Abstract:

Aiming at the problem of misleading the design of compensation parameters caused by inaccurate description of the high-frequency characteristics of the flyback converter, the small-signal model of the nonideal flyback converter operating in discontinuous conduction mode(DCM) is established by using the average switching model method, and the control loop transfer function containing high-frequency zero-poles is derived. Then the amplitude-frequency characteristics and phase-frequency characteristics of the control loop are analyzed, and the SIMPLIS simulation model and experimental prototype of the flyback converter based on the current mode control chip KP2201 are built for testing and verification. The simulation and experimental results show that the control loop based on the model prediction can effectively describe the operating characteristics of the system, the experimental results have good consistency in frequency response and dynamic response, which can provide a reference for designing stable systems in engineering applications.

Key words: high frequency characteristic, discontinuous conduction mode(DCM), flyback converter, small signal model