A Family of Isolated Buck-Boost Converters Based on Semiactive Rectifiers for High-Output Voltage Applications

Abstract—

A systematic method for developing isolated buck-boost (IBB) converters is proposed in this paper, and single-stage power conversion, soft-switching operation, and high-efficiency performance can be achieved with the proposed family of converters. On the basis of a nonisolated two-switch buck-boost converter, the proposed IBB converters are generated by replacing the dc buck-cell and boost-cell in the non-IBB converter with the ac buck-cell and boost-cell, respectively. Furthermore, a family of semiactive rectifiers (SARs) is proposed to serve as the secondary rectification circuit for the IBB converters, which helps to extend the converter voltage gain and reduce the voltage stresses on the devices in the rectification circuit. Hence, the efficiency is improved by employing a transformer with a smaller turns ratio and reduced parasitic parameters, by using low-voltage rating MOSFETs and diodes with better switching and conduction performances. A full-bridge IBB converter is proposed and analyzed in detail as an example. The phase-shift modulation strategy is applied to the full-bridge IBB converter to achieve IBB conversion. Moreover, soft-switching performance of all active switches and diodes can be achieved over a wide load and voltage range by the proposed converter and control strategy. A 380-V-output prototype is fabricated to verify the effectiveness of the proposed family of IBB converters, the SARs, and the control strategies.

High-Efficiency Coupled-Inductor-Based Step-Down Converter

Abstract—

This study mainly investigates a high-efficiency single-input multiple-output (SIMO) step-down converter. The proposed converter can step down the voltage of a high-voltage dc bus generated by the rectifier of an ac utility power to a controllable low-voltage output terminal and middle-voltage output terminals. In this study, a coupled-inductor-based SIMO step-down converter utilizes two power switches with the properties of voltage clamping for the middle-voltage switch, and soft switching for all power switches due to the appropriate choice of the corresponding device specifications. As a result, the leakage inductor energy of the coupled inductor can be recycled, and the voltage spikes on power switches can be alleviated. Moreover, the switching losses can be significantly decreased because of all power switches with zero-voltage-switching features. Therefore, the objectives of high-efficiency power conversion, high step-down ratio, and various output voltage with different levels can be obtained. The effectiveness of the proposed SIMO step-down converter is verified by experimental results of a converter prototype in practical applications.

Improved ZVS Three-Level DC–DC Converter With Reduced Circulating Loss

Abstract—

An improved three-level (TL) dc–dc converter is proposed in this paper. The converter contains two transformers. Like the conventional TL dc–dc converter, there are no additional switches on the primary side of the transformer. The rectifier stage is composed of four diodes in the center-tapped rectification. On the primary side of the transformer, the two transformers are connected in series. The middle node of the two transformers is connected to the neutral point of the split flying capacitors. Because it cooperates with the four-diode rectifier stage, the circulating current on the primary side of the transformer decays to zero during the freewheeling period. The zero-voltage switching (ZVS) of the leading switches is determined by energy stored in the output filter inductor, which is similar to the conventional TL converter. The ZVS of the lagging switches is determined by the energy stored in the magnetizing inductor of a transformer, rather than the energy stored in the leakage inductor. The proposed converter can reduce the output filter inductance. Because of the advantages given above, the efficiency of the proposed converter is far better than that of traditional methods. Finally, a 1-kW prototype was built to verify the performance of the proposed converter.

A Modified Dual Active Bridge Converter With Hybrid Phase-Shift Control for Wide Input Voltage Range

Abstract—

By inserting a small inductor between the transformer center tap and the midpoint of two split output capacitors in the dual active bridge (DAB) topology, this paper proposes a modified DAB converter for wide-input applications. A hybrid phase-shift (HPS) control scheme is proposed to allow all power switches to achieve practical ZVS over the full operating range; thereby, significantly minimizing the switching losses and alleviating electromagnetic interference. Moreover, the proposed control scheme does not significantly increase the conduction losses in comparison with the extended phase-shift (EPS) control. Therefore, the modified DAB can operate efficiently. The topology derivation and description are first presented. Then, the EPS and triple phase-shift (TPS) modulations are applied, and the corresponding operating principles and characteristics, including the soft-switching, power transfer, and root-mean-square current, are investigated in detail. To achieve practical ZVS operation of all switches over full operating range, while minimizing the conduction losses, the EPS and TPS are combined, and an HPS control scheme is proposed. Finally, experimental results from a 1.4-kW converter prototype with 200–400-V input and 400-V output are presented to verify the feasibility and advantages of the converter and control.

Soft-Switching Step-Up Converter With Ripple-Free Output Current

Abstract—

A soft-switching step-up converter with ripple-free output current is proposed. This converter is based on a voltage-boosting converter, named KY converter. Thus, the proposed converter has features of KY converter such as clamped switch voltage stresses to input voltage, nonpulsating output current and fast transient response. In addition, by utilizing an auxiliary circuit, the zero-voltage-switching (ZVS) of power switches is achieved. Therefore, the switching loss is reduced and the system efficiency is improved. Moreover, the auxiliary circuit cancels out the filter inductor current ripple. Then, ripple-free output current is achieved. The operational principle and a steady-state analysis of the proposed converter are provided in detail. In order to verify the theoretical analysis, experimental results based on a 60 W prototype at a constant switching frequency of 200 kHz are presented.

