Stability issues in cascade connected switching converters for DC microgrid applications

Microgrids consist of distributed electrical generation architectures which have some instability problems due to the cascade interconnection of the converters and their related negative impedance effect. In electric power distribution system, a point of load converter behaves as constant power load (CPL) which result in a well known destabilizing effect. In this paper, different strategies that have been used to eliminate this undesirable behavior will be discussed. Then, an alternative approach based on sliding mode control (SMC) and using canonical elements for power processing will be proposed to stabilize cascaded converters. The proposed approach will be illustrated using a system consisting of two cascaded boost converters behaving as Loss Free Resistors (LFR) supplied from a PV panel and connected to a 380 V dc bus of a microgrid. It will be shown that using LFRs and SMC could be a good strategy to stabilize cascaded boost converters. The theoretical results are verified using simulations and experimental measurements.