Conventional Converter Research Articles

A Detailed Assessment of the Power Quality Improvement of an Islanded AC Microgrid through Upgrading Conventional Grid-Feeding Current-Controlled Converters to Operate as Multifunctional Converters

The decarbonization of the global economy is one of society’s urgent objectives nowadays. Thus, the large-scale adoption of renewable energy sources, like solar and wind energy, seems to be the best pathway to achieving sustainable development. Thus, the microgrid concept has emerged as a solution to address concerns related to the intermittent nature and lack of inertia for such sources. Several studies involving microgrids have been published in the last few years. However, in most of them, power quality (PQ) disturbances and strategies to manage such disturbances are not considered, especially in the islanded operation mode. Hence, in this paper, a detailed assessment of the PQ of an islanded AC microgrid is conducted, considering the coexistence of a nonlinear load, voltage-controlled converters, and a current-controlled converter (CCC). The analyses consider two scenarios, depending on the operation mode of the CCC: (1) the CCC operating as a conventional grid-feeding converter and (2) considering a cost-effective upgrading of the conventional CCC to operate as a multifunctional converter. An experimental test bed is built to validate both scenarios. The presented results provide strong evidence that the AFF significantly improves the microgrid PQ and its suitability for dealing with PQ disturbances in real-world applications.

Performance investigation of a wave-driven compressed air energy storage system

The intermittent nature of waves causes a mismatch between the energy supply and demand. Hence an energy storage system is essential in the utilization of wave energy. This paper proposes a novel wave-driven compressed air energy storage (W-CAES) system that combines a heaving buoy wave energy converter with compressed air energy storage. Wave drives the heaving buoy to convert the wave energy to mechanical work that pumps water into a water-air compression chamber to form a liquid piston compressor. Air is compressed in the chamber and the wave energy is stored in the air. A numerical model was first developed in ANSYS-AQWA and validated using experimental data. Then this model was applied to evaluate the hydrodynamic characteristics, power generation capacity and thermodynamic behaviour of the W-CAES system under different wave conditions. Furthermore, the impacts of geometric parameters of the wave energy converter and compression chamber on the system performance were investigated. Results indicated that energy storage power was improved as the hydraulic cylinder area and storage pressure increased. The energy storage efficiency and round-trip efficiency could reach 60.5 % and 47.1 %, respectively under the isothermal compression process. By comparing the proposed W-CAES system with the conventional wave energy converter prototype under the same conditions, it showed that the proposed system yielded an increase in power output by up to 30 % under Tasmania wave conditions under an isothermal compression. The overall system wave capture factor is more sensitive to wave height than wave frequency. The capture factor can be as high as 20 % under Tasmania wave conditions. This study provides a new method for efficient wave energy conversion and storage.

A Symmetric Bipolar Quadratic Buck–Boost Converter With Synchronous Triple Switches

A novel non-isolated bipolar DC-DC converter is described in this study. The proposed converter provides negative and positive outputs with the same voltage level and common ground. It exploits three power switches with the synchronous operation, resulting in a simple controller and driver implementation. Compared with the conventional counterpart DC-DC converters, the proposed converter offers buck-boost ability with a wide control range of the switching duty cycle. Additionally, the proposed converter draws a continuous and smooth current from the DC input source, making it an excellent choice for renewable energy sources (RES) and energy storage systems (ESS). Likewise, the proposed quadratic converter can provide a higher voltage boost ability with the same switching duty cycle compared to the existing transformerless bipolar converters. Hence, it offers lower conduction losses and higher efficiency for the same demanded output voltages. Theoretical analysis and experimental results based on a sample prototype are presented to prove the proposed converter's performance in CCM mode.

Three Phase PFC Converter With Multilevel Inductive Switching Network

The rising power requirement of the on-board charger (OBC) demands high efficiency and high power density in the 3-phase power factor correction (PFC) converters. However, due to the large volume of boost inductors and filters of the conventional 2-level converters, their power density is limited. In this paper, multilevel inductive switching network (MISN) modules based on low-voltage switches are arranged in series at the ac-side to reduce the large size of inductors and filters. Besides, the operating principle and control strategy of the 3-phase MISN-PFC converter are analyzed. In addition, to determine the multiple variables of the MISN module, the design methodology is proposed based on the loss model and volume model for the multilevel converter. Finally, a 10kW prototype has been established to verify the analysis, where 99% efficiency at full load and 430W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density are achieved.

