In this paper, a high step-up quasi- Z Source (QZS) dc–dc converter is proposed. This converter uses a hybrid switched-capacitors switched-inductor method in order to achieve high voltage gains. The proposed converter have resolved the voltage gain limitation of the basic QZS dc–dc converter while keeping its main advantages, such as continuous input current and low voltage stress on capacitors. Compared to the basic converter, the duty cycle is not limited, and the voltage stress on the diodes and switch is not increased. In addition to these features, the proposed converter has a flexible structure, and extra stages could be added to it in order to achieve even higher voltage gains without increasing the voltage stress on devices or limiting the duty cycle. The operation principle of the converter and related relationships and waveforms are presented in the paper. Also, a comprehensive comparison between the proposed and other QZS based dc–dc converters is provided which confirms the superiority of the proposed converter. Simulations are done in power systems computer aided design (PSCAD) in order to investigate the maximum power point tracking (MPPT) capability of the converter. In addition, the valid performance and practicality of the converter are studied through the results obtained from the laboratory built prototype.

High Step-Up Quasi- Z Source DC–DC Converter

This article classifies, describes, and critically compares different modeling techniques and control methods for dual-active-bridge (DAB) dc–dc converters and provides explicit guidance about the DAB controller design to practicing engineers and researchers. First, available modeling methods for DAB including reduced-order model, generalized average model, and discrete-time model are classified and quantitatively compared using simulation results. Based on this comparison, recommendations for suitable DAB modeling method are given. Then, we comprehensively review the available control methods including feedback-only control, linearization control, feedforward plus feedback, disturbance-observer-based control, feedforward current control, model predictive current control, sliding mode control, and moving discretized control set model predictive control. Frequency responses of the closed-loop control-to-output and output impedance are selected as the metrics of the ability in voltage tracking and the load disturbance rejection performance. The frequency response plots of the closed-loop control-to-output transfer function and output impedance of each control method are theoretically derived or swept using simulation software PLECS and MATLAB. Based on these plots, remarks on each control method are drawn. Some practical control issues for DAB including dead-time effect, phase drift, and dc magnetic flux bias are also reviewed. This article is accompanied by PLECS simulation files of the reviewed control methods.

/pdf/modeling-and-advanced-control-of-dual-active-bridge-dc-dc-43lznhzo8j.pdf

Modeling and Advanced Control of Dual-Active-Bridge DC–DC Converters: A Review

This paper deals with an optimized three-level modulated phase shift control using particle swarm optimization (PSO) strategy based on the unified phasor analysis with an aim to improve the efficiency of the bidirectional dual active bridge (DAB) converter for the whole operation range. A unified mathematical model based on Fourier transform is built for the DAB converter. All possible operation states under the three-level modulated phase shift control are covered. Accurate complex mathematical expressions for the inductor current, the transmission power, and the reactive power are obtained. Both modulus and angle variables are illustrated with respect to the inner and outer phase shift angle with the phasor diagram. The proposed method is able to achieve the minimum reactive power under three-level modulated phase shift control by obtaining the optimal phase-shift angles directly. The cumbersome process of the optimal operation mode selection for different voltage conversion ratio and load conditions in conventional methods is overcome successfully, thus greatly simplifying the theoretical calculation and implementation difficulty. Simulation and experimental results in terms of the reactive power, soft-switching range, and efficiency are provided to verify the practical feasibility of the proposed method for the bidirectional DAB converters.

Reactive Power Minimization in Bidirectional DC–DC Converters Using a Unified-Phasor-Based Particle Swarm Optimization

Dual active bridge (DAB) dc-dc converters have several attractive features including auto-adjust bidirectional power flow, wide voltage gain range, and zero voltage switching (ZVS)-on capability. Various applications based on DAB including solid-state transformer in power grids and traction, energy storage system, and electric vehicle on-board chargers have been proposed by academics. Nevertheless, industrial applications based on DABs are still seldom mainly due to the circulating current and loss of ZVS problems under certain load and voltage gain conditions. There is an intensive research effort underway to solve these problems recently. This paper presents the state-of-the-art view in the cause of circulating current and loss of ZVS and surveys the solutions to these problems.

/pdf/circulating-current-and-zvs-on-of-a-dual-active-bridge-dc-dc-27nr378jm8.pdf

Circulating Current and ZVS-on of a Dual Active Bridge DC-DC Converter: A Review

Renewable energy generations have been attracting sustained attentions in academic and industry. Current-fed-isolated-bidirectional dc/dc converters (CF-IBDCs) are widely adopted in low-voltage high-current applications such as solar photovoltaic fuel cell with energy storage. This paper gives an overview and a comprehensive comparative evaluation of CF-IBDCs. The active clamped, dual half-bridge, L-L type dual active bridge, resonant-type, naturally clamped, and other type topologies of CF-IBDCs are investigated, analyzed, and compared regarding their circuit topological structures, operation characteristics, modulation methods, and soft-switching technologies. In addition, component cost models and loss models of converters are deduced and presented. On this basis, quantitative and comprehensive performance comparison of seven typical CF-IBDC topologies selected from each type is conducted in terms of costs, losses, weight, volume, and power density for the given system specifications and design constraints. Finally, the application range of different CF-IBDCs and future trend are presented to encourage further development.

