CJEE

Chinese Journal of Electrical Engineering ›› 2017, Vol. 3 ›› Issue (3): 44-51.

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A Design of Single-Switch Two-Stage DC-DC Converters With PWM And PFM for Off-Grid Solar Power System

Junkai Zhao*, Herbert H.C. Iu, Tyrone Fernando   

  1. School of Electrical, Electronic and Computer Engineering, The University of Western Australia,35 Stirling Highway, Crawley, WA 6009, Australia
  • Online:2017-09-25 Published:2019-11-01
  • Contact: * E-mail: yis@et.aau.dk.
  • About author:Junkai Zhao (S'15) obtained his B.Eng. degree in integrated circuits design and integrated systems from Xidian University, China, in 2010 and Master's degree in electrical and electronic engineering with distinction from the University of Western Australia in 2013. He is currently pursuing his Ph.D. degree at the University of Western Australia. His research interests are in power electronics, power conversion and renewable energy. Herbert Ho-Ching Iu (S'98–M'00–SM'06) received the B.Eng. (Hons) degree in electrical and electronic engineering from the University of Hong Kong, Hong Kong, in 1997. He received the Ph.D. degree from the Hong Kong Polytechnic University, Hong Kong, in 2000. In 2002, he joined the School of Electrical, Electronic and Computer Engineering, The University of Western Australia where he is currently a Professor. His research interests include power electronics, renewable energy, nonlinear dynamics, current sensing techniques, and memristive systems. Prof. Iu currently serves as a Guest Editor for the IEEE Transactions on Industrial Electronics and several other journals including IET Power Electronics. Tyrone Fernando (M'95–SM'05) obtained his bachelor of engineering with honours and the degree of doctor of philosophy from the University of Melbourne in 1990 and 1996 respectively. In 1996 he joined the University of Western Australia, School of Electrical Electronic and Computer Engineering where he is currently a Professor. His research interests are in functional observers, state estimation, control theory and power systems and biomedical engineering. Prof. Fernando has served as an Associate Editor for the IEEE Transactions on Information Technology in Biomedicine and also as guest editor for the Journal of Optimal Control Applications and Methods. He is currently an associate editor for the IEEE Transactions on Circuits and Systems II.

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Abstract: In this paper, a single-switch two-stage DC-DC conversion circuit is proposed for an off-grid solar power application. A photovoltaic(PV) panel powers the load and a storage unit(battery) via the proposed circuit. The battery is designed to balance the supply and the demand of power under different irradiation situations. Based on conventional cascaded DC-DC converters, the proposed design is developed with the single switch technique reducing size, cost and power loss. The control scheme in this design is pulse width modulation(PWM) with pulse frequency modulation(PFM). The PWM module is similar to conventional design except its ramp signal with a variable frequency is provided by a resettable integrator. As a result, the PWM and PFM modules regulate the two stages of the proposed circuit separately with the same switching control signal. In this paper, the modes of operation of the circuit are discussed as well as the control schemes. The design process is described along with the circuit analysis and comparisons with conventional design are made as well. A prototype has been built to verify the proposed circuit with simulation and experimental results.

Key words: Single-switch technique, photovoltaic power system, off-grid solar system, DC-DC conversion, resettable integrator, pulse frequency modulation(PWM), pulse width modulation(PFM)