I. Introduction
The dc distribution is becoming increasingly popular in various applications, including data centers, electric vehicle charging stations, and smart grid systems, due to its high efficiency and reliability [1], [2], [3], [4], [5], [6], [7], [8], [9]. To illustrate, consider the example of a data center application where the traditional ac power distribution suffers from inefficiencies caused by numerous power-conversion stages, as shown in Fig. 1(a) [10], [11]. Additionally, line-frequency transformers are bulky and lack scalability. Many efforts have been made to enhance the efficiency of the power delivery system in data centers through improvements in the power supply unit (PSU) and voltage regulators (VRs) [10], [11], [12], [13]. The number of power-conversion stages in dc distribution can be further reduced to only include the conversion from medium-voltage ac (MVac) to low-voltage dc (LVdc), as well as PSU and VRs, as shown in Fig. 1(b). In this type of dc distribution system, both PSU and VRs can be placed on the board. The solid-state transformer (SST) provides the power conversion with modularity and scalability from MVac to LVdc, as shown in Fig. 2, which also has a smaller volume in comparison with other solutions, such as line-frequency transformer with power factor correction (PFC) [14] and multipulse rectifiers with active filter [15]. Take the 400-V dc distribution in data center as an example, the overall efficiency can increase over 11% compared with the traditional ac architecture with much smaller footprint [4], [11], [12], [13], [14].
(a) Traditional power-conversion stages in a data center with a line-frequency transformer and (b) power conversion with SST.
SST system architecture for data center.
Typical PD. (a) Corona discharge. (b) Surface discharge. (c) Internal discharge.