An Overview and Comprehensive Comparative Evaluation of Current-Fed-Isolated-Bidirectional DC/DC Converter

The unified boundary trapezoidal modulation (TZM) control utilizing fixed duty cycle compensation and magnetizing current design for dual active bridge dc–dc converter is proposed in this paper. The fixed duty cycle compensation and magnetizing current design are first introduced to achieve the zero voltage switching (ZVS) of the power switches, which cannot be ensured with the conventional TZM control. As a result, all the power switches of dual active dc–dc converter can achieve ZVS and four switches can be turned off with very low current. Besides, based on the revealed power transfer characteristic, the power control variables including the duty cycles and phase-shift ratio can be unified without lookup tables or operation region division. With the proposed boundary TZM control, circulating current losses can be reduced and nonactive power is significantly suppressed according to the mathematic analysis, resulting in decrease of the conduction loss. A 1.6-kW laboratory prototype is built to verify the theoretical analysis and effectiveness of the proposed control.

Unified Boundary Trapezoidal Modulation Control Utilizing Fixed Duty Cycle Compensation and Magnetizing Current Design for Dual Active Bridge DC–DC Converter

In this paper, a novel current fed hybrid dual active bridge dc–dc converter is proposed, which is suitable for a low-voltage fuel cell power conditioning system. The high-frequency input current ripple can be reduced to minimum because the input side switches are always switched at 50% duty cycles in spite of the fuel cell voltage and the load variation. Notch filter is used in the voltage feedback path to reduce the low-frequency input current ripple when interfaced with a single-phase inverter load. All of the power devices can achieve zero voltage switching by the proposed control strategy. The mode analysis, the operation principle, zero-voltage switching (ZVS) conditions, and parameter design are given in this paper. A 1 kW prototype has been fabricated to verify the effectiveness of the proposed converter and control strategy.

Current-Fed Hybrid Dual Active Bridge DC–DC Converter for a Fuel Cell Power Conditioning System With Reduced Input Current Ripple

In this paper, a variable switching frequency space vector pulsewidth modulation control is proposed. It is used to achieve zero voltage switching (ZVS) for a three-phase grid-connected voltage source inverter with unity power factor. A wide range of ZVS can be realized without any additional sensors, auxiliary circuits, or current zero crossing detection circuits. The switching frequency can be easily calculated by a digital controller. The frequency variation range in a line cycle is only about 1.5 times at any specific load. An LCL filter is used to attenuate the high current ripples at the inverter side, and active damping is adopted to avoid the resonance and reduce the filter power loss. The switching loss can be significantly reduced by using silicon carbide mosfet s so that the conversion efficiency is high. The power density can also be improved due to the high switching frequency and the low inductance value of the filter. The operating principle, design considerations, and loss analyses are discussed in detail. A 3.5-kW simulation and experimental prototype interfacing a 350–400-V dc with a three-phase 110-V ac grid is developed to verify the performance of the proposed control strategy.

An SiC MOSFET Based Three-Phase ZVS Inverter Employing Variable Switching Frequency Space Vector PWM Control

A current-fed dual active bridge dc–dc converter using dual transformers is proposed for the energy storage system and electric vehicles, which is suitable to be used in wide input and wide output voltage range bidirectional power flow applications. Optimized switching pattern and the coupling relationship among all the controlled variables have been explored in order to minimize the leakage inductor current peak and rms value in spite of the load and voltage conversion gain variation, which can reduce the current stress in switches and conduction loss. Furthermore, wide ZVS range can be achieved. The preferred optimized working modes and real-time closed-loop implementation by employing the proposed control strategy are given. The ZVS conditions for each switch are discussed in detail. The turns ratio design is also demonstrated. The effectiveness of the proposed method is verified by the experimental results of a 1-kW prototype.

Leakage Inductor Current Peak Optimization for Dual-Transformer Current-Fed Dual Active Bridge DC–DC Converter With Wide Input and Output Voltage Range

In this article, a double degree-of-freedom variable control strategy with fixed frequency is proposed for a single-phase single-stage ac–dc rectifier based on dual active bridges. The proposed modulation strategy can achieve power factor correction without inner current ac current loop. In addition, the two control variables are calculated in real time without using look-up tables, and their combination not only achieves wider zero voltage switching range for switches but also lowers transformer current stress. The mode transition, the soft switching range, and working mode composition are analyzed. Besides, a 1-kW experimental prototype was built to verify the effectiveness of the control strategy.

Jiankun Zhang

Papers

Unified Boundary Trapezoidal Modulation Control Utilizing Fixed Duty Cycle Compensation and Magnetizing Current Design for Dual Active Bridge DC–DC Converter

Current-Fed Hybrid Dual Active Bridge DC–DC Converter for a Fuel Cell Power Conditioning System With Reduced Input Current Ripple

An SiC MOSFET Based Three-Phase ZVS Inverter Employing Variable Switching Frequency Space Vector PWM Control

Leakage Inductor Current Peak Optimization for Dual-Transformer Current-Fed Dual Active Bridge DC–DC Converter With Wide Input and Output Voltage Range

A Single-Stage Dual-Active-Bridge AC–DC Converter Employing Mode Transition Based on Real-Time Calculation