Research And Design On Quasi-Z-Source H-Bridge Cascaded Multilevel Inverter

With the development of society, our country is facing with more and more serious energy and environment pressure. Whereas people have more and more pursuit of higher material living level and better living environment, which urges us to reform in the energy field and find a new breakthrough. Developing clean energy, improving the technology innovation in the clean energy field is the key to relieving the energy crisis and alleviating environment pollution. From the development status of clean energy, in recent years, clean energy such as wind power, hydroelectric power, photovoltaic power, nuclear power, has a rapid development. The industrial development is closely related to technological progress in the field of power electronics, especially the improvement of power electronic inverter promotes wind power and photovoltaic industry. A novel topology cascaded multilevel inverter is researched in this paper, which has good application prospect in photovoltaic power generation and high voltage inverter.Quasi-z-source cascaded multilevel inverter is proposed by our country scholar, which combines advantages between quasi-z-source network and cascaded topology, and has the function of DC voltage boosting and good quality of grid current. This paper studies quasi-z-source cascaded multilevel inverter and several aspects are analyzed and discussed in the next.Firstly, the small signal model and steady state mathematical model are established in the paper. On the basis of small signal model, pole-zero map of quasi-z-source capacitor voltage is built, with parameter sweep of L, D and C. meanwhile the influence on the system of several parameters is analyzed, which provides basis for controller design.Secondly, power imbalance widespread in cascaded inverter is analyzed in principle, meanwhile both power balance control method in per phase used to restrain DC bus voltage drift and power balance control method between different phases used to keep symmetric output current are proposed. On this basis, the overall control strategies in single-phase and three-phase system are designed respectively, which includes grid current control, power balance control, DC bus voltage control and filter capacitor voltage control. In MATLAB software, simulation model is established to verify the validity of power balance control method and system control strategy.Thirdly, this paper analyses the problems in the design of software and hardware and several difficulties are figured out, including analog data acquisition, parallel communication between DSP and FPGA, logic circuit design method of modified CPS-SPWM, system operation sequence and so on. Based on main circuit parameters, 10kW prototype is established.Finally, based on the prototype, single-phase and three-phase experiments are carried out. With the condition of power unbalance, the feasibility of power balance control method and validity of overall control strategy are verified.