IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 8, AUGUST 2014
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Steady-State and Dynamic Input Current Low-Frequency Ripple Evaluation and Reduction in Two-Stage Single-Phase Inverters With Back Current Gain Model Jianhua Wang, Member, IEEE, Baojian Ji, Xuqian Lu, Xiang Deng, Fanghua Zhang, Member, IEEE, and Chunying Gong, Member, IEEE
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.
Manuscript received June 29, 2013; revised September 10, 2013; accepted November 2, 2013. Date of current version March 26, 2014. This work was supported in part by the National Natural Science Foundation of China (51207023), in part by the Doctoral Fund of Ministry of Education of China (20120092120051), in part by the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (12KJB470009), in part by the Natural Science Foundation of the Jiangsu Province of China (BK2010197), in part by the Prospective Project of Production, Learning and Research in Jiangsu Province (BY2011156), in part by the Science and Technology Supporting Program of Jiangsu Province (BE2011174), in part by the Special Funds for Major State Basic Research Projects of China (2007CB210303), and in part by the grants from Power Electronics Science and Education Development Program of Delta Environmental and Educational Foundation (DRE02006007). This paper was presented in part at the 2009 IEEE World Non-Grid-Connected Wind Power and Energy Conference and the 2012 IEEE Energy Conversion Congress and Exposition. Recommended for publication by Associate Editor S. K. Mazumder. J. Wang is with the Jiangsu Provincial Key Laboratory of Smart Grid Technology and Equipment, School of Electrical Engineering, Southeast University, Nanjing 210096, China (e-mail:
[email protected]). B. Ji is with the School of Automation and Electrical Engineering, Nanjing University of Technology, Nanjing 210096, China (e-mail: ji_baojian@126. com). X. Lu is with the Jinhua Electric Power Bureau, the State Grid Corporation of China, Dong Yang 322100, Zhejiang, China (e-mail: kuailelaiba521@ sina.com). X. Deng, F. Zhang, and C. Gong are with the College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210096, China (e-mail:
[email protected];
[email protected]; zjnjgcy@ nuaa.edu.cn). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2013.2292609
Index Terms—Average current mode control (ACMC), back current gain, band-pass filter, bandwidth limitation, input current lowfrequency ripple, interaction, notch filter, proportional-resonant filter.
I. INTRODUCTION HE existing infrastructures of electrical power systems are still dominated by alternate current (ac), which historically has been more convenient than direct current (dc) for transmitting electricity over long distances. So the most dc power generated by solar panels, fuel cell, and wind turbines needs to be converted to ac. At the same time, renewable power, by nature, is varying with time, weather, and environment, and it is not stable and somehow discontinuous. Having numerous renewable power sources on the grid, sometimes, stability and power quality issues are inevitable [1]. DC microgrid with less interference with ac grid emerges for local load could be a possible solution, where energy storage elements still need to be added to buffer power pulsation. For these reasons, two-stage or multistage architecture is widely utilized in renewable and energy storage powerconditioning systems (PCS) as Fig. 1 illustrated. The front-end dc/dc converter boosts the renewable energy output voltage to a proper level that could be converted into ac voltage [2]. Isolated converters with high-frequency-link (HFL) techniques and high gain nonisolated converters are two most attractive choices, depending on the application requirements [2], [3]. For low input voltage and low power rating solar microinverter (