Enhanced Excitation Converter With Parallel/Series DC-Link Based on TAB for DFIG to Improve the LVRT Capability Under Severe Grid Faults

The low-voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG) based on the conventional excitation converter is insufficient under severe grid faults. The reason is that the dynamic rotor electromotive forces (EMF) will far exceed the dc-link voltage. To solve this issue, this letter proposes an enhanced excitation converter with parallel/series dc-link based on the triple active bridge (TAB) for DFIG. The dc-link of the enhanced excitation converter consists of the TAB and switching circuit, replacing the capacitive-type dc-link. Based on this topology, the dc-link voltage can increase instantaneously during severe grid faults to resist rotor EMF and improve the LVRT capability of DFIG. Compared with existing LVRT schemes, the enhanced excitation converter enables DFIG to achieve LVRT and inject the reactive current requirements of the grid code into the grid under severe grid faults. Finally, experiments verified the effectiveness of the proposed enhanced excitation converter and its control strategy.

Contribution to the Development of a Smart Ultrasound Scanner: Design and Analysis of the High-Voltage Power Supply of the Transmitter

A smart ultrasound scanner plays an important role in the transition to point-of-care imaging. DC–DC bipolar converters are essential in the generation of the ultrasound burst signal as they power the piezoelectric transducer. The conventional bipolar converter has minimal output gain and high-voltage stress, and the longer duty cycle on the semiconductors produces high conduction losses and reduces the efficiency of the system. The transmitter supply voltage is minimal, necessitating the use of high-gain bipolar converters. This proposed study is concerned with the development of an improved high-output voltage gain symmetric bipolar DC–DC converter topology which may be suitable for applications such as powering a smart ultrasound scanner transmitter. The proposed converter combines the conventional single-ended primary inductor converter (SEPIC) with a voltage multiplier cell (VMC) to improve voltage gain, transistor duty cycle, efficiency, and reliability. The present study describes the working principle of the proposed converter. The analysis of the voltage gain is carried out in continuous current mode (CCM) and discontinuous current mode (DCM), taking into account the nonidealities of the device. The simulation of the proposed system is carried out in the numerical environment Matlab/Simulink in order to verify its characteristics. A prototype model is realized and the experimental study presented validates the theoretical arguments and simulations. Due to the advantages of continuous input current, self-balancing bipolar outputs, and small component size, the proposed converter is a suitable choice for smart ultrasound transmitters.

Design and development of modified high efficient high gain DC-DC converter for SPV standalone systems

&lt;p class="MDPI17abstract"&gt;&lt;span lang="EN-US"&gt;A conventional DC-DC converter is not viable for power conditioning in standalone solar photovoltaic applications. Switching losses are the primary reason for the poor performance of conventional DC-DC converters. To mitigate the issues in conventional DC-DC converters, a high efficient high gain (HEHG) DC-DC converter is designed and developed in this research work. Modified HEHG converter utilizes the passive components switched capacitors, coupled inductor, and resistor capacitor (RC) snubber circuit for minimizing the switching losses and improving the overall power conversion efficiency of the solar photovoltaic (SPV) system. In addition, a modified &lt;br /&gt; D-sweep maximum power point tracking (MPPT) algorithm is in-corporate into this system to improve the tracking efficiency of the SPV system. HEHG for a standalone system is designed using MATLAB/Simulink environment and developed the hard-ware prototype. As a part of the validation, real-time testing is carried out and compares the performance of the HEHG converter with a traditional DC-DC converter. The theoretical efficiency of the HEHG converter is 96.01%, and the real-time efficiency is 95.62%. Found that theoretical and practical values of performance parameters are closely tallying.&lt;/span&gt;&lt;/p&gt;

PV-based DC-DC buck-boost converter for LED driver

PV-based power generation is implemented in many places due to the exhaustion of carbon-based fuels and ecological challenges. The solar panels for electric power generation along with the battery for storing the extra power will help society during the future demand. This paper analyzes a tri-port converter and designs it for buck-boost operation using inductors and switches in the circuit. The voltage converter is designed to have electric Energy transfer from solar panel to LED lamp, solar panel to battery and battery to LED lamp. The voltage ratio of the proposed buck-boost voltage regulator is designed to be more as compared with the conventional buck-boost converter. Also, the proposed buck-boost Voltage regulator output voltage polarity is found to be the same as compared to the input voltage. The working battery is developed to have a bi-directional power flow to deliver power to the LED lamp and to store power from the solar panel. The switches are operated alternatively and make the mode of operation strategy simple. The design of the converter stability analysis of the system using a bode plot is done. The experimental results acquired from the prototype validate the design of the converter.

