DC Self-Adapt Frequency Regulation Method for Hybrid DC Power Supply Microgrid System

Frequency fluctuations will inevitably occur when the microgrid with hybrid DC power supply of line commutated converter (abbr. LCC)-voltage source converter (abbr. VSC) is disturbed. In order to keep the frequency within the specified range under the different kinds of disturbances, a DC frequency regulation method with self-adapt disturbance changes was proposed in the LCC-VSC supplying microgrid system. Firstly, the critical droop coefficient required to pull the system frequency into the specified range after disturbance was theoretically deduced, and based on this, a primary frequency regulation method of variable droop coefficient with self-adapt disturbance changes was proposed to rapidly control the disturbed system frequency within the specified range by means of the rapidity of DC reaction. Secondly, as the primary frequency regulation is still a differential regulation, the secondary frequency regulation strategy of variable reference power was proposed. Finally, a simulation model was established on the PSCAD/EMTDC platform. The results show that when the load changes within 12.5% and the light changes within 10%, the primary frequency regulation can restore the frequency deviation to within 0.2 Hz, and when the load changes within 15%, the secondary frequency regulation can achieve zero-error frequency regulation, which verifies the effectiveness of the proposed strategy.