Morphing Switched-Capacitor Converters with Variable Conversion Ratio

High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss

Supercapacitor assisted low dropout regulators (SCALDO) with reduced switches: A new approach to high efficiency VRM designs

Supercapacitor assisted low dropout (SCALDO) regulator is a new approach to develop high efficiency DC-DC converters with supercapacitors used for energy recovery. One limitation in these topologies is that in some configurations a large number of low-speed switches are required. If the SCALDO technique is adapted to build voltage regulator modules (VRM), it is necessary to reduce number of switches combined with a high current capable LDO. A new topology-variation with less number of switches can be achieved by reconfiguring the original SCALDO and adding an extra LDO to the circuit. The paper presents a summary of some preliminary work, and experimental results for a 2.5V proof of concept-prototype

Two new families of high-gain DC-DC power electronic converters for DC-microgrids

Distributing the electric power in dc form is an appealing solution in many applications such as telecommunications, data centers, commercial buildings, and microgrids. A high gain dc-dc power electronic converter can be used to individually link low-voltage elements such as solar panels, fuel cells, and batteries to the dc voltage bus which is usually 400 volts. This way, it is not required to put such elements in a series string to build up their voltages. Consequently, each element can function at it optimal operating point regardless of the other elements in the system. In this dissertation, first a comparative study of dc microgrid architectures and their advantages over their ac counterparts is presented. Voltage level selection of dc distribution systems is discussed from the cost, reliability, efficiency, and safety standpoints. Next, a new family of non-isolated high-voltage-gain dc-dc power electronic converters with unidirectional power flow is introduced. This family of converters benefits from a low voltage stress across its switches. The proposed topologies are versatile as they can be utilized as single-input or double-input power converters. In either case, they draw continuous currents from their sources. Lastly, a bidirectional high-voltage-gain dc-dc power electronic converter is proposed. This converter is comprised of a bidirectional boost converter which feeds a switched-capacitor architecture. The switched-capacitor stage suggested here has several advantages over the existing approaches. For example, it benefits from a higher voltage gain while it uses less number of capacitors. The proposed converters are highly efficient and modular. The operating modes, dc voltage gain, and design procedure for each converter are discussed in details. Hardware prototypes have been developed in the lab. The results obtained from the hardware agree with those of the simulation models. --Abstract, page iv

A multistage DC-DC step-up self-balanced and magnetic component-free converter for photovoltaic applications : hardware implementation

Abstract: This article presents a self-balanced multistage DC-DC step-up converter for photovoltaic applications. The proposed converter topology is designed for unidirectional power transfer and provides a doable solution for photovoltaic applications where voltage is required to be stepped up without magnetic components (transformer-less and inductor-less). The output voltage obtained from renewable sources will be low and must be stepped up by using a DC-DC converter for photovoltaic applications. 2 K diodes and 2 K capacitors along with two semiconductor control switch are used in the K-stage proposed converter to obtain an output voltage which is (K + 1) times the input voltage. The conspicuous features of proposed topology are: (i) magnetic component free (transformer-less and inductor-less); (ii) continuous input current; (iii) low voltage rating semiconductor devices and capacitors; (iv) modularity; (v) easy to add a higher number of levels to increase voltage gain; (vi) only two control switches with alternating operation and simple control. The proposed converter is compared with recently described existing transformer-less and inductor-less power converters in term of voltage gain, number of devices and cost. The application of the proposed circuit is discussed in detail. The proposed converter has been designed with a rated power of 60 W, input voltage is 24 V, output voltage is 100 V and switching frequency is 100 kHz. The performance of the converter is verified through experimental and simulation results

A plug-and-play ripple mitigation approach for DC-links in hybrid systems

© 2016 IEEE.In this paper, a plug-and-play ripple mitigation technique is proposed. It requires only the sensing of the DC-link voltage and can operate fully independently to remove the low-frequency voltage ripple. The proposed technique is nonintrusive to the existing hardware and enables hot-swap operation without disrupting the normal functionality of the existing power system. It is user-friendly, modular and suitable for plug-and-play operation. The experimental results demonstrate the effectiveness of the ripple-mitigation capability of the proposed device. The DC-link voltage ripple in a 110 W miniature hybrid system comprising an AC/DC converter and two resistive loads is shown to be significantly reduced from 61 V to only 3.3 V. Moreover, it is shown that with the proposed device, the system reliability has been improved by alleviating the components' thermal stresses

Merged Two-Stage Power Converter With Soft Charging Switched-Capacitor Stage in 180 nm CMOS

In this paper, we introduce a merged two-stage dc-dc power converter for low-voltage power delivery. By separating the transformation and regulation function of a dc-dc power converter into two stages, both large voltage transformation and high switching frequency can be achieved. We show how the switched-capacitor stage can operate under soft charging conditions by suitable control and integration (merging) of the two stages. This mode of operation enables improved efficiency and/or power density in the switched-capacitor stage. A 5-to-1 V, 0.8 W integrated dc-dc converter has been developed in 180 nm CMOS. The converter achieves a peak efficiency of 81%, with a regulation stage switching frequency of 10 MHz.Interconnect Focus Center (United States. Defense Advanced Research Projects Agency and Semiconductor Research Corporation

