Dynamical Modelling of Class-E Resonant Converter for Step-Down Applications Using Piezoelectric Transformers

A 1 to 5 Watts wide-range power supply demonstrator with a transoner-type piezoelectric transformer (PT) has been built in class-E topology to show and to model the dynamical functionality of an off-line power supply. While modelling the feedback closed-loop control, the ZVS or near-ZVS behaviour during transient response, was achieved by maintaining a sufficient transistor on-time, being constant. The dynamical modelling was applied for 0-3 Watts and 6 V output at input voltages between 85 and 260 V AC, using different PT sample parameter sets. The PT samples were all 2.3 mm thick, and had a diameter of 17 mm. The used fieldstop-IGBT 1 A-type showed always losses less than 700 mW over the full operating range at frequencies between 145 and 180 kHz. The application is suited for smart-card format power supplies below 5 mm thickness. Compared to the half-bridge, the class E concept, as a current fed topology, promises a larger control bandwidth at the same frequency, tracking the duty-cycle with the frequency instantaneously. Modelling the transient responses, the output voltage in the high frequency model was considered as a constant voltage source for the low frequency pass of the output network. The poles and zeros of the state-space matrices deliver the stability criteria after the used vectors of boundary conditions do not change in average any more. The measurements had been in good agreement with the partially applied differential equations analysis, and the SPICE simulation, as well. The control loop stability is given with proportional/integrating regulator up to integrating time constants of less than 20% of the switching period, while the regulation against line voltage by frequency modulation was completely achieved. The method provided a complete analytical dynamical design and modelling of the class-E DC-DC-converter, including the low frequency part, as the output rectification and charging capacitor, and the feedback loop, respectively