High step-up isolated forward-flyback DC/DC converter based on resonance with pulse frequency modulation
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ORIGINAL ARTICLE
High step‑up isolated forward‑flyback DC/DC converter based on resonance with pulse frequency modulation Zhiguo Zhang1 · Mingyu Liao2 · Dongrong Jiang1 · Xiaobin Yang2 · Shan Li1 Received: 27 June 2020 / Revised: 8 November 2020 / Accepted: 13 November 2020 © The Korean Institute of Power Electronics 2020
Abstract A high step-up isolated forward–flyback DC–DC converter with pulse frequency modulation (PFM) is presented in this paper. The proposed converter has features of both a forward and a flyback converter and can deliver energy during the turn-on and turn-off intervals in a switching period. In addition, by utilizing resonance it can achieve zero-voltage switching (ZVS) for the primary switches and zero-current switching (ZCS) for the secondary rectifier diodes. All of the power semiconductors operate under soft switching conditions. The structure of the proposed converter is simple and easily implemented. It also provides a high step-up voltage gain. The current stresses of the power devices in PFM are lower than those in pulse width modulation (PWM). Therefore, the converter efficiency in PFM is higher than that in PWM. The operation principle and characteristic of the presented converter are described in detail, and the converter performances for PWM and PFM are compared. A 160 W hardware prototype has been built, and experimental results verify the validity of the theoretical analysis. Keywords High step-up · PFM · ZVS · ZCS · Soft switching
1 Introduction Among the many renewable energy sources, solar energy is recognized worldwide as one of the most important resource because of its several advantages [1]. Generally, PV systems are widely used to generate electricity, where high step-up DC-DC converters are required to boost their voltage rates. High step-up DC–DC converters generally includes isolated and non-isolated types. Non-isolated types include coupled inductors [2–7], cascade topologies and switched capacitor topologies [8–12]. Although non-isolated high step-up converters have many advantages, they can cause a leakage current problem owing to the parasitic capacitance between solar cells and the ground. To solve this problem, high stepup converters with galvanic isolation are needed here [13, 14].
* Dongrong Jiang [email protected] 1
Energy Internet Engineering Research Center of Chongqing City, Chongqing University of Technology, Chongqing, China
National Engineering Research Center for Small and Special Precision Motors, Guiyang, China
2
There are many high step-up isolated topologies in the literature, such as Z-source based, bridge type, interleaved structure, primary parallel and secondary series (PPSS), forward type, and flyback type. When a high step-up converter has a large input current, the leakage inductance energy is usually high and may cause high voltage spikes across the switches. Z-source-based isolated converters can alleviated this problem to some extent [15, 16]. However, all of the switches in this converter operate in hard switching modes w
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