Reserved-Energy-Based Control Strategy for Enhanced Load Transient Response in Low-Capacitance Solid-State Transformers

Conventional solid-state transformer (SST) architectures based on the cascaded H-bridge converter typically require large high-voltage side capacitors to suppress low-frequency voltage ripples. These capacitors are further stressed during load transients, complicating efforts to reduce their capacitance. Large capacitor banks increase system footprint and reduce reliability, especially with high-power-density electrolytic capacitors. The capacitors absorb transient power imbalance between the input and output ports of an SST. Conventional control strategies often lead to uneven distribution of transient energy, placing disproportionate stress on certain capacitors and resulting in oversized capacitance requirements. To address these challenges, this article proposes a reserve-energy-aided control strategy for effective energy distribution across DC-link capacitors in low-capacitance SSTs. The proposed solution is validated using a 1-kVA, 230-V/250-V, 50-kHz single-phase SST prototype, demonstrating improved transient response and operational stability under varying load conditions.