INTRODUCTION

Due to the scarcity of the improvement of environmental awareness and fossil fuel energy, the renewable energy has drawn more attention1,2. Photovoltaic (PV) and wind power play a crucial role in industrial applications, reducing the pollution3. However, climate and weather patterns can cause renewable energy sources to produce inconsistent and intermittent output voltage 4. Buck-boost converter can regulate the voltage, which is suitable for renewable energy conversion5.
The typical buck-boost converter can achieve wide range of input voltage with simple structure, which has been researched in recent years6,7. However, its applications are limited by voltage gain and non-common ground8,9. To achieve these issues, the CUK, ZETA and SEPIC converter basic on buck-boost converter are proposed. However, the semiconductors are withstand high voltage stress and current stress 10.
To improve the above shortcomings, some transformerless single switch buck-boost converters are proposed. In Banaei and Bonab11, a ZETA converter based buck-boost circuit is presented to achieve higher voltage gain than traditional buck-boost converter. However, the improvement of voltage gain is limited. Converters in Gorji, et al.12 and Shu, et al.13 propose the quadratic voltage gain buck-boost converter that effectively increase the voltage with the narrow range of duty cycle. But the above quadratic buck-boost converters have disadvantage of high input current ripple. To achieve continuous input current and decrease the input ripple, the inductor is joined straightforwardly to the input source.14,15. Combing the quadratic cell and continues input current technology, converter in Zhang, et al.16 and Kumar and Krishnasamy17 are proposed to obtain high voltage gain only by adjusting the duty cycle. Coupled inductor is another technology which has been used widely in converter to improve the voltage gain by regulating the turns ratio. Considering the leakage inductor of coupled inductor, the passive clamp circuit can be employed to recycle the energy of leakage inductor and suppress the voltage spike of power switch18,19. Rong, et al.20proposes a passive clamp circuit-based buck-boost-Cuk converter that employs a coupled inductor to achieve higher voltage gain. But it is a non-common ground structure which increases the difficulty of control system and electromagnetic interference (EMI). In Alizadeh, et al.21, a single switch quadratic buck-boost converter based on coupled inductor is presented, which has the benefits of common ground and continuous input current. Also, it has the disadvantage that the voltage stress of the power switch is high.
To decrease the voltage stress and current stress on the semiconductor, dual switches structure is widely utilizing in power electronics converter22,23. Some dual switches buck-boost converters are proposed in the recent time. Combing continuous input and quadratic, a dual switches converter is proposed24. To further decrease the voltage stress of the power switches, a family of cascading of boost and ZETA structure converters are proposed in Veerachary and Khuntia25. Compared with the above relevant dual switches converter, converter in Okati, et al.26 has higher conversion ratio. To solve the effect of non-common and hold on the voltage gain with previous converter, a modified SEPIC converter is proposed in Wang, et al.27. A novel negative output buck-boost converter in Ding and Wang28 and a converter with interleaving two CUK converters in Taghizadegan Kalantari, et al.29 are proposed, which achieve wider conversion ratio than above dual switches converter and have non-common ground structure. Converter in Hosseinpour, et al.30 proposes a dual switches converter with common ground structure. The circuit achieves high voltage gain while minimizing the voltage stress of the switch through increment passive components’ number, which make the converter bulky.
Considering the above technology, this article proposes a dual switches buck-boost converter based on coupled inductor. Applying coupled inductor, high voltage gain can be attained by regulating both the duty cycle and the turns ratio. The quadratic- like voltage gain is achieved to wide conversion ratio. Moreover, the voltage stress and current stress are lower than traditional quadratic cell. The passive clamp circuit effectively suppresses voltage spike of the power switches, also recycling the energy of leakage inductor. Common ground between input sources and load reduces the EMI and difficulty of the control design. Therefore, the proposed converter can attain output voltage with stability and suitability for solving the issues of renewable energy applications.
In this paper, Section 2 analyzes the operation principles. The stead-state analysis, which includes the voltage gain and stresses of components, is discussed in Section 3. The component parameter design and power loss analysis for the proposed converter are discussed in Section 4 and Section 5, respectively. Section 6 is a comparison of the characteristics of the relevant converters which can demonstrate the superior of the presented converter. Section 7 demonstrates the experiment results with open loop and close loop in both step-up and step-down modes.