Enhanced grid current and DC voltage regulations for three level four leg rectifier DC microgrid under uncertainty and disturbances

Abstract

In this paper, an enhanced grid-side current and DC-bus voltage regulation method is proposed for a three-level neutral point clamped (NPC) four-leg rectifier (3LNPC-4LR) interfaces DC microgrid. Afractional-order extended state observer (FOESO) incorporated into an active disturbance rejection control (ADRC) is proposed for both the inner current and outer voltage control loops. The proposed FOESO-based ADRC aims to address critical challenges in 3LNPC-4LR by providing a robust control approach that ensures constant and fast dynamic DC-bus voltage, excellent grid-side current quality, and unit power factor, while guaranteeing good steady-state behavior under internal and external disturbances, including system uncertainty, coupling terms, and sudden change of linear and constant power loads,as well as grid voltage variations, which can adversely affect system performance and stability. Instead of proportional-inegral control and ESO-based ADRC methods, the FOESO-based ADRC method offers significant advantages in both control loops, including enhanced design flexibility, improved voltage and current tracking performance, superior disturbance rejection capabilities, reduced noise, high robustness to uncertainties and system variations, and increased system reliability with reduced cost and size. The effectiveness of the proposed method is validated through Hardware-in-the loop real-time simulations using OPAL-RT-OP5700 under varying loads, grid voltage conditions, system uncertainties, and constant power load.