the lifetime of battery and ensures safe and reliable operation of the whole system. The proposed EMS has been validated by simulation and experimental results.