Research On Three-level Soft Switching Inverters

With the change of energy structure all over the world, there is a great demand for clean energy and the development of photovoltaic (PV) and wind is receiving particular attention in recent years. Inverters are the core components of energy conversion and the inverter with miniaturization, lower harmonic pollution, higher efficiency, lower harmonic pollution and higher reliability has become the research emphasis of scholars. Furthermore, the soft-switch technology can solve the above problems very well, which can reduce the switching loss, the electromagnetic noise and high frequency electromagnetic interference, and improve the reliability of the power device. Therefore, the research of three level soft-switch technology has great value.1) Firstly, this paper introduces the research background of the three level soft-switch technology and outlines the development of the inverter and introduces the application of soft-switch with inverters.2) In order to research the micro process of IGBT for the soft-switch technology study, the equivalent model of IGBT is established and the process of turn-on and turn-off is analyzed. What’s more the calculation formula of IGBT switching loss is obtained on this basis. At the same time, the T-type three level inverter and its working principle are introduced. In this paper, the basic principle of space vector pulse width modulation and the carrier implementation method is described. Besides, the loss of T-type three level inverter is analyzed.3) The working process of the three level soft-switch inverter are minutely analyzed in theory and the mathematical model is built. The ability of zero voltage turn-off and zero current turn-on of this topology is verified through the simulation. And the basis of the selection of the buffer inductance and the buffer capacitor is given and the feasibility is verified through experiment.The process of turn-on and turn-off with hard switch and soft switch and their switch loss are compared respectively.4) For the different conditions of positive dead-zone, negative dead-zone and non-dead-zone, this paper analyzes the differences of commutation process, the change of switching loss and the influence to the fundamental wave of output current and the THD of current under these conditions and the best condition is obtained. The bad influence of circuit parasitic inductance to the soft switching is also analyzed. The resonance mechanism during the commutation process is analyzed and the parallel resistance capacitance resonant suppression method is proposed.5) Finally, a three level soft-switch inverter platform, which is designed with DSP28335 chip and CPLD as the control core. The theoretical analysis and experimental verification is carried out and the correctness of the theoretical analysis in this paper is proved.