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The undesirable harmonic distortion produced by distributed generation units (DGUs) based on power-electronic inverters presents operating and power-quality challenges in electric systems. The level of distortion depends on the internal elements of the DGUs as well as on the characteristics of the grid, loads, and controls, among others. This paper presents a comprehensive method, focused on power-quality indexes and efficiency for the design of microgrids with multiple DGUs interconnected to the ac grid through three-phase multi-Megawatt medium-voltage pulsewidth-modulated-voltage-source inverters (PWM-VSI). The proposed design method is based on a least square solution using the harmonic domain modeling approach to effectively consider explicitly the harmonic characteristics of the DGUs and their direct and cross-coupling interaction with the grid, loads, and the other DGUs. Extensive simulations and analyses against PSCAD are presented in order to show the outstanding performance of the proposed design approach. [ABSTRACT FROM PUBLISHER]

Integrating power electronics to the grid has introduced new small signal–signal stability challenges, which are commonly studied with average time-invariant models and, more recently, with harmonic state–space models. In both approaches, it is common to obtain the models by following an analytical formulation, which can be tedious and impractical in systems with different controllers and topologies, just to mention a few examples. This paper proposes a numerical approach based on shooting methods and the recursive evaluation of the time-variant Jacobian along the steady-state orbits to construct automatically a periodic linear time-variant model and its respective linear time-invariant model using the extended harmonic domain; these models include explicitly the harmonic components. The proposed modeling approach can be applied to systems with different converter topologies, controllers, and modulation techniques. A nonlinear periodic switched system (grid-connected parallel inverter-based microgrid) is used to validate the proposed linearization approach. • Applicable to periodic switched nonlinear systems. • Shooting methods compute the steady state directly. • Convergence to stable and unstable periodic steady-state solution. • Jacobian is computed numerically as a by-product of the shooting method. • The small-signal model considers the effects of any modulation pattern. [ABSTRACT FROM AUTHOR]