Abstract
This paper presents a decentralized control method for distributed generations (DGs) in an islanded direct current (DC) microgrid. In most typical DC microgrids, a decentralized control method is based on a voltage droop control method. However, the grid voltage differs from node to node due to line voltage drop, and hence the power sharing ratio among DGs cannot be matched with as desired value. Especially in an islanded DC microgrid including an energy storage system as a voltage source, it is difficult for DGs to maintain the charge state of the ESS in a decentralized way. To overcome this problem, state of charge (SOC)-voltage droop control is applied to the ESS. By using the proposed droop method, the SOC information can be assigned to the grid voltage, and hence the other DGs are able to support the SOC in a decentralized way. For DGs to enhance the accuracy of the SOC estimation, voltage drop is compensated for based on forecasting data and line impedance data. The simulation is modeled and implemented using Power System Computer Aided Design/Electromagnetic Transients for DC (PSCAD/EMTDC, version 4.2, Winnipeg, Manitoba, Canada) and the simulation results show that the capability to maintain SOC as well as the system voltage profile are improved by using the proposed method.
Highlights
Direct current (DC) microgrids are being increasingly developed and studied due to the fact that they are more efficient than alternating current (AC) systems from the perspective of energy conversion efficiency [1,2,3]
Voltage droop control method (V Droop): The voltage droop control shown in Figure 6 is applied to the distributed generations (DGs)
state of charge (SOC)-voltage droop and voltage droop control method (SOC-V Droop): SOC-voltage droop control shown in Figure 1 is applied to the energy storage system (ESSs) and the voltage droop control is applied to the DGs
Summary
Direct current (DC) microgrids are being increasingly developed and studied due to the fact that they are more efficient than alternating current (AC) systems from the perspective of energy conversion efficiency [1,2,3]. While the ESS is controlled in constant voltage mode, the output power varies according to change of system load In this case, the SOC should be controlled by other DGs and EMS. The most significant problem of the decentralized control method while using the ESS as a voltage source is the lack of SOC information for dispatchable DGs in an islanded DC microgrid. To overcome the disadvantages of the decentralized control method that is the focus of this paper (lack of SOC information), a power control method based on SOC and grid voltage with line voltage drop compensation is proposed.
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