Series and parallel transformer resonant DC–DC converter using optimal digital servo and repetitive learning control schemes

Abstract

A digitally processed repetitive learning control approach is presented in combination with a type-1 optimal digital servo control scheme of the resonant DC-DC converter using IGBT modules for a medical X-ray power generator. This scheme is considered for achieving a rapid transient response without any overshoot in addition to high-voltage characteristics with low ripple in its steady-state within a wide setting range of output voltage. To improve nonlinear voltage regulation performance of the series capacitor compensated transformer parallel resonant inverter-type fixed frequency, phase-shifted PWM DC-DC converter with a high-voltage transformer link, the repetitive learning control method is introduced into medical X-ray power generator systems using a series and parallel resonant DC-DC converter with high voltage transformer matching. This makes use of transformer parasitic parallel resonance with a series-compensated resonant capacitor connected to a transformer parasitic leakage inductor. The effectiveness of the repetitive learning control for this converter is discussed. A digital servo control scheme with error compensation loops is implemented to eliminate periodic voltage ripple fluctuations and abrupt voltage changes in the rectified DC input of this converter. This scheme also aims to realise good reproducibility, which is an important requirement in an X-ray power generator. The practical effectiveness of the repetitive learning control method and the type-1 optimal digital servo control scheme are confirmed by simulation analysis and experiments.