This work is focused on a step-down switched-inductor hybrid dc-dc converter (SIHDC) integrated in a small power wind energy conversion system (WECS). The converter has two roles, to maintain the wind turbine at the maximum power point by controlling the electric generator loading, and to charge a high power density supercapacitor, which is part of a hybrid storage unit that also contains rechargeable batteries. The paper points out the steady-state analysis of the converter in continuous and discontinuous current modes, specific for this application. The stability investigation is presented in detail, including the influence of the electrical generator. The parameterized small-signal transfer function of the control variable derived in this paper can be used to quickly obtain the information needed to evaluate the stability of any similar WECS. A current controller was designed to achieve a stable operation in continuous current mode, and afterwards the stability was checked for discontinuous current mode. A 5kW step-down SIHDC prototype was built and extensively tested, both in laboratory, by using a wind turbine emulator, and in a small power (5kW) WECS industrial platform. Experimental results obtained under real operating conditions confirm the theoretical analysis and laboratory tests, showing that SIHDC converter is a valid solution for low power wind energy conversion systems.INDEX TERMS Hybrid dc-dc converters, renewable energy, stability analysis, step-down dc-dc converters, switched-inductor, wind energy conversion system, wind turbine.
This paper proposes a bi-directional DC-DC converter used as interface between the battery stack and the DC bus in a microgrid application, highlighting its main feature that permits a large conversion rate, with a low number of semiconductors and without using transformers. Analytical descriptions, design aspects, digital simulation and preliminary experimental results are presented, in order to check its operation in both power flow modes, emphasizing the transition between step-up and step-down regimes. It is proved that a simple hysteresis controller is able to assure the stability and a smooth transition between battery charging and discharging modes. The transistors driving signals are complementary which gives the advantage of using a single PWM control.
A bidirectional hybrid switched inductor converter (BHSI) is proposed in this paper. The converter uses an inductor switching cell in order to achieve a wide voltage conversion range, smaller passive components, and lower stress on the active devices. Apart from these advantages, the introduction of the additional inductor in the switching cell does not increase the complexity of the control structure, as is usually the case with other topologies with multiple components. The BHSI is compared, in terms of inductor/capacitor energies and total device stress, to other state-of-the-art topologies and its advantages are highlighted. Two 3 kW prototypes were built, using Si-MOSFETs and GaN-FETs, in order to analyse their performances from the efficiency point of view, and to validate the theoretical findings. The stability analysis of the converter is performed and tested in a supercapacitor storage application, resulting in a good operation in both charge and discharge modes.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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