Abstract
The growing level of grid-connected renewable energy sources in the form of microgrids has made it highly imperative for grid-connected microgrids to contribute to the overall system stability. Consequently, secondary services which include the fault ride-through (FRT) capability are expected to be possessed characteristics by inverter-based microgrids. This enhances the stable operation of the main grid and sustained microgrid grid interconnection during grid faults in conformity with the emerging national grid codes. This paper proposes an effective FRT secondary control strategy to coordinate power injection during balanced and unbalanced fault conditions. This complements the primary control to form a two-layer hierarchical control structure in the microgrids. The primary level is comprised of voltage/power and current inner loops fed by a droop control. The droop control coordinates grid power-sharing amongst the voltage source inverters. When a fault occurs, the participating inverters operate to support the grid voltage, by injecting supplementary reactive power based on their droop gains. Similarly, under unbalanced voltage condition due to asymmetrical faults in the grid, the proposed secondary control ensures the positive sequence component compensation and negative and zero sequence components clearance using a delayed signal cancellation (DSC) algorithm and power electronic switched series impedance placed in-between the point of common coupling (PCC) and the main grid. While ensuring that FRT ancillary service is rendered to the main utility, the strategy proposed ensures relatively interrupted quality power is supplied to the microgrid load. Consequently, this strategy ensures the microgrid ride-through the voltage sag and supports the grid utility voltage during the period of the main utility grid fault. Results of the study are presented and discussed.
Highlights
The introduction of renewable energy sources (RESs) based distributed generations (DGs) known as distributed energy resources (DERs) into the modern electric power systems has raised significant challenges such as bidirectional power flow in the distribution system, stochastic generation nature of RESs, and distinctive fault current properties [1]
This strategy ensures the microgrid ride-through the voltage sag and supports the grid utility voltage during the period of the main utility grid fault
Various types of faults are simulated on the main grid and are switched on at time t = 1.3 s and assumed to be automatically cleared at t = 1.8 s
Summary
The introduction of renewable energy sources (RESs) based distributed generations (DGs) known as distributed energy resources (DERs) into the modern electric power systems has raised significant challenges such as bidirectional power flow in the distribution system, stochastic generation nature of RESs, and distinctive fault current properties [1]. MGs have served as a prospective platform where RESs are integrated into the modern-day distribution system with operational flexibility and controllability in either grid-dependent or autonomous modes [5]. MGimposes are determined renewable energy sources.voltage, grid-connected modes, the main grid most of by the renewable energy sources. In stand-alone operation, voltage and frequency are regulated using control supply standards [9]. These control voltage systemsand are frequency usually implemented any control of these schemes with multi-loop [8,10] These control systems are usually implemented in anyalpha-beta-gamma of these reference reference frames; synchronous direct-quadrature-zero coordinates, stationary frames; synchronous direct-quadrature-zero coordinates, stationary alpha-beta-gamma coordinates, coordinates, and natural three-phase coordinates [8,11]
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