Abstract
The interconnection of distributed energy resources (DERs) in microgrids (MGs) operating in both islanded and grid-connected modes require coordinated control strategies. DERs are interfaced with voltage source inverters (VSIs) enabling interconnection. This paper proposes a load demand sharing scheme for the parallel operation of VSIs in an islanded voltage source inverter-based microgrid (VSI-MG). The ride-through capability of a heavily loaded VSI-MG, where some of the VSIs are fully loaded due to the occurrence of an event is investigated. In developing analytical equations to model the VSI, the concept of virtual synchronous machines (VSM) is applied to enable the VSI mimic the inertia effect of synchronous machines. A power frame transformation (PFT) that takes the line ratios of the MG network into account is also incorporated to yield satisfactory transient responses of both network frequency and bus voltages in the MG network. A Jacobian-based method is then developed to take into account the operational capacity of each VSI in the VSI-MG. The resulting amendable droop control constrains the VSIs within their power capabilities when an event occurs. Simulation results presented within demonstrate the effectiveness of the proposed procedure which has great potential to facilitate efforts in maintaining system reliability and resiliency.
Highlights
The microgrid (MG) concept emanates from the evolution of electric power systems in which distributed energy resources (DERs) comprising distributed generation (DG), such as wind turbine generators (WTG), solar photovoltaic systems (PV), diesel engine generators (DEG), microturbine generators (MTG), along with energy storage systems (ESS) can be interconnected within a medium-voltage transmission or a low-voltage distribution network to supply power to connected loads [1,2,3,4]
This paper extends from an earlier work in [35] with the inclusion of a virtual active and reactive power frame transformation (PFT) and its feasibility to maintain system resilience in the parallel operation of voltage source inverters (VSIs)
With the aid of MATLAB, and applying appropriate numerical methods incorporating the virtual synchronous machines (VSM) and PFT concepts and in conjunction with the Jacobian-based method resulting in the amendable droop control, the following results are presented within
Summary
The microgrid (MG) concept emanates from the evolution of electric power systems in which distributed energy resources (DERs) comprising distributed generation (DG), such as wind turbine generators (WTG), solar photovoltaic systems (PV), diesel engine generators (DEG), microturbine generators (MTG), along with energy storage systems (ESS) can be interconnected within a medium-voltage transmission or a low-voltage distribution network to supply power to connected loads [1,2,3,4]. MG networks consisting of controllable connected loads can be operated in both grid-connected and islanded modes of operation. In the grid-connected operating mode, the bus voltages and network frequency are maintained by the utility grid. In the islanded operating mode, the DERs maintain the bus voltages and network frequency in the MG network. To enable interconnection in islanded and grid-connected operating modes, voltage source inverters (VSIs) are a class of power electronic converters that are interfaced with these DERs in alternating current MGs [6]. Some challenges include sharing of active (P) and reactive (Q)
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