Development of a Supercapacitor based Surge Resistant Uninterruptible Power Supply

Uninterruptible Power Supplies (UPSs) provide short-term power back-up to sensitive electronic and electrical equipments, where an unexpected power loss could lead to undesirable outcomes. They usually bridge the connected equipment between the utility mains power and other long term back-up power systems like generators. A UPS also provides a “clean” source of power, meaning they filter the connected equipment from distortions in electrical parameters of the mains power like noise, harmonics, surges, sags and spikes. A surge resistant UPS or SRUPS is one that has the capability to withstand surges, which are momentary or sustained increases in the mains voltage, and react quickly enough to offer protection to the connected equipment from the same. Usually UPSs run off battery power when the utility mains power is absent. But the SRUPS developed in this design project uses super capacitors instead of battery packs. The reason for this is that the high energy-densities and medium power-densities offered by super capacitors allow for it to serve two purposes. One is to provide the DC power to operate the UPS in the absence of mains power, as an alternative to batteries. Secondly, super capacitors can withstand heavy momentary high current/voltage surges due to its high energy-density characteristics. Also as the life-time of super capacitors is much higher than that of conventional batteries and as they do not need regular topping-up or inspection, the end result is a truly maintenance-free UPS. Most commercial UPSs do not have inherent surge protection capabilities. The UPS is one entity while a discrete surge protection module is inserted between the utility mains and the UPS to provide for transient surge suppression. In the proposed SRUPS, the super capacitor, because of their inherent capability to absorb transient surges, forms a protective front end to the actual UPS rather than needing to have the involvement of discrete protection devices

Hybrid and modular multilevel converter designs for isolated HVDC–DC converters

Efficient medium and high-voltage dc-dc conversion is critical for future dc grids. This paper proposes a hybrid multilevel dc-ac converter structure that is used as the kernel of dc-dc conversion systems. Operation of the proposed dc-ac converter is suited to trapezoidal ac-voltage waveforms. Quantitative and qualitative analyses show that said trapezoidal operation reduces converter footprint, active and passive components' size, and on-state losses relative to conventional modular multilevel converters. The proposed converter is scalable to high voltages with controllable ac-voltage slope; implying tolerable dv/dt stresses on the converter transformer. Structural variations of the proposed converter with enhanced modularity and improved efficiency will be presented and discussed with regards to application in front-to-front isolated dc-dc conversion stages, and in light of said trapezoidal operation. Numerical results provide deeper insight of the presented converter designs with emphasis on system design aspects. Results obtained from a proof-of-concept 1-kW experimental test rig confirm the validity of simulation results, theoretical analyses, and simplified design equations presented in this paper. - 2013 IEEE.Scopu

Design of Power Switched-Capacitor Converters and Their Performance Analysis in a Soft-Charging Operation

Switched-capacitor (SC) converters have gained more interest due to their high power density and appropriateness for small circuit integration. Building a SC DC-to-DC converter with only capacitors and switches is the main reason to seek a higher power density achievement. However, the SC converters suffer dominant losses related to their capacitors and switches. These losses can be determined and optimized by calculating the converter\u27s output impedance in its two asymptotic limits. We proposed a high voltage gain and a very low output impedance power switched-capacitor converter (PSC) with a lower number of components compared to other step-up switched-capacitor topologies. The high output efficiency and the higher power density are two fundamental aspects of the PSC converter. We can eliminate the current transient by applying the soft-charging technique that results a higher power density and a higher efficiency in PSC. The soft-charging operation is more preferable to the soft-switching technique (resonant operation) since it does not require any auxiliary components. Furthermore, soft-charging helps to resize capacitors and reduce the switching frequency of the PSC converter. Furthermore, a split-phase control design is proposed to achieve the complete soft-charging operation in a PSC. The control diagram was designed for a 1-to-4 PSC (two levels of the PSC) which controls eight switches to exhibit eight modes of operation. The complete soft-charging 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. In this research, we also proposed a two-level power switched-capacitor boost converter (PSC-boost) for a high voltage gain application by integrating a PSC converter and a conventional boost converter. The PSC switched-capacitors and the conventional boost converter are respectively cascaded as a primary and a secondary side of the proposed converter. Without alerting of the secondary side (conventional boost), the conversion ratio can be increased by adding more switched-capacitors cells. The proposed converter similarly acts as an MBC; however, it can maintain the rated voltage gain at a higher duty cycle. Unlike the MBC converter, the simulated voltage gain is closer to the calculated voltage gain for PSC-boost converter. In addition to the switched-capacitors insertion, a switched inductor model is used instead of the single inductor in the traditional boost converter. Five switches, five capacitors, seven diodes, and three inductors are used to build a PSC-boost switched-inductor converter. The PSC-boost converter accomplishes 94% efficiency which a higher rated power