Resonant Switched-capacitor Converter Research Articles

Ladder-Type Resonant Switched-Capacitor Converter Achieving 99.1% Peak Efficiency and 4750 w/in3 Power Density for High-Current Application

Ladder-Type Resonant Switched-Capacitor Converter Achieving 99.1% Peak Efficiency and 4750 w/in³ Power Density for High-Current Application

Self-Frequency Tracking for Fixed-Ratio Switch-Capacitors in Data Center Application without Extra Sensors

As research into data centers progresses, the importance of resonant switched-capacitor converters in power supply design becomes more evident. Practical applications reveal that the values of resonant capacitors and inductors may deviate from their nominal values due to various factors, leading to resonant frequency instability. This instability poses a challenge to power electronics technology, affecting system reliability and performance. This paper analyzes the effect of frequency deviation on system functionality, identifies the relationship between output voltage and switching frequency, and proposes a self-tracking frequency strategy to address this issue. Through experimental validation, this approach shows that it maintains synchronization between switching and resonant frequencies, reducing losses associated with frequency misalignment. Simulation and experimental results validate the converter’s stable operation and its ability to achieve zero-voltage and zero-current switching.

Universal Modeling Method and Reactive Power Optimization for Phase-Shift-Modulated Resonant Switched-Capacitor Converters

Universal Modeling Method and Reactive Power Optimization for Phase-Shift-Modulated Resonant Switched-Capacitor Converters

A Bidirectional Direct AC-AC Resonant SCC

A direct ac-ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant voltage regulator (CVR), and constant current regulator (CCR). Zero voltage switching (ZVS) and zero current switching (ZCS) operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference (EMI) noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

A General Analysis of Resonant Switched Capacitor Converters Using Peak Energy Storage and Switch Stress Including Ripple

This work presents a general analytical framework enabling large-signal characterization of resonant switched-capacitor (ReSC) power converters that accounts for passive component voltage and current ripple, for operation at and above resonance. From this, appropriate phase durations for minimized rms currents are derived, in addition to expressions for total passive component volume using an intuitive peak energy method. An example hardware prototype validates both the derived waveforms and timings—as well as total passive volume—through three comparable hardware configurations, one of which minimizes passive component volume. In addition, the proposed technique formulates analytical expressions for both rms currents and peak blocking voltages, facilitating refined loss estimation and component selection. Subsequent calculation of the large-signal Volt–Amp (VA) switch stress metric allows a more accurately quantified trade-off between active and passive components compared to prior work, which has not fully accounted for ripple. Four common ReSC topologies are exemplified throughout, with topology specific parameters documented for reference.

A Resonant Switched-Capacitor Converter for Neutral-Point Voltage Balancing of Three-Level Inverters

A Resonant Switched-Capacitor Converter for Neutral-Point Voltage Balancing of Three-Level Inverters

Geometrical State-Plane Analysis of Resonant Switched-Capacitor Converters: Demonstration on the Cascaded Multiresonant Converter

To realize high efficiency and high power density for resonant switched capacitor (ReSC) converters, it is critical to have a thorough understanding of the soft-switching mechanism and design the converter appropriately. However, this can be challenging as the soft-switching operation depends on multiple variables and its design difficulty increases quickly with respect to the topology complexity. This paper demonstrates a framework of using geometrical state-plane analysis to facilitate ReSC converter design. The methodology is first applied to a basic 2-to-1 ReSC converter, and then extended to a new 4-to-1 ReSC converter topology we proposed, herein named cascaded multi-resonant converter. This topology has reduced component count thanks to a new “switching bus” architecture. However, it comes at a cost as the converter has multiple resonances within each switching cycle, complicating the soft-switching design. Despite the high circuit complexity, the state-plane analysis neatly provides analytical equations of all state parameters, which are verified by simulations and experiments. Our hardware prototype achieves 6000 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density at 48-to-12 V conversion and 80 A continuous output. Its peak efficiency reaches 99.02%, and full-load efficiency reaches 97.67%, including gate drive loss. Both the power density and efficiency are superior to the state-of-the-art 48-to-12 V solutions.

