Abstract
Parallel connected inverters in islanded mode, are getting momentous attention due to their ability to increase the power distribution and reliability of a power system. When there are different ratings of Distributed Generation (DG) units, they will operate in parallel connection due to different output voltages, impedance mismatch, or different phase that can cause current to flow between DG units. The magnitude of this circulating current sometimes can be very large and damage the DG inverters and also cause power losses that affect power-sharing accuracy, power quality, and the efficiency of the Microgrid (MG) system. Droop control, improved droop control, and virtual impedance control techniques and modifications in the virtual impedance control technique are widely used to suppress the circulating current. However, the addition of the virtual impedance to each inverter to compensate the output impedance is resistive or inductive in nature. The resistive nature of the output impedance always causes a certain voltage drop, whereas the inductive nature of the output impedance causes phase delay for the output voltage. Both problems are addressed by the proposed control mechanism in this paper. Negative resistance, along with virtual impedance, is utilized in the proposed control strategy. The output impedance is to be maintained as inductive in nature to achieve good load sharing in droop control MGs. The simulation results validate the proposed control scheme.
Highlights
In a microgrid (MG) system the i-th power electronic interface is integrated utilizing different Distributed Generations (DGs) in both islanded and grid-connected mode
This paper presents the decentralized virtual impedancebased control technique for parallel-connected islanded MGs to suppress the circulating current
Implementing the proposed virtual impedance control scheme to an MG based on DG inverters connected in parallel, the circulating current is suppressed efficiently and the power sharing accuracy improves in the case of sudden load change
Summary
In a microgrid (MG) system the i-th power electronic interface is integrated utilizing different Distributed Generations (DGs) in both islanded and grid-connected mode. In the presence of local loads and large line impedance, MGs face voltage deviation issues and that causes an increase in the circulating currents and power sharing issues. In order to create a suppression of the circulating current a multi-loop control mechanism for parallel-connected inverter control is needed to improve system reliability and adaptability with effective utilization of droop capability with voltage and current control mechanism [21]. This paper presents the decentralized virtual impedancebased control technique for parallel-connected islanded MGs to suppress the circulating current. The proposed controller responded and mitigated voltage, frequency, and power sharing accuracy errors and the circulating current was suppressed effectively. The stability of the MG system was within the permissible limits
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