T11.4 - A Low Device Count Three-Terminal Active Capacitor with Low-Side Design for Effective Second-Harmonic Ripple Suppression

Single-phase power converters inherently generate a double-line frequency ripple current, which can stress the DC source. Conventional two-terminal active capacitor circuits suppress this ripple by offering a low-impedance alternate path, but they become ineffective when the source itself has low impedance at the ripple frequency. To overcome this, three-terminal active circuits have been introduced, which increase the source impedance while still providing a low-impedance path for the ripple current. However, their improved performance comes at the expense of additional active components. This digest proposes a novel three-terminal active DC-link architecture that requires the same number of active devices as conventional two-terminal solutions, yet achieves ripple suppression comparable to existing three-terminal methods. The proposed circuit also enables a complete low-side design, enhancing its cost-effectiveness and ease of integration. Experimental validation using a 500 W laboratory inverter prototype demonstrates a reduction in source current ripple to below 5%, confirming its superior practicality and effectiveness.