Research On An Improved Bi-Directional Quasi-Z-Source DC-DC Converter With Wide Voltage-Gain Range

As people pay more and more attention to environmental protection,renewable energy,such as wind power and photovoltaics,has gradually become a prefered choice of power generation.Meanwhile,electric vehicles and fuel cell vehicles show much potential in practice.In the renewable energy grid and electric systems of EVs or FCVs,high voltage-gain bidirectional DC-DC converters have become an indispensable part of the secondary conversion,which provides an access to a variety of energy storage devices.The traditional boost circuit isn’t acceptable to achieve high voltage gain in practical applications due to its own power loss.Compared with normal DC-DC converters,Z-Source Converter(ZSC)can achieve a relatively higher voltage conversion ratio within a narrow switch duty cycle range due to the existence of shoot-through state,and provides a new direction to achieving high voltage gain ratio.Nevertheless,the traditional Z-Source Converter cannot achieve bidirectional energy flow and high voltage conversion ratio,but owns huge start-up rush current.At the same time,under the light load operation,an abnormal operating state will occur,making it difficult to maintain a stable output voltage.In order to solve the above problems,this paper desigens an improved QZSC unit,and then proposes an Improved Bidirectional Quasi Z-Source DC-DC Converter(Improved B-QZSC)by evenly splitting the input power source and,and proposes an.With the unique circuit structure,proposed topology can realize a bidirectional flow of energy with a wide voltage gain range under the condition that the input and output terminals of the circuit share the same ground,and input current is continuous as well.In addition,during two different working states,the proposed circuit can automatically switch between five modes according to the situation of the circuit output load,thus effectively avoiding the occurrence of abnormal operating states and maintaining a stable output voltage.Compared with the existing typical bidirectional quasi Z-Source DC-DC converters,proposed topology owns a lower capacitance voltage stress and inductor current stress while maintaining a wide voltage gain range.Through sampling the inductor current and output voltage in the circuit,this paper applies a bi-directional double closed-loop control strategy to protect output voltage from being affected by input voltage disturbance and load switch.After completing theoretical analysis and control strategy design,simulation analysis is finished in MATLAB/SIMULINK,and experiment has been conducted in the laboratory at the same time.Both verifies that,with a wide voltage gain range,the proposed Improved Bidirectional Quasi Z-Source DC-DC Converter can work in three states(forward boost discharge,light load and reverse buck charge)simultaneously,and the output voltage bidirectional dual loop control strategy is effective.