AC-DC Converter Research Articles

Performance Enhancement of Single-Phase Two-Stage AC-DC Converter With Reduced DC-Link Capacitance

Single-phase two-stage AC-DC converters employed in electric vehicle (EV) chargers have the tendency to produce low frequency ripple due to input/ output power mismatch, making it necessary to use bulky DC-link capacitors. High voltage ripple at DC-link due to reduced capacitance, prompts poor input power quality and high low-line frequency ripple at the output of secondary-stage. In state-of-art, input power quality in converters with low DC-link capacitance is enhanced by using a digital low-pass filter (LPF). However, employing LPF to sensed DC-link voltage results in a non-optimum dynamic response and deteriorated stability margins. With the objective to improve input power quality, enhance dynamic performance and reduce secondary-side ripple for low valued DC-link capacitance AC-DC converters, a modified unit-template based model predictive (MUT-MPC) and a DC-link feedforward (DFF) controls are presented in this paper. The current feed-forward for the unit-template is controlled by predictive voltage error through an optimization process of cost function to improve input power quality and dynamic performance for primary AC-DC converter. Furthermore, a DC-link feedforward (DFF) control is implemented for secondary DC-DC stage, which reduces the low-frequency current ripple at the load. Finally, to verify the effectiveness of presented multi-objective control method in comparison with traditional controls, MATLAB simulations and experimental results are provided.

Operation Characteristics of Discontinuous Current Mode for a Dual-Active-Bridge AC-DC Converter with an Active Energy Buffer

Operation Characteristics of Discontinuous Current Mode for a Dual-Active-Bridge AC-DC Converter with an Active Energy Buffer

Switched Inductor Z Source Inverters for High Boost Applications

Abstract—This paper analyses a different configuration for the classical Z-Source Inverters (ZSI) which is named as Switched Inductor Z-Source Inverters (SL-ZSI) through simulation results. This configuration uses a unique impedance network that helps in the voltage adjustability. Comparing with the ordinary Z-source inverter, the new configuration provides more voltage inversion ability and enhances the output power quality of the main circuit considerably. The various applications of this configuration include DC-AC, AC-AC, DC-DC and AC-DC power conversions. Index Terms—Inverter, voltage source inverter (VSI), Z-source inverter (ZSI), switched inductor Z-source inverter (SI-ZSI)

Three-Phase Single-Stage Three-Port High-Frequency Isolated DC–AC Converter

Three-Phase Single-Stage Three-Port High-Frequency Isolated DC–AC Converter

Fast DC Charging Infrastructures for Electric Vehicles: Overview of Technologies, Standards, and Challenges

This paper is an overview of fast charging for electrical vehicles. Specifically, it analyzes the impact of Ultra-Fast Charging Stations (UFCSs) on the distribution grid and their role in the smart grids. Moreover, the paper defines the framework of UFC, its diffusion and the associated new trends. The most frequently used converters in the conversion stages of DC charging stations with integrated generation are analyzed. To achieve this goal four active front end AC-DC converters (unidirectional and bidirectional), three isolated DC-DC converters as well as two control architectures are explored. In comparing the targeted configurations, the main target is set on categorizing them based on supply voltage level, type of smart grid, and power flow of the converters. Further, the paper outlines a broad overview of main standards for UFCSs and evaluation of the reliability, data collection, and operation of UFCSs. The paper aims to to link the needs of the designers of charging stations to preferences of the commercial market.

A self-powered synchronous magnetic flux extraction interface for electromagnetic energy harvesting

In this work, a self-powered synchronous magnetic flux extraction (SP-SMFE) circuit is proposed for electromagnetic energy harvesting. It's a bridgeless direct ac-dc converter, that uses a large-value external inductor L to store and transfer energy. By comparing the voltage across L, SP-SMFE achieves the peak detection of the inductor current Iem without an external power supply and transfers the energy to the load when Iem reaches the peak value, which can maximize the energy extraction from the electromagnetic transducer. Simulation results show that the output power of SP-SMFE is much higher than that of the voltage doubler circuit under the load range of 1–100 kΩ and the frequency range of 20–140 Hz. The input ac voltage with 4 V amplitude is rectified and stepped up to 59 V dc by SP-SMFE at the load of 100 kΩ and the frequency of 40 Hz. Experiment results verify the effectiveness of the SP-SMFE circuit in power harvesting at low frequencies and large loads.

