Wide Voltage Conversion Ratio Research Articles

Extension of Zero-Voltage Switching Region of Wide Volage Ratio Range Dual-Active-Bridge Converter by LC Antiresonant Network

Zero-voltage switching (ZVS) for dual active bridge (DAB) with wide voltage conversion ratio has a contradiction with low conduction loss, especially under light power transmission. Root mean square (RMS) increase of inductor current is unavoidable just by optimizing modulation schemes. Inspired by the various frequency (VF) and various inductor (VI), this article proposes a DAB converter with the capability of regulating the impedance of the resonant tank to extend the ZVS region. With an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> antiresonant circuit in series with original inductor, the equivalent inductance of the resonant network of the proposed converter increases along with the switching frequency within the designed frequency range. Thereby, when the voltage mismatches and the transferred power decreases, a large impedance is obtained by slightly increasing frequency to help to achieve ZVS. Moreover, the proposed DAB is found that single phase shift (SPS) has nearly identical characteristics of ZVS and conduction loss compared with multiple phase shift modulation. The benefit of this is that the complexity of close-loop control is significantly reduced just considering the switching frequency and external shift phase. In addition, ZVS characteristics and optimal control method are analyzed in detail. Finally, a 2 kW 360-400V/40-60V prototype is built, and the main experimental results are provided to verify the feasibility of the proposed converter and soft switching range of all switches.

A family of single-switch wide-gain converters with low voltage stress

A new family of single-switch dc–dc converters with simple structure are introduced in this paper. Firstly, using the approach of a simple switching dual structure, a switched-capacitor–inductor (SCL) cell was presented. Then, a SCL cell can be combined with the conventional circuits (Buck, Boost, Buck–Boost, Sepic, Zeta, Cuk) to provide a wide voltage conversion ratio. Taking the derived Cuk converter as an example, the comparisons among another buck–boost converters are listed, the voltage gain of the derived converter is higher than other converters, and the voltage stress on the power device is less than other converters. Furthermore, the features of single switch, common ground, continuous input, and output current are satisfied simultaneously under the condition of using few components. Finally, the converter’s performance and the correctness of the analysis are validated with results from the experimental prototype.

A high‐frequency transformer‐based buck‐boost AC‐AC converter with high efficiency and wide range conversion ratio for DVR application

AbstractThis paper proposes an isolated single‐phase impedance‐source ac‐ac converter with a wide voltage conversion ratio and a safe commutation strategy. The new topology has noteworthy features like continuous input current, galvanic isolation, and non‐inverting and inverting buck‐boost modes with a wide voltage coverage. Also, only one switch operates with high‐frequency PWM signals, reducing the semiconductor switching loss. The galvanic isolation has been achieved by employing a high‐frequency transformer (HFT), eliminating low‐frequency transformers (LFT) from the topology. A safe commutation strategy has been designed and applied to the converter to mitigate the voltage and current spikes on power switches, which eliminates additional snubber circuits. A prototype has been designed to validate the suggested converter performance in stand‐alone and DVR applications. The peak obtained efficiency equals 96.1% and 94.9% in inverting and non‐inverting step‐down and step‐up modes, respectively, validated by an accurate power loss model and experimental results. Experimental results confirm the theory and operation of the proposed converter.

A Bidirectional Fast EV Charger for Wide Voltage Range Using Three-Level DAB Based on Current and Voltage Stress Optimization

Converter cost is the crucial concern while designing off-board electric vehicle (EV) chargers for high-voltage charging applications using advanced high breakover voltage power semiconductor switches. To solve this problem, multilevel topology is used with the typical dual active bridge (DAB) for the development of high-voltage and high-power EV charging. It offers low cost, compact, less complex control, highly efficient, and reliable development. This article presents the design and development of bidirectional off-board fast EV charger with voltage and current stress optimization for wide voltage range. It is designed with two-stage power conversion. Here, active front-end converter is connected to three phase grid and controlled through synchronous reference frame (SRF) d-q control approach for active rectification. The large range of power and voltage variation in off-board EV charger design makes it challenging to develop a controller that allows the converter to operate inside the zero voltage switching (ZVS) operating region. In this context, a detailed circuit analysis of dc–dc stage with dual phase shift (DPS) control under different operating conditions is presented to identify the coordinates of safe operating region with reduced voltage stress. To select the converter control parameters with optimum current stress in conjunction with reduced voltage stress, particle-swarm-optimization technique is applied to the identified operating regions. This provides a unique selection criterion for both control parameters over wide voltage conversion ratio. A coordinated control is designed based on the identified boundaries for easy implementation and less computation burden on microcontroller units (MCUs). A 7.2-kW system is designed and simulated on MATLAB/Simulink. A 3.3-kW laboratory prototype is designed to validate the identified operating points with wide battery voltage range under varying source and loading scenarios.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

