A PWM Fixed-Frequency and Constant Opening Time (COT) Hybrid Control Strategy for a Quasi-Resonant Forward-Flyback DC/DC Converter

With the development of science and technology, today's society has put forward higher requirements for the performance of power supplies in industrial systems such as aerospace, communication systems, mining and machinery. At present, distributed power supply system accounts for a large proportion in the power supply system. Miniaturization, standardization and modularization are the development trend of distributed system power supply. The research content of this paper is a wide-range input quasi-resonant forward and forward DC/DC converter applied to the rear stage of distributed power system. Firstly, a wide range quasi-resonant positive/negative DC/DC circuit topology based on positive/negative circuits is introduced in this paper. Secondly, the operation process of the wide range input quasi-resonant forward/forward converter in CCM mode, CRM mode and DCM mode is analyzed. Finally, according to the characteristics of the converter, the PWM fixed-frequency and Constant Opening Time (COT) hybrid control strategy is designed to control the closed loop of the circuit, which is a hybrid control method that specifies the frequency regulation duty cycle and the constant on-time regulation frequency.