A Nonlinear Disturbance Observer Based DC Bus Voltage Control for a Hybrid AC/DC Microgrid

DC bus voltage control is an important task in the control of a dc microgrid or hybrid ac/dc microgrid system. To improve the dc bus voltage control dynamics, traditional approaches are mainly based on feeding forward the load or source power. However, in the microgrid system with distributed dc sources and loads, the traditional feedforward based methods need remote measurement or communications. In this paper, a nonlinear disturbance observer (NDO) based dc bus voltage control is proposed, which does not need the remote measurement or communication with a true "plug-and-play" feature. Based on this observer, a novel dc bus voltage control scheme with pulse-width-modulation (PWM) dead-time compensation is developed. The proposed method can suppress the transient fluctuations of dc bus voltage, and improve the power quality in such a hybrid microgrid system. The performance of the presented control strategy has been successfully verified in a 30 kVA dc subgrid including battery energy storage system, photovoltaic power generation system and a dc load.