A Multiple-Modes Resonant Switched Capacitor DC/DC Converter With Variable Voltage Ratios

High step-down DC/DC converters with high efficiency and high power density are widely used in data centers, DC distribution grids and hybrid electric vehicles. In this paper, a new resonant switched capacitor converter is proposed, which can not only realize high step-down conversion, but also operate in multiple-modes to achieve various voltage ratios. The duty cycle can be allocated to one-half and one-third, enabling the converter to operate in double-mode and triple-mode accordingly. In addition, the state of the basic resonant cell can be switched between series and parallel, which enriches the operating modes, and thus allowing the converter to achieve different voltage ratios. Furthermore, the principle and strategy of switching between operating modes with different voltage ratios and switching between operating modes with same voltage ratio are presented. With the mode switching strategy, this converter can operate in the optimal mode over the wide voltage range and the full load range, thus achieves high efficiency over the full operating range. Finally, five operating modes are selected to verify the feasibility and the correctness of the theoretical analysis.

A Modulation Map for a Family of Phase-Shift-Modulated Resonant Switched-Capacitor Converters

In this article, a modulation map for a family of phase-shift-modulated resonant switched-capacitor converters (RSCs) which reflects the relationship between the control variables and converter characteristics is proposed to guide the converter operation and design in the expected voltage gain range, low component stress region, and zero-voltage-switching (ZVS) operation region. A hybrid modulation strategy combing phase-shift and variable frequency is applied to extend the voltage gain range and ZVS region. On the basis, the modulation map with the favorable operation region is obtained to assist the converter operation and design in the expected conversion ratio range, low component stress region, and ZVS operation region. Similar analyzing methods and modulation maps can be extended to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -mode RSCs and other phase-shift-modulated RSCs, providing operation and design reference for such converter families. A 43–60 to 150 V prototype of a triple-mode RSC with power level 225 W and peak efficiency 96.2% was designed and tested to verify the converter operation and validity of the proposed modulation map.

Short-Circuit Protection for Resonant Switched-Capacitor Converter

Short-circuit protection is critical and indispensable for resonant switched-capacitor converter (RSCC) to improve the reliability. Based on comparison of frequency control, duty ratio control and traditional variable frequency variable duty ration control (VFVDC-I), a novel variable frequency variable duty ratio control (VFVDC-II) is proposed for RSCC to suppress the short-circuit current. By analyzing the operation principle and short-circuit mechanism, the RSCC steady-state characteristics as well as the soft switching conditions under four methods are discussed. Then, the resonant characteristics of four methods are compared through state trajectory analysis. At last, the experiments are carried out to verify the correctness of theoretical analysis and feasibility of proposal method. The experimental results demonstrate that the proposed VFVDC-II avoids the voltage oscillation caused by narrow pulse and achieves the shortest transient response and the lowest peak resonant current at short circuit. Moreover, zero voltage switching is realized during turning on, which helps reduce the switching loss.

Multilevel Switched Capacitor LLC-DCX Converter With Embedded Filter

A multilevel switched capacitor LLC-DC transformer (LLC-DCX) converter with an embedded filter is presented for a power module of solid-state transformers. The proposed converter is a hybrid converter composed of resonant switched capacitor converters (RSCCs) and a previously reported ripple-cancel converter. In contrast to the conventional SCC, which faces the issue of an inrush hard-charging current during switching transition, the proposed converter can be implemented using a soft-charging operation without additional inductors. Further, it inherits the advantages of the two converters, including load-independent soft switching, automatic voltage sharing, automatic current sharing, reduction of the current ripple, an embedded filter function, constant voltage gain, and flexible extensibility. This paper comprehensively analyzes these characteristics and the conditions for soft-charging operation. The design theory based on the analysis is also presented. We fabricated a prototype of the proposed converter with input and output voltages of 900 V and 150 V, respectively and the rated output power of 2 kW to demonstrate the validity of the analysis and design.

