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In the paper by Patra et al., a single-inductor multiple-output switcher was presented to produce buck, boost, and inverted outputs simultaneously. Unfortunately, this study showed some unexpected mistakes, especially in state-space equations and in the calculation of output voltages. The objective of this note was to provide correct analysis and rectify the errors in this paper. Some tables and equations have been modified that were present in the initial draft of this paper. The obtained parameters in this work could be an effective supplement and extension for the original work in the paper by Patra et al. [ABSTRACT FROM AUTHOR]

The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and consequential current distortion of the three-phase load in the variable 360–800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d-axis open-loop duty cycle to inductor current transfer function, loop-gain of d-axis current controller with 3.8 kHz bandwidth and variable grid frequency 360–800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion. [ABSTRACT FROM AUTHOR]

Energy harvesting has attracted increased attention recently. Energy sources are present all around us, such as, mechanical vibrations, stress, strain, waste heat, sunlight or room light, electromagnetic rays, and chemical or biological sources. Vibration generators based on piezoelectric elements have been highlighted as low-power sources; however, their output power is very low, around the milliwatt or microwatt level, and thus, improving their performance is necessary to make the generated power usable. This paper investigates the use of passive devices to improve output characteristics of the vibration generators. The proposed circuits are a resonator and a passive rectifier. The proposed resonator consists of a parallel inductor and capacitor for $LC$ resonance. The $LC$ resonance equivalently reduces the internal capacitor of the piezoelectric elements. As a result, the output voltage and power are increased compared with that of conventional circuits. In addition, a boost-type current-improving passive rectifier is applied as the passive rectifier. The validity of the proposed circuit is numerically and experimentally verified. [ABSTRACT FROM AUTHOR]

This paper presents two high-voltage direct-current circuit breakers that have the capability of interrupting a short-circuit current within several milliseconds. They consist of a current-limit inductor, a current-control inductor, one or two mechanical switches, and a multilevel converter with phase-shifted-carrier pulsewidth modulation. The two breakers can commutate an almost zero current from the main branch to the auxiliary branch. This paper proposes an original breaker with low-voltage and high-voltage mechanical switches connected in series, followed by a simplified breaker with a single high-voltage mechanical switch. Finally, this paper includes experimental verification by two slightly different downscaled breakers rated at 300 Vdc and 150 Adc, as well as confirmation of an actual original breaker by circuit simulation using the “PSCAD/EMTDC” software package. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency single-phase T-type boundary conduction mode (BCM) microinverter. The conventional full-bridge BCM microinverter has achieved zero voltage switching (ZVS) and thereby improved the efficiency, but it suffers from high switching losses under light load conditions. The proposed T-type BCM microinverter reserves ZVS and uses a multilevel technique to further decrease the switching losses. The BCM operation with multilevel technique will have too low switching frequency when the grid voltage approaches half of the dc link voltage. To solve this problem, this paper adopts a third operation mode for the T-type switching leg to maintain the switching frequency above a minimum value. The corresponding mode transitions are also detailed to ensure a smooth operation. Because of the turn-offdelay of the freewheeling transistor, the actual lower current boundary deviates from the programmed one, which will distort output current. To address this issue, this paper also proposes a boundary compensation method. A prototype has been built for performance verification, which can test both full-bridge and T-type topology. Compared with the full-bridge BCM microinverter, the proposed T-type BCM microinverter has a higher efficiency over the whole load range. [ABSTRACT FROM AUTHOR]

This paper discusses dynamic behavior of a dual-active-bridge (DAB) dc–dc converter. Conventional phase-shift control methods for the DAB converter may cause dc offsets in both inductor current and transformer magnetizing current in transient states. The dc offset in the inductor current would introduce an excessive peak current through the switching devices. The dc offset in the magnetizing current may induce magnetic-flux saturation. Conventional methods simultaneously turn on and off the diagonal switches in each H-bridge converter and produce a square-wave voltage with a 50% duty ratio. In contrast, the proposed method in this paper independently controls each switch to modify the duty ratio in transient states. This paper clearly derives the requirements of each switch to eliminate the dc offsets in both currents with a settling time shorter than half the switching period. Experimental results using a 5-kW 20-kHz system verify the validity of the proposed control method, which is effective not only in a single step change, but also in a continuous change in the phase-shift reference. [ABSTRACT FROM AUTHOR]

The use of three-dimensional (3D) thermal simulations of magnetic components for power converters is limited to validation of final designs due to time consumption. A two-step homogenization is proposed to simplify them, while keeping good accuracy. The required equations and some guidelines are described in this paper. It can be applied to solid round wire, litz wire, or foil wound magnetic components. Considerations to extend its use to transformers, including the use of interleaving techniques and insulating tape, are explained. This method can reduce the computation time of 3-D simulations (seven times faster than usual simulations) while the convergence is assured even for complex structures or cases with litz wire. Finally, the method is experimentally validated with DC and AC excitation. [ABSTRACT FROM AUTHOR]

