Abstract
A highly reliable modular DC-DC converter that is well-suited to the medium -voltage direct-current (MVDC) grid applications is presented in this paper. Each power module in the proposed converter is designed and controlled such that it employs two small film capacitors for transferring the power from the source to the load. This feature eliminates the need for large electrolytic capacitors that are sensitive to high temperatures and have high failure rates. Furthermore, each power module is configured as an isolated converter, using an integrated high frequency transformer. Taking advantage of the leakage inductance of the transformer, the switches benefit from zero current turn-off and soft turn-on. Each power module sees only one switch or diode on the conduction path when transfering energy from the input to the link capacitors or from the link capacitors to the output, which results in relatively low conduction losses. Another advantage of the proposed converter is the possibility of having bidirectional flow of power. To form modular converters that facilitate sharing voltage or current in high power applications, the input terminals and output terminals of the power modules can be connected in series or in parallel. In this paper, an input-parallel output-series (IPOS) modular configuration is considered to increase the voltage blocking capability at the output and handle high currents at the input of the converter. In this paper, principles of the operation, design, and analysis of the proposed modular converter are discussed in detail, and performance of the modular converter is evaluated through simulations and experiments.