Extending DC Bus Signaling and Droop Control for Hybrid Storage Units to Improve the Energy Management and Voltage Regulation

Abstract

DC bus-voltage signaling (DBS) and droop control are often used in DC nano and microgrids with decentralized distributed energy resources (DERs). This technique effectively enforces the appropriate contributions of power sources and energy storage systems (ESSs) in steady-state situations. The usage of super capacitors (SCs) in conjunction with batteries in a hybrid energy storage system (HESS) has recently been shown to reduce the influence of high and fast current changes on the losses and lifetime of the battery units. However, regulating the HESS as a single unit eliminates the SC’s potential contribution in improving power quality in a DC nanogrid due to its high-power capabilities. This work discusses employing a dual-droop coefficient to expand DC bus signaling and droop control by introducing a second droop constant in the range of the ESS’s droop constant. The suggested droop constant allows the SC to participate in power-sharing in the steady state. The voltage regulation will improve by decreasing the DC bus voltage variation with the load or power variation in the DC nanogrid. Furthermore, in the droop zone, the battery’s current variation is less, resulting in a smoother transition in the battery current. In addition to this, the contribution that SCs make to the slow component is variable, which is something that might be accomplished by having a changing threshold voltage in the I vs. V curve.