Ing. Jakub Zedník

This paper presents an assessment of Solid State Transformer (SST) topologies from the usability in energy applications point of view. SSTs are nowadays at the center of researchers’ attention mainly due to reducing size and weight of traction transformers in railway vehicles. Our contribution aims to use the SST as a cornerstone of an Energy Router that should replace a typical distribution substation with a classical transformer. After a general overview of SST topologies classification an overview of design guidelines for key SST components (ferrite cores for medium frequency (MF) transformers, semicon-ductors and high voltage capacitors) is presented for two topologies that seem to be promising for energy applications: classical three-stage SST and two-stage SST with a low voltage DC link and galvanic insulation in the first stage. These two topologies are then compared from an economical point of view based on acquisition cost of key components in order to evaluate whether the technology has matured to be used commercially.

This paper deals with the design of all “power” capacitors in two variants of a solid-state transformer (SST) described in this work. SSTs are nowadays at the center of attention mainly due to reducing the size and weight of traction transformers in railway vehicles and in power transfer, where it should be part of an energy router that could replace the distributional transformer. In the case of three-stage SST, there are three types of capacitors: in submodules of a modular multilevel converter (MMC), in the MV-DC link, and on outputs of the galvanic insulation modules (DAB). In the case of two-stage SST, there are two types of capacitors: one type is in the DC link, and another type is on the outputs of the galvanic insulation modules, similarly as in the previous case. If we choose the same voltage levels for the DAB, we will get different numbers of DAB needed for the two variants of SSTs with different capacitors and medium frequency transformers (MF Tr).

One of the main challenges of current electric grid not only in the Czech republic is the integration of an increasing number of small and often unpredictable power sources, especially renewable ones. Transition to so called smart grids which should be an answer to this problem includes almost all components of electrical grid. This means that in the future there will be also some smart replacement of a distribution transformer. A device called energy router contains a power part - so called solid state transformer (SST) which could be such a replacement of the distribution transformer. This paper presents how such a device could be carried out and how control of electric power in the SST could be performed.

MMC is popular converter topology due to benefits such as low harmonic content, absence of filter or low capacity of the capacitors needed, to be mentioned among others. This paper presents general workflow for calculating the optimal value of MMC submodule capacity. The analysis is done for basic harmonic component based on energy flow.

This paper explains the term energy router with help of the similarity between the energy network and internet. Their main differences are discussed as well. Furteher, all main parts of energy router - power electronics module, communication module and intelligent network module - are described. The solution of the power electronics module (Solid State Transformer) is described in detail. The other part of the paper deals with the power flow control. The components of the intelligent network are introduced in the end of the paper.

Many buzzwords concerning the problematic of energy production and its effective (smart) utilization in industry as well as in households – like Smart Grid, Big Data, Industry 4.0, Energy Router, Green Energy etc. – are often used in many different meanings or even only for making one’s idea more attractive. Nevertheless, their definitions aren’t united or they don’t express the essence in their entirely. The aim of this paper isn’t to define some of the buzzwords; however, it tries to explain what is really a so called energy router and why is it spoken about in the context of existing and to the near future planned system of electrification in the central Europe. Some kinds of energy storage are integral to the modern grid. The short overview of energy storage devices is presented at the end. This text should make the understanding of the problematic in wider extent easier.