Ripple-based Control Technique And Dynamical Behavior Of Switching Power Converters

In order to improve the steady-state and transient performances of switching power converters and to provide the guidance for the design of circuit parameters of switching power converters, different control techniques, including analog control and digital control. of switching power converters and their dynamical behaviors are studied comprehensively in this dissertation. The content of this dissertation can be divided into three parts as follow.Part I:Analog control technique of switching power convertersBased on the ripple of output voltage and/or inductor current, the essences of analog control techniques, such as peak current mode (PCM) control, average current mode (ACM) control, valley current mode (VCM) control, V2 control and V2C control, of switching power converters are revealed. By adopting inductor current and output voltage weight factors. PCM control. V2 control and V2C control are unified as one kind of ripple-peak-based analog control technique.Valley voltage mode (VVM) control is proposed and compared with VCM control. Comparison result shows that VVM controlled switching converter has faster load transient performance than VCM controlled switching converter. Valley voltage/valley current mode (VVM/VCM) control is also proposed. It is pointed out that VVM/VCM control combines the advantages of VCM control and VVM control. It has fast transient response under both input voltage and load variation, and better anti-interfere ability. With the adoption of inductor current and output voltage weight factors, VCM control, VVM control and VVM/VCM control are also unified as one kind of ripple-valley-based analog control technique.Part II:Digital control technique of switching power convertersTime intervals of one-swiching-cycle time dealy existed in traditional digital control laws and the corresponding condition to overcome this one-swiching-cycle time dealy are discussed. Based on the condition to overcome the time dealy in the traditional digital control laws, improved digital control laws are studied comprehensively. Steady-state and transient performances of traditional digital control laws and improved digital control laws are compared. The comparison studies show that their steady-state performances are the same, and load transient performance of the improved digital control laws is much faster than that of the traditional digital control laws, which indicates improved digital control laws significantly improve the transient performance of switching power converter by overcoming the time delay.Unified ripple-based digital control laws, including peak ripple control, valley ripple control, and average ripple control, are proposed and studied. Based on different digital pulse-width modulations, such as leading-edge, trailing-edge, leading-triangle, and trailing-triangle modulations, the prerformances of switching power converter with various digital control laws are studied and compared. It is concluded that among the ripple-peak-based digital control laws, leading-edge modulation has excellent steady-state performance and load transient characteristics, followed by leading-triangle modulation; among the ripple-average-based digital control, leading-triangle and trailing-triangle modulations have excellent steady-state performance and load transient characteristics; and among the ripple-valley-based digital control, trailing-edge modulation has excellent steady-state performance and load transient characteristics, followed by trailing-triangle modulation.Asymmetrical dual-edge modulation (ADM) technique is proposed in the dissertation, which unifies all the pulse-width modulation techniques reported up to now. It is pointed out that traditional symmetrical dual-edge modulation (SDM). trailing-edge modulation and leading-edge modulation are special case of ADM. The general digital implementation of pulse-width modulation techniques, including trailing-edge, leading-edge, symmetrical trailing-triangle, symmetrical leading-triangle, asymmetrical trailing-triangle, and asymm-etrical leading-triangle modulations, is proposed. Traditional digital control laws and improved digital control laws with ADM are derived and studied. It is concluded that ADM has better steady-state performance and faster transient performance than conventional single-edge modulation and SDM. which indicates that ADM provides digitally controlled switching power converter with excellent steady-state and transient performances.By calculating the average inductor current with numerical integration algorithm, the corresponding control laws of digital average current (DAC) control and improved digital average current (IDAC) control with single-edge modulation are derived. Precondition and detailed process to calculate the average inductor current by four-point-mean (FPM) algorithm are deduced. The comparison between the stability of numerical integration algorithm and FPM algorithm is addressed. Comparison result shows that DAC control and IDAC control with FPM algorithm feature better stability than with numerical integration algorithm. In addition, digital triangle compensation technique is proposed in the dissertation to eliminate the subharmonic oscillation existed in DAC and IDAC control laws with single-edge modulation. Part III:Dynamical behavior of switching power convertersIt is revealed that PCM control and VCM control, peak voltage mode (PVM) control and VVM control, and peak voltage/peak current mode (PVM/PCM) control and VVM/ VCM control exhibit symmetries. Dynamical behavior of VCM controlled switching converter with resistive load or voltage source load is investigated. Research result indicates that inverse route to chaos through period-doubling bifurcation and border-collision bifurcation in a wide parameter range compared with PCM controlled switching converter are observed in VCM controlled switching converter. It is investigated that PCM and VCM controlled switching converters with resistive load or voltage source load exist symmetrical dynamical behaviors. With the adoption of slope-compensation-factor, the dynamical behaviors of PCM and VCM controlled switching converters with slope compensation are comprehensively investigated. Research results show that the slope compensation extends the stable operation ranges of PCM control and VCM control, without affecting the symmetrical dynamical behaviors existing in PCM and VCM controlled switching converters.The piecewise smooth switching and discrete iterative map models of PCM controlled and VCM controlled switching converters with current source loads are established in the dissertation. Based on which, dynamical behaviors of switching converters with current source loads are studied, and illustrated by simulation and experiment results. The research results reveal that there exist fast-scale bifurcation, slow-scale bifurcation, and complex subharmonic oscillation phenomena in PCM and VCM controlled switching converters with current source loads.