A Simple 24-Pulse Star Rectifier Combining Two Different Tap Converters

To further improve the harmonic mitigation capability of the double-star rectifier, a simple 24-pulse star rectifier using a conventional tap converter (CTC) and an improved tap converter (ITC) is proposed. The proposed rectifier comprises two double-star rectification units, a CTC, an ITC and an interphase reactor (IPR). The CTC and ITC first expand the double-star rectifiers into 12-pulse rectifiers, and provide a phase shift of 15°, then connect through an IPR to achieve the effect of quadrupling the number of pulses. This configuration solves the problem of limited pulse multiplication capability (pulse multiplication number≤3) of the existing passive tap converter, and upgrades the double-star rectifier to a novel 24-pulse star rectifier. The resulting rectifier shows an approximately sinusoidal input current with the absence of the 5th, 7th, 17th and 19th harmonics. The proposed scheme has the advantages of simple structure, small size, and being economically justified because the proposed scheme does not change the structure of the double-star transformer, and the capacity of CTC and ITC is only 3.49% and 6.29% of the output power, respectively. An experimental prototype with an output power of 1 kW is built to verify the correctness of the theoretical analysis.

ConverGenT: Automated Topology Generation and Analysis of Hybrid DC–DC Converters

Owing to their high efficiency and high power density, hybrid DC-DC converters are gaining attention in academia and industry. However, no systematic procedure is currently available for creating new converter topologies where the number of inductors and capacitors are different. This paper proposes ConverGenT, an automated topological synthesis and analysis framework for two-phase hybrid DC-DC converters with one inductor, two capacitors consisting of one flying and one output capacitor. Consequently, all the converter topologies of this type are discovered. In contrast to the conventional approach that relies on intuition, this method requires less time and generates a complete set of converter topologies in a systematic manner. These two key advantages ensure that no possible converter topology is missed, making this method superior to the conventional approach. After generating a topology, all information about the converter topologies can be analyzed and verified manually or automatically, and the most suitable topology for a given application can be selected. ConverGenT has identified 62 converter families, each with a maximum of six topologies per family, that outperform conventional converters in certain aspects, with at least eight of these topologies having been published within the last five years. Details on topologies and performance of these converters are in the Appendix.

Two-stage PV grid-connected control strategy based on adaptive virtual inertia and damping control for DC-link capacitor dynamics self-synchronization

Conventional DC-link voltage-controlled voltage source converter (VQ-VSC) controls DC-link capacitor voltage and reactive power output by using phase locked loop (PLL) for synchronous grid connection of new energy sources such as PV. However, the deterioration of dynamic performance in PLL can lead to instability in VQ-VSC control within a weak grid. To improve the stability of VQ-VSC grid connection, the DC-link capacitor dynamic self-synchronous grid-connected control strategy without using PLL is proposed in this paper. The converter virtual rotational inertia variability and virtual inertia damping frequency characteristics are analyzed based on the synchronous generator rotor rotation characteristics. The proposed control strategy provides adaptive virtual inertia and damping coefficients for DC-link capacitor self-synchronous units to dynamically match the inertia and damping requirements during frequency synchronization, and enables VQ-VSC to operate in grid-forming mode without changing the grid synchronization unit. Compared with constant virtual inertia-damping control and adaptive virtual inertia-damping control based on change rate of frequency, the simulation results demonstrate the effectiveness of the proposed control strategy, which significantly improves the grid connection stability of PV systems in weak grids.

Concert Exploration of DFIG Grid-integrated MMC using Artificial Intelligence

The performance of grid-connected wind turbine systems that use a Doubly Fed Induction Generator (DFIG) is explored in this work. In the suggested configuration, two conversion stages are present. In the first step, Alternating Current (AC) voltage is changed into Direct Current (DC) voltage. At this point, the conventional two-level converter is implemented. The second stage involves the conversion of DC to AC using a five-level Modular Multilevel Converter (MMC). Voltage fluctuation is observed in the DC link. It is anticipated that the Fuzzy Logic Control (FLC) approach will be able to adjust the DC link voltage at the MMC of the second stage of conversion. For the purpose of the Pulse Width Modulation (PWM) system, the current controller is accountable for regulating the current signals and the reference signals. As a result, the PI Controller (PIC) is being evaluated for use in this function. Carrier-based Phase Disposition (PD) PWM is employed for MMC switch control. The proposed controllers’ performance is validated in Matlab/Simulink.

