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Modular multilevel converters (MMCs) have become increasingly interesting in dc-dc applications, as there is a growing demand for dc-dc converters in high-voltage applications. Power electronics transformers can be used for high step-down ratio dc-dc power conversion, with high power rating and efficiency achieved. However, this arrangement requires a large number of high isolation voltage transformers and a complicated balancing control scheme. To provide a simple solution with inherent voltage balancing, this paper presents a new resonant MMC topology for dc-dc conversion. The proposed converter achieves high-voltage step-down ratio depending on the number of submodules. The converter also exhibits simplicity and scalability with no necessary requirement of high-voltage isolation transformers. By using phase-shift control, a much higher converter operating frequency is achieved compared to the switching frequency. Resonant conversion is achieved between the series inductor and submodule capacitors. The operation principle and theoretical analysis are presented in this paper, which have been verified by experimental results based on a bench-scale prototype. [ABSTRACT FROM AUTHOR]

To solve some problems caused by the ac control method used for the existing modular multilevel dc–dc converter (MMDC), this paper has proposed a new MMDC topology with a wide range of output voltage by means of dc control. By reconstructing the submodule structure, the converter has a power branch and an auxiliary balance branch, which are used to transmit dc power and balance the capacitor voltage, respectively. Both dc analysis and control method are adopted to establish a mathematical model so as to deduce the mathematical relationships between the key electrical parameters. Moreover, what have been done include analyzing the self-balancing principle of the capacitor voltage and the mechanism of the auxiliary balance branch, calculating the related parameters of the capacitor voltage fluctuation, and presenting a dc closed-loop control strategy based on a small-signal model. The analyses of the steady and dynamic states in combination with simulation and experiment show that the proposed converter can stably operate in the mode of dc control, with a large adjustable range of output voltage, a small fluctuation in voltage of the capacitor, and the ability of the inductor to suppress the spike of the auxiliary balance current effectively so as to reduce the impact on the device. [ABSTRACT FROM AUTHOR]

This paper proposes a new design with magnetizing inductance to achieve extended range soft switching of a current-sharing three-phase ac-link active-clamped zero-voltage switching (ZVS) current-fed dc/dc converter for low-voltage dc sources, i.e., battery, fuel cells, etc. The paper explains steady-state operation and presents steady-state analysis and design including magnetizing inductance effect. The proposed converter maintains ZVS of all power semiconductor devices over wide range of load and source voltage. Current sharing results in reduced peak currents and conduction losses. The proposed converter combines the merits of three-phase configuration with zero-current switching of rectifier diodes, making it a competitive topology in the area of power supplies/converters for medium power applications requiring high-voltage amplification ratio. Simulation results using PSIM 9.0 are given to verify the proposed analysis and design. An experimental converter prototype rated at 300 W has been designed, developed, and tested in the laboratory to verify and demonstrate the converter performance over wide variations in input voltage and output power for fuel cell applications. [ABSTRACT FROM PUBLISHER]

Power electronics solutions based on multiple converter configurations offer cost-effective solutions by integrating a number of components at input or output power stages. This paper proposes a new multiinput isolated three-level converter for renewable and sustainable energy systems adopting high dc link voltage. Multiple dc sources are integrated to the three-level dc/dc converter before the isolation stage, resulting in reduced part-count, determining dc link voltage level and allowing flexibility in transformer design. The proposed architecture eliminates two boost switches which are present in the two-stage counterpart. The input inductors are operated in discontinuous conduction mode; thus, power can be shared between input sources through proper selection of input inductors. A low voltage prototype has been designed to serve as a proof of concept. [ABSTRACT FROM PUBLISHER]

