Study Of IGCT-based Inverter Technology Applications

The dissertation studies some key problems about the inverter applications in high voltage variable-frequency drives and photovoltaic systems.Energy crisis is becoming more and more serious. There are two approaches to the crisis. One is energy saving. The other one is new energy exploiting. Variable-frequency drives are important technology of energy saving. New energy exploiting focused on solar energy. Yet the key technology in solar energy exploiting is the inverter technology. IGCT is the main device in an inverter. Therefore, it is imperative to study the key problems about the inverter applications in high voltage variable-frequency drives and photovoltaic systems. It is necessary to simulate IGCTs in their applications. To satisfy this necessity, the dissertation proposes a novel method based on four-module package. The IGCT is equivalently divided into four modules. These are:steady-state circuit, turn-on transient circuit, turn-off transient circuit and time-delay circuit. The IGCT model is constructed and the difficult problem of IGCT simulation is solved. The experimental results verify the correctness of the simulation study. The IGCT model can be used in any circuits with IGCTs, including inverters.Two IGCTs in series are often used in high voltage variable-frequency drives to increase total voltage. Yet the voltage will be unevenly divided because of the difference between these two IGCTs. Therefore, it is necessary to design a snubber circuit to protect the IGCTs. A series snubber circuit is designed and simulated with PSIM. The experimental results show that the IGCTs are well protected by the proposed snubber circuit.The dissertation analyzes the common multiple-cascade structure, the three-level NPC structure and multi-level voltage structure of the main circuits, points out their respective advantages and disadvantages. After thorough analysis and careful comparison, the three-level NPC (neutral point clamped) structure is chosen as the converter topology structure according to the actual situations of this project and the current development of power electronics. Much attention is paid to the analysis and design of the main circuit with the chosen three-level NPC structure. The dissertation also designs the control, protection and monitoring system of the inverter, studies the protection algorithms, completes hardware design and software development. It designs the hardware design and develops the software of the protection for the transformer, the rectifier-inverter circuits, and the motor.Heat sinking is critical to the safety and stability of the high voltage variable-frequency drives. A heat sinking system is designed considering the power diodes and the IGCTs as the main heat sources.The dissertation also studies problems in the inverter applications in photovoltaic systems. A grid-connected inverter is designed for the photovoltaic system. A model based on current hysteresis control is constructed and simulated with different filters. Simulation results are correct and rational. The model can be used in further researches on grid-connected photovoltaic systems.Finally, the dissertation summarizes the main research works and the obtained important conclusions, proposes the future research emphases and directions.