Improving the power density of a power converter has many benefits for systems integration. Aspects such as thermal management, weight, conformation to mounting locations, and the footprint of the converter all become critical factors as systems continue to scale down in size. The flying capacitor multilevel converter topology is of interest because it has characteristics which contribute to high power density. This paper presents a quasi-square-wave zero-voltage switching (ZVS) multilevel dc–dc converter. ZVS greatly reduces switching losses and enables high-frequency operation of the converter. A hardware prototype is implemented, built on a flexible polyimide substrate circuit board. Experimental results show a peak system efficiency above 98.1%, an effective switching frequency of up to 3 MHz, and a power output of 250 W. [ABSTRACT FROM AUTHOR]

Various methods have been presented in the past to emulate the electrical behavior of modular multilevel converters (MMCs). To meet the demands for the reliability aspect study of MMCs, this paper proposes a viable setup to emulate the thermal behavior and to investigate its feasibility for reliability testing and thermal model validation of the power modules in the MMC. The proposed mission profile emulator has three distinctive features: 1) capable of emulating and measuring the thermal stresses of power modules; 2) capable of implementing practical switching profile as a full-scale MMC; and 3) having significantly reduced requirement for dc power supply compared to existing setups used for electrical studies. Theoretical discussions, and simulations as well as the experimental results are presented to demonstrate the capability of the mission profile emulator both electrically and thermally. Moreover, this paper is accompanied by a video demonstrating how to measure the junction temperature of the power devices using the optical fiber and the thermal camera. [ABSTRACT FROM AUTHOR]

Analytical expressions that have been derived to calculate ac resistance and losses of magnetic devices at high frequencies have primarily used a one-dimensional approximation, and have used Cartesian coordinates or approximations that are equivalent to Cartesian coordinates. The result is Dowell's equation. This paper examines the effect of winding curvature on the losses relative to Dowell's equation by solving the problem completely in cylindrical coordinates. The error in Dowell's equation relative to a full cylindrical solution is found to be as great as 33% for some designs. A mathematical model is derived for the relative error between the two solutions, which can be used to assess the accuracy of Dowell's equation for a particular design, as well as a correction factor for Dowell's equation. The corrected Dowell's equation using the model is validated using finite-element analysis simulations as well as previously published experimental data. This paper is accompanied by Python codes to generate all data and figures used in the paper, a Python object that implements the derived mathematical model, and Lua scripts to run the finite-element simulations using FEMM. [ABSTRACT FROM AUTHOR]

In this paper, a new dc–dc high voltage gain converter with low-voltage stresses on switches and diodes is proposed. Even though, in the topology of the proposed converter there are not any coupled inductors and transformer utilized, the voltage conversion ratio of the proposed converter is considerable in comparison to its conventional types. Also, two switches of the proposed converter provide longer charge time for two inductors which make the proposed converter capable of providing high voltage gain without preselecting extremely large duty cycles. In addition, the number of power circuit components of the proposed structure are few and the voltage stresses on semiconductor elements are low. In this paper, theoretical analysis of the proposed converter for each operating mode is presented and the voltage gain, voltage and average current stresses of elements, maximum input current ripple, efficiency and equations of critical inductances are calculated. Moreover, to verify the capability of the proposed converter, it is comprehensively compared with other similar recently presented high voltage gain boost converters. Finally, an approximately 12 V/380 V and 520-W prototype of the proposed converter is implemented in laboratory to demonstrate its practical performance, then, the experimental results reconfirm each other and theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive multi-loop control scheme for inverters interlinking dc voltage sources to single-phase, low-voltage ac grids. Control self-adaptation is particularly useful in the case of weak grids that, due to frequent physical modifications (e.g., network reconfigurations and disconnection of generators/loads) and intrinsic lack of inertia, present strongly time-variant characteristics. The solution presented in this paper is based on a high-performance converter controller with auto-tuning capabilities. It is shown that the applied auto-tuning method can significantly widen the stability region of the interlinking converter, covering a broad range of grid impedance values. In addition, within the stable region, the controller maintains the nominal performance. Experimental results are reported validating the proposed approach in realistic operating conditions, including grid voltage distortion and variations of amplitude and frequency. [ABSTRACT FROM AUTHOR]

This paper presents an interleaved boost converter with a bifold Dickson voltage multiplier suitable for interfacing low-voltage renewable energy sources to high-voltage distribution buses and other applications that require a high-voltage-gain conversion ratio. The proposed converter was constructed from two stages: an interleaved boost stage, which contains two inductors operated by two low-side active switches, and a voltage multiplier cell (VMC) stage, which mainly consists of diodes and capacitors to increase the overall voltage gain. The proposed converter offers a high-voltage-gain ratio with low voltage stress on the semiconductor switches as well as the passive components. This allows the selection of efficient and compact components. Moreover, the required inductance that ensures operation in the continuous conduction mode (CCM) is lower than the one in the conventional interleaved boost converter. The distinction of the proposed converter is that the inductors’ currents are equal, regardless of the number of VMCs. Equal sharing of interleaved boost-stage currents reduces the conduction loss in the active switches as well as the inductors and thus improves the overall efficiency, as the conduction power loss is a quadratic function. In this paper, the theory of operation and steady-state analysis of the proposed converter are illustrated and verified by simulation results. A $\text{200-W}$ hardware prototype was implemented to convert a $\text{20-V}$ input source to a $\text{400-V}$ dc load and validate both the theory and the simulation. [ABSTRACT FROM AUTHOR]