An Optimized DPS Control Strategy for LCL Resonant Dual Active Bridge Converter for Wide Voltage Conversion Ratio

This article presents an improved DPS (IDPS) control strategy for LCL resonant dual active bridge converter. Due to the LCL resonant tank, the converter's working modes are analyzed by using the Fourier transform. According to the fundamental harmonics of the key waveforms, the condition of zero-voltage switching (ZVS) in different working modes is derived. The relationship between the conduction loss and load power is analyzed. To achieve ZVS with low conduction loss and seamless transitions between the forward and reverse power flow, an IDPS modulation scheme is proposed. The control strategy can cover all the load power. The conduction loss in the IDPS is compared with the enhanced DPS, which illustrates the lower conduction loss. Finally, a 1-kW experimental prototype has been built to verify the effectiveness of the IDPS control strategy.

DAB Based DC-DC High Frequency Link PET for Interconnecting MVDC-LVDC Grids

This paper proposes dual active bridge (DAB) based high frequency power electronic transformer (PET) for interconnecting medium voltage dc (MVDC) and low voltage dc (LVDC) grids for dc power distribution. The above proposed concept works on dual active phase shift principle and square wave HF modulation technique for bidirectional power transfer. Compared to the traditional dc transformer scheme, The proposed power electronic transformer (PET) can disconnect from LVDC distribution grid effectively as a dc breaker when a short circuit fault occurs in the distribution grid. The isolated DC-DC PET topology with a wide range of voltage conversion ratio is useful for High Voltage DC tapping. The DAB based on switched capacitor is connected to the medium voltage DC side and acts as an inverter. The proposed topology has the ability to transfer higher power, and lower circulating power, lower high frequency link voltage, and RMS current and peak values with the same transmission power in the MVDC side. This paper analyzes the topology, voltage and power characterization, control strategy in detail. Increase in the intermediate AC frequency will reduce the size of the transformer and other passive elements significantly in the circuit. The theoretical analysis is supported by MATLAB simulation.

A Voltage-Quadrupler Interleaved Bidirectional DC–DC Converter With Intrinsic Equal Current Sharing Characteristic for Electric Vehicles

A voltage-quadrupler interleaved bidirectional dc-dc converter with intrinsic equal current sharing is presented in this article. The proposed converter offers a wide voltage conversion ratio, which makes it suitable for interconnecting the energy storage unit with dc bus for electric vehicle applications. A high voltage gain and low voltage stress across switches are achieved by adopting the capacitive voltage-divider stage, which enables the designer to employ a low-voltage switch with a small on-resistance RDS(ON). As a result, it allows the converter to run more efficiently and cooler. An interleaved connection at the low-voltage side paves the way for reducing the current ripple, which reduces the filter size and increases the power-density. Moreover, a built-in equal current sharing is achieved for two interleaved phases without using a current-sharing control scheme. The operating principle, steady-state characteristics including the current and voltage stress of the switches, and comparison with other state-of-the-art bidirectional converters are carried out in detail. Finally, to verify theoretical analysis, a 2-kW scaled-down laboratory prototype of the proposed converter using Gallium-Nitride switches is implemented.

Optimal phase‐shift control of three‐level dual‐active bridge DC–DC converter with minimum reflux power for wide voltage conversion ratio range application

Three-level dual-active bridge (3L-DAB) DC–DC converter under conventional phase-shift (CPS) control would produce large reflux power and current stress, especially when the voltage conversion ratio is varied in a wider range, which will lead to high power loss and low system efficiency. An optimised phase-shift (OPS) control strategy is proposed to control the 3L-DAB operating at the point with minimum reflux power. The power characteristics of 3L-DAB under CPS control are analysed. Then the mathematical model of the reflux power is established, and the relationship equations among the reflux power, phase-shift (PS) ratios, and voltage conversion ratio are deduced. The minimum reflux power and optimal PS ratio are calculated by using the segmentation optimisation algorithm in different ranges of transmission power and voltage conversion ratio. Performance comparative analysis between CPS and OPS controls is carried out later. Adopting the proposed OPS control strategy, the reflux power of 3L-DAB is minimised, as well as reducing the current stress and increasing the efficiency in a wide voltage conversion ratio range. An experimental prototype was developed to verify the effectiveness of the OPS control strategy and the correctness of the theoretical analysis.

