Research On Active Damping Circuit To Solve The Stability Problem Of Two-stage Single-phase Conversion System

With the increasingly prominent problems of global stone energy and natural environment,new energy power generation technologies have been rapidly developed and widely used due to their high efficiency,pollution-free and geographical restrictions.It contains photovoltaic,fuel cells and wind turbine.The two-stage singlephase conversion system is the core part of new energy power generation technology,the stability of two-stage single-phase conversion system plays an important role in the utilization of new energy sources.So the stability problem of two-stage single-phase conversion system is researched in this thesis.The two-stage single-phase conversion system is composed of pre-stage boost converter and post-stage inverter.The function of pre-stage boost converter is to increase the low DC voltage to a high DC bus voltage.The function of post-stage inverter is to convert DC bus voltage into to AC output voltage,which can be used by users or connected to the power grid.Due to the interaction relationship between the output impedance of pre-stage boost converter and the input impedance of post-stage inverter,the two-stage single-phase conversion system is prone to stability problems.Therefore,by establishing a mathematical model,the closed-loop output impedance of the pre-stage boost converter and the closed-loop input impedance of the post-stage inverter are derived.According to the stability criterion of the two-stage conversion system,the instability factors of the two-stage single-phase conversion system are obtained.The common method to solve the stability problem of the two-stage single-phase conversion system is to parallel passive impedance(commonly DC-Link capacitors)at DC bus.However,passive impedance has some problems,such as large volume and difficult design of parameters.In view of the shortcomings of passive impedance,this thesis proposes the active damper converter for solving the stability problem of twostage single-phase conversion system.Firstly,the principle of active damping converter is analyzed in detail.Secondly,the parameters of storage capacitor and filter inductor in the main circuit are analyzed and calculated.Then,the control strategy of the active damper converter is analyzed,and the relationship between the equivalent input impedance and the control parameters is derived.According to the impedance characteristics of the two-stage single-phase conversion system,the control parameters and system parameters of the active damping converter are designed.Finally,the system simulation model is built in PLECS simulation software,the correctness of the active damping converter for solving the stability problem of the two-stage singlephase conversion system is verified.According to the reliability evaluation process of power electronic system,the reliability of passive impedance and active damping converter is compared and analyzed in this thesis,to provide scientific basis for the selection of engineering scheme.