Switched-capacitor Converter Research Articles

Comparison and Optimization of Non-isolated DC-DC Converters for Electric Vehicle Applications

This paper discusses the importance of electric vehicles in solving the problem of environmental pollution. In electric vehicles, DC/DC converter is a vital part to connect many electrical units with high voltage bus, so it plays a vital and indispensable role in electric vehicles. The paper analyzes the disadvantages of isolated DC/DC converter, and concludes that non-isolated DC/DC converter is a more suitable technical solution for electric vehicles. The research paper introduces a number of fundamental non-isolated DC/DC converter topologies before analyzing the technical optimization strategies of a number of DC/DC converters in general. which are Half-bridge converters, Cascaded Half-bridge converter (CHB), multi-phase interleaved parallel converter, tri-level converter, soft-switching converter, and switched-capacitor converter (SC converter). The benefits and drawbacks of these DC/DC converter optimization measures are compared, the findings can serve as a technical framework for guiding the application of DC/DC converter technology in the context of electric vehicles. Finally, this paper analyzes and looks forward to the development prospect of flying switched-capacitor DC/DC converters (FCDCs) technology, puts forward the existing technical problems, and gives suggestions for the solution of these problems, which is conducive to the wider application of this technical solution in electric vehicles.

Guest Editorial Special Section on Switched Capacitor Converters (SCCs)

Guest Editorial Special Section on Switched Capacitor Converters (SCCs)

Design and Flight Qualification of a Flying Capacitor Multilevel Converter for Electric Aircraft Applications

Multilevel switched-capacitor converters, such as the flying capacitor multilevel (FCML) converter, offer high energy density and efficiency, over a wide voltage range, making them suitable for applications in electrified aircraft. However, concerns of reliability due to the increased number of active and passive components have limited the use of high-level count converters in aircraft applications. This work addresses the challenges of designing a high-level count converter with the goal of extremely high efficiency and power density, with maintained reliability and flight readiness. We present detailed component selection and design techniques to achieve this goal, along with a high-performance 28.2 kW/kg, 99.52% efficient high-voltage dc-dc step-up power converter for experimental validation. Finally, we demonstrate successful completion of critical flight qualification testing of the hardware prototype, including thermal, shock and vibration.

Guest Editorial Special Section on Switched Capacitor Converters (SCCs)

Guest Editorial Special Section on Switched Capacitor Converters (SCCs)

A Generalized Topology Synthesis for the Switched-Capacitor Converter

Switched-capacitor converters (SCCs) have been developed for decades and applied successfully in many applications due to the merits of high-power density, high efficiency and low cost. In order to explore as many as possible SCC topologies, this article proposes a generalized topology which can cover the existing schemes of the SCCs and enable automatic generation of brand-new structures. Within this framework, topological interconnections or electric rating for the power components can be determined. By more topology options with different characteristics, it is beneficial for engineers to optimize design after comprehensive comparison. Besides, all the derived topologies are verified based on the parallel simulation and experiment. The selected optimum topology is presented in detail to demonstrate its advantages. It is expected to reveal the basic laws for the SCCs optimization, especially in complicated cases such as large number of power elements.

A 4:1 Switched Capacitor Converter With Low Flying Capacitors Voltage and High Efficiency

In this paper, a 4:1 switched capacitor converter (SCC) is derived. Compared with the Dickson 4:1 converter, the voltage of flying capacitors is lower and thus the effect of dc bias on multi-layer ceramic capacitor (MLCC) is reduced. With a limited number of MLCCs, the proposed converter achieves a higher efficiency, and it is suitable for the applications with limited volume such as mobile phone fast charging. A 20-V to 5-V prototype is built with 24 X7R MLCCs in 0805 package, and its efficiency is 1.7% higher than the Dickson 4:1 and 1.1% higher than the Series-parallel 4:1 at 16-A output current.

A Direct AC–AC Switched-Capacitor Converter With Input-Series Output-Parallel and In-Phase/Out-of-Phase Capabilities

In this paper, a bidirectional transformerless multi-level direct ac-ac switched-capacitor converter (SCC) is proposed with both in-phase and out-of-phase output voltage capabilities. This converter can be used for series compensator applications, such as dynamic voltage restorers (DVRs), to compensate grid voltage sag and swell phenomena by incorporating its input-output common ground. Its input-series output-parallel capabilities reduce voltage and current stresses of the converter components in multi-level configurations, which lead to higher efficiency and lower manufacturing costs for high-power applications. Furthermore, proper utilization of an interleaving control scheme can provide lower input and output currents ripples values and smaller filter sizes. The proposed SCC operation principle and its mathematical analyses are given, in detail. Additionally, its switching patterns have been developed with a safe-commutation strategy to obtain various output voltages. Subsequently, both single- and two-level SCC prototypes are implemented as series compensators for DVR applications. Moreover, experimental results are given to generate in-phase and out-of-phase regulated output voltages. The experimental results at 2 kW show that the output voltage changes are less than 3% under the steady-state conditions, despite the large input voltage changes from 140 to 300V. The converter maximum efficiency value is equal to 95.4% at maximum output power value.

