Small Signal Modeling and RHP Zero Analysis of Tri-state Boost Converter with Different Freewheeling Control Strategies

A tri-state boost converter with a switch across the inductor is studied in this paper, which eliminates a zero of control-to-output transfer function in the right half plane (RHP). Based on the analysis of operating principle of fixed freewheeling-time (FFT) controlled and constant reference current (CRC) controlled tri-state boost converters, the corresponding small signal models are established using the time average equivalent circuit method, which are verified through the SIMPLIS simulation results in frequency domain. Particularly, the analysis and comparison of control-to-output transfer functions corresponding to the two control techniques are given in this paper. The research results indicate that the absence of the RHP zero in CRC control is implemented as expected, but it reappears in FFT control. Finally, the theoretical analysis is verified by the simulation results performed in PSIM software in time domain.