A New Level Shifted Carrier Based PWM Technique for a Cascaded Multilevel Inverter Based Induction Motor Drive

The pulse width modulation (PWM) techniques are becoming the game changer for multi-pulse power converter fed multilevel inverter-based induction motor drive (IMD) due to their significant impacts on power quality. In this paper, a new level shifted carrier-based PWM technique is proposed for a 5-level cascaded H-bridge (CHB) multilevel inverter driven by a 36-pulse ac-dc converter based IMD. To meet the power quality demand of IEEE-519 at grid side, a modular transformer is used, and the transformer is coupled to form a 36-pulse ac-dc converter. A 5-level CHB multilevel inverter is utilized on the motor side, which uses the proposed carrier based PWM technique for switching action to ensure superior performance of the IMD. The proposed PWM technique is named as third-harmonic injected inverted sinusoidal carrier PWM (THI2SCPWM), which utilizes 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic injection principle with inverted sinusoidal signal to form the proposed carrier signal. The 5-level CHB inverter used in the IMD shows less power loss and total harmonic distortion (THD) with the proposed THI2SCPWM technique. Moreover, the IMD with the THI2SCPWM shows low stator voltage THD, stator current THD, and smooth dynamic response. Apart from these, the THI2SCPWM mitigates the torque ripple of the IMD. The motor drive system with the THI2SCPWM technique is modeled and its performance is simulated on MATLAB/Simulink environment. A scaled down experimental setup is utilized to validate the superiority of the proposed PWM technique.

Sliding-mode control for boost converters under voltage and load variations

&lt;p&gt;&lt;span lang="EN-US"&gt;Boost converters are employed in DC motors, switch-mode power supplies, and other applications. Practical implementation difficulties, reliance on variable-frequency units, and delayed dynamic responses to changes in load and voltage are the main drawbacks of different control methods for the boost converter. In this paper, two techniques were proposed with the target of controlling the boost converter to improve the efficiency of the converter's performance. The two techniques used in this paper depended on fixed-frequency mode instead of variable-frequency mode because of the demerits of the latter factor. The first technique is the sliding-mode control for the AC-DC converter to achieve power factor correction and reduce the harmonic ratio significantly while regulating the output voltage. This technique was used for the DC-DC converter to obtain a rapid dynamic response to control sudden or considerable changes in loads or input voltages with a regulated output voltage. Moreover, the two-loop cascade control is the second proposed technique for the DC-DC converter to achieve an excellent dynamic response under step loads or input voltage variations with an excellently regulated output voltage. Re-simulation results validated the proposed design approach and illustrated the proposed controller's robustness and faster response time.&lt;/span&gt;&lt;/p&gt;

Multilevel Converter Based on Series and Parallel Connections Using Floating Capacitor

The series connections of converter cells are interesting for high voltage applications, while parallel connections are for high current applications. The series/parallel is interesting for medium voltage and current applications because they present semiconductor devices with a lower rating in both voltage and current, thus, reducing the cost and size of the converters. This article investigates the configuration of a single-phase multilevel DC-AC converter based on series and parallel connections of H-bridges using floating capacitors to reduce the number of independent DC sources. The use of the floating capacitor has the limitation of working in certain operating regions. This article investigates which regions can work with floating capacitors and presents the mathematical model, general control strategy, pulse width modulation (PWM) strategies, and loss comparison with conventional series or parallel systems. Simulations and experimental results are presented to validate the control and PWM strategies used.

Efficient Wireless Power Transfer Topology for Phone Charging Application

Abstract: Wireless power transfer scheme used on phone chargers are expected to have high efficiency, and reliability. However, existing AC-DC converter schemes were shown to be susceptible to leakage inductance and have lower regulation or excessive power losses. Output voltage regulation is a concern for wireless power converter topologies due to the need for additional shunt devices at DC output. In this paper, literature survey on various wireless power transfer scheme is performed with specific focus on phone charging applications. A modified topology using impedance matching transformer is presented with circuit analysis and LT spice simulation results. It is shown that the proposed topology can deliver better output voltage regulation at various coupling coefficients indicating a superior circuit performance for various separation distances between transmitting and receiving coil.

A Single-Stage, Multi-Port Hybrid Power Converter Integrating PV and Wind Sources for a Standalone DC System

In this paper, a hybrid PV–wind-source- based multi-port converter focused on a standalone DC system is proposed. The proposed configuration is able to perform simultaneous three-phase AC–DC conversion and DC–DC conversion, ensuring simultaneous power extraction from these combined sources. The proposed converter is a single-stage converter that enhances dependability and eliminates redundant conversion stages with regard to the earlier configurations for the hybrid PV–wind sources. The operational aspects of the proposed converter are depicted, illustrating the regulation of load voltage and load power because of the dynamic output capability of PV–wind sources. Furthermore, the comprehensive control architecture to govern the concurrent conversion operations with the generation of three-phase modulating signals and duty ratio signal in accordance with the load voltage control is elaborated. Additionally, the modified sinusoidal PWM scheme for the proposed converter is elaborated, showing the unification of three-phase modulating signals and duty ratio signal for the generation of PWM pulses which facilitates the simultaneous power conversion processes. Finally, to validate the suitability of the proposed converter, the performance of the converter under various scenarios is investigated through simulation and experimental case studies.

