Discontinuous Conduction Mode Analysis of High Gain Extended-Duty-Ratio Boost Converter

A typical non-isolated photovoltaic (PV) microinverter requires a high conversion ratio in the dc-dc stage as well as needs to support a wide range of input-output voltage operation accommodating partial shading scenario. An extended-duty-ratio (EDR) boost converter is a good candidate for such application as it provides a high efficiency solution with a hybrid of interleaved inductor and switched capacitor configuration significantly lowering the switch voltage stress, switching losses, and providing inherent equal current sharing among the input phases. However, these advantages of EDR boost converter in continuous conduction mode (CCM) is only true for a limited duty ratio range. On the contrary, it is observed that the discontinuous conduction mode (DCM) can support a wider range of duty ratio operation, maintaining lower voltage stress on the devices and ensuring inherent equal current sharing among the boost inductors. Nevertheless, even in the DCM, the operation in the region with least voltage gain becomes very complex and requires a thorough understanding. This paper presents an extensive analysis of an EDR boost converter for DCM operation for all the operating regions. The operating characteristics of an EDR boost converter in DCM is analysed and its gain is derived. The detailed analysis presented in this paper enables in designing the components and judiciously deciding the operating range of EDR boost converter in DCM operation for any application. In order to verify the analysis, the simulation and experimental results from a 300 W EDR boost hardware prototype are also provided.