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Abstract This paper presents a fully soft switched high step‐up DC–DC converter based on quasi‐Z‐source converter. The voltage gain is boosted by combining coupled inductors and switched capacitor techniques. Moreover, a ZVT cell comprising of only a single switch and an inductor coupled to the quasi‐Z‐source inductor is utilized to reduce the magnetic cores and realize soft switching for all semiconductors without imposing any extra voltage or current stress on the converter elements. The main switch operates at zero voltage switching and zero current switching (ZCS) at turn‐on which is independent of the load and duty cycle variations. Hence, soft switching condition for the main switch at turn‐off is easily provided by a snubber capacitor. In addition, the reverse recovery problem of all the converter diodes is significantly mitigated by ZCS at turn‐off while the continuous current at the input source is maintained. In order to verify the theoretical analysis and the proposed converter operation, a converter prototype is implemented at 300 W and 100 kHz. Finally, a comprehensive comparison is performed between the proposed converter and other high step‐up converters based on quasi‐Z‐source structure, to demonstrate the merits of the proposed converter.

Abstract A fully soft switched high step‐up/down bidirectional converter is presented in this paper. The high voltage conversion ratio is achieved by a pair of coupled inductors along with a switched capacitor while all active switches operate at zero voltage switching. To provide soft switching condition for the main switches and absorb the leakage inductance energy of coupled inductors, active clamp circuits are utilized for both operating modes. Furthermore, all active switches body diodes which are utilized as converter diodes turn off at zero current switching (ZCS) and thus, the reverse recovery problem is eradicated. Additionally, the voltage stress of the main switches is reduced in comparison with the basic bidirectional buck/boost converter and thus, their drain‐source resistance is relatively lower which leads to considerably lower conduction loss. All the mentioned advantages along with relatively low number of components contribute to the converter efficiency. Theoretical analysis of the proposed converter is presented in detail for both operating modes and the experimental results from the implementation of a 300 W prototype circuit confirm the validity of the converter performance. A comprehensive comparison table between the proposed converter and the recent counterpart bidirectional converters is presented to demonstrate the converter advantages.

This paper presents a fully soft switched high step‐up DC–DC converter based on quasi‐Z‐source converter. The voltage gain is boosted by combining coupled inductors and switched capacitor techniques. Moreover, a ZVT cell comprising of only a single switch and an inductor coupled to the quasi‐Z‐source inductor is utilized to reduce the magnetic cores and realize soft switching for all semiconductors without imposing any extra voltage or current stress on the converter elements. The main switch operates at zero voltage switching and zero current switching (ZCS) at turn‐on which is independent of the load and duty cycle variations. Hence, soft switching condition for the main switch at turn‐off is easily provided by a snubber capacitor. In addition, the reverse recovery problem of all the converter diodes is significantly mitigated by ZCS at turn‐off while the continuous current at the input source is maintained. In order to verify the theoretical analysis and the proposed converter operation, a converter prototype is implemented at 300 W and 100 kHz. Finally, a comprehensive comparison is performed between the proposed converter and other high step‐up converters based on quasi‐Z‐source structure, to demonstrate the merits of the proposed converter. [ABSTRACT FROM AUTHOR]

A fully soft switched high step‐up/down bidirectional converter is presented in this paper. The high voltage conversion ratio is achieved by a pair of coupled inductors along with a switched capacitor while all active switches operate at zero voltage switching. To provide soft switching condition for the main switches and absorb the leakage inductance energy of coupled inductors, active clamp circuits are utilized for both operating modes. Furthermore, all active switches body diodes which are utilized as converter diodes turn off at zero current switching (ZCS) and thus, the reverse recovery problem is eradicated. Additionally, the voltage stress of the main switches is reduced in comparison with the basic bidirectional buck/boost converter and thus, their drain‐source resistance is relatively lower which leads to considerably lower conduction loss. All the mentioned advantages along with relatively low number of components contribute to the converter efficiency. Theoretical analysis of the proposed converter is presented in detail for both operating modes and the experimental results from the implementation of a 300 W prototype circuit confirm the validity of the converter performance. A comprehensive comparison table between the proposed converter and the recent counterpart bidirectional converters is presented to demonstrate the converter advantages. [ABSTRACT FROM AUTHOR]

