Analysis and control of isolated three-level AC-AC converter

Recently AC voltage regulators, which adopt the method of AC-DC-AC transformation, not only have the problems of big bulk and high noise, but also with high voltage switch stress and harmonic interferences. To solve these problems, a new kind of high frequency isolated three-level AC-AC direct converter is proposed, operational principle, frequency structure of the voltage in front of the output filter are deeply analyzed. Dual close-loop control strategy of voltage and current has been adopted. Voltage feedback loop applies transient voltage of PI adjustment to ensure the stable output voltage control, while inner current loop adopts the proportional adjustment to improve the current response by forecasting the current of the filtering inductor. Test results demonstrate the converter has the advantages of simple circuit, ideal output waveform, strong load adapting ability, lower voltage stress of switches, which is helpful to the design of new AC voltage regulators.