Constant-Frequency Capacitor Current Hysteresis Control of Buck Converter Using Reconstructed Ideal-Capacitor Voltage

For the case with electrolytic capacitors as the output capacitor, the traditional capacitor current hysteresis (CCH) controlled buck converter is always in over-damping state due to the ESR, and has a poor dynamic performance. Moreover, there is a problem of variable switching frequency operation in the CCH controlled buck converter. To solve these problems, an improved constant-frequency CCH (CF-CCH) control scheme using the reconstructed ideal-capacitor voltage is proposed in this paper. The ideal-capacitor voltage is reconstructed through a low-pass filter and an integrator, and introduced into the control loop to replace the actual output voltage. In the proposed CF-CCH control scheme, the damping ratio is designed as the optimum value 0.707, which is in under-damping state. Furthermore, the switching frequency is kept constant by disturbing the hysteresis bands with a pair of periodic ramp signals. In addition, the circuit design of the proposed CF-CCH control scheme is presented. Finally, the validity and superiority of the proposed CF-CCH control scheme are verified by simulation and experiments.