Research Of Double-power Asymmetric Three-level Inverter And Its Modulation

The inverter is an important component of Solar Electric Generation System, which can changes the unstable direct current into three-phase alternating current in order to achieve the grid-connected PV system. So the central research direction of the inverter is how to get high quality output voltage and output frequency and to reduce the harmonic currents. The large number of inverter switch and its complex structure and high costs are the major problems of the further development.Firstly, the paper introduces the current situation and the development of photovoltaic industry and research status of modern inverter, stressed the importance of researching multi-level inverter. Multilevel inverters are obtaining increased attention in industrial and military applications. Medium and high voltage systems can be driven with lower voltage devices using cascaded H-bridge, diode clamped or hybrid type multilevel inverters. The total harmonic distortion is also reduced as the number of levels in the multilevel inverters increases, the total harmonic distortion is also decreased. Multi-level inverter also play an important role in protect our environment.Secondly, the papers describe the topology structure and modulation method of three-level inverter in detail. Conventional inverter main contains a diode-clamped three-level inverter and cascaded multi-level inverter. It analyzed their topology structure, working principle, advantages and disadvantages. It introduced the principle of triangular carrier lamination method, injecting third harmonic pulse width modulation(THPWM), sub-optimal, DPWMMIN, DPWMMAX, DPWM1, SHEPWM, andSVPWM.Then, the paper proposes a double-power three-level inverter, The Pre-circuit of double power and double Buck converters supplies four levels voltage, and the inverter circuit works on different voltage by various situation. The working principle and controlling methods of the double-power three-level inverter during different models is analyzed. It analyzes the switch mechanism by applying DPWM1, 1/4 THPWM and introduces the steps of SVPWM in detail. And proposes a new strategy—phase M no moving. On the basis of the asymmetric inverter bridge, it proposes another new inverter topology with single-power double-Boost converter.Finally, modeling in MATLAB/SIMULINK, the simulation shows the feasibility the double-power three-level inverter topology structure and the valid of the modulation.