Switched-capacitor Converter Topology Research Articles

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.

Boosting Wide-Range Conversion Efficiency With Dynamic Voltage-Domain Stacking

This article presents dynamic voltage-domain stacking, which incorporates the attractive efficiency benefits of voltage-domain stacking into a wide-input-range conversion system. This is achieved by combining two novel switched-capacitor converter topologies with an integrated finite-state machine into a highly reconfigurable system. First, a zooming gearbox converter efficiently enables a wide input range while only implementing three conversion ratios. Second, a reconfigurable ladder converter continuously compensates for imbalance between the dynamically stacked voltage domains. A prototype has been fabricated in a 40-nm baseline CMOS technology to provide a stable supply voltage to four loads across an input voltage range from 4 V down to 0.55 V. Measurements show a best-in-class average efficiency of 80.1% and a peak efficiency of 92.1%.

Fast Performance Evaluation for Switched-Capacitor Converter Based on Convolutional Neural Networks

Switched-capacitor converters (SCCs) have been developed for decades and applied successfully in many applications thanks to their merits of high power density, high efficiency, and low cost. Existing SCC evaluation methods do not provide an efficient and effective way to estimate their performance. This paper proposes a new evaluation performance method for SCCs that transforms the topology optimization issue into a more typical non-linear regression problem. The SCC topologies are described by the adjacent matrix. A CNN model is then selected to solve the regression problem. Experimental results confirm that this CNN model greatly shortens the calculation time while performing better than other machine learning algorithms.

Miniaturized Energy Harvesting Systems Using Switched-Capacitor DC-DC Converters

This tutorial brief reviews highly-integrated switched-capacitor (SC) DC-DC converter topologies for miniaturized energy harvesting (EH) IoT systems. Aiming to provide a concise overview of SC converter-based EH interfaces, we first discuss the system level design considerations for energy balancing between source, storage, and load under different environmental conditions. The key factors dominating the energy extraction and power conversion efficiencies, including the source adaptation strategies and SC power stage intrinsic losses, are outlined to establish a fundamental understanding on the EH system performance. After studying different state-of-the-art SC topologies in terms of their rational boost voltage conversion ratio (VCR) generation flexibility, loss characteristics, and implementation tradeoffs, we further introduce two advanced SC converter-based EH system examples, highlighting the SC converter operation in enhancing the EH system functionality and performance. The pros and cons of different SC converter topologies for EH systems will also be discussed.

A new type of switched capacitor converter for energy harvesting system

An energy harvesting system requires a power converter with its compact size and high power efficiency. Following the trend, this study suggests a new switched capacitor converter (SCC). The proposed converter is designed by a parallel- and cross-connecting two Fibonacci topologies. This connection leads the proposed SCC to generate its multilevel outputs as well. The proposed SCC has the lowest output resistors under five times conversion ratios from the theoretical analysis and comparison of two different SCC topologies. Simulation results confirm that the proposed SCC can be operated over 90% power efficiencies under 100 mW.

Hybrid Control Strategy Dual Resonance Core-Based Step-Up/Down Switched Capacitor Converter With Reduced Frequency Range for Wide Output Voltage Application