In a dual active bridge (DAB) dc–dc converter, modulating the phase-shift ratios can suppress reactive power and increase the efficiency under non-unity voltage gain conditions. Derivation of the optimal phase-shift ratios to achieve the minimum reactive power is challenging because a DAB can operate in four different scenarios (forward/backward, buck/boost) and each scenario has five operating modes. This paper first introduces a transformation in which different DAB operating scenarios (forward/backward, buck/boost) can be equivalent to one another; then optimization of only one scenario (forward/buck) is required. Next, for the five modes in forward/buck scenario, based on a graphical method, this paper proves that each operating point of Modes 1, 2, and 5 can be mapped into that of Mode 3 with lower conduction losses, and only two modes require detailed analysis. The optimization process of these two modes are derived step-by-step. Global optimal phase-shift signals that minimize the reactive power under four different DAB operating scenarios (forward/backward, buck/boost) are presented. A simple table and control block diagram are presented for practical implementation of global reactive-power minimization control. Experimental comparison with other modulation schemes verifies the efficiency improvement of the proposed control method. [ABSTRACT FROM AUTHOR]

In this paper, a current controller for a parallel operation of inverters is described. When inverters operate in parallel, it is a well-known fact that the inverter current is composed of the average current (AVC) and the zero-sequence circulating current (henceforth ZSCC), which inevitably flows between inverters under the parallel operation. Considering this, previous studies concentrated on reducing ZSCC. However, in this paper, it is found that the inverter current has another component, a differential current, in addition to the two components of AVC and ZSCC. Based on these three decomposed current components, three equivalent circuits are derived from n-paralleled inverters. To minimize the differential current and improve the regulation performance of the total output phase current, a decomposed current control scheme is proposed from equivalent circuit models. The proposed algorithm is applied to a system consisting of three paralleled two-level inverters with small shared inductance whose dc links are connected in common. Additionally, synchronous pulsewidth modulation is employed as the PWM method for each inverter. The proposed current controller is compared with two conventional current controllers, one where each inverter controls its own currents and the other where only AVC is controlled. Through experiments, it is shown that these conventional controllers have limitations and the proposed current controller overcomes these limitations. The effectiveness and feasibility of the proposed control scheme are verified through experimental results. Especially, both theoretical analysis and experiment results verify that the proposed method is robust with regard to parameter errors. [ABSTRACT FROM AUTHOR]

Switching behavior analysis is an indispensable step for evaluating the steady-state performance of a bidirectional dc–dc converter and a prerequisite for soft-switching modulation design. For dual-bridge series resonant dc–dc converters (DBSRCs), the commonly used fundamental harmonic approximation (FHA) does not usually provide predictions accurate enough for reliable analysis and design. This paper discloses the exact closed-form solution for the zero-voltage switching (ZVS) operation conditions of DBSRCs for the most general case, in which all modulation quantities—i.e., phase shift, duty cycles, and switching frequency—are included. The proposed approach relies on a geometrical analysis of the converter state-plane trajectory, and allows us to analytically predict the ZVS or hard-switching state of any switch and for any given converter operating point. By inherently capturing the effects of all tank harmonics, the model disclosed in this paper shows higher accuracy than the conventional FHA-based approach, and translates into a practical tool for ZVS prediction and optimization at the converter design stage. Based on the derived analytical results, switching behavior of DBSRCs with minimum rms current trajectory (MCT) modulation is investigated, and an effective design choice of resonant-to-switching frequency ratio is presented, which contributes to reduced switching losses and enhanced efficiency. Furthermore, a variable frequency modulation scheme is formulated, achieving ZVS operation of all transistors over a wide input/output voltage range and efficiency improvement versus MCT technique. The analysis and conclusions are validated via extensive experimental tests on a 700 W DBSRC prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a variable off-time control method for a single-phase microinverter operating in the discontinuous conduction mode (DCM) for efficiency improvement. First, the fixed off-time control method is analyzed. The concept is to fix the off-time of the active switch throughout a line cycle for all output powers and scale the on-time of the active switch to shape a sinusoidal output current. Then, based on the fixed off-time control method, a variable off-time control method is proposed to modulate the preset fixed off-time in order to decrease the switching frequency during ac line zero-crossings and light load conditions. Compared with existed fixed-frequency DCM control or boundary conduction mode control, the variable off-time control is more flexible to optimize the efficiency under different load conditions as the switching frequency range can be automatically adjusted according to the output power. The switching frequency is high at heavy loads to limit the maximum peak current and is low at light loads to increase the light load efficiency. In addition, a predictive on-time method is adopted to simplify inverter control and reduce hardware costs. The parameter design principle is detailed in this paper. A 300 W prototype is built to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for evaluating self-capacitances and parasitic capacitors between physically adjacent turns in multiconductor systems—with a special focus on single-layer air-core inductors. To this end, the paper proposes the use of standard cells, which correspond to a minimal and basic turn, layer, or macrolevel arrangement of a winding in reference to its patterns of stored electrostatic energy. A standard cell embraces mathematical rules derived by means of a curve fitting approach through a set of finite element analysis (FEA) simulations. Besides, it is applied in a matching routine wherein self- and stray capacitances are evaluated according to the relative position of each turn, layer, or macrolevel arrangement along the length of the winding. Finally, the analytical technique is validated by comparing frequency-domain results obtained from an implemented SPICE model and laboratory measurements. [ABSTRACT FROM PUBLISHER]

