A hierarchical control of microgrid based on droop controlled voltage source converter

Droop control implemented in microgrid has some limitations, such as introducing frequency and voltage deviation, reactive power sharing errors due to disproportional line impedance and so on. To solve the operation and control problems of micro-grid based on droop control, this paper proposed a novel hierarchical control strategy of micro-grid according to different time scales. In primary control, the power sharing limitations of conventional droop control is revealed and larger droop gains are adopted to improve power sharing. In secondary control, the no load frequency and voltage set points of droop characteristics are adjusted, improving the voltage and frequency quality. In addition to the regulation of micro-grid´s voltage and frequency, seamless transition control between interconnection and islanding mode is designed in secondary control. Finally, the performance of the proposed control strategy is verified by digital time-domain simulation studies in PSCAD/EMTDC software environment.