Guest Editorial: Special Section on Switched Capacitor Converters (SCCs)

Guest Editorial: Special Section on Switched Capacitor Converters (SCCs)

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

Microbial Fuel Cell as Battery Range Extender for Frugal IoT

The simplest DC/DC converter for supplying an Internet-of-Things device is definitely a switched-capacitor converter. The voltage from a mere 1.2 V battery may be stepped up to 2 V. A quite large operating frequency is required in order to reach the smallest possible output impedance value of the DC/DC converter. The overall efficiency is then limited even more so if the power area density of the system should be large. The article details how a microbial fuel cell may substitute one capacitor in the switched-capacitor converter, achieving a better efficiency at a much lower operating frequency. In that perspective, the microbial fuel cell acts as a kind of battery range extender. Some limitations exist that are discussed. A simple converter is experimentally evaluated to support the discussion. Substituting a microbial fuel cell inside a 100 μW switched-capacitor converter compensates for losses in the order of 5% of efficiency. Moreover, the microbial fuel cell extends the lifespan of the battery, as 1.6 V output voltage is still possible when the battery voltage drops to 0.8 V. More than 94% efficiency is measured for a range of output power between 100 μW and 1 mW, which is sufficient to address a lot of frugal IoT applications.

Series-Parallel Multiresonant Switched-Capacitor Converters and the Optimal Operation Region

In this paper, Series-parallel (SP) Multi-resonant Switched-capacitor Converters (MRSCCs) are proposed by incorporating resonant tanks into the traditional SP switched-capacitor converter (SCC) and adopting the on-time fixed frequency modulation. Compared to the traditional SP SCC with hard-switched operation, high transient current spike and inability for lossless voltage regulation, the proposed SP-MRSCC in the optimal operation region owns the merits of soft-switching operation, complete soft-charging feature, low transient current spike, as well as continuous, wide and efficient voltage-gain variation range even at light-load condition. A comprehensive analysis of operation principle, boundary conditions and component stress in four operation modes is provided to assist converter operation and design in the optimal operation region. On one hand, the upper limit of a defined loaded quality factor <i>Q_crit</i> is derived to avoid the appearance of a knee in the gain curve. On the other hand, the current overlapped region- that is, mode 1 and 2- is found to have better operation performance with wider voltage-gain-variation range and lower component stress. On the basis, the synchronous SP-MRSCC is proposed to reduce the conduction loss significantly in high-order circuit and step-down applications. A quantitative comparison between the proposed SP-MRSCC and other counterparts is given to outstand the aforementioned advantages. A 100W 4X SP-MRSCC prototype was designed and tested to verify the above analyses, which has the potential to be utilized for connecting 12V and 48V DC buses between traditional and future data centers.

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.

Transformerless bidirectional switched-inductor switched-capacitor converter

ABSTRACT This research presents a unique bidirectional converter based on the active switched-inductor and switched-capacitor networks of the ASL-SU2C converter. The converter’s primary advantages are its high voltage gain and reduced switch stress. This was accomplished by the converter using three inductors, two switched-capacitors, two switches, and diodes. Switches are used in place of diodes to enable bidirectional power flow in the proposed work, and synchronous rectification is used to boost efficiency by reducing conduction losses. Two inductors and two switches on the low voltage side of the converter aid in lowering the average switch current and, consequently, the current stress. The control operation is made simpler by the fact that two switches on the high voltage side (HVS) have one duty cycle and the other two switches on the low voltage side (LVS) have a different duty cycle. Consequently, two switches will always have identical duty cycles. In order to validate the theoretical findings, the performance of the transformerless bidirectional switched-inductor switched-capacitor (TBSISC) topology is examined in steady state, compared to that of other bidirectional converters, its efficiency is calculated, and experiments with a 500 W prototype are conducted.

A Phase-Shift-Modulated Resonant Two-Switch Boosting Switched-Capacitor Converter and Its Modulation Map

In this paper, a Phase-shift-modulated (PS) Resonant Two-switch Boosting Switched-capacitor Converter (RTBSC) and its modulation map are proposed. Compared with the traditional RTBSC, all diodes are replaced by active switches and then phase-shift modulation is applied. The advantages of the modified topology are obtained as follow. 1) The voltage gain can be regulated efficiently either below or above the nominal value even at light-load condition, making it suitable for applications with voltage fluctuations; 2) The conduction loss is reduced by replacing all diodes in RTBSC with low turn-on resistance transistors, especially for high-order and high-gain configuration; 3) All switches achieve the zero-voltage-switching (ZVS) turn-on operation; 4) The soft-charging property smooths the current profile. Aside from the topology modification, a comprehensive analysis of operation principle, voltage gain, component stress and ZVS region is given. On the basis, a modulation map with the optimal operation region is proposed. It provides a guideline to operate and design such converters in the target gain range, low component stress and ZVS region, making up for the lack of modulation map and design guideline in aforementioned literatures. A 120W prototype with low-voltage side 43-60V and high-voltage side 150V was designed to verify the above analyses.