In recent years, very high frequency (VHF) converter has attracted much attention. However, with rich parasitic parameters and complex resonance links, there are some great difficulties to the modeling of such systems. Taking the on-off controlled VHF resonant boost converter as an example, this paper presents an accurate modeling and analysis method that considers multiple parasitic parameters. First, the closed-loop VHF converter system is divided into a main network and a parasitic oscillation network. Then, based on the operation analysis, an equivalent circuit model characterized by a time-varying input voltage source and two variable duty-cycle controlled switches is proposed. It worth noting that both the time-varying input and the controlled switches take into account the influences of the parameters. Furthermore, the periodic approximate analytical solution of the output voltage in the on stage is obtained by using the equivalent small parameter method to the proposed circuit model. And then combining the solution of the parasitic oscillation network and on-off state switching conditions, the steady-state waveform of output voltage can be obtained quickly. Finally, a prototype with operating frequency of 21.44 MHz is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper studies the high power density bidirectional dc–dc converter with interleaving, soft-switching, and near critical conduction mode (near-CRM) operation. Systematic design and control methods are proposed to enhance the effectiveness of passive currents balancing between multiple interleaved phases without using individual phase current feedbacks. This paper first analyzes the zero voltage turn-on operation, including the turn-off energy diversion by the added snubber capacitor and the turn-off resonance models. Second, the intrinsic inverse co-relation between the phase current deviation and the resulting effective duty cycles variation is quantitatively formulated and modeled as a closed-loop mechanism that balances the currents passively. Then, the design constraints of the system parameters including the snubber capacitance, dead time, and valley currents of the near-CRM mode are formulated to guarantee the effectiveness of counteracting the current unbalance. Finally, a variable switching frequency control is proposed to actively control the valley current and maintain the current balancing effectiveness throughout the operating range. An IGBT-based 20-kW three-phase interleaved prototype with the maximum efficiency of 99.1% is constructed to verify the proposed design and control methods. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active-clamp forward converter (ACFC) with a lossless-snubber on the secondary-side, which combines a resonant capacitor and a clamping diode with an output inductor in parallel. The conventional ACFC achieves zero-voltage-switching on switches of the primary-side during dead time for reducing the switching loss and voltage spike. Unfortunately, on the secondary-side of transformer, the voltage spike damages the free-wheeling diode and rectifier diode due to the reverse recovery current and junction-capacitor of the diode and leakage inductance of the transformer. This paper proposes a lossless-snubber on the secondary-side operation for reducing the voltage spike on the free-wheeling diode and forward-rectifier diode. Therefore, the converter proposed in this paper is suitable for high-output-current applications. Experimental results are shown to verify the analysis and design procedure of the proposed forward converter. [ABSTRACT FROM AUTHOR]

The instantaneous output power of the two-stage single-phase grid-connected photovoltaic (PV) inverter pulsates at twice the line frequency ($2f_{{\text{o}}}$), generating second harmonic current (SHC) in the front-end dc–dc converter and PV panel, which will affect the maximum power point tracking operation and deteriorate the overall conversion efficiency. The generating mechanism of the SHC is analyzed in this paper and it is pointed that in order to eliminate the SHC in the front-end dc–dc converter and PV panel, the voltage loop gain of the front-end dc–dc converter should be high enough at $2f_{{\text{o}}}$. Since there is a −180° phase abrupt at the resonant frequency of the input side filter capacitor and the inductor, the system may be unstable. To cope with this problem, the inductor current feedback active-damping scheme (ADS) is adopted. For further improving the loop gain at $2f_{{\text{o}}}$ , proportional–integral–resonant regulator with ADS (PIR + ADS) is proposed in this paper. Besides, a step-by-step closed-loop parameters design method is presented. Finally, a 3-kW two-stage single-phase grid-connected PV inverter has been fabricated and tested, and the experimental results verify the feasibility of the proposed control schemes. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions. [ABSTRACT FROM AUTHOR]

Recent studies have proved that sustainable saturation operation of Ferrite Power Inductors (FPIs) allows reducing the inductor size and increasing the power density in Switch-Mode Power Supply (SMPS) applications. This paper discusses a new behavioral model for reliable prediction of ac power loss in FPIs, including the effects of saturation. The new model has been identified by means of the Genetic Programming (GP) algorithm combined with a Multi-Objective Optimization (MOO) technique, starting from large sets of power loss experimental measurements. The proposed ac power loss model uses as input variables the voltage and switching frequency imposed to the inductor by the SMPS operation, while the dc inductor current is used as a parameter expressing the impact of saturation. Such quantities can be easily determined for whatever converter topology and in real-world switching operation, thus confirming the readiness and the easiness-to-use of the proposed behavioral model. The results of experimental tests presented in this paper prove the reliability of the power loss predictions, also by correctly accounting for the impact of inductors saturation. [ABSTRACT FROM AUTHOR]

