Guangyong Zhu

Switched-capacitor power supplies: DC voltage ratio, efficiency, ripple, regulation

A comprehensive and accurate steady-state analysis of a step-up DC-DC switched-capacitor power converter is performed. No approximations, such as average techniques, are invoked. Parasitic elements such as diode forward voltages, on-resistances of transistors and equivalent-series resistances of capacitors are included into the model. The converter performance functions, i.e. DC voltage ratio, efficiency, output voltage ripple, are expressed in terms of the number of switched-capacitor stages, number of capacitors per stage, values of the capacitors and parasitic elements, switching frequency and load. Design criteria aiming at high efficiency, low ripple and achievable output voltage are formulated. Trade-offs between the efficiency requirement and good regulation capability are discussed.

A single-switch AC/DC converter with power factor correction

A new single-switch, one-stage power factor correction converter with output electrical isolation is proposed in this paper. Its steady state analysis and design procedure are presented. The configuration of this converter is achieved by combining a boost circuit and a forward circuit in one power stage. To relieve the voltage spike caused by the leakage inductance of the power transformer, two bulk storage capacitors are adopted. Due to its simplified power stage and central circuit, this converter presents a better efficiency (87%), lower cost and higher reliability. Detailed steady state analysis results show that the proposed converter has both good power factor correction and excellent line and load regulation capabilities. To verify the performance of the proposed converter, a design example is given with its PSPICE simulation and experimental results, measuring power factor of 0.99.

Steady-State Characteristics of Switched-Capacitor Electronic Converters

By performing a detailed analysis of switching-mode power supplies based on swithed-capacitor circuits, their fundamental steady-state characteristics are found. A few basic step-down and step-up c...

Small-signal modeling of a single-switch AC/DC power factor correction circuit

In this paper, a small-signal model for a new single-switch single-stage switched-mode power-factor-correction (PFC) converter is presented. The model is obtained by applying the small-signal perturbation technique to the circuit equations derived from the state-space averaging method. By applying the perturbation and averaging techniques over one switching cycle, the DC and small-signal equivalent circuit representations of this converter are derived. The result shows that this converter exhibits the transfer characteristics of a second-order low-pass system for the output-to-input transfer function and that of a combined second-order low-pass and band-pass system for the output-to-control transfer function. The validity of the proposed mathematical model was verified by the given experimental results for a specified design example.

DC-to-DC converter with no magnetic elements and enhanced regulation

A switched-capacitor-based (SC) step-up DC converter is proposed. It contains no inductors and transformers, thus it can be realized in small size, exhibiting low weight and high power density. Two switched-capacitor circuits, operating in antiphase in each half-cycle, are used to control the energy flow from an unregulated voltage source to a regulated output. The capacitors are charged and discharged according to a designed sequence. To enhance the line and load regulation capability, in each half-cycle, each charging interval is split into two subintervals, which are followed by noncharging subintervals whose duration is dictated by the pulsewidth modulation (PWM) feedback circuit. The new converter is advantageous for applications in which significant line drops are likely to occur.

A new switched-capacitor dc-dc converter with improved line and load regulations

A new switched-capacitor (SC) step-down dc-dc converter is presented. It exhibits smaller size, lighter weight and stronger regulation capabilities than previous SC converters of the same power ratings. Its operation principles and analysis are described in detail and an accurate as well as an approximate expression governing input, output and circuit parameters is presented. A discussion on the achievable conversion efficiency is also given. A 12 V/5 V prototype based on the proposed topology has been implemented and tested. Theoretical prediction of its regulation and efficiency is verified experimentally.

Modeling of conduction losses in PWM converters operating in discontinuous conduction mode

In this paper, a non-ideal PWM switch model considering conduction losses is developed. This issue was considered in the past only with the assumption that the inductor current ripple is negligible compared with its average value. Derivation of the new model is based on the energy loss invariant principle. The resulting model can be applied to simulating large inductor current ripple conditions. Accuracy of the proposed model is verified through Pspice simulation using the buck and boost converters.

Large-signal modeling of a single-switch power factor correction converter

This paper proposed an extended PWM switch modeling approach which does not rely on identifying a physical three-terminal switch in a converter. Such converters are very popular in power factor correction (PFC) applications. The modeling approach is illustrated by an example using a single-switch PFC converter. Verification of the derived model is provided, which demonstrates the validity of the proposed approach.

Large-signal simulation of a distributed power supply system with power factor correction

A large signal simulation for a distributed power supply system is presented in this paper. The system is composed of two parallel-connected switched-mode power factor correction (PFC) converters utilizing a central limit control technique. This technique allows one voltage loop compensator to be shared by all the PFC converters. The design of such a compensator is discussed and the system performances with regard to unequal cable resistances and load changes are reported. The resulting system features a universal input with a power factor greater than 0.98 and provides excellent current sharing among the converter modules.

Closed-loop design for two parallel connected converters with power factor correction

A large signal simulation for two parallel converters in a distributed power supply system is presented in this paper. The distributed system is composed of switched-mode power factor correction (PFC) converters utilizing a central limit control technique. This technique allows one voltage loop compensator to be shared by all the PFC converters. Design of such a compensator is discussed and the system performances with regard to unequal cable resistances and load changes are reported. The resulting system achieves a power factor of about 0.98 and provides an excellent current sharing between the two converter modules.