Design and analysis of an input-series quasi-resonant flyback high-voltage SMPS based on an integrated transformer

An input-series quasi-resonant (QR) flyback high-voltage switching mode power supply (SMPS) based on an integrated transformer has been designed and analysed. It is capable of converting a high DC input voltage to lower DC voltage to power the control components of high-power converters in a DC microgrid. An integrated transformer, combined with identical duty cycle control, is adopted to achieve automatic equalization of the series modules effectively even without employing any voltage or current equalization control strategy, of which effect is analysed theoretically. The design of the control system, based on QR flyback SMPS is given, which is implemented by peak current control, and a DCM small-signal model for the designed SMPS is established, which indicates that the system has high stability and accuracy to ensure normal operation across a broad range of input voltages. Finally, the validity of the theoretical analysis and the proposed method is demonstrated by the development of a 48 W SMPS experimental prototype, which is composed of three input-series modules. The overall efficiency of the prototype has been improved due to the adoption of QR. The proposed design and analysis methods can be extended to other input-series isolated DC/DC topologies.