Electroactive polymer (EAP) actuators have been investigated to convert electrical energy into mechanical deformation in autonomous microrobots. The use of dielectric EAP actuators comes with several challenges to address requirements such as high excitation voltages, explicit driving signals, and low conversion efficiency. External bulky and heavy power sources are used to generate and provide required excitation voltages. The development of a miniature, high voltage gain, and highly efficient power electronic interface is required to overcome such challenges and enable autonomous operation of miniature robots. In this paper, a bidirectional single-stage resonant dc–dc step-up converter is introduced and developed to efficiently drive high-voltage EAP actuators in mobile microrobots. The converter utilizes resonant capacitors and a coupled inductor as a soft-switched LC network to step up low input voltage. High-frequency soft-switching operation owing to LC resonance allows small footprint of the circuit without suffering from switching losses, which in turn increases the efficiency. The circuit is capable of generating explicit high-voltage actuation signals, with capability of recovering unused energy from EAP actuators. A 4-mm × 8-mm, 100-mg, and 600-mW prototype has been designed and fabricated to drive an in-plane gap-closing electrostatic inchworm motor. Experimental validations have been carried out to verify the circuit's ability to step up voltage from 2 to 100 V and generate two 1-kHz, 100-V driving voltages at 2-nF capacitive loads. [ABSTRACT FROM PUBLISHER]

This paper describes an integrated power management IC with bidirectional current capability, aimed at compensating differences in output current between series-connected cells in concentrating photovoltaic (CPV) systems. The integrated 3.6-MHz power stage allows building a small-form-factor converter per cell. A hysteretic current-mode controller regulates the bidirectional converter's current to equalize neighboring cell voltages. A phase-locked loop controls the inductor current ripple around the average value to stabilize the switching frequency. The use of hysteretic current-mode control with a novel bidirectional senseFET scheme provides inherent current protection and high reliability. The converter can operate from an input voltage as low as 1.8 V and with an inductor current up to $\pm$1.5 A, while achieving a system efficiency above 90% for current mismatches between cells up to 60%. Measurement results show that the converter maximizes the output power of series-connected CPV cells with mismatched output currents. [ABSTRACT FROM AUTHOR]

Obviously for the correct operation of conventional boost converters, all components should work correctly. Interleaved boost converters having several stages, can be used to increase the reliability. So in this paper, a reliability comparison is done between the conventional boost converter and the interleaved structure. Two different operation modes are defined for the interleaved boost converter: half-power and full-power operation modes. The reliability calculation is based on the Markov model of the converters. The power loss effect of converter components on their failure rates, and therefore, on the reliability of converter has been assessed. For the first time different failure rates have been considered for different operation modes. Also a laboratory prototype of a two-stage interleaved boost dc–dc converter has been built up and the failure rate of components in different operation modes are calculated practically. Results show that in addition to other benefits, interleaved structure has higher reliability and as the power increases, there will be a decrease in the reliability. [ABSTRACT FROM AUTHOR]

In power electronics applications, magnetic components are often subjected to nonsinusoidal waveforms, variable frequencies, and dc bias conditions. These operating conditions generate different losses in the core compared to sinusoidal losses provided by manufacturers. In the conception and design stage, lack of precise losses diagnosis has unacceptable effects on system's efficiency, reliability, and power consumption. Since virtual prototyping is used to predict and improve system's behavior before realization, losses and behavior prediction of components is possible. Circuit simulators and their compatible components models are required. This paper is summarized by proposing nonlinear dynamic model of powdered material magnetic core for use in circuit simulators. It includes the material's nonlinear hysteresis behavior with accurate winding and core modeling. The magnetic component model is implemented in circuit simulation software “Simplorer” using VHDL-AMS modeling language. Waveforms and losses of a powder core inductor in a buck converter application are simulated and compared to measured ones. The model is validated for different ripple currents, different loads, and a wide frequency range. DC bias is taken into account in both continuous and discontinuous conduction modes. [ABSTRACT FROM AUTHOR]

In this paper, the general design of a battery buffer system (BBS) consisting of a dc/dc converter and electric double layer capacitors for an electric vehicle is presented. This is intended to save the regenerative braking energy and to support the battery during acceleration. The design of a multiphase converter in interleaved operation with nonideal coupled inductors is stated to minimize volume and power losses while maintaining given current ripple limitations. A reduced sensor current-sharing control method is developed and its correct choice of the sensor position is explained. The peak efficiency of the designed and built converter can be measured to nearly 99%. The corresponding BBS is implemented in a lead-acid battery powered electric lift truck propulsion system. The system operation with and without the BBS is compared to examine the behavior and the overall efficiency. It can be shown that the traction battery stress can be strictly reduced as well as the temperature rise in the battery. Furthermore, the efficiency can be increased in the range of 5-6%. The battery's lifetime improvement is estimated by means of the difference in the temperature rise to approximately 20%. [ABSTRACT FROM AUTHOR]