Voltage-Oriented Control-Based Three-Phase, Three-Leg Bidirectional AC–DC Converter with Improved Power Quality for Microgrids

Renewable energy sources (RESs) and energy storage schemes (ESSs) integrated into a microgrid (MG) system have been widely used in power generation and distribution to provide a constant supply of electricity. The power electronics converters, particularly the bidirectional power converters (BPCs), are promising interfaces for MG infrastructure because they control the power management of the whole MG system. The controller of BPCs can be designed using several different control strategies. However, all the existing controllers have system stability, dynamics, and power quality issues. Therefore, this study demonstrates the development of an LCL-filtered grid-connected bidirectional AC–DC converter’s (BADC) control strategy based on voltage-oriented control (VOC) to overcome these issues. The proposed VOC-based inner current control loop (ICCL) is implemented in synchronous dq-coordinate with the help of proportional-integral (PI) controllers. An observer-based active damping (AD) is also developed in order to estimate the filter capacitor current from the capacitor voltage instead of directly measuring it. This developed AD system helps to damp the resonance effect of the LCL filter, improves system stability, and also eliminates the practical challenges of measuring capacitor current. The proposed controller with AD is able to realize bidirectional power transfer (BPT) with reduced power losses due to the elimination of passive damping and improved power quality, system dynamics, and stability. The mathematical modeling of the suggested system was developed, and the structure of the system model was established in the MATLAB/Simulink environment. The performance of the proposed system was validated with real-time software-in-the-loop (RT-SIL) simulation using the OPAL-RT simulator for a 16 kVA converter system. The real-time (RT) simulation results show that the BADC with the proposed control scheme can provide better dynamic performance and operate with tolerable total harmonic distortion (THD) of 2.62% and 2.71% for inverter and rectifier modes of operation, respectively.

Optimal Sizing and Management of Hybrid Renewable Energy System for DC-Powered Commercial Building

DC power may be more efficient than AC power in certain applications, especially when it comes to local generation and storage. This is because AC power requires extra equipment to convert it to DC power, which can lead to energy losses. Using DC power, on the other hand, makes it easier for devices to use it directly, resulting in higher energy efficiency. Additionally, using DC power can reduce equipment capital costs as it eliminates the need for additional AC–DC conversion equipment. Finally, DC power systems can offer new communication capabilities, including plug-and-play for generation and storage devices, making it simpler to integrate these systems into existing infrastructure. This paper analyzes the optimal size of a photovoltaic/PEM fuel cell system to supply a certain DC commercial load in NEOM city. To identify the best size of the PV/PEMFC, minimizing the cost of energy (COE) and minimizing the net present cost (NPC) are considered. The paper studies three sizes of PEMFCs: 15 kW, 20 kW, and 25 kW. In addition, five different PV modules are selected: Axitec 450 Watt, Jinko 415 Watt, REC Solar 410 Watt, Seraphim 310 Watt, and Tongwei 415 Watt. The results of the study confirmed that the best size of the hybrid system comprises a 15 kW PEMFC, a 267 kW Tongwei PV array, a 60 kg electrolyzer, and a 20 kg hydrogen tank. Under these conditions, the COE and NPC are 0.293 USD/kWh and 498,984 USD, respectively.

Life extension of AC-DC converters for hydrogen electrolysers operating as part of offshore wind turbines

Energy resources based on green hydrogen are nowadays beginning to enjoy wide adoption and draw considerable interest. There are different types of hydrogen production, but it is green hydrogen that is becoming an attractive energy development capable of replacing blue and grey hydrogen as well as fossil fuels, Thereby the carbon footprint will be reduced for a number of industrial processes. Proton exchange membrane electrolyzers used for the production of environmentally friendly hydrogen have one key shortcoming, which is the short service life of the equipment. This paper presents a comparative study of the commonly applied PLL control of AC-DC converters. To improve the control of the proton exchange membrane of the electrolyzer, a vector control arrangement is adopted, which allows, by relying on cascade control loops, maintaining different DC link voltage levels and thereby extending the DC link input voltage variation range.

A current-source DC-AC converter and control strategy for grid-connected PV applications

This paper presents a two-stage current-source DC-AC converter for grid-connected PV applications which is composed of an input step-up stage, followed by a step-down stage and an unfolding inverter. A decentralized control strategy of the DC-DC stage allows maximizing the renewable energy harvest using an Incremental Conductance MPPT algorithm and synthesizing an output current to be injected into the grid with low harmonic distortion. Double-loop PI controllers are used for the boost stage. The DC bus voltage of the buck stage is regulated using a PI controller, and an inner Proportional-Resonant (PR) controller tracks a sinusoidal reference. The PR controller proposed in this paper, includes a reduced number of resonant stages meeting the energy quality required by standards, which results in good stability margins. Finally, a SOGI-FLL algorithm synchronizes the inverter operation with the grid. Experimental results show an excellent dynamic response of the system, and the injected current complies with the IEEE Std. 1547–2018 specifications regarding harmonic content using a control law with a low computational burden.