SOC 밸런싱 기능을 갖춘 새로운 배터리 스위칭 시스템

The conventional dual-voltage automotive system has a large size and high cost due to its magnetic components. To eliminate the magnetic components, previous research adopted switched-capacitor converters. However, to provide the proper output voltage with small capacitance, high switching frequency should be employed, which leads to high energy loss and EMI problems. To mitigate the drawbacks, the battery switching system using some switches was considered. This system has charging and discharging modes through series or parallel battery connections. However, the batteries can be under-utilized and unbalanced due to the state of charge (SOC) problem. Therefore, this paper proposes a new battery switching system with SOC balancing capability. The proposed system only adds a few switches, in which switching in the order of battery connection can be applied. Through this structure, all batteries can be utilized and balanced. In addition, battery switching can be controlled simply. To confirm the validity of the proposed system, a 160 W prototype was implemented and experimented.

Five-Level Step-Up Switched-Capacitor Grid-Connected Inverter

The objective of this paper is to propose a new five-level step-up switched-capacitor grid-connected inverter (FSSGI) The proposed FSSGI, which is composed of a switched-capacitor converter (SCC) and an dc-ac unfolder, is able to operate in standalone and grid-connected mode. Compared with conventional step-up inverter topologies, the advantages of the proposed FSSGI include high conversion efficiency, self-balancing of capacitor, and voltage stress reduction on the switches for low power applications. In addition, the leakage current cause by the high common mode voltage (CMV) can be reduced since the unfolder is only switched at the low frequency. Also, the electrolytic capacitor can be replaced with the long lifetime film capacitor by reducing the required capacitance. The principle of operation, voltage gain analysis, and design methodology are described in this paper. Finally, the computer simulations and hardware experimental results are shown to verify the performance of the proposed FSSGI. A 400-W prototype is built and tested, and the peak and rated power conversion efficiency are 97.89% and 97.45%, respectively.

A Fully-Integrated Micro-Display System With Hybrid Voltage Regulator

A fully-integrated active matrix light-emitting diode (AMLED) micro-display system is demonstrated in this paper. The system consists of a 36 × 64 AMLED array chip based on GaN-on-Silicon epilayers and a silicon driving chip integrating an on-chip hybrid voltage regulator, pixel drivers, and peripheral circuits. Then two chips are bonded with low-cost Au-free flip-chip bonding technology. As such, this system is able to directly operate with a battery without any external passive components. Multiple techniques were proposed to achieve the system integration: (1) A fully-integrated hybrid voltage regulator consisting of a step-up switched-capacitor (SC) converter cascaded by a step-down linear voltage regulator was fabricated in a 0.18 μm CMOS technology. It achieved only 1.38% output voltage ripple without external capacitors, and be able to deliver a maximum power of 216mW with peak efficiencies of 91% in the linear mode and 78% in the SC mode; (2) Micro-LEDs are fabricated on GaN-on-Silicon substrate that significantly suppresses the light crosstalk between pixels and reduces the cost; (3) An Au-free flip-chip bonding technique is developed to reduce the bonding cost and achieved reliable connections between AMLED array chip and silicon driving chip. The whole system achieved 635 pixel/in (PPI) pixel density. Images and videos with 4-bit grayscale could be rendered. This prototype achieved a high integration level and demonstrates the tremendous potential of the highly efficient, low cost fully integrated AMLED micro-display system.

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 Dynamically Reconfigurable Recursive Switched- Capacitor DC–DC Converter With Adaptive Load Ability Enhancement

Multiple voltage conversion ratio (VCR) recursive switched-capacitor (SC) dc–dc converters, based on several basic 2:1 converters, are widely used for on-chip power supplies due to their flexible VCRs for higher energy efficiency. However, conventional multiple VCR SC converters usually have one or more 2:1 converters unused for some VCRs, which results in lower power density and chip area wastage. This article presents a new recursive dc–dc converter system, which can dynamically reconfigure the connection of all on-chip 2:1 converter cells so that the unused converters in the conventional designs can be reused in this new architecture for increasing the load-driving capacity, power density, and power efficiency. To validate the design, a 4-bit-input 15-ratio system was designed and fabricated in a 180-nm BCD process, which can support a maximum load current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{0.71}\,\text{mA}$</tex-math></inline-formula> and achieves a peak power efficiency of 93.1% with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$105.3\,\mu \text{A/mm}^{2}$</tex-math></inline-formula> chip power density from a 2-V input power supply. The measurement results show that the load-driving capacity can become 6.826×, 2.236×, and 2.175× larger than the conventional topology when the VCR is 1/2, 1/4, and 3/4, respectively. In addition, the power efficiency under these specific VCRs can also be improved considerably.

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.