Microgrid islanding can improve the reliability of distribution networks by enabling load to be supplied even after a fault has occured nearby. The generation and load devices in microgrids are commonly interfaced by power electronics, causing a lack of inertia in the network. When microgrids transition from grid-connected to islanded operation after a fault, fast dynamics occur which have to be evaluated to assess stability during and after the transition. Their stability can be evaluated by time-domain simulations, however detailed and validated models of power electronic loads and distributed energy resources are required. This paper proposes component-based models of different types of power electronic loads, and single and three phase distributed energy resources. The models are validated with a variety of voltage and frequency transient experiments. A case study is performed where a modified version of the Cigre European LV residential network is islanded after a fault occurs. The results of the proposed, constant impedance and exponential load models are compared. The results indicate that the proposed models should be used for accurate analysis of the voltage and frequency stability during microgrid islanding simulations. [ABSTRACT FROM AUTHOR]

Here, the setup of a three-phase 100 A linear amplifier is proposed. This work focusses on the use of this linear amplifier as power element for machine-emulation. In contrast to common power electronics, a linear amplifier avoids ripple content in the output current caused by switched-mode operation. [ABSTRACT FROM AUTHOR]

Summary: This paper analyses current‐fed (current source) isolated dc‐dc converters that are proposed for various renewable energy and dc microgrid applications, such as photovoltaic, fuel cell, or energy storage systems. The analysis addresses current‐fed (boost) full‐bridge converters that achieve clamping and soft switching without dedicated external auxiliary circuits, such as snubbers or clamps. Such converters have certain limitations that can lead to degraded performance and feasibility due to high circulating energy or low silicone utilization at some operating points. The current study reveals these limitations, highlighting advantages and drawbacks of selected snubberless converters at different operating conditions. The relation between the rms input current and the isolation transformer primary current as well as the cumulative rms current of primary semiconductors is used as figure of merit for converter characterization. This approach can be extended and applied to other topology types and used as a universal tool for performance assessment of snubberless converters without auxiliary circuits for particular operating conditions in various systems. [ABSTRACT FROM AUTHOR]

Magnetic components in power electronic equipment usually suffer from nonsinusoidal excitations. In this paper, a brief description about the existing core loss calculation methods for nonsinusoidal excitations is given. Then calculation formulas of aforementioned methods for two typical excitation waveforms, that is, square and rectangular with variable duty cycle ${D}$ , are derived. Core loss of nanocrystalline FT-3KS, under above two nonsinusoidal excitations, is measured on an established test setup. The accuracy and applicability of each method are discussed theoretically and verified experimentally, especially in terms of different duty cycles and frequencies. It is found that the waveform coefficient Steinmetz equation (WcSE) is more applicable for the case of relatively small harmonics content of magnetic field intensity ${H}$ (normal duty cycle region), while the improved generalized Steinmetz equation (IGSE) has better precision where the harmonics count (extreme duty cycle region). In addition, the IGSE can better follow the changing trend of core loss with ${D}$ and have better frequency applicability than WcSE, which is proven to be not valid in low frequency (where the static hysteresis loss dominates). The results can provide reference for core loss prediction under nonsinusoidal excitations. [ABSTRACT FROM AUTHOR]

Two main methods for controlling switching converters exist in the literature. The direct one is the voltage mode control, which suffers from some disadvantages such as slow response to load variations and an input voltage-dependent total loop gain. The current mode control can overcome these problems but at the expense of extra cost and more complex control design. V1 concept is a new promising control technique for designing voltage mode control of buck-type converters with an optimal response similar to current mode control. In this paper, the dynamics and the stability of buck converters under V1 control are studied. In particular, subharmonic oscillation limits in the parameter space are addressed. First, a closed-loop state-space model is derived and then used to formulate an analytical matrix-form expression for predicting the stability limit of the system. Using this expression, multi-parametric stability boundaries are obtained. It is shown that the equivalent series inductance of the output capacitor can narrow the stability region. It is also demonstrated that the integral action in the feedback loop of a V1-controlled buck converter has a negligible effect on the subharmonic oscillation boundary. The theoretical analysis is validated through numerical simulation of the circuit-level switched model of the system. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper analyses the impact of operating modes and nonideal power supply conditions on the efficiency of modern low-voltage power electronic devices. The sophisticated circuits and controls implemented in such devices are expected to result in increased efficiencies, higher operating power factors, and reduced harmonic emissions. However, the interactions of individual PE devices with the supplying network will impact exchanges of powers at fundamental system frequency and nonfundamental (i.e., harmonic) frequencies. This paper correlates the obtained results for harmonic performance and efficiencies over the entire range of operating powers of the considered PE devices using both standard definitions and some alternative interpretations. [ABSTRACT FROM PUBLISHER]

