Connectivity and Bidirectional Energy Transfer in DC Microgrid Featuring Different Voltage Characteristics

In this paper, the connectivity issues related to linking two DC buses featuring different voltage characteristics, in terms of voltage level and ripple, in a DC microgrid are identified, analyzed and discussed. A controlled DC-DC converter was used as the main bidirectional energy transfer enabler between the two buses. The focus of this paper is on how to achieve the best controllability and performance levels of the bidirectional converter when it is linking a DC bus with a relatively high voltage ripple to another with small ripple. The operating fundamentals of a buck-boost converter and its current control algorithm are explained. Different operation and control schemes are also presented. An experimental test setup was devised to investigate and compare the performance of each configuration. A three-phase full wave diode rectifier was used to achieve the high voltage ripple bus, whereas a three-phase controllable IGBT based rectifier was used as a pure DC bus. The results of the various experiments run for bidirectional power flow show that depending on the configuration of the system, better controllability and lower current ripple can be achieved by the proper selection of current and feedback.