Study On Reducing Second Low-frequency Ripple Control Strategy In Two-stage Single-phase Inverter

As global energy problems gradually increase,clean energy such as solar energy and wind energy are widely used in distributed generation systems.As an important part of the distributed power system,the two-stage single phase inverter has the problem of double line-frequency ripple.Suppressing double line-frequency ripple can not only improve the efficiency of the converter but also increase the stability and service life of the distributed system.It is important to study its suppression control strategy.Firstly,this paper analyzes the principle and hazards of double line-frequency ripple generation mechanism in two-stage single phase inverters.Combined with the bus port impedance,the front stage DC/DC converter of the two-stage single phase inverter is divided into DC bus voltage control converter(BVCC)and DC bus current control converter(BCCC),and mathematical models of which are established respectively.The DC bus port impedances of BVCC and BCCC are calculated in detail.Based on the impedance angle analysis,the principle,advantages and disadvantages of suppressing the double line-frequency ripple based on different methods including closed loop design,virtual impedance and power decoupling are summarized.Aiming at BCCC,an improved peak current mode control has been proposed,Small signal model of the voltage mode control,peak current mode and improved peak current mode control are established and compared.It is found that the improved peak current mode is the superiority of the DC bus port impedance,that is,better double line-frequency ripple suppression of BCCC compared to the other two methods.The theoretical analysis is verified by simulation.Finally,a 1 kw digital-analog hybrid Boost experimental prototype with TMS320F28379 D as the core is designed,combined with a 1 kw single phase inverter.The feasibility of the improved peak current mode control and the effectiveness of double line-frequency ripple suppression are verified.Experimental results show that the proposed peak current mode control can achieve lower input PV voltage ripple and better MPPT efficency than conventional peak current mode control.