A Unique Approach for the Mitigation of Sympathetic Inrush Condition in Solid-State Transformer

Abstract

Solid-state transformers (SST) or Power Electronics Transformers (PET) have features like high power density, less weight, ease of integration with renewable energy resources, etc. Therefore, SST is gaining popularity, as a replacement for traditional line-frequency transformers (LFT). Electrical distribution transformers are ordinarily connected in radial structures hence, the problem of sympathetic inrush current ascends in most cases. Hence, for replacing LFT with SST in the distribution network protection of SST from the sympathetic inrush phenomenon is of utmost importance as it entails various power electronic switches which are very sensitive to overcurrent. Therefore, this paper proposes a phase angle control (PAC) technique for the mitigation of sympathetic inrush current (SIC). In the proposed technique, the percentage of second harmonic (Po <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S$</tex> H) injected during sympathetic inrush condition at the input terminal is measured for each cycle. Then, depending on the content of PoSH, the phase angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\emptyset$</tex> between the primary and secondary voltage of the high-frequency transformer is reformed. To validate the effect of sympathetic inrush current, a simulation is carried out wherein LFT is connected in parallel with SST and by controlling the phase angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\emptyset$</tex> , the magnitude of the input current is controlled within the limit. Thus, allowing continuous power flow without any interruption or damage to SST. The results of the proposed technique obtained from the simulation indicate that the PAC technique is capable of eliminating SIC in SST.