Transformation of conventional transformers for enhanced DC mitigation in AC power networks with advanced grid support

Abstract

The flow of quasi-DC or DC in AC networks may trigger half-cycle saturation of electrical grid transformers that could lead to their internal heating or grid collapse. Apart from the requirement of DC mitigation measures, the conversion of conventional power grid into an intricate network demands the need for power equipment with dynamic control capability. The transformers provide the most strategic point in the grid for the introduction of DC protection and grid-support features. This paper proposes a fractionally rated power-electronics module coupled to neutral and ground terminals of conventional transformers that delivers efficient power network protection against quasi-DC or DC flow with different advanced grid-support features injected on the transformer primary. The proposed concept is validated on an experimental hardware prototype employing power hardware-in-the-loop (P-HIL) configuration of Typhoon HIL-402 and compared with the simulation results in this paper. Also, a transformer and associated module protection approach employing a hybrid bypass switch has been suggested and experimentally validated in this work. The experimental results validate the capability of the module to counter DC injection, perform harmonics mitigation, voltage control or unbalance compensation, impedance matching and power flow control at the same injection point.