The solid-state transformer (SST) is a developing technology which is being integrated in low and high-voltage power systems, supporting the integration of renewable energy in smart grid applications and fast charging stations for electric vehicles (EV). SST is becoming more critical in certain applications of advanced power distribution systems as it provides several advantages over the conventional transformer including its controllability, small weight and size, potential low cost, and simplicity of connection for offshore wind farms. However, some challenges arise in modular SST design and implementation including control architecture for equal power balancing, protection, and communication compatibility that need to be addressed. This paper provides an overview of different SST communication protocols and offers prospects, applications, and future directions for research and development. A control architecture for input and output voltage balancing is presented for a direct power conversion (DPC) type SST system. A detailed SPI communication protocol is also provided which allows the implementation of decentralized operation of the modular SST system.

One of the main limitations in using high voltage and medium voltage DC grids is the issues related to the current-limiting devices and circuit breakers. These devices should be able to handle large currents in the normal operation condition and block high DC currents in a few microseconds in the case of DC faults. Moreover, they are required to dissipate huge amounts of energy stored in the transmission line inductances. In this paper, four configurations of DC circuit breakers from three general groups are evaluated and the results are compared in terms of the time required by the breakers to interrupt the current, maximum DC breaking current, rated voltage, efficiency and current state of development. The performance of DC circuit breakers is evaluated when a line to ground DC fault happens in a 9 module/2 terminal DC system. Simulation results were obtained using Real Time Digital Simulator (RTDS) and PSCAD.

Advantages and disadvantages of expert systems are discussed. An overview of expert system applications being developed or considered high potential is given.>