Research On Degaussing Power Supply With High Precision Current

The degaussing system is an effective method of magnetic protection for ships,which is composed of degaussing control equipment,degaussing power supply and degaussing winding.The degaussing power supply provides a high-quality current to the degaussing winding,thereby effectively canceling the earth magnetic field of the ship.Therefore,the degaussing power supply is an important part of the degaussing system.The popular configuration of the degaussing power supply consists of a phase-shifted full-bridge converter and a current commutator.The phase-shifted full-bridge converter has the demerits,including the difficulty of achieving zero-voltage-switching(ZVS)for the lagging leg at light load,the voltage oscillation on the secondary rectifier diode,and secondary duty cycle loss due to the resonant inductor.Meanwhile,there is zero-crossing distortion in the output current.In order to improve the overall efficiency of the degaussing power supply and obtain high precision positive and negative output current without zero-crossing distortion,this thesis proposes a new configuration of the degaussing power supply,which consists of a DCX-LLC resonant converter and a dual-quadrant buck converter.The unipolar pulse width modulation(PWM)is adopted for the dual-quadrant buck converter,and the pulsating frequency of the voltage across the filter is twice the switching frequency,leading to a reduced filter size.In the dual-quadrant buck converter,the resonant peak of the LC filter tends to cause system instability,and the capacitive current feedback active damping scheme is adopted in this thesis for daming the resonant peak.The effect of the digital control delay on the system loop gain and capacitor current feedback active damping are analyzed,and the design procedure of the capacitor current feedback coefficient and current regulator is presented.In addition,an optimized sampling-point selection method at different duty cycles is proposed,which makes the output current sampling points are as far as possible away from the switching instants,and thus reduce the influence of the switching noise on the output current control precision.Finally,a 180-W prototype of the dual-quadrant buck converter is designed and tested in the lab,and the experimental results are provided.It is shown that the efficiency is quite high,no zero-crossing distotion ocuurs in the output current,and the output current control accuracy is high.