The influence of a filter inductor on the steady-state performance of a parallel-type resonant converter is elaborated and analyzed in this paper. By steady-state operation analysis, it is shown that the ripple current of the filter inductor results in an inaccurate prediction of fundamental harmonic approximation (FHA), and such problem would become serious when the filter inductance is small. In order to portray such feature, an improved fundamental harmonic approximation (IFHA) is proposed. Unlike an FHA equivalent circuit, an equivalent inductor is added to the ac resistance parallelly in an IFHA equivalent circuit. Due to that, the equivalent inductor branch takes account of the ripple current of the filter inductor, and the IFHA is expected to own higher accuracy and can be used in a parameter design procedure. In this paper, the equivalent inductor expressions of full-bridge rectifier and current-doubler rectifier are derived as examples. In order to verify the theoretical analysis, a 500 W LCC resonant converter is built as a prototype. The close-loop experiment results show that small filter inductance would lead to the failure of output voltage regulation and hard-switching operation of power switches. And open-loop experiment results show the IFHA gives more accurate predictions than those of FHA. [ABSTRACT FROM AUTHOR]

In data center and telecommunication power supplies, the front-end dc–dc stage is required to operate with a wide input voltage range to provide hold-up time when ac input fails. Conventional LLC converter serving as the dc–dc stage is not suitable for this requirement, as the normal operation efficiency (at 400 V input) will be penalized once the converter is designed to achieve high peak gain (wide input voltage range). This paper examined the operation of the LCLC converter and revealed that the LCLC converter could be essentially equivalent to a set of LLC converters with different magnetizing inductors that are automatically adjusted for different input voltages. In nominal 400 V input operation, the LCLC converter behaves like an LLC converter with large magnetizing inductor, thus the resonant current is small. In the hold-up period, when the input voltage reduces, the equivalent magnetizing inductor will reduce together with switching frequency reducing, thus the converter achieves high peak gain. In this paper, a new design methodology is also proposed to achieve optimal utilization of the two resonant capacitors for high power application. To verify the effectiveness of the LCLC converter for hold-up operation, comprehensive analysis has been conducted; a detailed step by step design example based on capacitor voltage stress is introduced; an experimental LCLC prototype optimized at 400 V, with input voltage range of 250–400 V and 12 V/500 W as output has been presented. [ABSTRACT FROM AUTHOR]

This paper proposes an improved zero current detection for critical conduction mode (CRM) control, which can compensate the input current distortion caused by the signal propagation delay and the existence of the negative resonance current. A unified variable on-time calculation method is also proposed to unify the formulas under the zero-voltage-switching condition and the valley-switching condition. Since these two methods are dependent on the boost inductance and device junction capacitance, which may be different from the nominal values, effort is needed to compensate the deviation on these two parameters. In this paper, an online monitoring method is proposed to compensate the numerical deviation. The proposed method only needs to sense the input voltage, output voltage, and the reverse flow time of the inductor current, leading to a high power quality in the entire input and load conditions. The experimental results of the proposed methods are demonstrated on a 200-W GaN-based CRM boost power factor correction prototype. With the proposed methods, the input current total harmonic distortion is only 0.78% at 110 VAC input with full load and 2.1% at 220 VAC input with full load. [ABSTRACT FROM AUTHOR]

In this paper, a new soft-switching bridgeless single-phase power factor correction (PFC) converter is presented and analyzed. Employing an auxiliary switch, the input current dead angle that is the main drawback of the existing buck-type PFCs is omitted, and thus, the power factor (PF) is improved, which is the main contribution of the paper. Proposed PFC converter operates under discontinuous conduction mode (DCM) and draws sinusoidal input current from power supply inherently. All switches and diodes are turnedonandoffunder soft switching, which leads to low switching losses and elimination of diode reverse recovery problems. Also, minimum numbers of semiconductor devices are in the power flow path that reduce the conduction losses. A 120-W laboratory prototype is implemented and experimental results verify the validity of theoretical analysis and show efficiency of 92.1%. In addition, total harmonic distortion (THD) of 3.3% is achieved and the input current harmonics complies with IEC61000-3-2 Class D requirements. [ABSTRACT FROM AUTHOR]

A high step-up dc–dc converter is proposed in this paper. The presented converter benefits from some advantages such as high voltage gain and continuous input current, which makes it suitable for the renewable energy applications. The presented converter is based on the SEPIC converter. However, the converter voltage gain is improved by employing a coupled inductor and two voltage multipliers. A passive clamp circuit is also added to the proposed converter that increases the voltage gain and reduces the voltage stress on the main switch. Thus, a switch with low $R_{{\text{DS(on)}}}$ will be needed that decreases the conduction loss. Besides, the voltage stress on the output diode in the proposed converter is reduced, which alleviates reverse recovery problem. The steady-state analysis of the proposed converter is discussed in this paper. The analysis is verified with experimental results under the output power of 245 W. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-efficiency photovoltaic (PV) converter for grid connection through a high-leg delta transformer. The converter is composed of a symmetrically connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. As a result, this circuit configuration enables to reduce the power losses in both boost converter and inverters. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in the switching power loss. Experimental results confirm that the proposed circuit configuration makes it possible to improve its European efficiency from 91.6% to 94.5%. Moreover, system performance is evaluated on the assumption of maximum power point tracking operation. [ABSTRACT FROM AUTHOR]

