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Square wave control of 3-level NPC inverter for large capacity high-speed drive systems

This paper presents an improved method to achieve the high control performance of 3-level inverter for large capacity high-speed drive systems. Usually, due to the limit switching frequency of high voltage high power devices, the output frequency of the inverter is low in most cases. To achieve higher output frequency, the square wave modulation (SWM) is adopted. However, the use of the normal SWM decreases the control performance of the inverter and deteriorates the dynamic behavior of the drive systems because of less control freedom in per fundamental period. The proposed method with the improvement of the normal SWM has twelve freedoms and the optimum operation region of this method is given. Experimental results show that the proposed method can be applied in three level NPC inverters especially for large capacity high-speed drive systems.