Robust and autonomous dc bus voltage control and stability analysis for a dc microgrid

In this paper, a novel approach for robust and autonomous dc bus voltage control in a dc microgrid has been proposed. A nonlinear disturbance observer (NDO) only with local information is designed firstly to track power disturbances caused by load changing or the volatility of the renewable sources in the dc microgrid. With the observer, voltage droop method has been adopted in achieving power sharing and autonomous operation of a dc microgrid. Furthermore, an improved current feedforward is developed to suppress wide fluctuations of the dc bus voltage during transients. In addition, a notch filter has been used to effectively eliminate the second harmonic ripple components in the inductor currents of the droop control units to improve the power quality. The effectiveness of the proposed control scheme is verified on a laboratory prototype including two bidirectional dc-dc converters supplied by two programmable dc power supply systems, a dc load with a resistor connected to the dc bus via a buck type dc-dc converter and a three-phase unbalanced ac load.