Strategy Study On SVPWM Method For Three-level Inverters

Multilevel converters have been widely used in high-voltage and high-power application fields. Among many of modulation strategies, Space Vector Modulation has been one of the most popular research points. The main advantages of the strategy are the following: it provides larger under modulation range and offers significant flexibility to optimize switching waveforms, it is well suited for implementation on a digital computer, it has higher DC voltage utilization ratio.Initially, suming up the development prospect of power electronic technology and the development status of multilevel inverter control technology . Based on the principle of two-level inverter, three-level inverter is studied on and the advantages and disadvantages of the three-level inverter's three canonical topology structure are comprehensively compared. The three-level inverter with diode clamped is introduced, which is analysised about advantages to the two-level inverter. It embodys the important significance of the subject research.Secondly, the paper is based on the fundamental topological structure of three-level neutral point clamped inverter. The fundamental principle of three-level pulse-width modulation space vector controlled inverter is emphatically analysised. A kind of space vector pulse width modulation algorithm by synthesizing the nearest three vectors to reference vector is presented. The judgment rules for large sector and triangle region is proposed and the corresponding output sequence of the synthesis reference voltage vector is put forward.The function sequence of switch vector is optimized.It makes algorithm easy to be realized by controling middle point voltage.Thirdly, the reason caused the imbalance of DC bus capacitor's voltage of Three-level inverter is analyzed. And the effect of neutral-point voltage is also analyzed in paper, which is caused by the big vector, the middle vector and the small vector. The vectors are found, which are able to affect the fluctuation of neutral-point voltage. The conclusion is obtained that it could control the voltage of neutral-point by using time distribution on the coupled small vectors.At last, the SVPWM modulating means of three-level inverters is simulated by MATLAB, and the correction of modulating means is proved.