Research On Switched-capacitor Converters And Their Control Methods

Switched-capacitor(SC)converters are comprised of only switches and capacitors.Compared with inductor based converters,they have advantages such as light weight,small form factor,and high power density.They are a type of variable structure systems.In the past,SC converters were mainly introduced for the low power applications and monolithic integration.Most of SC converters have been controlled with open-loop control and some other simple linear feedback controls.However,the simplicity of these approaches sacrifices performance with slow dynamic response,narrow operation region and large voltage ripple.With increasing attentions paid on SC converters for the sake of promising future of full integration,the associated modeling techniques are developing in a fast pace,recently.However,most modeling methods are based on the assumption of steel output DC voltage which requires infinite filter capacitor and steady-state calculation.The dynamical performance of SC converters is an important aspect which should be focused on.The traditional modeling methods are based on the steady-state of SC converters.When the size of output capacitor is reduced,accompanied by noticeable output ripple,previous modeling methods may suffer inaccuracy problem.Based on the traditional control and modeling methods,this paper provides two different modeling methods and two different control methods.In combination with the basic dual-phase SC converters and Two-Switch Boosting Switched-Capacitor(TBSC)converters,the research of nonlinear control methods is conducted.The main research contents and contribution are as follows:A charge balance transient calculation(CBTC)and dynamic capacitor ampere-second balance transient calculation(CASBTC)modeling methods are provided in this paper for SC converters.The aspect of filter capacitor is considered in the CBTC modeling method.What's more,the flying capacitance,duty-cycle and frequency are all included in these two modeling methods.These modeling methods provide prediction of the dynamic circuit behaviors with the flying capacitors,variable duty-cycle and frequency condition and more physical insights of circuit parameters impacts on equivalent output impedance,which is essential for circuit optimization and output regulation.Based on the charge balance and one-cycle control method,an extension of one-cycle control(OCC)method for SC converters is proposed in this paper,featuring fast dynamic response,wide line and load operation range,and simplicity in implementation.Experiment results show that the external disturbance can be rejected in one switching cycle by the OCC controlled SC converter with robust performance and good regulation.When compared to other control methods,the proposed nonlinear control loop exhibits superior dynamic performances as well as ability in suppressing input and load disturbances.Based on the large-signal CASBTC model for SC converters in this research study,a constant on time variable frequency one-cycle control technique(CVFOCC)for low power and high power SC converters is presented in this paper.It is designed to accomplish the continuous variable conversion ratio and fast dynamical response speed to reject the external disturbance.This control method addresses the regulation issue on the SC converters.The simulation and experiment results show that the external disturbance of SC converters could be immediately rejected by the proposed control method.What's more,in the light load condition,the SC converters with the proposed control method could achieve higher efficiency than the linear constant frequency control method.The good line and load regulation are demonstrated.The proposed control method is stable and global.It can work in a wide operation range with a simple control circuit.It can highly improve the application of SC converters.