Research On Combination Mode Multi-Level AC-AC Converter

The DC switch unit is defined by analyzing the basic converters of Buck, Boost and Buck-Boost. And the DC switch unit is combined to form the AC multi-level switch unit. And the basic multi-level AC-AC converters are obtained by applying the AC multi-level switch unit in the basic converters. Combination mode multi-level AC-AC converters are proposed by combining two basic AC-AC converters, which including Buck TL-Boost combination mode three-level AC-AC converter, Buck-Boost TL combination mode three-level AC-AC converter, Buck TL-Boost TL combination mode three-level AC-AC converter. The operation principle and control strategy of Buck TL-Boost combination mode three-level AC-AC converter are investigated, and the voltage control of clamp capacitor is realized. It is proved by the simulation in PSPICE that topology method of combination mode multi-level AC-AC converter is feasible and the operation principle is correct. And the combination mode multi-level AC-AC converters are improved into combination mode multi-level AC-AC converters with the input and output sharing the same ground (the improved Buck TL-Boost combination mode three-level AC-AC converter; the improved Buck-Boost TL combination mode three-level AC-AC converter and the improved Buck TL-Boost TL combination mode three-level AC-AC converter).The four operation modes and control strategy of the improved Buck TL-Boost combination mode three-level converter are investigated, and the voltage-united control strategy is proposed. Voltage control of the floating capacitor is realized in multi-level AC-AC converter and voltage stresses of the switches are analyzed and the parameters of the main components are designed. Its operation principle is proved by simulation. Then the sample is made. The correctness of operation principle and control strategy of the improved Buck TL-Boost combination mode three-level AC-AC converter is proved by experiment. The primary experiment result is given, and the power factor in network side, the total harmonic distortion and the efficiency are tested and analyzed.