Abstract：Three-level (TL) AC switch unit is produced by two-level AC switch unit connected together in series manner. TL AC converter is produced by applying TL AC switch unit in basic converter. By combining Buck mode TL and Boost mode AC converters, a novel cascade mode AC chopper was proposed. The AC chopper can chopper unsteady high AC voltage with distortion into regulated sinusoidal voltage with low THD. The AC chopper, which is suit for high input voltage fields, has such following fetures as less power stages, bi-directional power flow, lower voltage stress in the front stage, low THD of output voltage, Buck and Boost mode conversion, unchanged voltage stress in the back stage. The operation principle was also investigated. For cascade mode TL AC chopper, control strategy of flying capacitor voltage was also presented. The AC chopper and the control strategy are fully proved by experimental results.
[1] Gupta R K, Mohapatra K K, Somani A, et al. Direct-matrix-converter-based drive for a three-phase open-end-winding AC machine with advanced features[J]. IEEE Transactions on Industrial Electronics, 2010, 57(12):4032-4042. [2] 张超华, 汤雨, 谢少军. 基于Buck-Boost的AC-AC变换器设计[J]. 电工技术学报. 2007, 22(8): 52-56. [3] 汤天浩, 孙今英, 韩金刚. 一种多电平逆变电路新的组合方式[J]. 电工技术学报, 2008, 23(2): 49-55. [4] 阮新波. 三电平直流变换器及其软开关技术[M]. 北京: 科学出版社出版, 2006. [5] Vazquez N, Lopez H, Hernandez C, et al. A different multilevel current-source inverter[J]. IEEE Transactions on Industrial Electronics, 2010, 57(8): 2623-2632. [6] 李永东, 肖曦, 高跃. 大容量多电平变换器[M]. 北京: 科学出版社, 2005. [7] Rodriguez J, Mussa S A, Heldwein M L, et al. Three-level ZVS active clamping PWM for the DC-DC Buck converter[J]. IEEE Transactions on Power Electronics, 2009, 24(10): 2249-2258. [8] Agamy M S, Jain P K. Performance comparison of single-stage three-level resonant AC-DC converter topologies[J]. IEEE Transactions on Power Electronics, 2009, 24(4): 1023-1031. [9] Defay F, Llor A, Fadel M. Direct control strategy for a four-level three-phase flying-capacitor inverter[J]. IEEE Transactions on Industrial Electronics, 2010, 57(7): 2240-2248. [10] Wang C, Li Y. Analysis and calculation of zero- sequence voltage considering neutral-point potential balancing in three-level NPC converters[J]. IEEE Transactions on Industrial Electronics, 2010, 57(7): 2262-2271.
2012, Vol. 27 
