Research On Active Power Decoupling Control Strategy For Single-Phase Photovoltaic Inverters

In photovoltaic power generation system,power converter is one of the important components.Single-phase inverter is the key component of low power photovoltaic power generation system,its reliability determines the safety and efficiency of the whole photovoltaic power generation system.However,due to the power imbalance between the two sides of single-phase inverter,the DC side will produce two times of the base frequency pulsation power.The pulsating power will cause secondary ripple voltage or current to be generated on the bus at the DC side,propagate to the DC side power supply and inject the current source,which will not only affect the quality of grid-connected current,but also reduce the utilization efficiency of the photovoltaic array.The conventional measure is to parallel electrolytic capacitors on the DC side to absorb pulsating power,but the service life of electrolytic capacitors is much smaller than that of photovoltaic power modules,and the ripple suppression effect is limited,and the power loss is large.Therefore,based on single-phase grid-connected photovoltaic inverters,this paper proposes an active power decoupling strategy based on model predictive current control,which uses thin-film capacitors with a longer life to reduce power loss while suppressing secondary ripple on the DC side.Firstly,the generation mechanism and influence of secondary ripple in single-phase grid-connected inverters are introduced in this paper,and the working principle that active power decoupling topology based on Buck circuit can suppress secondary ripple is analyzed.The relationship between power loss and average voltage and voltage amplitude of decoupled capacitor is obtained by analyzing and calculating its working constraints and power loss.Secondly,this paper proposes an active power decoupling strategy based on model predictive current control and a method to reduce power loss.In order to obtain more ideal steady-state performance,the virtual vector and model predictive control algorithm are combined to simplify the system control design and obtain higher decoupling capacitance voltage control precision.By building an active power decoupling circuit model,the effectiveness of the proposed control strategy in suppressing DC voltage ripple is verified.Through the establishment of the electric heating model of the switching tube,it is verified that the proposed control strategy can make the active power decoupling circuit have lower power loss.Finally,in order to verify the reliability of the proposed control strategy,the reliability analysis of the power decoupling inverter system is carried out based on the task profile.Based on the annual temperature task profile,the lifetime of switching tubes and capacitors is predicted based on fatigue damage accumulation theory and Monte Carlo analysis method,considering temperature changes and device parameter fluctuations.By establishing the unreliability function of the device and the series reliability block diagram method,the life prediction and reliability evaluation of the whole system are carried out.The results show that the control strategy proposed in this paper effectively extends the life of single-phase inverter system.