The Research On Control Method And Soft Switching Of A New Quadratic Boost Converter

With the development of society,human demand for fossil fuels is becoming serious increasingly,but global environment has been polluted by the harmful gases produced by burning of fossil fuels.For the purpose of implementing the strategy of sustainable development,the use of new energy has focused the attention of scholars at home and abroad.In the new energy system,high-gain DC-DC converter is an indispensable link.The voltage gain can be effectively increased by cascading two or more Boost converters,but if there are too many cascading units,the increase in the number of components will cause a significant drop in operating efficiency,and the increase in the number of switches will also bring about the complexity of the controller design.Therefore,the quadratic boost converter formed by cascading two boost converters becomes the best choice.This paper studies a new quadratic boost converter.The advantage of this converter is that it not only has high voltage gain,but also the inductor current,the voltage and current stress on the switching device are smaller,thereby improving the working efficiency.The new converter has the following four working modes: CCM-CCM mode,CCM-DCM mode,DCM-CCM mode and DCM-DCM mode.This paper analyzes the working principle of the four modes in detail,establishes a mathematical model,derives the small signal model,and the Laplace transform is used to obtain the transfer functions between the state variable and the duty cycle in the circuit,the frequency domain characteristics are analyzed,the energy transfer method is studied,which provide a theoretical basis for the parameter design of the converter and the research of the controller.The voltage mode control,current mode control and model predictive control of this new converter are designed.Firstly,the voltage mode control is studied by sampling the output voltage,the compensation network in the voltage mode control is designed,and the rationality of the design is verified by the compensated Bode plot.Aiming at the problem of slow dynamic response of voltage mode control,current mode control is further studied.The design steps of the current controller are explained,and a double closed-loop control system of voltage and current is realized.Theoretically,it has higher stability margin and control loop accuracy than the voltage mode control.In order to reduce the system volume and increase response speed,the model predictive control is designed in this paper.The working principle of model predictive control is introduced,and the mass functions that can be used for single-loop control,double-loop control and multi-loop control are given.The controller under single-loop control is designed by minimizing the mass function,and in order to reduce the use of sensors,Luenberger observer is designed to observe the load of this converter.In order to further improve working performance by reducing switching losses,the auxiliary resonance circuit is introduced on the basis of the new converter to realize the soft switching of the two main switches.Through the various working modes and equivalent circuit diagrams of the converter,the working principle is explained,the working waveforms of the main components in a switching cycle are given,the working sequence of the main switch and auxiliary switch is designed.The parameters of the auxiliary circuit are designed.The correctness of the theoretical analysis is verified by MATLAB / Simulink simulation.An experimental platform for the new converter is built.Firstly,the driving circuit of the main switch is designed to realize the simultaneous switching of two MOSFETs.Then,the voltage mode control and current mode control of the converter are realized by using the hardware circuits.Finally,the model predictive control and soft switching experiments are completed with the help of DSP.The experimental results verify the correctness of the above theoretical analysis and design.