Power density and size are important features in compact ac–dc power adapters today. The push for power density, however, requires high conversion efficiency to reduce thermal stresses and smaller magnetics to fit into the required volume. Flyback converters have traditionally been adopted in compact power adapters due to their simplicity, acceptable performance, and low cost. In this paper, we present the design and fabrication of a high-density laptop adapter with a single-stage clamped series-resonant converter as a possible alternative for power adapters in portable electronics. The target is to achieve power densities and scalability in power from 45 to 100\,\mathrm{W}. The converter is frequency controlled and all switches exhibit zero-current switching. In this paper, we show that by utilizing the magnetizing inductance, the converter can be tuned for zero-voltage switching, and by adding a switched capacitor circuit to extend the input voltage range, we can realize a very compact design that is suitable for power adapters with or without power factor correction. Low transformer stresses compared with Flyback-type designs enable high densities, even with a resonant magnetic. Prototype test results with a 45-W laptop adapter are presented. Results are presented from a prototype design demonstrating high efficiency with a power converter density of 8.5$  W/{\mathrm{in}}^3 and means to further increasing the conversion efficiency with synchronous rectification are discussed. [ABSTRACT FROM PUBLISHER]

The dc-to-dc boost converter is a singleswitch, single-inductor, switching circuit used to efficiently transform energy from one dc voltage level to a greater voltage level of the same relative polarity. For a specific resistive load range, as the duty cycle decreases, the boost converter inductor enters a discontinuous current mode of operation - the output load current having decreased to a definable level. This paper analyses the fact that a further reduction of load current, as the duty cycle decreases towards zero, will always result in the re-emergence of a continuous inductor current condition. Further, at the other load extreme, high-current, progressively for increasing load current, starting at low duty cycle conditions, the minimum inductor current always increases from a fixed normalised current level, for a specific load range. These and other hitherto unexplored boost converter properties are analysed and verified mathematically and with PSpice simulations. [ABSTRACT FROM AUTHOR]

In power electronics, the switching elements are controlled by pulse width modulated (PWM) signals making their currents on and off repeatedly. This might cause electromagnetic interference (EMI) problems especially in switched mode power supplies. One method for mitigating the EMI is to use the frequency modulation technique in the control signal of the switching metal-oxide-semiconductor field-effect transistor. According to this approach, frequency of the PWM signal is modulated in order to spread its spectrum and hence reduce the EMI levels. This paper presents the theoretical analysis for the spectrum of a frequency modulated PWM signal. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The interleaving technique is necessary for LLC resonant converters to achieve high power level. The advantages include expanded power capacity, lower output ripple current, and higher light-load efficiency by using phase shedding. However, conventional frequency-controlled LLC converters will lose regulation in individual phases if all the phases are operating at the same switching frequency, causing load sharing problem. Existing load sharing solutions for interleaved LLC converters all have limitations. In this paper, a switch-controlled capacitor (SCC) modulated LLC converter (SCC-LLC) is presented to solve the load-sharing problem. With constant switching frequency, interleaving and phase shedding can be achieved. A 600-W, two-phase interleaved constant frequency SCC-LLC prototype is built to verify the feasibility and demonstrate the advantages. [ABSTRACT FROM AUTHOR]

Full-bridge single-stage (FBSS) ac-dc converters allow to regulate both the output voltage and the input current that achieves a near sinusoidal waveform using only the four bridge transistors. Independent of this feature, these converters still need to be optimized in order to become an interesting and attractive solution for modern switch mode power supplies with power factor corrector (PFC) function. One of the most important improvements needed is the downsizing of the dc bus capacitor C b with the inherent cost reduction. However, this action introduces complex issues in the regulation of the input current and it is also responsible for the generation of high output voltage ripple. The new contribution of this paper consists in the introduction of a set of power circuit optimizations and control techniques in a FBSS PFC converter that solves the referred issues in order to enable the reduction of the dc bus capacitor's size and cost. These procedures are based in the use of a free wheeling circuit that improves the light load operation and in the application of one shot nonlinear modulator, in order reduce the output voltage ripple even when the dc bus ripple is high. The possibility of using, in the proposed topology, a reduced ratio capacitance/watt lower than the typical values used in commercial applications (0.7-0.5 μF/W for 385-450 V, respectively), while maintaining the accurate input current regulation, is also theoretically proved. The developed concepts, solutions and design criteria are detailed described in the paper. The correspondent theoretical study is verified trough experimental results token in an optimized FBSS topology prototype. [ABSTRACT FROM AUTHOR]

This article proposes a systematic approach to determine the most suitable analogue redesign method to be used for forward-type converters under digital voltage mode control. The focus of the method is to achieve the highest phase margin at the particular switching and crossover frequencies chosen by the designer. It is shown that at high crossover frequencies with respect to switching frequency, controllers designed using backward integration have the largest phase margin; whereas at low crossover frequencies with respect to switching frequency, controllers designed using bilinear integration with pre-warping have the largest phase margins. An algorithm has been developed to determine the frequency of the crossing point where the recommended discretisation method changes. An accurate model of the power stage is used for simulation and experimental results from a Buck converter are collected. The performance of the digital controllers is compared to that of the equivalent analogue controller both in simulation and experiment. Excellent closeness between the simulation and experimental results is presented. This work provides a concrete example to allow academics and engineers to systematically choose a discretisation method. [ABSTRACT FROM PUBLISHER]

