A Comparative Study of Two Controllers for Single Stage Three-Level AC/DC Converters

This paper studies the performance of two control strategies applied to a new single-stage three-level resonant AC/DC converter. Two control techniques are studied in order to achieve : i) tightly regulate the output voltage, ii) input current shaping as well as iii) DC-bus voltage regulation over the whole input voltage and loading range. The two controllers are: a) variable frequency pulse width modulation control and b) variable frequency phase shift control. The first controller uses pulse width modulation to regulate the DC-bus voltage to a pre-specified value, whereas the second employs phase shift control to achieve this target. The variable frequency is used to regulate the output voltage. Using these methods of control greatly reduces the frequency range required for output voltage regulation from no-load to full-load. The operation principles and limitations for both controllers are studied and the different topologies to which each controller can be applied. The performance of the two control techniques is studied for a three level LCC resonant half bridge converter with an input inductor connected to the lower pair of switches