Research On The PWM Strategy Of Three-level Inverter

Inverter as the key installation for electric energy conversion, is the important guaranty for the broad application of electricity. With the development of society, the demand of high-voltage and high-powered inverter is gradually becoming very urgent, but the requirement for high voltage stress of power switches and high power loss limit its development. Three-level topology is one of the important ways to alleviate these two restrictions. PWM(Pulse Width Modulation) is one of the key technologies of inverter, which can affect various performance indexes of the inverter. Therefore, it has a practical significance to have an in-depth study of the modulation types and performance of PWM strategy, which can provide a theory of the choice of PWM strategy in the practical applications of inverter.T-type three-level inverter is one of the most widely used topology of multil-level inverter. Therefore, this paper takse the T-type three-level as the structure of inverter and focuses on the types and performance of PWM strategy, the main content of which are as follows:In the first part, the types of PWM strategy are studied deeply and its main content are as follows: First, the modulation principle and essential relationship of two basic PWM strategies which based on space vector and triangle carrier are analysed and its unified modulation models are builded. Then, based on these two unified modulation models, nice different kinds of PWM strategies are obtained from continuous PWM and discontinuous PWM respectively, which including eight kinds of discontinuous PWM strategy.In the second part, the performance of PWM strategy are studied deeply and its main content are as follows: the DC side neutral voltage fluctuations, DC side capacitive current ripple, power switches switching dissipation and AC side output voltage harmonic are taked as four evaluation basises of the performance of PWM strategy. an method based on carried and the accumulated charges to analysis the neutral voltage, an improved method based on carrier and current RMS(Root Mean Square) to analysis the capacitive current ripple and an improved method based on carrier and Fourier series to analysis the voltage harmonics are proposed. Finally, based on the methds above and the method based on average switching dissipation to analysis the switching dissipation, the four evaluation basises of nice different kinds of PWM strategies obtained in part one are analysed and compared in detail.In the third part, the MATLAB/Simulink simulation model and experimental platform of T-type three-level three-phase inverter are biluded and its design parameters are offered firstly. Then, nice defferent kinds of PWM strategies offered in this paper are realized by simulation and experiment. Finally, the results of the four evaluation basises of nice defferent kinds of PWM strategies are verified by simulation and experiment.