Performances of Multi-Configuration Piezoelectric Connection with AC-DC Converter in Low Frequency Energy Harvesting System

Harvesting energy by capturing vibration from low frequency energy have been explored extensively. In essence, a single piezoelectric transducer or an array of piezoelectric connections are used to convert kinetic energy into electrical energy in order to produce low frequency energy. In this paper, multi-configuration array piezoelectric connections are used to investigate the performances of different converter circuit types in low energy harvesting applications. This research utilized three pieces of circular piezoelectric sensor to test the combinations of array connection. There are four options for the piezoelectric sensor configuration: parallel (P), series (S), parallel-series (PS), and series-parallel (SP) while the full wave bridge rectifier (FWBR), parallel voltage multiplier (PVM), and parallel Synchronized Switch Harvesting on Inductor (P-SSHI) converter circuit are chosen AC-DC converter circuits. The system is assessed using a variety of load configurations, including 10 kΩ and 1 MΩ with a 3 Hz input frequency. In order to produce the highest possible output of collected power, the observation focuses on identifying the ideal combination of array piezoelectric connections with AC-DC converter. The result shows that 3-Parallel (3P) piezoelectric connection obtained a higher power output among the other types of array piezoelectric which was 5.97μW. The FWBR circuit generated the highest output power with 2.42μW for a combination of piezoelectric sensors array of 3P connection with the AC-DC converter.

Guest Editorial: Special Issue on Emerging Topics of High-Frequency High-Power Density DC–AC Conversion Technologies

Guest Editorial: Special Issue on Emerging Topics of High-Frequency High-Power Density DC–AC Conversion Technologies

A Single-Stage AC–DC Converter Based on Semi Dual-Active-Bridge With Decoupled Inductor Current Modulation Strategy

In this article, a novel decoupled inductor current modulation strategy for a single-stage AC-DC converter based on semi-dual-active-bridge (semi-DAB) is proposed, which helps to minimize the total harmonics distortion (THD) and improve the conversion efficiency. The transformer turns ratio is designed in an optimized method for higher conversion efficiency. Only two control variables are used. And the converter could achieve wider output voltage range and high power factor without mandatory current tracking loop and look-up tables. In addition, losses, THD and backflow power comparisons between the decoupled inductor current and the optimal peak current modulation are presented. The power transfer capability, mode transition mechanism, soft switching range and mode operation region and parameter design are analyzed. Switches can achieve zero-voltage-switching (ZVS) within wide operating rang and rectifier diodes can achieve zero-current-switching (ZCS) off in all operation situations. Besides, a 1kW experimental prototype was built to verify the effectiveness of the proposed control strategy.

The VSC-HVDC Transmission System Performance Assessment

As the use of renewable resources increases the transfer of power from remote area to consumer is a big challenge. Therefore, Voltage Source Converter High Voltage Direct Current (VSC-HVDC) transmission is gaining more popularity for integration of renewable energy generators to the consumers using smart grid. Even after many advantages of HVDC transmission system it is not used popularly due to unexpected instability in the system. However recent developments in semiconductor devices and control techniques the HVDC link operation in transmission system becomes easier. In this paper VSC based HVDC system is designed with AC-DC converter model for power flow assessment of both sides of HVDC link. To analyze the proposed model a simulation model of 75km DC line with voltage source converter (VSC) based AC-DC converter model on both side of DC line is designed in a MATLAB environment. HVDC link efficiency is calculated by analyzing power flow through AC lines at both ends of HVDC line.

Performance improvements of power converters for high power induction motor drive

This paper deals with a reliable transformer configuration with simple wiring and less number windings for twenty-four pulse AC-DC converter, which is used in medium voltage drive system so that it can adverse the effects produced by harmonics currents fed into the grid by converters that do not affect other consumers connected to the same electrical grid. Apart from this, a five-level symmetrical multilevel inverter configuration is used by cascading four two-level voltage source inverters. It is designed with less quantity of components counts like; power switches, diodes and electrolytic capacitors. Because power quality impacts the suitability of electrical power for consumer electronics, an attempt is made in this work to improve power quality through the connecting high-pulse converter at the grid end instead of 12-pulse and modified level-shifted pulse width modulation for a multi-level inverter at the drive end. Performance of the described topology is verified in the laboratory using a drive-through MATLAB/Simulink environment and a prototype at a reduced scale. The feasibility and effectiveness of the proposed topology are demonstrated by a comprehensive comparison with recently reported schemes. Promising results validate this new concept.