Research And Design Of A Novel Four-input Terminals Asymmetric Three-level Inverter

As the energy crisis and environment pollution becoming more serious, the limitations of traditional fossil energy have been encouraging countries in the world to develop the renewable and clean energy. It is the main form of the development of the renewable energy that transforms the new source energy into alternating current,and the current can be used by electrical load and power grid. The inverter is the core device of the electrical energy conversion and its circuit topology and performance directly determined the power quality. The thesis focus on the two-stage three-level inverters, and the circuit topology and modulation of inverters is analyzed. This paper presents a double-power four-input terminals asymmetric three-level inverter topology with Pre-Buck converter and uses the modulation of the third harmonic injection, and the simulation shows the feasibility of the inverter system.First, the thesis reviewed the research background and development of the inverter technology. Different topologies of inverters are introduced according to different standards. Circuits and advantages and disadvantages of three-level inverters were introduced and analyzed. And the paper studied the working principle of two-stage inverters, which has a wide range working voltage and can be controlled independently. The front stage DC/DC converter of traditional inverters always is the boost converter, while boost converter increased system costs and switching loss sharply. And for this problem, the thesis presents a novel four-input terminals asymmetric three-level inverter.Second, this thesis analyzed the circuit and working principle of the novel inverter. Front stage circuit provided four levels by two DC powers and two Buck converters, and the DC side voltage was adjusted by two Buck converters. As the voltage amplitude of switching tube of Buck converters is much more lower than Boost converters while switch is off and so is the current amplitude of switching tube while it is on and Buck converters can be not working or working with small power under the stable states, the novel inverter can reduce front-stage system’s costs and switching loss. Back stage circuit is linked to four levels provided by front stage, andthe back stage inverter circuit works on different voltage by various situation, so that can further reduce the back stage’s switching loss.Next, different modulations were introduced and working principles were analyzed, and this paper used the modulation of third harmonic injection. The paper compared the novel inverter and traditional inverters, and the regulation of DC side voltage, total harmonic content of inverter output and front-stage’s power under different voltages were analyzed.Last, the simulation shows the feasibility and superiority of the novel four-input terminals asymmetric three-level inverter topology.