On-line efficiency optimization in flyback dc-dc converters over wide ranges of operating conditions

Abstract

This paper presents a look-up table based digital control approach to on-line efficiency optimization over wide ranges of operating conditions. The proposed digital controller allows programmable modes of operation based on off-line efficiency characterization and optimization. Applied to a flyback dc-dc converter, the controller adopts valley switching in discontinuous conduction mode (DCM), which significantly reduces the MOSFET turn-on switching loss. Furthermore, solutions to the problem related to undesirable frequency hopping, commonly observed in other valley-switching control schemes, are presented. Dynamic operation of the controller demonstrates smooth mode transitions and consistent transient responses over various operating conditions. Experimental results show that efficiency of a low-cost 65-W flyback prototype exceeds 92% at all operating points over approximately 3:1 range of input voltages and 10:1 range of loads.

Computationally efficient fixed-parameter digital control of power converters

“…2. Due to some implementation difficulties [2], [3], the optimum switching frequencies are transformed into equivalent switching valleys and saved into a look-up table (LUT), which is essentially the efficiency optimizer block in Fig. 1.…”

“…In order to maximize the converter efficiency, an off-line optimization procedure, as described in [2], [3], is applied to pre-calculate the switching frequency as a function of input voltage and output load. The optimal switching frequencies for different input voltages is illustrated in Fig.…”

“…Due to the nature of these approaches, the controller has to use a variable switching frequency in order to minimize the total losses occurring inside the system. As the properties of the converter loss is strongly nonlinear, it is impossible to analytically express the optimal switching frequency as a simple function of the flyback converter parameters and external excitations [2], [3]. The wide variation of the input voltage and output load, in addition to the variable switching frequency, pose a serious challenge to designing a stable and efficient compensator for such a system.…”

A high-efficiency bidirectional buck-boost DC-DC converter

“…1. The design optimization is performed in a manner similar to the approaches described in [4,5,6,7]. A relatively simple loss model is developed and used in automated design iteration loops organized to gain insight into the effects key design parameters have on power losses and efficiency.…”