Control Strategy Of Diode Clamped Three-level Inverter

With the rapid development of power electronics technology, inverter control technology has been steadily progressing, high power multi-level inverter has become a hot topic. Compared to a conventional two-level inverter, as the three-level inverter has relatively low requirements on the element to withstand high voltages, with less switching loss, the output waveform is good, etc. it has been increasingly used in medium-voltage and high voltage variable frequency system. Although the more number of inverter level is, the output voltage waveform better, however, to consider the actual hardware conditions, the complexity of the control system and other issues,the three-level inverter become the best choice.This paper describes the topological structure and working principle of diode clamped three-level inverter, and then introduce the multi-carrier modulation strategy.Multi-carrier modulation of three Level Inverter is a direct extension of two-level modulation method, so some of the conclusions the two-level modulation also apply to the three-level multi-carrier modulation. For example, only when the carrier ratio is odd, single-phase PWM waveform inverter circuit output can be symmetrical in positive and negative half cycle. Simulation model of multi-carrier modulation strategy is imulated in Matlab/Simulink simulation environment. The simulation results verify the rationality of the three level multi-carrier modulation strategy.After mastering the basic operation mechanism of the three level inverter, this paper gives a detailed description of the space vector modulation strategy of diode clamped three level inverter. Respectively analyzes the traditional space vector modulation strategy and the space vector modulation strategy based on 60° coordinate system. Respectively analyzes the traditional space vector modulation strategy and60° coordinate space vector modulation strategy. Build a three-level inverter space vector modulation model on the basis of theoretical analysis. Through the simulation of three-level inverter traditional SVPWM strategy and 60° coordinates SVPWM modulation strategy, simulation waveforms verify the correctness of the theory.In order to verify the actual effect, build the experimental prototype platform of diode clamped three level inverter. The hardware part includes the main circuit of the inverter and the isolating drive circuit, the software part uses DSP56F805 to realize the design. The experiment is carried out on the platform, and the results show thecorrectness and feasibility of the modulation strategy and simulation modeling.