This paper focuses on the zero-voltage ride-through (ZVRT) capability of a transformerless back-to-back (BTB) system intended for installation on a power distribution system with many distributed power generators. The BTB system consists of two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) and their ac sides are connected to a common ac mains via ac-link inductors. This paper provides an experimental discussion on the DSCC-based BTB system under voltage sags by using a three-phase 200-V 10-kW downscaled system. Experimental results show that the BTB system is equipped with ZVRT capability without causing any overvoltage and/or overcurrent even under the most severe voltage sags. [ABSTRACT FROM PUBLISHER]

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation. [ABSTRACT FROM PUBLISHER]

This paper presents the design, modeling, and characterization of 3-D-printed air-core inductors for high-frequency power electronics circuits. The use of 3-D modeling techniques to make passive components extends the design flexibility and addresses some of the fabrication limitations of traditional processes. Recent work [1]– [9] has demonstrated the feasibility of incorporating air-core inductors in high-frequency ( $>$10 MHz) switching power converters. These implementations have used discrete wire wound solenoids and toroids, and planar components that use printed circuit board traces or microfabrication techniques to make air-core inductors. However, realizations of such components have limitations in performance and applicability including open paths conducive to the flow of leakage fields, and difficulties in achieving optimal cross section to minimize loss. Along with the current effort of involving 3-D printing technology to make inductors [10], [11], we propose the use of 3-D printing and casting/plating techniques as a simple and accessible alternative that adds flexibility and functionality to the air-core inductor design for high-frequency power conversion at moderate to high-power (e.g., tens to thousands of watts) and high-voltage (greater than 100 V) levels. In this paper, we present several examples of air-core inductors realized using 3-D printing and casting/plating techniques to give an idea of the geometries that are possible to design. Moreover, we show that some of these designs can lead to improved electrical performance. This paper also describes the tools used by the authors to design, fabricate, and characterize the electromagnetic performance of the air-core inductors. The software used to generate the 3-D scaffolds for the inductors are freely available and easily accessible. Readers are encouraged to explore more possibilities of geometries that can lead to better performance with the ease of manufacturing. As progress in additive manufacturing continues, we envision 3-D printing of a complete scaffold structure that after plating (or casting) will contain all resonant passive components of an RF switching converter. Toward this goal, we present a 70-W prototype 27.12-MHz resonant inverter that incorporates some of the 3-D-printed components developed for this paper. [ABSTRACT FROM AUTHOR]

This paper presents the modular multilevel cascade converter based on double-star chopper-cells, which is intended for grid connection to medium-voltage power systems without using line-frequency transformers. The converter is characterized by a modular arm structure consisting of cascade connection of multiple bidirectional pulsewidth modulation chopper-cells with floating dc capacitors. This arm structure requires voltage-balancing control of all the dc capacitors. However, the voltage control combining an averaging control with an individual-balancing control imposes certain limitations on operating conditions. This paper proposes an arm-balancing control to achieve voltage balancing under all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is confirmed by computer simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper presents a novel dc–dc converter incorporating a distributed impedance-source network ( Z-source network, or Z-network) to achieve the buck (step-down) and boost (step-up) function of a transformer-isolated dc–dc converter. In this paper, the distributed impedance source network composed of an array of inductors and capacitors is coupled between power source and main switching devices. The great and unique feature about the distributed impedance source network dc–dc converter is that unlike the traditional V-source or I-source converters, it can be open- and short-circuited without damaging switching devices. Therefore, the desired buck and boost function can be achieved. Moreover, converter reliability can be greatly improved. A dc–dc converter using this proposed concept is built and tested. Its performances are verified with experimental results. [ABSTRACT FROM PUBLISHER]

Constant on-time V^2 control for point-of-load buck converters has instability issues in the cases that the output capacitors' RC time constants are small. This paper intensively studies the proposed solution using capacitor current ramp compensation, which is a superior solution featuring fast response and universality. A frequency-domain small-signal model based on describing function method is proposed in this paper. The time-domain large-signal response to the load step change is analyzed. The analysis illustrates the unique transient response behaviors of the capacitor current ramp compensated V^2 control. The design optimization methodology based on frequency-domain and time-domain analysis is presented. The proposed model and the design guidelines are verified by the experimental results. [ABSTRACT FROM AUTHOR]

Class $E^2$ DC–DC converter composed of Class $E$ power amplifier (PA) and rectifier is a promising candidate for MHz wireless power transfer. It is soft-switching based and able to achieve high efficiency at MHz frequency. However, the converter implemented through traditional static design is sensitive to the variations of operation condition. Its performance gets deteriorated when DC load and coil coupling deviate from their respective optimum values. This paper demonstrates that the degradation of system efficiency is mostly due to the mismatch of PA load, and the efficiency drop can be efficiently improved by adding an L-type impedance matching network (IMN) after PA. A fixed IMN is sufficient to maintain a high efficiency, while a tunable IMN is required to ensure stable output power when operation condition dramatically changes. Key techniques, particularly system-level optimization, are discussed in this paper that ensure high efficiency over a wide range of variation in operation condition and also with reduced capacitor/inductor tuning ranges in the IMN. The 6.78-MHz Class $E^2$ DC–DC converters with and without the fixed/tunable IMN are fabricated and measured for validation purposes. The experimental results show that both high efficiency ( $>$66%) and stable output power (around 9 W) are maintained for the tunable converter when there are variations in the DC load and coil coupling. [ABSTRACT FROM AUTHOR]