A ZVS Grid-Connected Full-Bridge Inverter With a Novel ZVS SPWM Scheme

Abstract—

A zero-voltage switching (ZVS) grid-connected full-bridge inverter and its modulation schemes are investigated. A novel sinusoidal pulse width modulation scheme for the ZVS full-bridge inverter (ZVS SPWM) is proposed in this paper. The ZVS SPWM is evolved from the double-frequency SPWM by adding gate drive to the auxiliary switch. The ZVS condition is analyzed and the circulation loss of the resonant branch is optimized by adjusting the energy storage in the resonant inductor. The reverse recovery of the body-diode of MOSFET is relieved and ZVS is re-alized for both main and auxiliary switches. The filter inductors are significantly reduced with higher switching frequency. The design guideline of resonant parameters and the implementation of ZVS SPWM in DSP controller are introduced. The ZVS SPWM scheme is verified on a 3-kW inverter prototype. According to the experimental result, peak efficiency as 98.8% is achieved.

An Open-Switch Fault Diagnosis Method for Single-Phase PWM Rectifier Using a Model-Based Approach in High-Speed Railway Electrical Traction Drive System

Abstract—

The converter with a single-phase rectifier, a dc-link circuit and a three-phase inverter is widely applied in high-speed railway electrical traction drive system. The fault frequency of single-phase rectifier is higher than that of three-phase inverter. Thus, this paper presents a new and fast model-based approach for open-switch fault diagnosis of the single-phase pulse width modulation rectifier, based on the mixed logical dynamic model and residual generation. It requires no additional hardware but only some measurements and command signals which are available in control system. This diagnosis method is quite suitable for electrical traction application due to the fast diagnosis time, simple structure and high reliability. Experimental results confirm the effectiveness and accuracy of the proposed algorithm. It is shown that such diagnosis method can locate the faulty switch in a few milliseconds which is important to avoid catastrophic consequences.

Double-Deck Buck-Boost Converter With Soft Switching Operation

Abstract—

This paper presents a novel two-stage buck-boost converter with a soft switching operation. The proposed converter is constructed of two identical buck-boost converters working in parallel. The converter units are connected to each other by an inductor as a bridge. This inductor plays an important role in the soft switching operation of the converter by maintaining the voltage applied to switches at zero at switching intervals. The utilized method is called the zero-voltage switching. It is shown that the structure of the proposed converter is significantly efficient in the reduction of switching losses, leading to the improvement of the converter effi-ciency. Moreover, because of the parallel operation of two identical converters, the output voltage and the input current contain fewer ripples than those of a single converter with the same specifications. Also, utilizing only one inductor as an extra element to achieve this goal makes the proposed converter more economical and reliable with a simpler structure. The detailed analysis of the circuit operation is provided in eight modes. The proposed method is implemented in a laboratory test circuit within the range of 100–220 W output power validating the accuracy of the proposed converter.

A New Hybrid Boosting Converter for Renewable Energy Applications

Abstract—

A hybrid boosting converter (HBC) with collective advantages of regulation capability from its boost structure and gain enhancement from its voltage multiplier structure is proposed in this paper. The new converter incorporates a bipolar voltage multiplier, featuring symmetrical configuration, single inductor and single switch, high gain capability with wide regulation range, low component stress, small output ripple and flexible extension, which make it suitable for front-end PV system and some other renewable energy applications. The operation principal, component stress, and voltage ripple are analyzed in this paper. Performance comparison and evaluation with a number of previous single-switch single-inductor converters are provided. A 200-W 35 to 380 V second-order HBC prototype was built with peak efficiency at
95.44%. The experimental results confirms the feasibility of the proposed converter.

A Dual-Transformer Active-Clamp Forward Converter With Nonlinear Conversion Ratio

Abstract—
This paper proposes a dual-transformer active-clamp forward converter (DT-ACFC) with nonlinear conversion ratio (NCR), which combines two forward converter units. Since only two active switches are needed, the cost and the circuit complexity can be lowered. To reduce switching loss, the proposed converter fulfills zero-voltage switching by employing the leakage inductance of the transformer and additional resonant inductance. By paralleling the transformer secondaries and changing the circuit architecture of each secondary side, we can make the output load current evenly shared among four output inductors such that the current stress and conduction losses of the output rectifiers can be decreased significantly. Moreover, the nonlinear step-down conversion ratio leads to a high duty utilization ratio for the proposed converter. Therefore, the DT-ACFC with NCR is suitable for applications of high output current and a wide input voltage range. Experimental results are shown to verify the theoretical analysis of the proposed forward converter.