Step-up/down three-phase resonant high-frequency ac-link inverters

A new family of three-phase resonant inverters with a high-frequency (HF) ac-link and zero-voltage switching is introduced. In these inverters, the maximum output voltage is not limited to the dc-bus voltage, and the converters can conveniently operate in the step-up and step-down modes in both the forward and the reverse directions. The HF ac-link of the converters is composed of an ac inductor and a small ac capacitor. The link inductor is the main component for transferring power, and the link capacitor provides partial resonances for the zero voltage switching of all the power switches. The link inductor can be replaced by a small HF transformer to achieve galvanic isolation. This transformer is substantially smaller and more efficient than the conventional line-frequency three-phase isolation transformers. The total number of switches of the proposed unidirectional dc-ac converter is as low as seven, suitable for the low power applications. By adding three more switches, the converter can transfer power in both directions. The basic operation of the new converters includes six modes and is described in detail. A detailed analysis of the introduced topology is also given to reveal its behaviour at various operating points. Several simulation and experimental results are given to demonstrate the effectiveness of the proposed power converters.