To support the development of high-frequency ac microgrids in terms of compact design, high-voltage gain and low total harmonic distortion (THD), a buck–boost dual-leg-integrated step-up inverter is proposed in this paper. The inverter is formed by integrating a buck–boost converter into a conventional single-phase full-bridge inverter by sharing the upper switch and the body diode of the lower switch in both bridge-legs. Consequently, the component count is significantly reduced over the step-up inverter counterparts. In addition, to address the drawbacks of hybrid modulation methods adopted by existing dual-leg-integrated inverters, such as double-variable control, and high THD of output voltage/current at high input voltage and heavy load conditions, unipolar frequency doubling sinusoidal pulse width modulation scheme is adopted in this inverter. As a result, the modulation ratio M becomes the only control variable to regulate the output voltage/current and the control is simplified. The THD of the proposed inverter output can remain low throughout the entire input voltage range and load power range. This paper presents the topology derivation procedure, operation principle, and steady-state characteristics of the proposed inverter. To validate the effectiveness of theory, experimental results of a 400 W hardware prototype, where the output voltage frequency is at 500 Hz, are reported. [ABSTRACT FROM PUBLISHER]

Recently, a magnetic pad called the tripolar pad (TPP) has been introduced for inductive power transfer (IPT) systems. This paper evaluates the effective coupling factor and leakage magnetic field of a 20-kW IPT system that uses a combination of TPP and circular pad (CP) topologies over a range of lateral displacements. The results show that the effective coupling factor and the leakage magnetic field of the TPP–TPP system are substantially better when the secondary is displaced away from ideal alignment. Leakage magnetic field is reduced up to 43% compared to the CP–CP system at the worst-case misalignment, which is due to the ability of the TPP–TPP system to generate and capture different types of magnetic field shapes. Simulation methods for both the TPP and CP are validated in the laboratory using a 2-kW system operating at 85 kHz. [ABSTRACT FROM PUBLISHER]

A new modulated carrier control (MCC) method is proposed in this paper for a power factor correction (PFC) boost converter, which provides high power factor (PF) and low total harmonic distortion (THD) in wide input voltage and load range. The proposed MCC method employs a zero current duration (ZCD) demodulator that detects ZCD in each switching cycle to estimate current conduction duration of the boost inductor. Using the estimated signal of the ZCD demodulator, the proposed controller generates a compensated duty signal with a PFC converter to properly operate in continuous conduction mode (CCM) or discontinuous conduction mode (DCM). Unlike the conventional MCC PFC converter where the line current is distorted in DCM resulting in poor PF and high THD, the proposed MCC method can provide higher PFC performance regardless of CCM and DCM while maintaining the simple control loop of conventional MCC control method that does not require inner current loop and using relatively small inductance. In this paper, the operational principle of the proposed method has been discussed. To verify the proposed method, it has been tested on a 400-W PFC boost converter. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase power factor correction (PFC) rectifier to achieve high power factor, wide output voltage range, and ripple power decoupling without using electrolytic capacitors. It consists of two parts: PFC circuit and output voltage regulation circuit. The load side is involved in both parts, which is different from the regular two-stage conversion structure. The proposed rectifier can be directly applied to low voltage cases due to the wide output voltage range. And the decoupling capacitor voltage can be smaller than the peak grid voltage, which reduces the voltage stress. Besides, the low-frequency ripple power buffer is implemented without a dedicated power-buffering controller. This paper first introduces the circuit structure, operation principles, and control method. Then, the system design consideration is given. Finally, the effectiveness of the proposed topology is verified by the simulations and experimental results. [ABSTRACT FROM AUTHOR]

An optimal dual-phase-shift control strategy of an isolated buck–boost converter is proposed in this paper. The theoretical analysis of dual-phase-shift control strategy is complemented, and the three-dimensional graphs of the output current versus two control variables are given. The optimal operating point is determined by the peak current of a clamped inductor and is shown as control trajectories in the three-dimensional graphs. Moreover, with the optimal dual-phase-shift control strategy, low current value, soft-switching operation, wide input voltage range regulation, whole load range regulation, and high-efficiency performance can be achieved. Furthermore, parameter design method deriving from the minimum peak current of the clamped inductor is given. At the end of this paper, a 1000 W-output prototype is fabricated to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

A switched-capacitor-based dual-switch dc–dc converter with a high-boost voltage gain is proposed in this paper. The proposed converter can obtain a high-voltage gain with a small duty cycle, which decreases the voltage stress and the conduction loss on the power switches. This paper presents the key waveforms, the operating principles at the continuous conduction mode and the discontinuous conduction mode, and the parameter design. Moreover, a comparison between the proposed converter and other nonisolated converters has been completed. To verify the operating principle, a 200 W prototype is constructed with an input voltage of 25–50 V and an output voltage of 200 V. The simulation and experimental results are shown. [ABSTRACT FROM PUBLISHER]

