Design And Reliability Evaluation Of A Single-phase Converter With AC Or DC Side Power Decoupling Module

In single-phase converters,the instantaneous power of the AC output contains average power and pulsation power at twice the grid frequency.The pulsation power delivered to the DC side of single-phase converter will induce a low frequency ripple current at twice the grid frequency and bring damage to the DC source.Usually,DC-Link electrolytic capacitor is installed at the DC bus to store the pulsation power at the DC side and to balance the instantaneous power of the DC and AC side so that the low frequency ripple at the DC side is reduced and power decoupling is achieved.However,because the ripple current is of twice the grid frequency and relatively low thus a high value of DC-Link capacitor capacitance is needed leading to the high dissipation and low reliability of DC-Link capacitor.Therefore,the use of DC-Link electrolytic capacitor defines the power density and operation lifetime of single-phase converters.In active power decoupling methods,active circuit is used to reduce or transform the pulsation power from the DC side of single-phase converter,so that the needed DC-Link capacitor capacitance can be reduced the reliability can be enhanced.Among active decoupling methods,power decoupling module containing film capacitors can realize power decoupling at the DC or AC side of single-phase converter and realize the plug and play of power decoupling without limitation of single-phase converter structures applicable to cascaded single-phase converter.This paper focuses on comparative study of power decoupling module application at the DC or AC side of single-phase converter providing theoretical foundation for converter reliability evaluation.First,the operation principle of power decoupling module in both topologies is demonstrated based on circuit analysis and mathematical modeling and use double line frequency ripple circulation path to prove the mitigation effect.Meanwhile,mathematical model of component stress and power decoupling module capacitor under both topologies is constructed and the effect of power decoupling module on system components dissipation as well as component stress is analyzed providing theoretical guidance for application of power decoupling in both topologies.Based on the above theoretical analysis,the comparative reliability evaluation of converter system is realized under three kind of topologies including traditional power decoupling method and power decoupling module at the DC or AC side.For DC-Link capacitor of these three topologies,DC-Link capacitor current spectrum is obtained using double flourier analysis and refined dissipation and thermal as well as lifetime model is used to evaluate the reliability of DC-Link capacitor.Reliability comparative study of power devices in three topologies is analyzed based on dissipation and thermal model to obtain the junction temperature variation and lifetime model is used to evaluate the reliability of power devices.Depending on components reliability analysis,the comparative study of systematic reliability in three cases is evaluated using RBD(Reliability Block Diagram)method and Weibull distribution.Simulation verification of application of power decoupling in H bridge DC side and AC side is realized using MATLAB/Simulink for electrical modeling and simulation and PLECS for thermal modeling and simulation,and experimental platform is constructed to verify the validity of power decoupling module analysis in both topologies.