Study On Interleaved Tri-state Boost Converter

Interleaved tri-state Boost converter(ITBC)is widely used in new energy power generation systems with low-voltage high-current input and high-voltage output,which requires low-current ripple input and fast dynamic performance.ITBC combines the advantages of interleaving and pseudo continuous conduction mode(PCCM).It not only reduces the input current ripple,and it is beneficial to extend the life of photovoltaic cells,fuel cells,etc.,but also eliminates the right half plane(RHP)zeros of the traditional interleaved Boost converter.Therefore,ITBC is taken as an example,and the control strategy and implementation method of ITBC with low input current ripple and fast dynamic response are researched.Firstly,the operating principle of ITBC is analyzed,taking the operating mode with the duty ratio of boost interval greater than 0.5 as an example,and there are six operation modes in a switching cycle.The small signal model of ITBC is established using the time average equivalent circuit method,and the influence of the fixed off-time control,constant reference current(CRC)control,dynamic reference current(DRC)control and fixed freewheeling-time control on the RHP zero of ITBC is analyzed by deriving the control-to-output transfer functions.The research results show that the RHP zero exists when the fixed freewheeling-time control is adopted,while it is not in the others,indicating that the freewheeling control strategy will affect the RHP zero of the control output transfer function of ITBC.Frequency domain simulation verifies the theoretical analysis.Secondly,the influences of the rising and falling slope of the inductor current,the duty ratios corresponding to the boost,capacitor-charging,freewheeling interval and the constant reference current on the input current ripple of ITBC are analyzed in detail.The operating mode of ITBC is divided,the corresponding expression of input current ripple is deduced,and the relationship between the input current ripple and the duty ratio of capacitor-charging interval is researched.The research results show that by increasing the duty ratio of capacitor-charging interval,the operating mode of ITBC can be changed and the input current ripple can be reduced.The current mode fixed off-time control strategy is adopted,which can meet the inductor current sharing effect and ensure that it operates in the mode of minimum input current ripple in wide load range.Simulation and experiment verify the theoretical analysis.Finally,Based on the analysis of the principle of the operating mode that achieves the minimum input current ripple,the dynamic reference current is designed in detail.The power level and the whole small signal models of the current mode fixed off-time and current mode DRC controlled ITBC are built separately,and the control-output transfer functions and output impedances of the two control strategies are derived.Thus their bandwidth and low-frequency output impedance are compared.The research results indicate that adopting current mode fixed off-time or current mode DRC control strategy,ITBC can meet the inductor current sharing effect and ensure that it operates in the mode of minimum input current ripple in wide load range.Comparing with the current mode fixed off-time control,the current mode DRC controlled ITBC has faster load transient response speed.The efficiency of the two control strategies is high,and the greater the duty ratio of capacitor-charging interval,the higher the efficiency.Simulation and experiment verify the theoretical analysis.