Comparative Performance Analysis of Grid-Forming Strategies Applied to Disconnectable Microgrids

In the scenario of growing penetration of Distributed Generation (DG) units, grid-forming (GFM) strategies are emerging as important candidates to become key players in future low inertia grids. These methods are either based on emulation of synchronous machines at different levels of abstraction or based on the behavior of nonlinear oscillators, the so-called dispatchable Virtual Oscillator Control (dVOC). However, it is not clear which are the strengths and weaknesses of each GFM technique in a general comparative scenario of operation in systemic operation. In this work, part of this question were addressed, where firstly a novel Linear-Droop dVOC-based strategy is proposed and qualitatively compared to another dVOC-based strategy and to Conventional Doop Control in a application scenario of a disconnectable low-voltage microgrid with the aim of evaluating the transient and steady state performance in scenarios of (dis)connenction of loads in both grid-connected and islanded operating modes through time-domain simulations via PSIM™. dVOC-based methods presented overall superior transient performance compared to Droop Control, reaching settling times 8x faster for islanded-mode operation and 4x faster for grid-connected operation. Furthermore, for operation with higher X/R ratio dVOC-based methods presented overall superior transient and steady-state performance compared to Droop Control. On the other hand, the results showed that dVOC-based methods regulates inverter output voltage and frequency based on droop relationships of internal oscillator model quantities, making unclear what is the behavior of quantities at the output of the inverter, which may degrade effectiveness of active and reactive power sharing between GFM units.