The first stage of a battery charger in electric vehicles is a power factor correction (PFC) circuit, which creates a second harmonic in the dc link. This harmonic is typically filtered through a bulky dc-link capacitor. In the conventional battery chargers, another dc/dc stage is utilized to regulate the battery current. In this paper, the second harmonic in the dc link is analyzed in detail and a new load current compensation technique is proposed. The proposed technique replaces the second stage dc/dc converter with a bidirectional dc/dc converter connected in parallel with the load, and requires a secondary energy source, i.e., a small-size capacitor. The capacitor injects 180° phase-shifted second harmonic current to the dc link. Thus, the dc-link capacitor can be reduced significantly as it is only sized for high-frequency ripples rather than being sized for low-frequency content. The proposed method is generalized for resistive and battery loads with voltage- and current-source PFC circuits. A 360 W prototype is developed to experimentally verify the proposed technique. A 72 V/10 A·h battery module is charged by filtering an oscillating power of 360 W using a two-quadrant bidirectional dc/dc converter and an UC module, demonstrating a peak charging current of 16 A. [ABSTRACT FROM AUTHOR]

The paper discusses two approaches to multiphase nonisolated dc-dc converter design. An approach based on independent phases is directly compared to an approach using coupled phases. The comparison is performed through theoretical analysis of respective conversion functions, input and output filter requirements, and required input inductor size. Three-dimensional (3-D) high-power-density computer aided design (CAD) models and full-scale 56 kW prototypes based on both approaches were designed, built, and experimentally compared. As expected, the approach with independent phases has a considerable advantage regarding the low-power conversion efficiency where the efficiency can be up to 2% higher than with the coupled approach. On the other hand, the design with coupled inductors can reach power density as high as two times that of the independent phase design (87 kW/L versus 44.2 kW/L). Therefore, the use of coupled inductors may be very beneficial for space critical applications. In case of the electric vehicle power train, both factors may be very important and the suitable approach should be chosen based on system design priorities. [ABSTRACT FROM AUTHOR]

This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case. [ABSTRACT FROM AUTHOR]

A digital-control single-inductor triple-output (SITO) dc-dc converter is presented in this paper. The dc-dc converter features a proposed pre-sub-period inductor-current control that can deliver more load-current by individual subconverter and reduce crossregulation among different subconverters simultaneously. The proposed digital-control SITO dc-dc converter is implemented by a commercial 0.35-μm CMOS process. The chip area is 1600 μm × 1700 μm. The dc-dc converter is capable to be configured as two buck subconverters and one boost subconverter. The measured maximum power efficiency is 83.5%. [ABSTRACT FROM AUTHOR]

In this paper, a new single-switch soft-switching isolated converter is introduced. In the proposed converter, the transformer parasitic elements are used as resonant elements to transfer energy and to attain soft-switching condition. The proposed converter does not require output inductor just like the flyback converter, and the transformer core does not store energy just like the forward converter. The proposed converter is analyzed and its advantages over conventional converters are discussed. Also, experimental results are presented to justify the validity of theoretical analysis. [ABSTRACT FROM AUTHOR]

Within the photovoltaic (PV) power-generation market, the ac PV module has shown obvious growth. However, a high voltage gain converter is essential for the module's grid connection through a dc-ac inverter. This paper proposes a converter that employs a floating active switch to isolate energy from the PV panel when the ac module is off; this particular design protects installers and users from electrical hazards. Without extreme duty ratios and the numerous turns-ratios of a coupled inductor, this converter achieves a high step-up voltage-conversion ratio; the leakage inductor energy of the coupled inductor is efficiently recycled to the load. These features explain the module's high-efficiency performance. The detailed operating principles and steady-state analyses of continuous, discontinuous, and boundary conduction modes are described. A 15 V input voltage, 200 V output voltage, and 100 W output power prototype circuit of the proposed converter has been implemented; its maximum efficiency is up to 95.3% and full-load efficiency is 92.3%. [ABSTRACT FROM AUTHOR]

