DC Capacitor-Less Solid-State Variable Capacitor

Abstract

H -bridge-based single-phase applications have second-order harmonics on the dc-link voltage. Conventionally, the second-order harmonics are filtered by bulky dc capacitors to maintain the constant dc-link voltage, which results in poor power density and low reliability. However, in applications, such as the solid-state variable capacitor (SSVC), the constant dc-link voltage is unnecessary since the dc link is disconnected from the load or source. This article proposes a dc capacitor-less SSVC, which removes the dc capacitors from the topology. The dc voltage is supported by the ac-side voltage directly. Only a 0.03 per unit (p.u.) capacitor is needed to filter the switching-frequency harmonics. This enables the proposed SSVC to use the snubber capacitors to achieve the function of the 0.03-p.u. filtering capacitor. Other capacitors can be removed from the dc-link busbar. The modulation, modeling, and control strategy of the proposed dc capacitor-less SSVC are provided in this article. The proposed dc capacitor-less SSVC is validated by the experiment.