Cascade Multi-level Inverter Space Vector Modulation Technique

Multilevel converters have been widely used in high-voltage and high-power application fields. And it is possible to enhance the quality of inverter's output voltage obviously by using multi-level inverters. 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 wave forms, it is well suited for implementation on a digital computer,it has higher DC voltage utilization ratio.Firstly, The main circuit topology and the modulation scheme of multi-level inverters is introduced.The topology and work principle of cells cascaded converter is expatiated particularly; The current control mode of cascaded multilevel inverter is discussed, mainly including carrier modulation and space vector modulation. Their respective characteristics and basic principles are analyzed. The detailed description of the space vector Modulation SVPWM basic Principle was shown given away of calculating each vector time when a set of space voltage vector into each of the small triangle。Secondly, With a 2 cells 5 levels inverters, the application of space vector modulation technology is analyzed.Inα-βcoordinate plane, a concept of characteristics quadrangle and characteristics network is presented. The paper uses the basic switching to traverse the vertex of the sector only along the side of characteristics network. This paper found that it can be divided into two kinds of characteristics networks with the radius range of reference vector's locus. Characteristics quadrangle is used to analyze the switching route which has the minimum switching times in characteristics networks. A switching frequency optimized SVPWM algorithm is put forward, which is useful to depressing the switching times of power devices effectively. Simulated by the Matlab software and compared with those by the phase disposition sinusoidal modulation (PD SPWM) method, the total switching times is only 37% of PD SPWM.At last, an experiment platform is set up with 2 cells 5 levels inverters. The Switching frequency optimized SVPWM algorithm is realized on the experiment platform. And the correctness and the effectivity of the modulation algorithms are proved.