A modular SCR-based DC-DC converter for medium-voltage direct-current (MVDC) grid applications

A reliable modular dc-dc converter that is well-suited to the MVDC grid applications is proposed in this paper. This converter benefits from zero current turn-off and soft turn-on switching; hence, it can use naturally commutated switches such as silicon-controlled rectifiers (SCR). SCRs offer numerous advantages over other types of switches, among them are simple control, long lifetime, low losses, low cost, and availability at both high voltage and high current ratings; therefore, use of SCRs in the proposed converter is expected to improve its attributes. The behavior of each power module in the proposed modular converter is similar to that of a Quasi-Square-Wave Ćuk converter. Each power module is designed and controlled such that it employs a very small film capacitor for transferring the power from the input to the output. This feature eliminates the need for electrolytic capacitors that have high failure rates. Furthermore, each power module can be configured as an isolated converter, using an integrated high frequency transformer. Another advantage of the proposed converter is the possibility of having bidirectional flow of power. The input 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. Design and analysis of the proposed modular converter are discussed in this paper. Moreover, its performance is evaluated through simulations and experiments.