| With the shortage of the energy and ever increasing of the oil price, more and more researchers and industrial companies focus on the renewable and green energy sources, especially the solar arrays and the fuel cells. How to boost the low voltage of these renewable sources to a high voltage for the grid-connected applications is a big issue. In these applications, high efficiency and high step-up front-end DC/DC converters are necessary. The major considerations for high step-up converters are the large input current and the high output voltage. How to avoid the extreme duty cycle and how to reduce the peak current are the main concerns in these applications. The concept of winding-cross-coupled inductors (WCCIs) is proposed in this dissertation. Base on this concept, some general isolation and non-isolation basic cells are presented. Then, a family of high step-up, high efficiency and high power interleaved Boost converters with WCCIs are derived by employing the active clamp or passive-lossless clamp schemes. The relationship between the isolation and non-isolation converters with WCCIs is explored and a general law for the topology derivation from the isolation converters to the non-isolation ones is summarized.Firstly, the concept of winding-cross-coupled inductors (WCCIs) is proposed in this dissertation. A novel isolated interleaved Flyback-Boost converter is derived by adopting the proposed WCCIs. And the leakage energy can be recycled and the MOSFET turn-off voltage spikes can be suppressed by employing the active clamp solution. With some topology variations, only one set of active circuit is necessary for the interleaved two phases to realize the ZVT soft switching performance for both the main and the clamp switches. The output diode turn-off current falling rate is controlled by the leakage inductance, which alleviates the output diode reverse -recovery problem. The primary-parallel-secondary-series (PPSS) structure is employed rather than the primary-parallel-secondary-parallel (PPSP) structure to get a higher voltage gain and to reduce the output diode voltage stress.Then, a non-isolated basic cell with WCCIs is proposed in this dissertation. A non-isolated high step-up interleaved Boost converter is derived by inserting the proposed WCCIs between the power MOSFETs and the output diodes of the conventional interleaved Boost converter. The derived high step-up interleaved Boost converter extends the voltage gain, reduces the switch voltage stress and minimizes the peak current. The active clamp circuits are adopted to achieve the ZVT soft performance of the main and the auxiliary switches, which reduces the switching losses and improves the efficiency. The output diode turn-off current falling rate is' controlled by the leakage inductance of the WCCIs to alleviate the output diode reverse-recovery problem. The passive-lossless clamp solution can be derived from the active clamp solution by some topology variations. The proposed high step-up interleaved Boost converter with WCCIs and passive-lossless clamp circuits can realize ZCS turn-on performance of the switches, suppress the switch turn-off voltage spikes and alleviate the output diode reverse-recover)' problem. Furthermore, a non-isolated basic cell with WCCIs is proposed. And a family of DC/DC converters is deduced from the proposed basic cell, which is suitable for high step-up/step-down conversions. Then a series of DC/DC converters with WCCIs and active clamp circuits or passive-lossless clamp circuits are summarized for high efficiency, high power and high step-up/step-down applications. A clear picture is made in this dissertation on the general law and structure of the WCCIs for DC/DC conversion in high step-up/step-down applications.Furthermore, another non-isolated basic cell with WCCIs is proposed in this dissertation. A high step-up ZVT interleaved Boost converter with WCCIs and reduced active-clamp switch numbers is derived. Only one set of active clamp circuit is necessary to handle the leakage energy and absorb the MOSFET turn-off voltage spikes. With some topology modifications and by adding another two small capacitors, the voltage ringing on the output diode is clamped and a built-in LC low pass output filter is formed by the leakage inductance and the additional capacitors. So the output current ripple is cancelled. Moreover, a series of interleaved DC/DC converters are realized based on the proposed non-isolated basic cell with WCCIs, which can achieve high step-up/step-down conversions.Last, the relationship between the isolated transformer and the non-isolated high step-up autotransformer is analyzed and the inherent relationship between the proposed isolated and non-isolated converters with WCCIs is explored. Furthermore, a general law for the topology derivation from isolation converters to non-isolation ones is summarized.The voltage gain of the proposed converters in this dissertation is extended and the extreme duty cycle is avoided, which minimizes the peak current, reduces the conduction losses. The MOSFET voltage stress in the low voltage side is reduced, which low-voltage MOSFETs with low RDS_ON can be adopted to reduce the losses. The output diode turn-off current is controlled by the leakage inductance of the WCCIs, which alleviates the output diode reverse-recovery problem. Soft switching performance is achieved by employing the simple, but effective active-clamp or passive-lossless clamp schemes, which reduces the switching losses and improves the reliability of the power devices. Furthermore, the WCCIs with interleaved structure are available to increase the power level, reduce the magnetic size and improve the transient response.A lot of simulated and experimental results are given in this dissertation. And some analysis and design are shown on how to optimize the proposed high step-up and high efficiency interleaved Boost converters in the industrial applications. A 3kW PV grid-connected demo system is successfully built and tested in the laboratory to verify the validity of the theories in this dissertation.
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