| Generally, the three-phase inverters adopt three-leg structure. But, when it is applied to the three-phase unbalanced loads condition, its three-phase output voltages will be dissymmetrical. Three-phase four-leg topology is proposed to solve this problem. The topology is known to produce balanced three-phase voltages even under unbalanced load conditions. Comparing with the other three-phase four-wire inverters, its size and weight are smaller.At the beginning, the merits and faults of several other methods which can solve the unbalanced load question are analyzed. According to the analysis, the conclusion is that the structure of the three-phase inverters which is adopted in this thesis is superior to the other topology. Then compare two algorithms which are used by the four-leg structure, and come to the conclusion that the algorithm based on a-b-c coordinates is simple and is benefit to the realization in digital way.After that, the principle of three-dimensional space vector modulation in a-b-c coordinates is introduced. Thanks to using of a-b-c coordinates, the algorithm is much simpler and more intuitive than inα-β-γcoordinates, drastically reducing the complexity of modulations algorithm. And we supplied the calculation formulation in chapter four.Thirdly, the simulation model is built using simulation software. The model is built according to topology which is mentioned just now. The simulation results match with the analysis ones.Finally, write the program of DSP, complete the experimentation. The digital signal processor TMS320F2812-PGFA of TI is adopted as the controller, the simulation results are verified. The three-phase four-legged inverter with 3-D SVM in a-b-c coordinates can output the excellent three-phase AC voltages under the unbalanced load conditions.
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