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A novel beta-quasi-Z-source (β-qZS) converter is proposed for an isolated dc–dc converter with the buck (step-down) and boost (step-up) functions. The β-qZS isolated dc–dc converter addresses the common challenges such as components stresses, reliability, suppression of switch voltage overshoot, size, and power derating in the existing impedance source-based isolated dc–dc converter applications. In addition, the proposed topology dealt with operating duty cycle constraint and loss of duty cycle phenomenon in the Z/qZS galvanically isolated dc–dc converters. This article describes the configuration and provides the principle of operation for the proposed β-qZS converter topology. A laboratory prototype is developed, and the experimental results satisfy the theoretical analysis. [ABSTRACT FROM AUTHOR]

This article proposes a three-phase six-switch switching-cell current source inverter (H6-SC-CSI) and a modified switching scheme of space vector pulsewidth modulation (SVPWM). Compared to the conventional three-phase six-switch current source inverter, the H6-SC-CSI has no open-circuit possibility, thus, the inverter reliability is greatly enhanced. In addition, the overlap-time can be minimized; hence, the output waveform quality can be considerably improved. Due to the presence of switching-cell capacitors, a conventional switching sequence of the SVPWM is modified for the inverter to operate properly. A 2.2 kW hardware prototype is built and tested to verify the effectiveness of the proposed PWM. [ABSTRACT FROM AUTHOR]

In this article, two configurations of the quadratic quasi-Z-source (Q-qZS) isolated dc–dc converters are presented, namely continuous input current and discontinuous input current configurations. The operating principles and steady state of the continuous input current topology analyzed in this article is characterized with the following features: 1) wider operating range due to buck and boost functions in a single stage; 2) draws continuous input current; 3) low input current ripple compared with other qZS-based isolated dc–dc converters; 4) better reliability and good immunity against EMI noise; 5) common ground between the input source and the inverting bridge; and 6) continuous control over the entire operating range. Compared with other qZS-based isolated dc–dc converters, lower current stresses on active and passive components used are realized. Hence, the total magnetic volume/energy required by the proposed converter is reduced with the potential of achieving high power density. A prototype of 40–140 V input voltage, 300 V output, and 550 W rated power is developed to validate the performance of the proposed converter presented. [ABSTRACT FROM AUTHOR]

The LLC resonant converter offers a promising solution for dc power conversion. The input-parallel output-parallel system offers low specification switches to use in high power applications. Moreover, the interleaving of the converters reduces the requirement of input and output passive filters, providing better dynamic performance and higher power density. However, the tolerances in the designed resonant components and the unavoidable mismatch in the circuit parameters lead to unbalanced estimated tank gain characteristics. Consequently, the zero-voltage-switching is lost, a serious imbalance in currents appears, and a thermal runaway is likely to occur. The proposed method utilizes the existing magnetics of resonant inductors and self-alleviates the imbalance in the output, input, and tank currents without increasing active or passive components, dedicated balancing controls, and expensive sensors. A 4 kW four-phase prototype is tested during steady state, transients, and phase-shedding modes to validate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes a single-phase five-level current source inverter with an inductor cell based on the switching-cell (SC) structure. Compared to the conventional inverter, the proposed structure has no open-circuit problem; thus, its reliability is greatly enhanced. The overlap-time inserted in the driving signals can also be minimized to improve the output waveform quality. The proposed inverter's operation is analyzed herein, and the design guideline of SC capacitors is discussed. In addition, the SC extension for the n-level topology is provided. A 1-kW prototype is built and tested to validate the effectiveness of the proposed structure. [ABSTRACT FROM AUTHOR]

Conventional dual-active-bridge dc–dc converters require a dedicated voltage balancer or feedback control when they are used for a bipolar LVdc distribution system. This article proposes a dual-active-half-bridge (DAHB) converter with voltage balancing. The proposed converter is composed of a conventional DAHB converter with an additional inductor and capacitor voltage balancer (LCVB). The LCVB is added between the transformer and the output of the DAHB converter. Although the LCVB increases the switch current, it can balance the two output voltages without additional active switching device and feedback control under unbalanced load conditions. In addition, compared with the conventional DAHB converter, the LCVB can increase the zero-voltage-switching range of the DAHB converter and has no detrimental effect on the operation modes and performances. A 2.8-kW prototype was built and tested to verify the performances of the proposed converter. [ABSTRACT FROM AUTHOR]

