Stability and Control of Hybrid AC/DC Microgrids

Hybrid AC/DC microgrids are considered as viable solutions to reduce energy conversion losses in microgrids. However, hybrid AC/DC microgrids are susceptible to stability issues during high penetration of dynamic loads (e.g., induction machines). The non-linear dynamics of induction machines, result in sustained voltage/frequency oscillations following disturbances in the microgrid, which is a major challenge for stable operation of the hybrid AC/DC microgrid. This issue is even more severe when the hybrid AC/DC microgrid is operated at autonomous mode. The PEC based energy storage systems (ESSs) are used as an effective solution for power balancing in the microgrid; hence with the fast response of the PEC, microgrid voltage/frequency could be stabilised rapidly. This chapter discusses the stability and control aspects of hybrid AC/DC microgrids to address the drawbacks of these systems. A supplementary power oscillation damping controller for the ESS is demonstrated for damping the low-frequency oscillations (LFOs) in the microgrid. Furthermore, the dynamic characteristics of the loads in the microgrid can change constantly which requires re-tuning of the pod controller. This is addressed by an adaptive neuro-fuzzy inference system (ANFIS) based POD controller which has been shown to be more effective due to its ability to adjust the gain based on the frequency deviation, and handling more non-linearity in the system dynamics. Furthermore, this chapter presents a hybrid AC/DC microgrid architecture incorporating a central energy storage system with a coordinated control strategy between the central ESS and the inter-linking converter (ILC) to maintain the stable operation of the microgird.