Research On Push-Pull Forward Resonant DC/DC Converter

Under the background of achieving a carbon peak by 2030 and carbon neutrality by2060 in China,it is of great significance to develop and promote the renewable energy generation system to promote energy-saving and carbon reduction transformation of coal power.In the renewable energy generation system,there are many low input voltage applications.It is necessary to use its power to raise a low input voltage(generally lower than 100V)to a high-voltage DC bus.In this thesis,the push-pull forward converter suitable for low input voltage applications is selected for research.The resonant network is introduced on the traditional topology to realize the soft switching of the primary main power switches,further improving its efficiency performance.Therefore,two types of the push-pull forward resonant converter are proposed.The LLC resonant network is introduced into the secondary side of the push-pull forward converter to form the push-pull forward LLC resonant converter.Based on detailed analysis of its working principle,the First Harmonic Approximation is used to model and analyze the converter,obtain its gain expression,and analyze its gain characteristics.The resonant parameters are designed within the required gain range,providing a reference for the hardware design of the experimental prototype.In addition,the soft switching conditions of the converter and the relationship between the the primary side branch currents is discussed.A 1kw experimental prototype is built to verify the correctness of the converter’s working principle and the rationality of the designed parameters.The peak efficiency at full load is 95.2%.Because the push-pull forward LLC resonant converter still uses variable frequency control,it will deviate from the optimal operating point when performing the gain adjustment.When the operating frequency range is wide,it is not conducive to designing of magnetic components such as transformers.In order to further optimize push-pull forward resonant converter,the rectifier structure of the secondary side of the push-pull forward resonant converter is optimized.Based on the traditional quadruple voltage rectifier structure,the push-pull forward resonant converter with PWM control is proposed by using the first two capacitors as resonant capacitors and introducing a bidirectional switches.The converter adopts fixed frequency control.The fixed working frequency is the resonant frequency.By adjusting the duty cycle of the secondary two additional switches,there are two modes of double voltage resonant rectifier and quadruple voltage resonant rectifier in a switching cycle to adjust the output voltage.The proposed converter,under PWM control,can not only achieve zero voltage soft switching of all switches on the primary and secondary sides,but also achieve twice the wide voltage gain range adjustment.After analyzing the working principle of the converter,the gain expression of the converter is obtained through time domain analysis,and its gain characteristics are analyzed.A 1k W experimental platform has been built.The experimental results show that the PWM control of the converter can achieve twice the gain range adjustment,and the Zero Voltage Switching can be achieved at the primary and secondary side of the converter.The peak efficiency at full load is96.1%.