This letter proposes a modified double-dual-boost (DDB) high-conversion-ratio dc–dc converter. The proposed converter is derived from the existing DDB converter by a simple yet effective circuit modification and inherits all the advantages of the existing DDB converter. In addition, the input and output can share a common ground due to the circuit modification, enabling the use of low-side gate drivers for all switching devices. When compared with the existing DDB converter, the proposed converter requires only one more capacitor, and the seemingly two inductors can be integrated into a single inductor. Thus, the overall magnetic volume is the same as the conventional converter. To validate the performance of the proposed converter, a 2-kW prototype was fabricated and tested. [ABSTRACT FROM AUTHOR]

In this letter, an asymmetrical pulsewidth modulation (PWM) scheme is proposed to solve the output voltage unbalance and voltage gain issues of the input-parallel output-series (IPOS) converter when $D < 0.5$. With the proposed scheme, the natural output voltages balancing and high step-up conversion ratio can be extended when $D < 0.5$. As a result, combined with the conventional PWM scheme, the duty cycle limitation of the IPOS converter is completely eliminated without any extra components or dedicated control. A 2-kW prototype of the IPOS converter was built and tested to verify the performance of the proposed PWM scheme. [ABSTRACT FROM AUTHOR]

This article presents current-fed (CF) full-bridge (FB) isolated dc–dc converter using quasi-Z-source network. Owing to its inherent buck–boost and clamping function, the proposed converter can effectively eliminate start-up and switch voltage overshoot problems. In addition, when compared with the conventional CF-FB converter with active clamp, switch current stress is much reduced and less active switches are required. Operation principles of the proposed converter are analyzed in detail. The simulation and experimental results with 1-kW prototype are also provided to verify theoretical analysis. [ABSTRACT FROM AUTHOR]

This article presents a novel two-channel light emitting diode (LED) current balancing method using current-fed (CF) quasi-Z-source (qZS) dc–dc converter. The proposed LED driver is simple in structure and requires minimal number of component counts. Currents flowing through the two LED strings are automatically balanced owing to charge (amp–sec) balance condition on capacitors in the CF–qZS network. Since current balancing is achieved automatically by passive components, current control of the proposed converter is very simple. In addition, the proposed circuit uses only one active switch and one diode. The operating principle and characteristics of the proposed two-channel LED driver are analyzed in detail. To verify validity of the proposed converter, 80 W prototype is built and tested. [ABSTRACT FROM AUTHOR]

Conventional current source inverter (CSI) suffers from open-circuit problem during switch transition. Thus, overlap-time should be inserted in the gate signals for safe commutation. The overlap-time distorts output current waveforms and increases total harmonic distortion of output current. Moreover, it reduces the current source utilization of the inverter. To solve these problems, this article proposes a new three-phase four-leg switching-cell (SC) CSI, abbreviated as H8-SC-CSI. With the help of the SC structure, the reliability of the proposed inverter is greatly enhanced as open-circuit concerns are eliminated. In addition, with the intrinsic voltage clamping action of the SC structure, switch voltage overshoot at turn-off is mitigated. In the proposed CSI, the switch overlap-time can be minimized or eliminated because the inductor current can flow through the SC capacitors. A 1.2 kW prototype inverter is designed and tested to verify the feasibility of the circuit. [ABSTRACT FROM AUTHOR]

In this article, a current balancing coupled inductor (CBCL) based asymmetrically configured quad-active-bridge (QAB) converter is proposed. The QAB converter provides high-frequency isolation for a dc–dc stage of a solid state transformer (SST), as well as provides a modular solution to the SST medium-voltage (MV) dc link. The proposed CBCL ensures current balancing among/three active H-bridges without using any dedicated controller and without expensive sensors when transferring equal power from MV to low-voltage side. The proposed CBCL is the integration of three inductors of the active H-bridges required for power transfer and zero-voltage-switching and does not require an extra magnetic volume. Experimental results are presented to validate the performance. [ABSTRACT FROM AUTHOR]

