| In order to improve the steady state property and dynamic performanceand to guide the design of the parameters about the converter, we propose anovel hysteresis control method with indirect feedforward based on thecapacitance of charging and discharging, the family of improved hysteresiscontrol, dynamic behaviours and the application in the Buck and Boostconverters. The work mainly includes three parts. Part I and II focus on theBuck converter research. Part III focuses on the Boost converter.Part I: Hysteretic PWM Control Method Based on Capacitor Chargingand DischargingA hysteretic PWM control method based on the capacitor charging anddischarging (CCDFH) is proposed. The proposed control method based on thecharging and discharging of capacitance regulates the output voltage ofswitching converters by the indirect input voltage feed-forward control, outputvoltage feedback control. The design of the control method is easy. The controleffect is excellent and has good performance of steady state and dynamic. Itdoesn’t need the error amplifier compensation network design, thus decreasesthe quantity of the device and compensates the hysteresis control frequencyconversion features, it has quasi constant frequency effects. In this part thesteady and dynamic state characteristic analysis is performed. Also the theeffects of control parameters on the stability of the circuit is analysisqualitatively and quantificationally.As to the changes of the input voltage lead to the evolution of the outputvoltage steady state to chaotic state, the simulation is perfomed.It proves theinput voltage of the main circuit change can cause the output state ofchaos.Aim to the influence of filter capacitance values on the output voltage,the simulation verifies the effectiveness of the filter capacitor output size canreally lead to chaos. In addition the output voltage ripple formula is verified bysimulation. We deduce the method of determining the filter capacitor ESRcritical value. It is verified with simulation and theoretical analysis and showsthe effectiveness of the ESR formula. Part II: Adaptively Regulated Hysteretic Window Control MethodBased on Capacitor Charging and DischargingThe improved variable hysteresis window control, variable thresholdcontrol (high threshold and low threshold value) are proposed.The proposedimproved control methods not only retains the virture of the CCDFH, but alsoimproved the dynamic state performance.The composite feedforward hysteresiscontrol method is proposed.It combine the feedforward control and indirectfeedforward control with the output feedback while the load or the inputvoltage is changed. It through the change of the input voltage to automaticallyadjust the hysteresis width and make use of the characteristics of capacitorcharging and discharging rate to adjust output voltage, and make the dynamicperformance improved and steady state effect better.A new adaptive hysteresis band controller with indirect input voltage feed-forward for buck converter is also presented. Indirect feedforward control loopis mainly used to respond to the input voltage change, change the capacitorcharging and discharging rate and then change the duty ratio. Feedback controlincludes two control loops (Rfand k2loop), Rfloop feedback control throughthe change of the output voltage control capacitor charging and discharging rate,in turn, change the duty ratio, k2feedback control loop is mainly feedback thechange of output voltage to hysteresis threshold to quickly adjust the duty ratio,realize the rapid and stable output.In this control method the duty regulatingmainly includes the capacitor charging and discharging and hysteresis threshold.In this design the three control loops together to achieve the useful control ofthe key influence factor, plays a good control results.Part III: A Novel Hysteretic PWM Control Method for a BoostConverter with Constant Switching FrequencyIt is not easy to realize excellent dynamic performance only by the voltagemode feedback control because the boost converters basically have poordynamic characteristics. We proposes a novel hysteresis PWM control methodwith constant switching frequency.The control circuit need fewer devices andreduced the size of the system,can be easily integrated and has high powerdensity, satisfing the converter requirement of light, small and thin. In thedynamic response characteristics, the control circuit has a good overshootamount and convergence time is superior to the traditional PWM control circuitwhen the load steps up and down. The power output range is wider, make upfor the conventional hysteresis control frequency variation problem, has thequasi constant frequency characteristic. |
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