Comparison of line and load converter topologies in a bipolar LVDC distribution

Low voltage direct current (LVDC) distribution is a new low voltage distribution concept. In this study, potential line and load converter topologies for a bipolar LVDC 1500 V distribution system are compared. It is possible to supply the LVDC network by one or two line converters and the line and load converters can be connected to 750 V DC or 1500 V DC. 12-pulse half-controlled thyristor bridges, two- and three-level PWM converters and Vienna-rectifiers can be used as the line converters and two- and three-level single-phase half and full PWM bridges and three-phase converters can be used as the load converters in the LVDC distribution. The bases for the converter comparison are size of required LCL- and LC-filters, voltage and current stresses of the power semiconductor switches and the capability to operate with bidirectional power flow in the case of line converters. Furthermore, the bases of the load converter comparison are the capability to operate with reduced DC voltage and the capability to feed a half-wave rectifying load. According to the simulation results, the most suitable line converter is the three-level converter if a bidirectional power flow is needed and the Vienna-rectifier if a unidirectional power flow is adequate. The balancing circuit needs to be added to the LVDC network to maintain the voltage balance of the DC capacitors if the LVDC network is supplied by one line converter and the DC link is loaded asymmetrically. According to the simulation results, the most suitable single-phase load converter topologies connected to 750 V DC are the two- and three-level full bridges and the most suitable load converter topologies connected to 1500 V DC are the three-level topologies.

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