Research On Single-Stage Three-Level AC/AC Converter

The concept of three-level is led into AC/AC converter which have not DC link in this paper.A series of circuit topologies with its input and output unsharing the same ground are proposed in this paper which include Buck, Boost, Buck-Boost, Cuk, Sepic and Zeta single-stage three-level (TL) AC/AC converter. Those converters, which are suit for high input voltage field, have many advantages such as low voltage stress of the switches, single-stage power conversion, three-level voltage waveform, low THD of output voltage, strong load adapting ability, etc. The voltage stress of switches of those converters is half of that of two-level converter. Then those converters are improved, and a series of circuit topologies with its input and output sharing the same ground are proposed.The operation principle of the converter is analyzed in details. The external characteristic of this converter is analyzed in CCM mode and DCM mode. The transient voltage of output and the transient voltage of balance capacitor double feedback control strategy is investigated which is applicable to single-stage TL AC/AC converters.PSPICE simulation of Buck-Boost single-stage TL AC/AC converter is given. The correction and advance of the converter are verified by PSPICE simulation. And the correction of the double feedback control strategy is also verified. The principle test of Buck-Boost single-stage TL AC/AC converter is made. The performances are input voltage U₁=220±10%VAC (50Hz), output voltage Uo=180VAC(or 240VAC)(50Hz), the rated capacity S=500VA, switching frequency Fs=50kHz. The result of the experiment is analyzed. Principle test waveforms of two-level and three-level AC/AC converter are compared.