A Modified Implicit Z-Bus Method for an Unbalanced Hybrid AC-DC Microgrids

Abstract

This study proposes a power flow algorithm based on the modified implicit Z-bus method for an unbalanced hybrid AC-DC microgrid (HMGs) operated in islanded mode. In this paper, a 4-wire multi-ground ac microgrid and a bi-polar DC microgrid are coupled through interlinking converters (ICs). Microgrid (MG) elements are represented through sequence component models. In contrast to grid-connected systems, where frequency and voltage are constant, changeable frequency and voltage are employed for power synchronization amongst AC and DC microgrids. In this work, a load flow algorithm for hybrid AC-DC microgrids considering various load models (constant load, voltage, and frequency-dependent load) and distributed generation is developed. The proposed algorithm is validated on 12-bus and 47-bus hybrid microgrid test systems. The obtained result is compared with result of newton rapson-method (NR) and time domain-based simulation modules to show accuracy of the proposed method.