This paper proposes a decentralized current-sharing control strategy to endow fast transient response to paralleled dc–dc converters systems, such as dc microgrids or distributed power systems. The proposed controller consist of two main control loops: an external voltage droop control for current-sharing proposes and an internal current loop. The external droop control loop is designed as a voltage loop with embedded virtual impedance, which avoids the use of a slow voltage loop and a separate extra virtual impedance loop that may limit the system bandwidth. The internal current loop, thanks to the external control loop simplification, plays a major role in the system bandwidth, so that an adaptive proportional-integral (PI) controller is proposed for this matter. In the paper, two different droop control methods have been modeling, designed, simulated, and tested: The conventional virtual-impedance-loop based V–I droop and the proposed embedded-virtual-impedance based I–V droop. In order to compare the dynamic response performances between two droop controllers, their state-space models have been developed and analyzed in this paper. The results show that the dynamic response of the I–V droop control is faster than that of the conventional V–I droop control. Furthermore, by analyzing the effects from I–V droop control parameters, the errors can be reduced faster by enlarging the proportional terms, but with no fluctuations, and then completely eliminated by restoring back to small proportional values. Meanwhile, there exists a tradeoff phenomenon between the fast dynamic response and good steady-state performance; thus, an adaptive PI controller is proposed to both improve dynamic response and guarantee good steady-state performance simultaneously. Experimental results are shown to verify the accuracy of the models and the effectiveness of the proposed control framework. [ABSTRACT FROM PUBLISHER]

This paper presents a phase-shifted dual-half-bridge converter, which achieves zero-voltage switching (ZVS) for the leading-leg switches and zero-current switching (ZCS) for the lagging-leg switches. The proposed converter contains two paralleled half-bridge inverters in the primary side. The rectifier stage is composed of six diodes connected with the form of full-bridge rectification. The ZVS condition is created by the output filter inductor and leakage inductor, while the ZCS condition is created by the blocking capacitors. A wide range of soft-switching operation can be achieved with small leakage inductors. Compared with the traditional phase-shifted full-bridge converter, the proposed converter can obtain a three-level output rectified voltage, and the power is transferred from the primary side to the secondary side during the whole period, which can significantly reduce the current ripple of the output filter inductor. In this paper, the operation principle and relevant analysis are presented. A laboratory prototype is built to verify the performance of the proposed converter. [ABSTRACT FROM PUBLISHER]

This paper proposes a new bidirectional resonant dc–dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc–dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid nonisolated dc–dc commutation cell, which is generated by the integration between conventional commutation cell and ladder-type passive switched capacitor (SC) cell. From the resulted hybrid cell are derived three different dc–dc converters: a buck-type, a boost-type, and a buck–boost-type. The three structures are analyzed in this paper and are presented the topological stages, static gain characteristics in continuous conduction mode and discontinuous conduction mode, steady-state analysis. The analyses are generalized in relation to the number of switched-capacitor cells employed, which allows the increase of the rated gain of the converters by adding more SC cells. In addition, the proposed hybrid nonisolated dc–dc commutation divides naturally the voltage stress among the semiconductors and capacitors of the power stage. A 1-kW prototype was developed to verify the operation of the three proposed converters and their theoretical analysis. For the buck-type topology, designed with an input voltage of 600 V and output voltage of 450 V, a peak efficiency of 99.2% and efficiency at rated power of 99% were obtained. [ABSTRACT FROM PUBLISHER]

This paper designs three distribution devices for the smart grid, which are, respectively, novel transformer with dc bias restraining ability, energy-saving contactor, and controllable reactor with adjustable intrinsic magnetic state based on the magnetically tunable nanocomposite material core. First, the magnetic performance of this magnetic material was analyzed and the magnetic properties processing method was put forward. One kind of nanocomposite which is close to the semihard magnetic state with low coercivity and high remanence was attained. Nanocomposite with four magnetic properties was processed and prepared using the distribution devices design. Second, in order to adjust the magnetic state better, the magnetization and demagnetization control circuit based on the single-phase supply power of rectification and inverter for the nanocomposite magnetic performance adjustment has been designed, which can mutual transform the material's soft and hard magnetic phases. Finally, based on the nanocomposite and the control circuit, a novel power transformer, an energy-saving contactor, and a magnetically controllable reactor were manufactured for the smart grid. The maintained remanence of the nanocomposite core after the magnetization could neutralize the dc bias magnetic flux in the transformer main core without changing the transformer neutral point connection mode, could pull in the contactor movable core instead of the traditional electromagnetic-type fixed core, and could adjust the reactor core saturation degree instead of the traditional electromagnetic coil. The simulation and experimental results verify the correctness of the design, which provides reliable, intelligent, interactive, and energy-saving power equipment for the smart power grids safe operation. [ABSTRACT FROM PUBLISHER]

Sheppard–Taylor power factor correction (ST-PFC) rectifier could obtain a high power factor due to its capability of overcoming the control detuning issue. However, it needs a bulky electrolytic capacitor at the load side to buffer the double-frequency ripple power (DFRP), which reduces the reliability and power density significantly. This paper proposes a control method to divert the DFRP to the small energy transfer capacitor. Consequently, the bulky electrolytic capacitor is replaced with a small film capacitor. The proposed method is carried out by introducing the freewheel state (one switch is turned on and the other is turned off) into the control. So no extra hardware is added, which makes the proposed method cost-effective. A low electromagnetic interference emission is also achieved due to the continuous input–output currents. In addition, the proposed method can be extended to other topologies easily. This paper first gives the detailed analysis of the proposed control method, and then introduces the controller design. The selection of the passive components is also briefly discussed. Finally, the simulation and experimental results verify the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]