Research On Topology Generation Method Of Coupled Inductor Voltage Doubler Cell Based High Step-Up Converter

The global energy crisis and environmental pollution promote the sustainablity of the human society. More and more researchers and industrial companies focus on the renewable and green energy sources applications. In the photovoltaic (PV) generation system, the relatively low output voltage of the PV arrays should be converted to a high one by employing a high step-up DC-DC converter in order to supply the grid-connected inverters. The converter topology and conversion efficiency are the key issues to improve the structural flexibility and system efficiency, which become an important academic research field in the recent years. In this paper, a summary of existing high step-up converters is made to give a guidance for high step-up converter generation at the beginning. And then the concept of coupled-inductor-voltage-doubler-cell (CIVDC) is proposed, which is used as a basic circuit cell to obtain a series of novel high-performance converters in both isolated and non-isolated versions for high step-up applications. Finally, the universal topology derivation method based on CIVDC is summarized to improve the circuit voltage conversion ratio.Firstly, the concept of CIVDC is proposed in the dissertation. By introducing CIVDC to the conventional Boost converter, a novel single-phase non-isolated converter is derived to solve the shortages of the Boost converter in the high step-up applications. The voltage gain is extended, the extremely high duty-cycle is avoided, and the voltage stress of the switch is decreased in the proposed converter. Therefore, the current ripple of the circuit and the conduction losses of the switch can be decreased. Meanwhile, the passive-clamp and active-clamp schemes are adopted to depress the switch turn-off voltage spikes, recycle the leakage inductance energy, and make the switch work with ZCS/ZVS soft-switching condition, which reduce the switching losses. The reverse-recovery problem of the output diode is partly solved due to the leakage inductance. Moreover, when the main switch is in the ON state, the coupled inductor transfers the energy like a transformer. When the main switch is in the OFF state, the coupled inductor transfers the energy as a filter inductor. Therefore, the volume of the magnetic core is reduced due to the full utilization of the coupled inductor. Furthermore, the universal topology derivation methodology based on CIVDC is summarized to improve the circuit voltage conversion ratio in the single-phase converter, which can be used to derive a series of high efficiency high step-up converter topologies and provide a new generation law for the topology derivation. Secondly, by connecting the secondary windings of two CIVDC based single-phase converter, an interleaved converter is obtained to reduce the input and output current ripples effectively and improve the system volume. Thus the impact of the input and output capacitors is reduced and the system reliability is enhanced. The series connection of the secondary windings makes the converter suitable for high output voltage applications. Moreover, the current sharing in the input and output can be realized naturally without any additional control strategy. In addition, another two interleaved topology generation methods based on CIVDC single-phase converter are proposed. And the derived interleaved high step-up converters not only cover many existing converter topologies, but also generate more novel converter structures.Then, CIVDC is introduced to the isolated converter with parallel-input and series-output structure to handle the large input current and high output voltage in high step-up applications. The voltage gain of the converter extends further and the input current sharing is fulfilled naturally due to the series connection of the secondary windings. The leakage energy is recycled and the ZVS turn-on soft-switching is implemented due to the adopted active clamp circuits. Furthermore, an improved CIVDC is proposed to reduce the voltage stress of the secondary-side components in the high output voltage system. Also, the voltage balance of the output capacitors is realized naturally, and the voltage gain is further improved. The improved CIVDC provides a new topology deduction principle in high step-up applications.Finally, based on CIVDC converters, the industrial applications of the modular PV generation system, the vehicle power inverter, and the regenerative electric load are implemented. The experimental results hae demonstrated that the proposed converters are excellent candidates for high step-up applications, which benefits the development of the renewable energy generation system.