Notice of Violation of IEEE Publication Principles <br><br>"Hybrid Control Strategy Dual-Resonance-Core Based Step-Up/Down Switched Capacitor Converter with Reduced Frequency Range for Wide Output Voltage Application" <br> by Zhangyong Chen, Yubo Han, Yunfeng Wu, Zhengdong Lu, Xiangyu Liu and Changhua Zhang, <br>in the IEEE Transactions on Power Electronics, Early Access <br><br>After careful and considered review of the content and authorship of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE’s Publication Principles. <br><br>This paper contains copied and improperly cited content from the paper cited below. <br>"Dual Resonant Switched-Capacitor Step-Down Polarity Inverter" <br> by Benjamin Y. Brown, Keyue Ma Smedley, <br>in a MS Thesis, University of California, Irvine, 2019 <br><br> <br/> Wide voltage range converters are significant for photovoltaic power generation system, battery charging, etc. Resonant converter has been preferred topology for these applications, however, some demerits exist: 1) Difficult to realize wide voltage gain range and low circulating current losses; 2) Widely regulated switching frequency to adapt to wide voltage gain range; 3) Poor regulation at light load. Based on above-mentioned shortcomings, dual-resonance-core based step-up/down switched capacitor converter topology is presented in this paper. Utilizing hybrid control strategy, non-overlapping control strategy is used in the Buck-type mode and overlapping control strategy is applied in the Boost-type mode with common switching frequency range, and therefore, reduced frequency range in the presented converter is achieved. Moreover, wide voltage gain range can be obtained due to step-up/down capacity in the proposed converter. Furthermore, conversion ratio of proposed converter can be reduced to zero theoretically by using dual-resonance-core existed in the resonant switched capacitor converter. Finally, comprehensive operational principle analysis and performance analysis are provided, and a 48V to 2890V/100W prototype is built to verify the analysis.

Comparative Study of Switched Capacitor Converter Topologies for Wearable Devices

As wearable devices with low input voltages have drawn much attention from academic and industrial fields, the use of switched capacitor converters (SCC) also increases. This is because the wearable devices are required to utilize small size power converters and SCCs have no bulky circuit components such as magnetic components. Many kinds of SCCs have been suggested but they are based on three fundamental SCC topologies that are Dickson, series-parallel and Fibonacci topologies. In this study, three topologies are theoretically analyzed and simulated. With the results from them, a comparison is conducted to provide future circuit designers with a standard to choose a proper SCC topology for wearable devices.

A novel intermediate bus converter topology for cutting edge data center applications

As new technologies emerge data centers and servers have established themselves as one of the largest and fastest growing consumers of power. While switched capacitor converter topologies have some very attractive features, namely low reliance on magnetic components and high efficiency, several critical factors have prevented their adoption in high current data center applications. The family of converters proposed are novel intermediate bus converter that demonstrates the highest performance yet achieved for 48 V to 12 V conversion with up to 2.5 kW/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density, higher than 99% peak efficiency, and 97.2% full load efficiency for 12 V/70 A output. The reduction of voltage stress across the MOSFETs as well as extremely low reliance on magnetics are the key driving factors behind this high efficiency and power density, and are achieved without a sensitive resonant design or the usage of complex control technique.

An analytical approach for parallel switched capacitor converter

A switched capacitor converter (SCC) is a kind of inductor-less power converters. The fact that the SCC has no magnetic components leads to reduce the size as well as electromagnetic interference (EMI) and electromagnetic compatibility (EMC) problems. Until now, many types of SCCs have been suggested. Among those topologies, single type topologies have room to improve their power efficiency. A solution is to merge two single topologies and to design a parallel topology. In previous researches, the parallel SCC topologies were analyzed, neglecting either their slow switch limit (SSL) or fast switch limit (FSL). In this study, applying a circuit model including both SSL and FSL, the output impedance of the parallel SCC topology is derived to improve the accuracy of the modeled output impedance. The theoretical analysis is verified by the simulation results. This study can provide future circuit designers with more accurate characterization of the parallel SCC topology.

Time-Domain Modeling and Analysis of Switched-Capacitor Converters

This article proposes time-domain modeling and analysis of switched-capacitor converters (SCCs) by homogenizing the state-space model, resulting in a closed-form expression of the output voltage as a function of time without requiring discretization and subsequent numerical solution. The proposed technique facilitates obtaining the steady-state output voltage at any arbitrary time within a period, rather than at one discrete time at the beginning or end of the clock period. Circuit-level simulations for various SCC topologies, viz. , series–parallel (SP), ladder (LD), Fibonacci (FB), and Dickson (DK), show excellent agreement of the time-domain behavior as well as the equivalent resistance of the converter with the proposed technique. The proposed technique gives more than an order-of-magnitude improvement in simulation time. Experimental data for SP and LD topologies have been used to validate the accuracy of the proposed technique.

