Analysis of a Fifth-Order Resonant Converter for High-Voltage DC Power Supplies

Abstract—Power transformer is one of the most complex parts of power converters. The complicated behavior of the transformer is usually neglected in the power converter analysis and a simple model is mostly used to analyze the converter. This paper presents a precise analysis of a fifth-order resonant converter which has incorporated the resonant circuit into the transformer. The derived model, which is based on the accurate model of the power transformer, can fully predict the behavior of the fifth-order resonant converter. The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle fromno load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio. A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.

(Index Terms—Fifth-order resonant converter, high-voltage dc power supply, phase-shift fixed-frequency control approach, steady state analysis, zero voltage switching (ZVS) operation.)

An Optimal Control Method for Photovoltaic Grid-Tied-Interleaved Flyback Microinverters to Achieve High Efficiency in Wide Load Range

Abstract—Boundary conduction mode (BCM) and discontinuous conduction mode (DCM) control strategies are widely used for the flyback microinverter. The BCM and DCM control strategies are investigated for the interleaved flyback microinverter concentrating on the loss analysis under different load conditions. These two control strategies have different impact on the loss distribution and thus the efficiency of the flyback microinverter. For the interleaved flyback microinverter, the dominant losses with heavy load include the conduction loss of the powerMOSFETs and diodes, and the loss of the transformer; while the dominant losses with light load include the gate driving loss, the turn-off loss of the power MOSFETs and the transformer core loss. Based on the loss analysis, a new hybrid control strategy combing the two-phase DCM and one-phaseDCMcontrol is proposed to improve the efficiency in wide load range by reducing the dominant losses depending on the load current. The optimal design method based on the boundary condition of the hybrid control is also presented. The experimental results verify the benefits of the proposed control.

(Index Terms—AC module, grid-connected, interleaved flyback, microinverter, photovoltaic (PV).)