Hybrid Current Mode Control for Phase-Shift Full-Bridge Converter

Abstract

A phase-shift full-bridge (PSFB) converter is used for various power devices because of its simple control and low switching loss. However, if the balance of the primary side current is not maintained, the magnetizing inductance of the transformer is saturated and can be damaged. Therefore, it is crucial to balance the primary side current through the peak current mode control. During the peak current control mode, subharmonic oscillation occurs when the duty is 0.5 or more. Therefore, it is suppressed by slope compensation. The slope depends on the output voltage. Because it is difficult to change the slope in real time depending on the output voltage, the maximum slope value is selected to suppress the subharmonic oscillation for all values of duty ratio. Nevertheless, when the maximum slope value is used, the response speed is delayed because of overcompensation. To solve these problems, hybrid current mode control that combines both peak and valley current mode control has been proposed. This study proposes a hybrid current mode control method for PSFB converters, while considering the magnetizing current and ineffective duty. When this method is used, subharmonic oscillation does not occur for all duty ratio values and input/output voltage fluctuations.