Research On Topology And Control Of High-Gain Z-Surce Inverter

In new energy generation system, the traditional inverter plays an important role in the process of energy conversion and transmission. But the voltage source inverter is a buck inverter. At the same time, it is necessary to add dead time to avoid the phenomenon of shoot-through state in the same bridge arm. However, the dead time will cause the distortion of output waveform. The current source inverter has similar problems. In 2002, Professor Peng presented a novel topology structure, namely Z-source inverter. Owing to its own unique impedance network, the Z-source inverter has accomplished in coupling the dc-to-dc converter to the inverter main circuit. By using the shoot-through state, the Z-source inverter can buck and boost its output voltage. In addition, it has a wide range of output voltage. Thus, the Z-source inverter effectively overcomes the drawbacks of traditional inverter. At present, the research of Z source inverter has attracted the attention of many scholars. But along with the popularization and application, someone finds that Z source inverter has its own shortcomings.In order to improve the conventional Z source inverter, scholars at home and abroad have launched a series of studies, which includes new topologies, pulse width modulation methods, modeling and controlling methods, application fields and so on. Therefore, the research on Z source inverter has practical significance. This paper mainly focuses on the topology structure to improve the conventional Z-source inverter, such as the weak boost ability, high capacitor voltage and discontinuity of the input current. Two new Z-source topologies are proposed, namely switched-capacitor Z-source inverter and high-gain Z-source inverter. Switched-capacitor Z-source inverter employs a unique switched-capacitor impedance network in the conventional Z-source inverter. Based on the quasi Z-source inverter, high-gain Z-source inverter is formed by introducing the structure of switch inductor and transformer. As a result, the boost ability of high-gain Z-source inverter is determined by three factors:the switch inductor’s number N, the transformer turn ratio n, and shoot-through duty cycle. This paper deeply analyses the topology, operating principle and power flow process over a switching cycle in the high-gain Z-source inverter. Z-source inverter and its new topologies all make use of the shoot-through state to boost the output voltage. Therefore, PWM control strategy for Z-source inverter could be realized based on the modification of traditional PWM control strategy. This paper makes a comparative analysis of the performance in five kinds of modulation strategies, including simple boost modulation, maximum boost modulation, maximum constant boost modulation, boost modulation with third harmonic injection, and SVPWM strategy of shoot-through subsection. Based on the simple boost modulation, high-gain Z-source inverter is compared with the switched- capacitor Z-source inverter and three latest topologies:quasi Z-source inverter, switch inductor Z-source inverter, and trans-Z-source inverter. And it has a stronger boost ability, continuous input current, and ability of restraining the inrush current.This paper introduces the design method of the high-gain Z-source inverter in detail, which includes the design of main circuit and control circuit. In the end, a 650VA prototype is built up. The simulation and experimental results are given to verify the accuracy of theoretical analysis.