Per-Unit Dynamic Models for Grid-Following Photovoltaic Inverters

Per-unit models are frequently utilized in power-system analysis. The common approach that is followed is to outline base values for pertinent parameters and signals, and then normalize them to obtain dimensionless and per-unit models. While per-unit dynamic models for synchronous generators are widely documented, those for inverter-based resources are not as common. In this paper, we put forth a per-unit dynamic model for a standard grid-following photovoltaic inverter model. The topology we examine is a single-stage dc-ac voltage-source inverter interfaced to the grid via an LCL filter; the dc side includes the PV array interfaced to the inverter with a dc-link capacitor. The control architecture includes: a maximum power point tracking (MPPT) algorithm, a controller for regulating the dc-side voltage, a controller to regulate reactive power, an inner-loop current controller, and a standard synchronous-reference-frame phase locked loop for grid synchronization. We anticipate the proposed per-unit dynamic models being useful across scales (residential, commercial, and utility-level) and applications (modeling, time-domain simulations, control design, validation) to a wide range of stakeholders (researchers and practicing engineers).