An Adaptive Virtual Resistance Method Based on a Superimposed Frequency for Power Distribution in DC Microgrids

In DC microgrids, the superimposed frequency droop method is an attractive decentralized power distribution method. However, the practical application of this method is challenged by limited maximum loading, non-negligible bus voltage drop, significant small-AC-signal ripple on the DG output currents, and incomplete modeling and controller design. These issues may lead to system instability, severe bus voltage drop, and decreased reliability. To overcome these challenges, an adaptive virtual resistance method is proposed in this paper. Compared to the traditional control scheme, the improvements include two parts. Firstly, the small-AC-signal reactive power passes through a proportional-integral regulator and a saturator instead of a proportional regulator to generate the regulation value. Secondly, the generated regulation value is multiplied by the local output current and then used to regulate the voltage command rather than being directly applied for regulation. A large-scale system model under the proposed control method is established, while an optimal controller design method considering both stability and transient performance is developed based on the genetic algorithm. Results from both simulations and experiments demonstrate the effectiveness and advantages of the proposed control method.