ZVS Resonant Switched Capacitor Converter with 1.5X Fixed Step-Up Ratio for EV Batteries

ZVS Resonant Switched Capacitor Converter with 1.5X Fixed Step-Up Ratio for EV Batteries

A Low Voltage Stress PFC Rectifier Based on Nonoverlapping Strategy Using Resonant Switched-Capacitor Converter

In order to break limited step-down ratio range and poor regulation capacity in the conventional resonant switched-capacitor converters for rectifier application, a single-stage ac/dc rectifier based on the dual-resonance switched-capacitor converter is proposed in this article. Through utilizing a dual-resonant structure and nonoverlapping strategy to realize wide continuous voltage gain of the proposed converter, high power factor (PF) and low total harmonic distortion (THD) based on the narrow dead zone are guaranteed by operating at high step-down conversion ratio in this converter topology. Moreover, the voltage gain is concentrated between resonant frequency and double resonant frequency to achieve a narrow switching frequency range for rectifier application. Furthermore, operating at flat voltage stress curves to obtain low voltage stress character. Comprehensive mode analysis, input PF and THD, and stress analysis are given, and analysis results indicate that the proposed power factor correction converter can work with soft turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and zero-current turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ; high efficiency is realized. Finally, an experimental prototype with 85–130 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> input and 47 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> /44 W output is built and tested for verifying the operation modes and PFC performance, and the comparison between different rectifiers and the proposed one is provided.

An optimized multi-modular resonant switched capacitor converter

The switched capacitor converters have the advantages of high efficiency and high power density, which are widely used in data centers, distributed photovoltaic power generation, and other fields. In this paper, an optimized multi-modular resonant switched capacitor converter (MMRSCC) is proposed for an intermediate bus converter in the power supply system of data centers. By removing the inductance of part of the coupled resonant circuit, the converter can eliminate the influence of the parameter difference of passive components, and no additional voltage clamp circuit is needed, which improves the power density. At the same time, the half-bridge with the same switching action on the rectifier side is combined into one, which reduces the number of switching devices and is more conducive to improving the voltage conversion efficiency. In addition, the inductor of the basic unit of the resonant switched capacitor with the same state is shared to reduce the volume of the passive device, further improve the power density, and optimize the MMRSCC. Finally, the correctness of the topology is verified by simulation on the PLECS.

Hybrid Resonant Switched-Capacitor Converter for 48–3.4 V Direct Conversion

As the power required by modern data center processors increases, the power architecture must be adapted; for example, 48 V distribution voltage allows to reduce copper losses by a factor 16 with respect to the use of traditional 12 V power architecture. In order to generate the required processor core voltage, a two-stage approach is usually preferred, where the intermediate bus voltage is generated using an unregulated resonant dc–dc converter as, for instance, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter. Compared to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLCs</i> , hybrid resonant switched-capacitor converters (ReSCCs) make it possible to achieve large voltage conversion ratios without the need of high turns ratio transformers. In this letter, a novel hybrid ReSCC that performs a 48–3.4 V direct conversion is presented. A prototype of the proposed converter has been implemented, capable of providing a continuous output power of 440 W with a maximum efficiency of 96.3% at 30 A load current.

Continuously Adjustable Modular Bidirectional Switched-Capacitor DC–DC Converter

This letter proposes a switched capacitor (SC)-based continuously adjustable modular bidirectional dc–dc converter. The structure of the proposed converter consists of three types of modules, series–parallel SC converter module, regulating module, and resonant SC converters module. A basic configuration of three modules working in buck operating mode is analyzed in detail. The boost mode operation is symmetrical to the buck mode. The regulation module provides all regulation capability, and the other two modules operate at fixed duty cycle and provide the main conversion ratio. A prototype of the basic configuration was built to verify the theory. The peak efficiency of the prototype is 97.15%.

