Dispatchable Virtual-oscillator-controlled Inverters with Current-limiting and MPPT Capabilities
Minghui Lu, Rahul Mallik, Brian Johnson, Sairaj V. Dhople
Abstract
Photovoltaic (PV) inverters typically have a multiloop control architecture to facilitate extraction of maximum possible dc-side power and its transfer to an ac-side grid interconnection. In this paper, we integrate dc-side controls that modulate the dc-link voltage for peak PV power harvest with an ac-side dispatchable virtual oscillator controller (dVOC) that synchronizes to the grid. In particular, maximum power point tracking is realized via integral control which then generates a dc-link voltage command. From there, dc-side voltage regulation is achieved by modulating the power reference sent to the ac-side dVOC. The dVOC yields an ac voltage command which is tracked with nested voltage- and current-control loops in the synchronous reference frame. Ac-side functions are topped off with an ac-side current limiter to ensure proper operation during large grid transients. We then analyze the eigenvalues of this interconnected system and its participation factors to demonstrate timescale separation of the various control loops. The proposed framework is substantiated via simulations and experiments.