| The multi-phase Series Capacitor Buck Converters(SCBCs)can effectively improve the performance of power supply systems in modern data centers and electric vehicles.The series capacitor structure is a new topology developed based on interleaved and switch capacitor structures.This structure combines the advantages of switch capacitors and interleaved structures,allowing for high-frequency operation in a smaller volume,improved current carrying capacity,lower voltage stress,and enhanced efficiency.However,traditional control schemes limit the application range of series capacitor converters.Additionally,during typical DCM operation,SCBCs face two problems of phase unit current imbalances and reverse conduction.This dissertation focuses on multiphase SCBCs with high voltage step-down ratios and self current sharing capabilities.The research aims to extend the current balancing optimization control of converters to cover the arbitrary-phase structure,the whole duty ratio range,and all operational conditions.The research is divided into three main areas:Self current sharing control strategy based on average phase shift.Addressing the limited self current sharing capability of traditional control in SCBCs within specific operating regions,the state matrices for multi-phase SCBCs are proposed,resolving the self current sharing and linear step-down ratio issues across the whole duty cycle range for both two-phase and three-phase SCBC structures.To investigate self current sharing characteristics across the entire operating range,the operating states in the optimal-case and worst-case opearating intervals are analyzed,and summarize the current and voltage characteristics of arbitrary-phase SCBCs across all opearating intervals,revealing the reasons for the failure of phase unit self current sharing when the duty cycle exceeds a certain range.To address these issues,the principles of capacitor charge balance and inductor volt-second balance were applied,specifically focusing on the study of current balancing optimization control for two-phase and three-phase SCBCs.By adjusting the time matrices corresponding to the state matrices of capacitor currents and inductor voltages,a self current sharing optimization control strategy that effectively achieves self current sharing across the entire duty cycle range and linear multiple voltage step-down ratios for tow and three phase topologies was proposed.Arbitrary phase minimum self current sharing constraints and master slave phase shift self current sharing control.To tackle the challenge of self current sharing directly through state matrices in higher-phase SCBCs,arbitrary phase minimum self current sharing constraints are introduced,along with the master-slave phase-shifting control strategy,effectively resolving the comprehensive self current sharing problem for arbitrary-phase SCBCs.An approach was introduced that is based on the basic topology of SCBC and arbitrary switch modes and their durations,resulting in minimum self current sharing constraints applicable to arbitrary-phase SCBCs.These constraints are based on time constraints associated with switch states and significantly simplify the design process.The theory demonstrating the inherent linear multiple voltage step-down characteristics of SCBC converters under current balancing constraints was provided.This theory is only related to the duty cycle of the last phase unit,further simplifying the control strategy.The minimum self current sharing constraints provide multiple solutions to self current sharing problems of SCBC.The theoretical analysis and experimental results of the MSPS self current sharing control scheme based on four-phase SCBC demonstrate that the minimum self current sharing constraints and typical schemes can achieve self current sharing of phase units and linear multiple voltage step-down ratios across the entire duty cycle range.Self current sharing control strategy for various operational conditions.In response to the distinction between SCBC operation in DCM and CCM,an edgeconnected phase-shift self-balancing control strategy is proposed,effectively addressing the self-balancing issue of SCBCs across various operational modes,including CCM and DCM.Analysis of SCBC under DCM operation revealed two major drawbacks: 1)automatic current sharing could only be achieved in a very small range,the reason is the differences of the switch mode in DCM operation.Consequently,self current sharing schemes discussed in CCM operation become ineffective in DCM operation.2)Under ultra-light load conditions,the current flows through the diode path shared by the current phase unit and the subsequent phase unit,leading to negative current conduction.Addressing these problems,a specific mode current path determinism is used,which is applicable to balancing the rising slopes of currents and limiting the current paths of phase units.An extensible edge-connected phase-shift(ECPS)modulation method was proposed to solve these issues.This method is applicable to both CCM and DCM modes.The self current sharing scheme extends the operational range to 0 < D ≤ 1/2,eliminating the phenomenon of negative current generation under ultra-light load conditions.Applying the proposed edge-connected phase-shift modulation method to a three-phase SCBC experimental prototype demonstrated phase-to-phase current self-balancing,identical current waveforms with the same slope and duration,and the elimination of negative currents.Additionally,the proposed strategy is extensible and applicable to SCBC topologies with a higher number of phases.In conclusion,the dissertation systematically presents a series of feasible solutions for achieving phase unit self current sharing and linear multiple voltage step-down characteristics in multi-phase series capacitor buck converters under various structures,operating conditions,and operational ranges.These solutions enable converters to achieve optimal performance in any application scenario,providing robust theoretical guidance and technical support for the practical application of multi-phase SCBCs. |
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