In this article, a novel single-phase single-stage transformerless inverter is proposed for grid-tied and standalone applications. The proposed inverter has low leakage current and can perform both buck and boost functions. Furthermore, compared to the conventional state-of-the-art buck–boost inverters, it can achieve high power density because the magnetic volume is reduced significantly. In addition, high power conversion efficiency can be realized because only one switch operates at a high frequency. Moreover, there is no need for inserting high-frequency dead-time between the switches because only one switch receives high frequency and all other switches receive line frequency signals. In order to verify the performance of the proposed topology, a laboratory prototype is designed for 500 W, and the experimental results are provided as well. [ABSTRACT FROM AUTHOR]

In this letter, an asymmetrical pulsewidth modulated (PWM) scheme is proposed to solve the inductor current unbalance and nonlinear voltage gain issues of the series-capacitor (SC) high-conversion-ratio (HCR) converter when D > 0.5. With the proposed scheme, the converter can achieve both current balancing and high step-down conversion even for D > 0.5. As a result, combined with the conventional PWM scheme, the duty cycle limitation of the SC-HCR converter is completely eliminated. A 2-kW prototype SC-HCR converter was fabricated and tested to validate the performance of the proposed PWM scheme. [ABSTRACT FROM AUTHOR]

Unlike voltage-source inverters (VSI), the power decoupling element in current-source inverters (CSI) is inductor. Inductor has a long lifetime and makes the CSI more reliable. However, the traditional CSIs suffer from open-circuit problem and dangerous voltage spikes are generated if the input inductor current is intermitted. Therefore, to avoid the voltage spikes, overlap-time should be inserted in the gate signals. But these intervals distort the output currents and reduce the current source utilization. To address these issues, a novel three-phase CSI is proposed in this article. The proposed inverter is originated from the conventional seven-switch CSI named CSI7 by adding only two small film capacitors. The film capacitors along with the pre-existing diodes of the CSI7 ensure that there is always a path for the inductor current, and thus the open-circuit issue is resolved. The elimination of open-circuit issue enhances the reliability and allows to minimize the overlap-time. This will improve the quality of output currents as well. Moreover, simulation and experimental results are provided at the output power of 950 W to verify the effectiveness of the proposed inverter. [ABSTRACT FROM AUTHOR]

This paper introduces a direct PWM split-phase boost ac-ac converter with a high voltage gain, natural output voltage balancing, no duty-ratio limitation, and no commutation problem. Although under unbalanced load conditions, the two output voltages still are equal without auxiliary circuits and/or any dedicated controller. Moreover, the input current ripple is significantly decreased due to the interleaving effect. With a proper asymmetrical PWM scheme, the converter can work in the entire range of the duty cycle. In addition, the commutation (dead-time) problem is eliminated. The operation of the proposed structure is validated with a 500 W prototype converter. Experiment results obtained under various load conditions such as inductive, nonlinear, extreme load, and load scenarios are also provided. [ABSTRACT FROM AUTHOR]

This study proposes a novel balanced two-phase interleaved LLC resonant converter. The LLC resonant converter offers a promising solution for dc power conversion. This converter can achieve high efficiency and high-power density by implementing zero-voltage-switching (ZVS) for primary switches and zero-current-switching for secondary rectifier diodes. The input-parallel output-parallel systems that increase their power ratings by connecting two converters in parallel allow the use of low-current rated switches in high-current applications. Moreover, the input and output passive filter size requirements in the two-phase interleaved converters are reduced, and they provide higher power density and improved dynamic performance. However, the estimated tank gain characteristics become imbalanced due to the tolerances and the inevitable mismatch of the resonant parameters. Accordingly, this system operates outside the ZVS region, and a severe current imbalance with thermal runaway will occur. The proposed method achieves the perfect balance of input, output, and tank currents utilizing the existing resonant inductor magnetics without additional active or passive components, expensive sensors, and dedicated control schemes. The proposed method retains the advantages of the conventional LLC resonant converter over the operating frequency range. Mathematical analysis and experimental results are presented to validate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic voltage restorer to solve the voltage sag problem that causes the most serious economic loss among various grid accidents. The proposed method, which uses a direct AC–AC converter, consists of a simple controller unlike methods using a voltage source inverter that is controlled using complex operations. Unlike the energy storage type, there is no additional energy storage device, which reduces system cost. In addition, unlike the back-to-back type, energy conversion loss is reduced by one stage conversion. A switching cell-structured direct AC–AC converter that solves the rectification problem without a separate sensor is a reliable structure that reduces the volumes of the passive filters by increasing the switching frequency. In addition, using interphase voltages, it can take a wide range of voltage compensations to compensate for most of the voltage sag in various situations. In this paper, the background of the study is revealed and the operating principles and control schemes of the proposed system are analyzed. Then, the validity of this study is confirmed through simulation and experiment results. [ABSTRACT FROM AUTHOR]

