Abstract
For reliable operation of an islanded microgrid, at least one of its distributed resources should assume the responsibility of forming the off-grid power system. This responsibility is usually assumed by energy storage systems based on their capability of compensating the unbalance between generation and consumption. However, the storage units lose this capability when they reach the maximum and minimum limits of charge. Under these conditions, the regulation of the power grid may be assumed by another unit with enough capability or the power balance should be adjusted coordinately. This paper proposes a coordination architecture for islanded ac microgrids, which considers the appropriate charge profiles for battery-based energy storage systems. The architecture is based on distributed decision-making mechanisms, which use only local measurements for determining the operation mode of each unit independently. The coordination relies on a bus-signaling method, which enables the distributed units to have a global perception about the operation of the microgrid, without any communication infrastructure. The proposed architecture includes cooperative operation between distributed energy storage systems for achieving the equalization of the states of charge. Experimental results in a lab-scale microgrid with network configuration validate the proposed strategy under different operational conditions.
Highlights
T HE use of variable renewable energy sources (RESs), such as photovoltaic (PV) and wind-turbine (WT) generators, has facilitated the electrification of remote sites such as telecommunication stations or small villages, thanks to the availability and low environmental impact provided by the primary energy resource [1]–[4]
The network configuration of the islanded microgrid considered for this case study is shown in Fig. 1, in which the distributed energy resources (DERs) and balanced loads are parallel connected in a common point of coupling
Once the right nominal values of the droop coefficients have been selected for ensuring a stable operation of the microgrid, it is important to determine the local asymptotic stability of the equilibrium points, which ensure that all initial conditions after the transitions in the operation modes will result in trajectories that converge to the equilibrium points
Summary
T HE use of variable renewable energy sources (RESs), such as photovoltaic (PV) and wind-turbine (WT) generators, has facilitated the electrification of remote sites such as telecommunication stations or small villages, thanks to the availability and low environmental impact provided by the primary energy resource [1]–[4]. A coordination architecture for an islanded ac microgrids with distributed ESSs has been proposed in [21], which is based on seamless transitions between VCM and PCM in the DERs in accordance with particular operating conditions and a frequency bus-signalling method. This approach allows a faster transition between VCM to PCM for the ESSs, reducing the inertia that may cause overcharge in the storage devices.
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