Coordinated Two-Stage Operation and Control for Minimizing Energy Storage Capacitors in Cascaded Boost-Buck PFC Converters

Cascaded boost-buck PFC (CBBPFC) converters offer a wide voltage conversion ratio and a near-unity power factor but require a large output electrolytic capacitor, leading to poor reliability and power density. In this paper, a coordinated two-stage operation and control strategy is proposed to significantly minimize the capacitor requirement without any other hardware changes. In a conventional CBBPFC converter, the boost and buck stages either operate independently nor complementally. In contrast, the proposed method operates the two stages in a concerted manner, so it is possible to use the dc-link capacitor with certain voltage fluctuation to buffer the power imbalance between the AC input and DC output. A new coordinated control strategy and a fluctuation-ratio based design consideration are developed to coordinate the operation of the two stages, further complement the system design. A 200W CBBPFC prototype based on the design concept exhibits a maximum reduction of the output capacitor by 83%, a peak efficiency of 95.8%, and a power factor of 0.99.

Single‐stage ZETA‐SEPIC‐based multifunctional integrated converter for plug‐in electric vehicles

A single-stage-based integrated power electronic converter has been proposed for plug-in electric vehicles (PEVs). The proposed converter achieves all modes of vehicle operation, i.e. plug-in charging, propulsion and regenerative braking modes with wide voltage conversion ratio ( M ) [ M <; 1 as well as M > 1] in each mode. Therefore, a wide variation of battery voltage can be charged from the universal input voltage (90-260 V) and allowing more flexible control for capturing regenerative braking energy and dc-link voltage. The proposed converter has least components compared to those existing converters which have stepping up and stepping down capability in all modes. Moreover, a single switch operates in pulse width modulation in each mode of converter operation hence control system design becomes simpler and easy to implement. To correctly select the power stage switches, a loss analysis of the proposed converter has been investigated in ac/dc and dc/dc stages. Both simulation and experimental results are presented to validate the operation of the converter.

Common Grounded H-Type Bidirectional DC-DC Converter with a Wide Voltage Conversion Ratio for a Hybrid Energy Storage System

Hybrid energy storage systems (HESS) play an important role in maintaining the power balance of a direct current (DC) micro-grid. A HESS is mainly composed of high power density super-capacitors (SCs) and high energy density batteries. According to the operational requirements of an SC, a bidirectional DC-DC converter with the characteristics of a good dynamic response and a wide voltage conversion ratio is needed to interface the SC and a high-voltage DC bus. In this paper, a novel common grounded H-type bidirectional converter characterized by a good dynamic response, a low inductor current ripple, and a wide voltage conversion ratio is proposed. In addition, it can avoid the narrow pulse of pulse width modulation (PWM) voltage waveforms when a high voltage conversion ratio is achieved. All of these features are beneficial to the operation of the SC connected to a DC bus. The operating principle and characteristics of the proposed converter are presented in this paper. A 320 W prototype with a wide voltage conversion ranging from 3.3 to 8 in step-up mode and 1/8 to 1/3 in step-down mode has been constructed to validate the feasibility and effectiveness of the proposed converter.

Step‐down converter with wide voltage conversion ratio

A non-isolated dc–dc converter with a wide step-down voltage gain is presented, which combines one coupled inductor and two energy-transferring capacitors. The corresponding voltage conversion ratio is much lower than that of the traditional synchronously rectified buck converter, and the proposed converter can achieve an extremely low output voltage by adjusting the turns ratio and duty cycle. Furthermore, the proposed converter can achieve zero-voltage-switching turn-on, and the leakage inductance energy of the coupled inductor can be recycled to the capacitors, thereby causing the voltage spikes on some of the switches and all diodes to be quite low. In this study, theoretical deductions and experimental results are given to verify the feasibility and effectiveness of the proposed converter.