In this article, we proposed a bidirectional dual active bridge (DAB) converter adopting a boost-up function. The proposed converter can be implemented by adding only one capacitor to the high voltage side without additional active components. By utilizing the boost-up function, the proposed converter can achieve higher output power than the conventional DAB converter under the same leakage inductance condition. In comparison with the resonant converter in addressing the output power limitation, the proposed converter can reduce the switching and conduction losses due to the low turn-off and circulating currents, and complex control is not required to drive the synchronous rectifier. Furthermore, the direction of the output power can be easily changed with a simple control circuit. Experimental results from the proposed converter with a 3 kW rated power, 28-V low-side voltage, and 600-V high-side voltage are demonstrated to verify the proposed works. [ABSTRACT FROM AUTHOR]

Like conventional two-switch leg converters, the three-switch leg converters also have short-circuit risks and a dangerous shoot-through current is generated if switches of the same leg are turned on simultaneously. In this article, a new dual-buck structure is proposed for three-switch leg converters. The proposed structure is reliable because of no shoot-through concerns and high quality of output waveforms can be obtained due to the reduction in pulsewidth modulation deadtime. Unlike the conventional dual-buck three-switch leg that uses many passive components such as four current limiting inductors and three external diodes, the new dual-buck three-switch leg uses only one current limiting inductor with two external diodes. To verify the performance, the proposed three-switch legs are used in single-phase dual-output inverter and detailed theoretical analysis, simulation, and experiments are performed. Both continuous and discontinuous modulation schemes are applied and it has been figured out that discontinuous modulation scheme can improve the dc-link voltage utilization in the common-frequency mode of operation. [ABSTRACT FROM AUTHOR]

The traditional neutral point clamped (NPC) inverter has short-circuit problem. The risk of short-circuit can be decreased by using dead-time in the switching signals. However, the dead-time decreases the achievable output voltage and causes distortion in the waveforms. To overcome the short-circuit problem, dual-buck NPC (DB-NPC) and split-inductor NPC (SI-NPC) inverters have been researched. However, the voltage stress of the two external diodes in the DB-NPC inverter is higher. On the other hand, the SI-NPC inverter has a problem of generating huge voltage spikes in the dead-time, which can destroy the semiconductor devices. In addition, the SI-NPC inverter cannot provide reactive power. This article presents a family of NPC inverters consisting of single-phase, three-phase, and cascaded inverters. The proposed inverters have no short-circuit and dead-time issues, therefore no high voltage and current spikes are caused. Also, the dead-time in the switching signals can be minimized. As a result, the magnitude of the output waveforms can be increased, and quality can be improved. Unlike the DB-NPC inverter, the voltage stress of all the semiconductor in the proposed inverter is lower, and unlike the SI-NPC inverter the proposed inverter provides reactive power. In this article, the proposed three-level NPC inverter is analyzed, designed, and tested. The voltage stress of the semiconductor devices in the proposed inverter is half of the source voltage, whereas in the conventional DB-NPC inverter the voltage stress of the two external diodes is the source voltage. In addition to the aforementioned benefits, the proposed cascaded inverter reduces the total number of inductors. To verify the analysis, detailed simulation, and experimental results of the proposed three-level inverter with input voltage 640 V, output power 1.2 kW, and output voltage 220 Vrms are provided. [ABSTRACT FROM AUTHOR]