| Serious environmental problems have emerged in the world because of the massive use of fossil fuels.The greenhouse effect has led to the rise of sea level year by year and the melting of polar glaciers.If it continues,it will pose a threat to human survival and development.Against the background of China’s "double carbon" goal,The installed capacity of clean energy and its proportion in the total energy use have increased year by year.Therefore,technologies related to clean energy have attracted the attention of scholars all over the world.High-gain DC-DC converter applied in photovoltaic system has become a research topic of many scholars.There is a large gap between the output voltage of the photovoltaic panel(less than50V)and the voltage required by the inverter bus(380～800V).Therefore,a high voltage gain converter is required between the output of the photovoltaic panel and the inverter for connection.The traditional Boost converter can no longer adapt to the current demand for high voltage rise ratio,and may even bring many problems and defects.In order to make up for the deficiency of the traditional converter boost capacity,this paper combines the advantages of existing boost technology and proposes a Quasi-Z Source Soft Switching Converter(QZSSC).This converter is based on the traditional quasi-Z source framework,uses switch tubes to replace the original diodes,and combines the coupling inductance and switched capacitor boost technology to improve the overall boost capability of the circuit,Through the reasonable design of the coupling inductor,the ZVS conduction of both switches is realized,and the loss of the switch in the conduction process is avoided.At the same time of replacing the switch,the original passive clamping circuit is converted into an active clamping circuit.The capacitive clamping structure avoids the problem of voltage spike caused by parasitic inductance when the switch state changes.The introduction of coupling inductance increases the adjustment dimension of the circuit output voltage,which is not only limited to the adjustment of the duty cycle,making the adjustment of the output voltage more convenient and flexible.Starting from the idea of converter construction,this paper introduces the theoretical method of converter construction in detail,and makes a detailed theoretical analysis for this specific converter after putting forward QZSSC.Firstly,this paper analyzes the steady-state performance of topology,the operation mechanism of each mode and the energy transfer relationship of the converter in a cycle under the CCM state are studied.Furthermore,this paper calculates the stress of the device and compares the gain and stress with the same type converters.Based on the stress,this paper quantifies the influence of parasitic parameters on loss and gain and the realization conditions of soft switching effect.These analyses lay the foundation for the physical design of the converter.Determining the controllability of the converter is the premise of the control system design.In this paper,the controllability of QZSSC is analyzed by using the switched system theory.Then the controller is designed according to the small signal model of QZSSC.The simulation experiment is carried out using the model in Simulink and the effect of the controller is verified.Finally,according to the stress conditions of the steady state analysis and the realization conditions of the soft switch,the parameters of the 200 W experimental prototype are designed.This paper completes the prototype test of QZSSC.The experimental results show that the theoretical analysis under steady state is correct,and that QZSSC is operational and the construction theory is successful.Then a closed-loop control experiment was carried out,and the dynamic control effect of the controller was tested by switching the input voltage and load.The corresponding experimental results further explain the validity of analysis under steady state and closed-loop control theory of stress and efficiency. |
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