| With the development of portable devices and the increase in complexity,there are more and more functional blocks inside the devices,while different functional blocks commonly require different power supply voltages.Using multiple single-inductor single-output(SISO)dc-dc converters for the portable devices will cause high cost and large size.It is a suitable and cost-effective solution to use single-inductor multiple-output(SIMO)dc-dc converter in portable devices,which can generate multiple voltage levels with only one inductor.However,due to the outputs are coupled to the same switching node,they would suffer from a cross-regulation effect.Cross-regulation could affect the system stability and performance in the steady and transient situations.Therefore,it is significant to study the cross-regulation suppressing of the SIDO switching converter.In order to solving the cross-regulation problem in continuous conduction mode(CCM)SIMO switching converter,the single-inductor dual-output(SIDO)switching converter is taken as the research object,and a current-mode control technique is proposed in this dissertation.The control circuits and operation principles under different inductor current trends and switching sequences are introduced.Moreover,the SIDO boost converter operating in CCM is taken as an example to establish the small-signal model.Based on which,the optimal compensator design is presented.And then,the cross-regulation and transient performance are analyzed via Bode plots.In addition,the stability condition for current mode controlled CCM SIDO boost converter is studied by using Routh-Hurwitz criterion.Finally,experimental results verify the correctness of the theoretical analysis.The research results indicate that the proposed current-mode control technique can significantly improve the load transient response,and suppress the cross-regulation of SIDO switching converter.The stability of current-mode controlled CCM SIDO switching converter depends on the input voltage and output voltage.Aiming at the problem that the stability of the current-mode controlled SIDO switching converter is limited by the input and output voltage range,as well as each control loop needs a compensator,this dissertation proposes a novel voltage-mode variable frequency control technique for CCM SIDO buck converter without compensator in control loop.The transfer condition for different switching sequences is derived.The reason,which the converter can operate stable with small or even zero equivalent series resistances(ESRs)of the output capacitor,are analyzed theoretically.Moreover,the critical ESR for different inductor current trends is deduced.The research results show that the voltage-mode variable frequency control CCM SIDO buck converter technique has improved transient response and reduced the cross-regulation.Furthermore,different from the voltage-mode variable frequency controlled SISO switching converter,the output capacitor ESR has no effect on the stability of voltage-mode variable frequency controlled CCM SIDO buck converter.This control technique can work stably with small or even zero ESR.Finally,an experimental prototype platform is implemented to verify the correctness of the theoretical analysis.Considering voltage-mode constant-freewheeling controlled pseudo-continuous conduction mode(PCCM)-PCCM SIDO buck converter has slow load transient performance,and exists cross-regulation between its two outputs,a V~2 constant-freewheeling control technique for PCCM-PCCM SIDO buck converter is proposed in this paper.The efficiency expression of V~2 controlled PCCM-PCCM SIDO buck converter is derived.The efficiency curves are presented for different load conditions,which show that the efficiency is significantly decreased under light load.To increase the efficiency,a V~2 controlled CCM-PCCM SIDO buck converter with dynamic-freewheeling technique is presented.The corresponding sampling-data models of the V~2 constant-freewheeling controlled PCCM-PCCM SIDO buck converter and V~2dynamic-freewheeling controlled CCM-PCCM SIDO buck converter are established,the operation-state regions can be obtained with the circuit parameter varying.An experimental prototype platform is built to compare and analyze the different control techniques.The results show that,the V~2 constant-freewheeling controlled PCCM-PCCM SIDO buck converter has fast load-transient performance and small cross-regulation.However,the efficiency for light load condition is low.The V~2dynamic-freewheeling controlled CCM-PCCM SIDO buck converter can improve the efficiency while maintain the low cross-regulation and fast transient response.Finally,the dynamic behaviors of current-mode controlled SIDO switching converter within wide-range circuit parameter variations are analyzed.According to different inductor current trends,the corresponding inductor current borders are defined.On this basis,a unified discrete-mapping model of these different inductor current trends is established and the boundary equations of system stability and CCM-discontinuous conduction mode(DCM)mode shifting are derived in the meantime.The dynamic behaviors with the variations of circuit parameters in different inductor current trends are analyzed in detail,and theoretical analysis of period-doubling bifurcation and tangent bifurcation are presented.Taking the inductor current in“up-down-down”trend as an example,the bifurcation behaviors of ramp compensation are analyzed in detail.The research results indicate that the SIDO switching converter has different bifurcation sequences with the same circuit parameter varying for different inductor current trends.Introducing the ramp compensation can effectively broaden the stable period-1 region and CCM operation region.Operating regions of the converter are given in this paper,which provides theoretical guidance in designing current-mode controlled SIDO switching converters.Experimental results are presented to verify the correctness of theoretical analysis and unified discrete-mapping model. |
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