The Cascaded Resonant Converter: A Hybrid Switched-Capacitor Topology With High Power Density and Efficiency

Resonant switched-capacitor (ReSC) converters have efficient utilization of both active and passive components, and hold the potential to achieve higher efficiency and higher power density than conventional switched-capacitor (SC) and magnetic-based converters. This article presents a new hybrid/resonant SC converter topology, comprising two cascaded 2-to-1 ReSC converters, to address high-conversion-ratio applications. The proposed cascaded resonant converter has a simple structure and operation principle and can achieve one of the best overall metrics among popular ReSC topologies. A 36-60-V input 4:1-fixed-ratio bus converter prototype for data center application is designed and constructed. We present detailed design guidelines and discussions to address practical challenges, such as component variations and interstage decoupling requirements. With 48-V input and operating at the typical zero-current switching mode of ReSC converters, the prototype achieves a peak efficiency of 98.85% (including gate drive loss) and a power density of 2500 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , both of which are significantly higher than the state of the art. Furthermore, we propose a zero-voltage switching method to improve light-load efficiency. Through this control method, which greatly reduces the output capacitance loss, the prototype can maintain an efficiency above 97% starting from 3% of the rated load, with a peak of 99.0%.

A Monolithic Voltage-Scalable Fibonacci Switched-Capacitor DC–DC Converter With Intrinsic Parasitic Charge Recycling

Switched-capacitor converter (SCC) features a compact solution due to its magnetic-less structure, which fulfills the high density requirement in low power applications. Compared to other SCC topologies, Fibonacci switched-capacitor converter (FSC) utilizes the least number of flying capacitors to perform any voltage conversion. This paper proposes a monolithic voltage-scalable FSC, which can be used in energy harvesting applications. The challenges to implement on-chip FSC are addressed. The parasitic charge loss is substantial in FSC. Therefore, a charge recycling technique exploiting the presence of parasitic capacitors in each other phase of FSC has been employed resulting in 27% reduction in the power loss, which improves the overall efficiency by 12.7%. For a proof of concept, the proposed converter is implemented in 0.5-μm CMOS technology on 4-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> die area. The postlayout simulation is carried out using Virtuoso ADE. With 0.3-V input voltage, the system achieves 47.5% peak power efficiency with 5-μW load.

A Performance of the Soft-Charging Operation in Series of Step-Up Power Switched-Capacitor Converters

Due to their high power density and appropriateness for small circuits integration, switched-capacitor (SC) converters have gotten more interests. Applying the soft-charging technique effectively eliminates the current transient that results in a higher power density and a higher fundamental efficiency. Achieving the complete soft-charging operation is impossible by using the conventional control diagram for any SC converter topology. In this paper, we proposed a split-phase control to achieve the complete soft-charging operation in a power switched-capacitor (PSC) converter. The proposed control diagram was designed for a 1-to-4 PSC converter (two-level of the PSC converter). The implemented split-phase diagram successfully controls eight switches to exhibit eight modes of operation. In addition to the current transient elimination, the complete soft-charging allows us to reduce capacitor sizes. However, reducing capacitor size negatively increases the output voltage ripple; hence, an output LC filter is needed. The complete soft-charging achievement accomplishes a 96% efficiency due to the lower output impedance and the dead time switching. LT-Spice software has been used to verify the proposed control and the results were compared with hard-charging and incomplete soft-charging operations.

Modelling, simulation and experimental investigation of a new two input, series‐parallel switched capacitor converter

A new series-parallel switched capacitor converter topology capable of operating off two independent input sources and generating target output voltage in buck or boost mode is presented. Operation principle, conversion ratios, modelling considerations in different operation modes and extensive loss analysis are derived. The converter is robust and may be operated off one or two input sources, having the ability to change conversion ratio over a wide range. The proposed model assumes that the conduction losses are proportional to the average current flowing through each of the charge pump capacitor in a switching phase. Capacitor current instantaneous waveform in the complete charge, partial charge and no charge modes are captured in simulation and experiment. Model predicted equivalent resistance, output voltage and instantaneous capacitor current waveform concur excellent with simulated and experimental values, rendering the new converter as an excellent candidate for two and single input source applications.