This paper presents an alternative to the traditional dc-dc converter interfacing the battery with the inverter dc bus in plug-in hybrid electric vehicle (HEV) traction drives. The boost converter used in commercial HEVs meets with obstacles when it comes to upgrading the power rating and achieving high efficiency while downsizing the converter. A four-level flying-capacitor dc-dc converter is explored that can overcome these drawbacks by dramatically reducing the inductance requirement. A special case of the four-level converter, the 3X dc-dc converter, operates at three discrete output/input voltage ratios, thus further reducing the inductance requirement to a minimal value (almost zero). When further compared to its switched-capacitor dc-dc converter counterparts, the 3X dc-dc converter can be operated at variable output/input voltage ratios without sacrificing efficiency, and it lowers the capacitance requirement by utilizing the parasitic inductance. The operating principle, current ripple analysis, the transient control to limit the inrush current, and power loss analysis are introduced. Experimental results of a 55-kW prototype are provided to demonstrate the principle and analysis of this topology. [ABSTRACT FROM AUTHOR]

Multiport dc/dc converters are widely employed in hybrid energy generation systems to provide stable power to key loads with high power density. In this paper, the switch duty cycle and the phase angle of the interleaved converters are employed as two control freedoms to achieve decoupled voltage regulation within a certain operating range among different ports, which is referred to as pulsewidth modulation plus phase angle shift (PPAS) control scheme. An interleaved bidirectional buck-boost converter and a full-bridge converter are integrated together to derive a combined three-port dc/dc converter for photovoltaic (PV)-battery hybrid energy systems, which is adopted as a typical example to explore the clear performance of the proposed PPAS control strategy. The bidirectional buck-boost converter and the full-bridge converter share the same power MOSFETs in the primary side, which simplifies the circuit structure and improves the power density. The duty cycle of the interleaved bidirectional buck-boost converter is adopted to realize the maximum power point tracking and the voltage balance between the battery and the PV cell in the primary side. Furthermore, the phase angle of the interleaved buck-boost converter is employed as another control freedom to achieve accurate secondary output voltage regulation. Finally, a 100-W PV-Battery energy system is designed and tested to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

A new 16-phase interleaved bidirectional dc/dc converter is developed featuring smaller input/output filters, faster dynamic response and lower device stress than conventional designs, for hybrid vehicle applications. The converter is connected between the ultracapacitor (UC) pack and the battery pack in a multisource energy storage system of a hybrid vehicle. Typically, multiphase interleaved converters require a current control loop in each phase to avoid imbalanced current between phases. This increases system cost and control complexity. In this paper, in order to minimize imbalance currents and remove the current control loop in each phase, the converter is designed to operate in discontinuous conduction mode (DCM). The high current ripple associated with DCM operation is then alleviated by interleaving. The design, construction, and testing of an experimental hardware prototype is presented, with the test results included. Finally, a novel soft switch topology for DCM operation is proposed for future research, to achieve zero-voltage switching (ZVS), or zero-current switching (ZCS) in all transitions. [ABSTRACT FROM AUTHOR]

Maximum power transfer in solar microgrid applications is achieved by impedance matching with a dc–dc converter with maximum power point tracking by the incremental conductance method. Regulation and dynamic control is achieved by operating with continuous conduction. It can be shown that under stable operation, the required output inductor has an inductance versus current characteristic, whereby the inductance falls off with increasing current, corresponding to increasing incident solar radiation. This paper describes how a variable inductor whereby the inductor core progressively saturates with increasing current meets this requirement and has the advantage of reducing the overall size of the inductor by up to 75% and increases the operating range of the tracker to recover solar energy at low solar levels. [ABSTRACT FROM AUTHOR]