위상시프트 제어법을 적용한 공진형 스위치드 커패시터 DC-DC 컨버터의 특성

This paper deals with a transient characteristics improvement of a resonant switched capacitor converter(RSCC)based on phase shift control method, which has capability of accurate voltage regulation by means of applying a voltage feedback control. The analysis in this paper reveals that the RSCC may superpose an unwanted current on the resonant current and cause voltage fluctuation and/or over current in a transient state. This paper proposes a modified phase shift control method including the sequence and timing control of the gate signals, resulting in elimination of the unwanted current from the resonant current. Experimental results verify the validity of the proposed control method.

Modeling and Comparison of Passive Component Volume of Hybrid Resonant Switched-Capacitor Converters

Hybrid and resonant switched-capacitor (SC) convertersenable efficient utilization of both active and passive components, and have the potential to achieve higher efficiency and higher power density than conventional SC and magnetic-based converters. One or more added inductors offer an additional degree of freedom in the design space. It is of great interest to understand the tradeoffsbetween capacitor and inductor size and volume allocation. In this article, we analyze the reactive energy processed by the passive components and use it to calculate the total passive component volume. It is shown that the total passive component volume of resonant SC (ReSC) converters can be expressed as a function of flying capacitor voltage ripple, and the optimized capacitor voltage ripple that minimizes the total volume is dependent on topology specific parameters and the relative energy density ratio between capacitors and inductors. Moreover, we also demonstrate through theoretical analysis and experimentation that ReSC converters use significantly less passive component volume than conventional SC and buck converters for the same amount of power converted. Next, to compare different ReSC topologies, a normalized passive volume parameter is proposed for simple and fair comparison. This can be used along with a normalized switch stress parameter (based on switch VA ratings) to create a framework to showcase the relative performance of different topologies. This framework can be used to visualize and compare the passive and active component utilization among different topologies. Additionally, the proposed reactive power analysis is extended to hybrid converters with regulation capability.

Isolated Resonant Switched Capacitor Converter With Voltage Self-Balancing Ability

This article proposes an isolated resonant switched capacitor converter (I-RSCC) for high-voltage applications. The dc capacitors’ voltages achieve self-balancing with the resonant switched capacitor units (RSCUs). The voltage stress of the switching devices is reduced. The isolated rectifier (IR) is used for galvanic isolation and energy transfer. The number of switching devices is reduced by multiplexing parts switching devices functions, which helps the compact design. In this article, the topology and operation principle of I-RSCC are introduced in detail. Then, the output characteristics of I-RSCC are analyzed, including the voltage balance operation, the energy transmission path, the voltage conversion ratio, and the output power. The design example of I-RSCC is also presented. Finally, a 10-kW prototype is built to verify the feasibility of the proposed I-RSCC topology. The results show that soft switching is realized, and the maximum operation efficiency is 96.5% and above 96% at the rated power.

An Overview of Non-Isolated Hybrid Switched-Capacitor Step-Up DC–DC Converters

The increasing interest in renewable energy sources has brought attention to large voltage-gain dc–dc converters; among the different available solutions to perform a large voltage-gain conversion, this article presents an overview of non-isolated dc–dc converter topologies that utilize switched-capacitor circuits, i.e., diode-capacitors voltage multipliers. The review includes combinations of a traditional power stage with a diode-capacitor-based voltage multiplier, such as the multilevel boost converter. This article starts by reviewing switched-capacitor (SC) circuits, different topologies, and different types of charge exchange; it provides a straightforward analysis to understand the discharging losses. It then covers the multilevel boost converter and other topologies recently introduced to the state-of-the-art. Special attention is put on SC circuits with resonant charge interchange that have recently been probed to achieve very good efficiency. An additional contribution of the article is new proof of the discharging losses in resonant switched-capacitor circuits focused on the initial and final stored energy in capacitors, and this proof explains the relatively large efficiency obtained with SC resonant converters.