Design and Simulation of a Hybrid-Solid State Transformer with HEMP/GMD Mitigation Capabilities

A high-altitude electromagnetic pulse (HEMP) or naturally occurring geomagnetic disturbance (GMD) has the potential to impact electric power grids by inducing low-frequency common-mode (CM) currents. When these currents flow through grounded power transformers, they can drive the transformer core into magnetic saturation, degrading performance and potentially causing system failures. This work introduces a hybrid solid-state transformer (H-SST) that integrates a conventional magnetic transformer with a power-electronic-based solid state transformer. The proposed H-SST mitigates the harmful effects of HEMP/GMD-induced currents, thus enhancing grid resilience. Additionally, the H-SST also provides operational capabilities to the grid, including power factor correction, voltage regulation, and a fail-normal mode that ensures continued load service even if the power electronics malfunction. An overview of the H-SST architecture, power electronics, and control strategy is presented, and its performance is evaluated across normal and abnormal HEMP/GMD grid scenarios.