A novel bridgeless flying capacitor multilevel rectifier

SummaryA novel transformerless three‐phase unidirectional bridgeless flying capacitor (UBFC) rectifier for medium‐voltage and high‐voltage applications is presented in this paper. The rectifier consists of three single‐phase rectifiers in wye connection; the DC outputs of the three single‐phase rectifiers are connected in parallel to provide a high common DC‐link bus, which makes it convenient to connect with neutral point clamped (NPC) or flying capacitor (FC) multilevel inverters. To avoid phase‐to‐phase current circulation, an additional inductor and diode are added to each single‐phase rectifier. Compared with conventional bidirectional multilevel converters, only half IGBTs are used, the voltage stress is lower, and the line‐frequency transformers are no longer required, which makes the proposed rectifier has a series of advantages such as reduced cost, simplified control complexity, increased reliability and improved overall efficiency. The basic operating principle of the proposed rectifier in continuous conduction mode is discussed; an improved carrier‐based level‐shifted pulse‐width modulation (PWM) method integrated with voltage balancing and the double closed‐loop control strategy are proposed to achieve more voltage levels and keep the flying capacitors in balance. The feasibility of the proposed rectifier is verified by the simulation and experimental results.

A single‐stage bridgeless isolated positive output Cuk configuration‐based unidirectional onboard battery charger

SummaryAs power factor correction rectifiers play a key component of electric vehicle (EV) battery charger, the advancements in designing of improved power quality‐based EV charger become more significant in modern era. This article exposes a single‐stage bridgeless isolated positive output (BIPO) Cuk PFC converter with a noninverted output signal. The input diode rectifier present at the input is redeemed by the bridgeless topology that eliminates the serious power quality (PQ) issues and proffers the eminent charging solution for the light electric vehicles (LEV). Unlike the conventional Cuk converter, the noninverted outcome of the BIPO converter does not require a separate amplifier for converting negative to positive output voltage. The preferred charger utilizes a single voltage and current sensor to synchronize the battery charging control in the constant current (CC) and constant voltage (CV) phases of charging. Therefore, the converter encompasses intrinsic zero current switching (ZCS) and offers low‐cost solution to the charger with reduced control complexities. The extensive state space approach is executed to analyze the marginal stability of the presented system. Moreover, the detailed loss modeling is addressed to show the charger's efficacy curve at the standard conditions. A hardware prototype of 350 W, 60 V/4 A charger is implemented to validate its steady‐state and dynamic performance.

Electrically controllable broadband reflective linear cross-polarization conversion based on liquid crystals.

This paper presents an electrically controllable reflective broadband linear polarization (LP) converter based on liquid crystals (LCs) for cross-polarization conversion (CPC) in the terahertz frequency range. The proposed structure achieves a high polarization conversion ratio (PCR) exceeding 0.9 within the frequency range of 236.8 - 269.6 GHz. A vital feature of this design is the dynamic control of polarization conversion by re-orienting the nematic liquid crystal molecules through voltage bias switching between 'on' and 'off' states, allowing for precise manipulation of cross-polarized and co-polarized reflected waves. Experimental results validate the simulation outcomes, demonstrating excellent agreement. In contrast to conventional reflective polarization converters with fixed frequency responses, the proposed electrically controllable polarization conversion offers significant potential in imaging and optical communications.

Design and implementation of a cost-efficient clamping capacitor boost converter for a hybrid renewable energy system for increased gain to fulfil demands

Power generation plants are built in rural areas to meet the power demands and empower the financial status. The existing method of electrical power generation is difficult to meet the growing population as they are turning to hybrid renewable energy systems to meet the increasing demand. They were also not focused on power saving and flow with reduced power loss. The power generated from hybrid renewable energy systems is distributed to rural areas through a DC-DC converter. The DC-DC converter converts the Hybrid Renewable Energy System (HRE) output into a high DC voltage transmitted in a bus. The proposed HRE system consists of solar and wind plants in the network. So, for transferring, saving, and utilizing the power generated from the hybrid renewable energy system, a cost-efficient clamping capacitor boost converter (CCBC) with increased voltage gain is proposed. The CCBC has a clamping capacitor in-built with 2-diodes and 2-capacitors. The voltage gain produced using the proposed CCBC is doubled with the conventional converters. There is no high range of power spikes in the converter's capacitor. This paper explains the architecture and the complete functionality of the CCBC with the simulation results in detail. The simulation results conclude that the proposed CCBC provides cost-efficient high voltage gain converters for HRE systems, providing more than 500 W, which fulfills the demand of a single rural area.

