A Soft-Switched Hybrid-Modulation Scheme for a Capacitor-Less Three-Phase Pulsating-DC-Link Inverter

A soft-switched hybrid-modulation (HM) scheme is outlined for a dc-link-capacitor-less three-phase high-frequency (HF) pulsating-dc link (PDCL) isolated multistage inverter. The overall inverter comprises a front-end isolated dc/pulsating-dc converter followed by a pulsating-dc/ac converter. Because the two stages are directly connected without a dc-link capacitor, the intermediate link is a PDCL instead of a fixed-dc link as in conventional HF-link inverters. The HM modulates the pulsating-dc/ac converter such that, two of its converter legs are line-switched, while the third leg of the pulsating-dc/ac converter is switched under zero-voltage-switching condition. This is achieved by first modulating the dc/pulsating-dc converter to achieve a specific encoding of the PDCL signal, which in turn, is exploited by the modulation scheme of the pulsating-dc/ac converter to mitigate its switching loss without requiring any auxiliary circuit. Operation of the pulsating-dc/ac converter using the soft-switched HM scheme is validated using a prototype 1 kW, 72-V (dc)/208-V (ac) HF inverter.