Abstract: To raise the utilization ratio of lithium-ion battery in portable devices, a novel green-switch controller IC is proposed to constitute a 4-switch cascade buck–boost prototype, which is capable of outputting non-inverting step down and step up voltages. According to the relations between the input and output voltages through duty ratio, a finite state machine automatically determines the work method of converter namely buck method, boost method or transition method by combining peak and valley current programmed mode so as to improve the line regulation over the entire input voltage range. A three-phase seamless transition method is introduced into the controller. Its additional advantage is to lower output ripples. Furthermore, a special burst mode is added to reduce the power consumption during light-load operation. An elaborately designed circuitry and rigorous stability analysis further improves the seamless performance. The controller IC is designed and fabricated in 1.5μm BCD (Bipolar-CMOS-DMOS) technology with an area of 8.75mm2 and applied to a 2.7V–4.2V/3.3V, maximum output power 1.65W buck–boost converter. It features over 90% conversion efficiency during normal application and still remains over 80% under standby mode. The experimental results show that all functional and performance targets are successfully achieved as expected. [Copyright &y& Elsevier]

A new active clamping zero-voltage switching (ZVS) pulse-width modulation (PWM) current-fed half-bridge converter (CFHB) is proposed in this paper. Its active clamping snubber (ACS) can not only absorb the voltage surge across the turned-off switch, but also achieve the ZVS of all power switches. Moreover, it can be applied to all current-fed power conversion topologies and its operation as well as structure is very simple. Since auxiliary switches in the snubber circuit are switched in a complementary way to main switches, an additional PWM IC is not necessary. In addition, it does not need any clamp winding and auxiliary circuit besides additional two power switches and one capacitor while the conventional current-fed half bridge converter has to be equipped with two clamp windings, two ZVS circuits, and two snubbers. Therefore, it can ensure the higher operating frequency, smaller-sized reactive components, lower cost of production, easier implementation, and higher efficiency. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 200-W, 24-200 Vdc prototype are presented. [ABSTRACT FROM AUTHOR]

The use of photovoltaic (PV) systems as the energy source of electrical distributed generators (DG) is gaining popularity, due to the progress of power electronics devices and technologies. Large-scale solar PV power plants are becoming the preferable solution to meet the fast growth of electrical energy demand, as they can be installed in less than one year, as compared to around four years in the case of conventional power plants. Modular multilevel inverters (MMIs) are the best solution to connect these large-scale PV plants to the medium-voltage (MV) grid, due to their numerous merits, such as providing better power quality, having higher efficiency, providing better reliability, and their scalability. However, MMIs are still progressing and need some improvement before they can be implemented safely in the industrial, medium, and high voltage networks. The main purpose of this paper is to review the present MMIs topologies when used in PV applications. The review aims to present a comprehensive study of the various recent submodule circuits associated with MMI topologies. Maximum power point tracking (MPPT) control schemes for PV inverters will be explored extensively. Then, the different control strategies of PV MMIs will be presented and compared to give a holistic overview of the submodules balancing techniques, ranges, and capabilities under balanced and unbalanced grid conditions. In addition, the paper will discuss the future of PV MMIs systems in electricity networks. [ABSTRACT FROM AUTHOR]

• This paper proposes topologies A,B and C of acdc buck–boost converters for MV applications, with 'A' and 'C' have been identified as promising. • Topologies 'A' and 'C' facilitate scalability to higher and lower MV applications, with 'C' uses a novel parallel charging of inductors. • The theoretical principles that underpin the operation of the proposed topologies are established and verified using simulations and experiments. This paper proposes three topologies of single-stage three-phase ac–dc buck–boost converters suitable for medium-voltage and high-power wind energy conversion systems (WECS). The proposed converters draw sinusoidal input currents with nearly unity power factor from wind generators over wide range of ac voltages and frequencies. The proposed converters reduce the voltage and current stresses on the self-commutated switching device compared to existing solutions; thus, promising for new generation of relatively cheap WECSs. The proposed converters operate in Discontinuous Condition Mode (DCM), with their ac terminals connected to three-phase generator with open ended windings, or to ac supply using three single-phase transformers with isolated windings at converter side. The validity of the proposed converters and its detailed theoretical analysis and discussions are confirmed using PSCAD/EMTDC simulations, and further corroborated by experimentations, considering different operating conditions. [ABSTRACT FROM AUTHOR]