Abstract
An intrinsically stable microgrid, operated by inverter-interfaced distributed energy resources (I-DERs) is introduced in this paper. The microgrid is built upon a systematic design method, which is adapted from the operation of the synchronous machine (SM). The proposed method analogizes the dynamics of the dc-link in I-DERs to the rotor dynamics in synchronous generators (SGs) and utilizes the capacitor as energy storage. Thus, the proposed mechanism relaxes battery usage for frequency control, and by using the capacitive stored energy, provides a high fault ride-through capability, which is suitable for both on-grid and off-grid applications. Based on stability analysis of the SG and the dynamic state matrix eigenvalues for multimachine power system, the dc-link capacitor of I-DERs is characterized in the context of microgrid. The dc-link capacitor stores kinetic energy similar to the rotor of the SG and provides inertia in transients without the need of battery storage. The inverter angle responds to the change of the dc link voltage (energy). The dc-link voltage is then controlled similar to the field control pertaining to the SG. Finally, a governor-like mechanism is applied to maintain dc-link voltage stability. Simulation and experimental results are provided to show the effectiveness of the proposed design mechanisms.
Highlights
Unlike virtual synchronization methodology, which uses the virtual angular speed as the basis for the speed control, this paper proposes a model based on a physical state
The state-space equations are developed for single- and twomachine test configurations, and eigenvalues are calculated, which depend on the inertia and control parameters in the system
Each synchronous machine adds four states onto the system including three states representing inverter flux-decay model and one state representing the dynamic of the governor with primary frequency control
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Widespread integration of inverter-interfaced distributed energy resources (I-DERs) raises two major concerns about operation of the power grids; namely, the small fault ride-through capability and the decrease in the level of power system inertia due to the renewable sources. I-DERs do not play a major role in the frequency stability of the grid. Regardless of the amount of available energy in the primary source of
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