Steady-State and Dynamic Input Current Low-Frequency Ripple Evaluation and Reduction in Two-Stage Single-Phase Inverters With Back Current Gain Model

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Abstract
Due to nonlinear time-varying characteristic of a single-phase dc/ac inverter, its front-end dc/dc converter tends to draw an alternate current ripple current at twice the output frequency, which may cause interaction issues, e.g., stability problem and input ripple current limit in distributed generation systems. A novel method is proposed to evaluate the behavior of low-frequency input current ripple. This approach is based on back current gain Ai (s) (input current to output current) model of the dc/dc converter. The theoretic model with different control schemes is verified in Saber environment. It is indicated and proved that the average current mode control strategy is more effective as compared with linear voltage mode control and open-loop control schemes. Design principles are presented based on Ai (s) as guidelines. Dynamic response with bandwidth limitation is also discussed and improved with proposed proportional-resonant (PR) filter placed based on Ai (s) model. Detail simulation and experiment results for different linear control and nonlinear control strategies, 50 and 400 Hz, buck-type stand-alone two-stage single-phase systems are provided to verify the proposed back current gain model and PR-filter solutions.

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