High Step-Up Current-Fed Diode-Clamped Resonant Converter for Overloaded Fuel-Cell Vehicles

We propose a high step-up current-fed diode-clamped resonant converter for overloaded fuel-cell vehicles. The electric motor is able to demand short-time peak torque during sudden acceleration phase or long-time excessive torque when the fuel-cell vehicles are overloaded. Then, the conventional converter suffers from a high current spike at the secondary-side switches. The proposed converter incorporates diode-clamped cell on the secondary side, and therefore does not have the high current spike, but retains the benefits of the conventional converter such as high step-up function, ripple-free characteristic, and soft switching capability. When the output power is over its maximum nominal value, the secondary-side switches are switched off with complete zero-voltage-switching (ZVS) and the secondary-side diodes are off with zero-current-switching (ZCS). As a result, the proposed converter exhibits high efficiency and long-term operation under the nominal power and even at peak power. Furthermore, we have analyzed voltage gain, ZVS/ZCS region, and current/voltage stress on the active power components when the output power is over its maximum nominal value, which is different from those when the output power is in its nominal range. The theoretical analysis of the proposed converter is presented, then validated using a laboratory-built prototype.

A Structure-Reconfigurable LLC Resonant Converter With Wide Gain Range

In this paper, a structure-reconfigurable LLC (SR-LLC) resonant converter is proposed for wide output voltage applications. The converter can operate in half-bridge mode or full-bridge mode by modulating the driving signal of the switches. Four operation modes with scaled voltage gains are obtained by the independent or combined operation of resonant tanks. Compared with the conventional full-bridge LLC converter, the voltage gain range is greatly extended without extra switches. The consistent resonance parameters of two tanks allow four operating modes to have the same resonant frequency, which facilitates the design of magnetic components. Moreover, zero-voltage switching (ZVS) of the primary-side MOSFETs can be achieved in all modes. A 3.3-kW prototype with 75 V-450 V output voltage is built to verify the feasibility and effectiveness of the proposed converter. The peak efficiency of the prototype is 97.3%, and the efficiency curve is smooth in the ultra-wide output voltage range.

Control Scheme Based on Improved Odd-Harmonic Repetitive Control for Third-Harmonic Injection Two-Stage Matrix Converter

The third-harmonic injection two-stage matrix converter (3TSMC) not only inherits the advantages of the conventional two-stage matrix converter (TSMC), but also has simple modulation strategy and low switching losses. The injection current control is the key to achieving sinusoidal input currents of 3TSMC. The injection current reference consists of the third harmonic and its odd harmonics, making it difficult to obtain high control accuracy with a proportional integral (PI) controller. In this paper, a control scheme is proposed for the injection current of 3TSMC, which consists of an improved odd-harmonic repetitive controller (IORC), a PI controller and a feedforward controller. Compared with the conventional repetitive controller (CRC) and existing odd-harmonic repetitive controllers (ORC), the IORC has the highest gains and bandwidths at odd-harmonic frequencies, offering the proposed control scheme high control accuracy and fast transient response. The stability conditions of the system with the proposed control scheme are analyzed, and the design guidelines for the control parameters are provided on this basis. The experimental results demonstrate the effectiveness of the proposed control scheme.

Nonisolated High-Step-Down DC–DC Converters With Low Component Count and Voltage Stress

This paper proposes two new non-isolated high step-down DC/DC converters. The converters' voltage conversion ratio and their semiconductor components' voltage stress are improved compared to the conventional buck converter. By coupling the inductors of the first proposed converter, its volume and price is reduced. By employing a clamp circuit with low elements to the first proposed converter, the second proposed converter is introduced, in which its voltage conversion ratio and the voltage stress of components are improved significantly; thus, in high input voltage applications, high-quality components (switches with low on-resistance and diodes with low forward voltage) can be used. In these converters, the leakage inductances of the coupled inductor are clamping, and their energy is recovered. The proposed converters have fewer elements than related high step-down counterparts' converters leading to lower volume and losses due to lower elements, increasing efficiency. The switches of the proposed converters are switches simultaneously, reducing the converters' control circuit complexity. This paper discusses the theoretical analysis and operational principle of both proposed converters. Besides, to verify their performances, experimental results of the converters with 155-24 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> input and output voltage are presented.