A MHz LCLCL Resonant Converter Based Single-Stage Soft-Switching Isolated Inverter with Variable Frequency Modulation

Compared to the typical two-stage isolated inverter which includes an isolated dc-dc and a pulse-width-modulated dc-ac, the single-stage approach features for lower component counts, less control complexity, better efficiency and power density with an isolated dc-rectified sine stage and a line frequency unfolder. In the literature, SRC and LLC are mostly utilized for the isolated dc-rectified sine stage which is the key part of an efficient single-stage inverter design. This paper introduces a novel MHz LCLCL converter based single-stage, soft-switching isolated inverter with variable frequency modulation. The paralleled LC within the LCLCL resonant tank can naturally create a zero voltage gain at their resonant frequency, which shows superior characteristics for rectified sine wave generation. With the proposed LCLCL resonant tank design method, simpler control and better output ac voltage waveform quality for different load conditions can be obtained. To verify the proposed resonant tank design method and the LCLCL converter based single-stage isolated inverter topology, a GaN based 380 V
dc
- 600 V
ac
, 1.2 kW prototype is built and tested. Under different load conditions, the measured total harmonic distortion of the output voltage can always keep around 2% with 97.0% peak efficiency for the overall inverter.