A novel droop control method based on virtual frequency in DC microgrid

Abstract

In the DC microgrid with traditional droop control, the inconsistency of circuit parameters and line impedance results in the diverse droop characteristics of DC-DC converters, which reduces the current sharing accuracy of converters. Meanwhile, droop control inevitably leads to DC-bus voltage deviation and the secondary control has the problem of poor communication fault tolerance. To improve the control performance of DC microgrid, a droop control method based on virtual frequency is proposed by simulating the frequency droop control mechanism in AC microgrid. A virtual voltage with a frequency proportional to the output current is constructed and shared among the converters through low bandwidth communication (LBC). The phase difference among virtual voltages generates virtual reactive power, which is calculated by Fourier transform to coordinate the output current of each converter. The algorithm can keep high performance under some communication faults and can guarantee that the converter with serious communication faults can automatically exit the current sharing control without affecting other converters. Moreover, the actual reactive power and harmonics wouldn’t be introduced, and the power quality of the microgrid can be ensured. The stability of the algorithm is demonstrated by small-signal analysis and mathematical calculation. Finally, simulation and experiment show that the algorithm has high current sharing accuracy, excellent communication fault tolerance and plug-play performance.