Research And Design Two-stage Three-level Inverter With Midpoint Adjustable

Energy is an important material base for human life. Traditional non-renewable energy are less able to satisfy the demand for energy in human society. The development and use of new energy become the key to solve the problems of energy. In many new energies, solar energy is valued by every nation in the world for its advantages such as cleanness and renewable. Inverter is a key point for power conversion in photovoltaic power system. It is important to improve the efficiency of, inverter as much as possible. With widely application of high-power devices, the control precision and efficiency of inverter needed to be improved further. Two-stage Photovoltaic Inverter is widely used for its widen the range of DC input-series voltage, simple controlling method and good system stability and synchrony. This paper take the Two-stage three-level inverters as the research object, a new kind of Neutral point adjustable Two-stage three-level inverters is proposed. Then, modulation methods is presented and give simulation result.This article first introduces the research background of inverter technology and development of the status quo, Analysis the operating principle and evaluate the merit of three kinds of basic three-level inverter. A kind of T-type three-level inverter derives from NPC inverter is improved and used for new circuits.Aiming at large loss of switch of ordinary two-level inverter boost circuit, the connection of pre-circuit and post-circuit have not been used reasonably,blind controlled of neutral point voltage balance and so on,a new Two-Stage midpoint adjustable three-level inverter is present. Analyze circuit topology and working principles of midpoint voltage adjustable in detail. Taking a three-level flying capacitor inverter as an example,working principles and applicability of carrier cascade, optimized switching frequency PWM,eliminate the certain harmonics PWM and space vector PWM are analyzed. This paper use 1/4 Three Harmonic Injection and flat-topped wave PWM as subsequent-stage modulation methods, analysis and compare the total harmonic distortion of inverter output voltage of two kinds of methods. The results of simulation show new circuit is feasible and advanced. On the basis of theory and simulation analysis,we uses the STM32F103VBT6 as the kernel processor to design a new circuit based on two-stage midpoint adjustable three-level inverter. Then, the hardware system is introduced in detail.At last, the main work of this paper is summarized and predicted.