Small-Signal Analysis and Compensator Design of Flyback Converters with Variable-Frequency Peak-Current Control for USB-PD Application

• Main Authors: Ping-Sheng Wu, 吳炳昇
• Other Authors: 陳景然
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/vea47a

碩士 === 國立臺灣大學 === 電機工程學研究所 === 106 === Flyback converters have been widely adopted in low-power adapters for many portable devices, mainly because of its simplicity and electrical isolation characteristic. In order to achieve high conversion efficiency over the entire load range, the variable-frequency peak-current mode (VFPCM) control scheme is often used in this topology. With this control scheme, the converter switching frequency can be automatically adjusted according to output load level, and therefore, maintains high efficiency under both the heavy-load and the light-load conditions. In this thesis, a flyback converter with VFPCM control used for the up-and-coming universal serial bus power delivery (USB-PD) application is the focus. For such an application, the converter has to supply various output voltage levels for powering different loads. Compared with traditional adapter application, the operation range of this specification is much wider and the stability issue of VFPCM controlled flyback converter becomes more severe. In this thesis, a detailed description of the circuit control behaviors throughout a complete wide operation range is given. Depending on the output load condition, there are four control modes for this converter. The small-signal models for each of four control modes are reviewed. Since only one compensator is used for keeping the converter stable, a worst case analysis of uncompensated loop gain transfer functions is indispensable. Based on the analysis, a design strategy of compensation network for USB-PD application is proposed. Simulations are conducted and a hardware experimental circuit is built to verify the validity of the proposed strategy.