Hybrid Smart Transformer for Enhanced Power System Protection Against DC with Advanced Grid Support

The flow of DC in AC networks leads to half-cycle saturation of power transformers that causes their internal heating, large draw of reactive power and ultimate grid collapse. Transformerless power electronics-based module integrated between the neutral and substation ground of traditional transformers has previously been proposed that provides power system protection against DC flow in grid along with a variety of advanced grid-support features. The technique has already been tested and verified on a controller hardware-in-the-loop (C-HIL) platform. In this paper, the proposed strategy is evaluated on a laboratory scale hardware prototype utilizing Typhoon power hardware-in-the-loop (P-HIL) strategy. The experimental results verify the promising performance of the proposed scheme in nullifying the effect of DC injection, performing harmonics isolation and voltage regulation. Also, an effective transformer and converter protection scheme utilizing a hybrid AC/DC solid-state switch has been proposed and evaluated in this paper.