A Light-Load-Efficient 11/1 Switched-Capacitor DC-DC Converter With 94.7% Efficiency While Delivering 100 mW at 3.3 V

This paper demonstrates a 2-phase 11/1 switched-capacitor (SC) DC-DC converter that provides an output voltage $V_{OUT}$ of 3.3 V from an input voltage $V_{IN}$ in the range of 37.4 V–39 V . SC converters, unlike their inductive buck counterparts, do not rely on the pulse-width modulation (PWM) duty cycle to set the voltage conversion ratio (VCR) as this is determined by the SC converter topology. Consequently, SC DC-DC converters do not require a very low duty cycle, resulting in a short $t_{on}$ for the full-input-voltage-rated high-side switch and significant driver power consumption. Instead, a two-phase SC converter is found to be an excellent candidate for high-ratio voltage conversion as it maintains a 50% duty cycle and exchanges few components of high voltage rating with more that are rated for lower voltage.

A General Method for Analyzing Resonant and Soft-Charging Operation of Switched-Capacitor Converters

Traditionally, switched-capacitor (SC) converters have suffered from high transient currents, which limit both the efficiency and power density of such converters. Soft-charging operation can be employed to eliminate the current transients and greatly improve the power density of SC converters. In this approach, a second-stage magnetic converter is cascaded with the SC stage to act as a controlled current load. Another approach is to use resonant SC converters with zero-current switching. This paper shows that resonant and soft-charging operations of SC converters are closely related, and a technique will be proposed, which achieves either operation by adding a single inductor to existing SC topologies. In addition, since most preexisting resonant or soft-charging SC converters were devised in an ad-hoc manner, this paper formulates an analytical method that can determine whether an existing conventional SC converter topology is compatible with the proposed approach. A number of common SC topologies are analyzed, including Dickson, series-parallel, ladder, Fibonacci, and doubler configurations. Through comparison to simulated results, as well as experimental work, the proposed method is validated and a family of high-performance SC converters is obtained.

Design and Analysis of Output Voltage Regulation in Multi-Phase Switched Capacitor Converters

A new regulation method based on duty cycle control of the average currents in the multi-phase switched capacitor converters (SCC) is proposed, analyzed, and verified experimentally for the no effective charging case, also known as the fast switching limit. The regulation is accomplished by adjusting the value of the SCC equivalent resistance. To this end, the time slots allotted to each of the SCC topologies are adjusted, while the total switching period is kept constant. The time slots are represented by master and slave duty cycles. By this, the SCC output voltage is expressed analytically as a function of the master duty cycle. In a similar way, analytical expressions for the voltages across the flying capacitors and for the average currents in each of the topologies can be obtained. Excellent agreement was found between the theoretical and experimental results.

On the Input Resistance of a Reconfigurable Switched Capacitor DC–DC Converter-Based Maximum Power Point Tracker of a Photovoltaic Source

The use of a switched capacitor (SC) dc-dc converter for tracking the maximum power point (MPP) of a photovoltaic (PV) array with the possibility of partial shading is described. The SC converter topology can be reconfigured to maximize conversion efficiency depending on the solar radiation and load. A new control scheme for MPP tracking based on tuning the input resistance (RIN) of the SC converter MPP tracker with a battery tied load to match the output resistance of the array at MPP is proposed. RIN of the SC converter MPP tracker is studied extensively. The limits of RIN and its sensitivity to Pulse-width modulation (PWM), frequency modulation (FM), and circuit parameters of the SC converter are analyzed. Based on the sensitivity analysis, the proposed control scheme consists of an inner FM loop for fine control, an outer PWM loop for coarse control, and a provision to increase the dynamic range of RIN with adjustments of certain converter circuit parameters. A hardware prototype of a 10-W SC converter-based MPP tracker is built. Experimental measurements on the hardware model confirm the theoretical analysis. An algorithm to implement the MPP tracking control scheme is also tested.