Research On Improvements Of Thesystem Characteristics Of The Wide-range Output Adjustable Power Supply

The wide-range output adjustable power supply plays a key role in some occasions such as producing, processing, reaserch and testing etc. Those occasions require the power supply with excellent stability and dynamic characteristics. However, there are few studies on the stability and dynamic characteristics of the wide-range output adjustable power supply. Based on this background, a wide-range output adjustable power supply is developed, which adopts the FB-ZVZCS converter with saturated inductor series in primary side as topology and average current mode control as its control method, based on this prototype, the system characteristics of the wide-range output adjustable power supply is analysed.The modeling of average current mode control is complicated, the traditional average model which ignores the feedback of sideband frequency components can’t predict the sub-harmonic oscillation. In this paper, the system is modeled by the novel three-terminal equivalent circuit model, the small-signal equivalent circuit model for average current mode control is obtained, this model has high accuracy, can predict the sub-harmonic oscillation and provides the guarantee for the control loop design of the system.Based on the small-signal equivalent circuit model for average current mode control, a new method is proposed for PI-type current compensator to obtain good current regulation. The effect of steady working points to the control loop design is analysed, and a proposed voltage compensator design method suiting for wide-range variable working points is presented. Following the design method, the system can not only ensure the global stability but also achieve wide control bandwidth to improve the dynamic response rate.To the wide-range output adjustable power supply with average current mode control, fixed external ramp causes over compensation at the low voltage output, it will bring the excess phase delay to the control-to-output transfer function, so system bandwidth is limited. In order to solve this problem, an external ramp autotuning method with constant damping coefficient Q is presented, to make each steady working point under appropriate ramp signal, the change in the steady working point has no effect on the system’s control loop design, avoid the problem of bandwidth limitation. The peripheral circuit on the basis of the control chip UCC3895 is designed to realize the external ramp autotuning.On the basis of theoretical analysis and simulation, an experimental platform was built, the experimental results verify the validity of the control loop design method and the external ramp autotuning method, the system has good stability and dynamic response rate under different steady working points.