Converter Architecture Research Articles

FD Cell-Free Massive MIMO Systems With Downlink Pilots: Analysis and Optimization

We consider a full duplex (FD) massive multiple-input multiple-output (mMIMO) cell-free (CF) system, where a large number of multi-antenna FD access points (APs) jointly serve multiple FD user equipments (UEs). The APs transmit precoded downlink pilots for the UEs to estimate the effective downlink channel. For this system, we derive closed-form uplink and downlink spectral efficiency (SE) expressions by considering i) radio-frequency (RF) impairments at the APs and UEs; ii) dynamic resolution analog-to-digital converter/digital-to-analog converter (ADC/DAC) architecture at the APs and low-resolution ADC/DACs at the UEs; and iii) spatially-correlated Rician channels. We then maximize the non-convex global energy efficiency metric by using the block minorization-maximization technique, which decomposes the main optimization into multiple convex surrogate sub-problems. We analytically show that the SE gain obtained with downlink training is limited for practical CF systems with RF and ADC/DAC impairments, Rician channel and pilot contamination. We also extensively investigate the impact of FD interferences on the downlink training gain.

Synthesis and Implementation of a Multiport Dual Input-Dual Output Converter for Electric Vehicle Applications

In recent years, multiport DC-DC converters are seen in a variety of power converter applications in electric vehicles. The design of multiport converter architectures plays a major role in DC microgrids and electric vehicle applications. This research examines a modified multiport converter structure interface with dual inputs and dual outputs used in electric vehicles. The versatility of accommodating energy sources with varying voltage and current nature characteristics is the most notable feature of this converter. During operation, the proposed architecture can offer a boost as well as buck operations at the same time. The suggested dual input-dual output (DIDO) converter is built with fewer components and a simpler control technique which makes it more dependable and the converter is cost-effective. Furthermore, this structure allows the power to flow in both directions making it to be utilized in electric vehicle battery charging during regenerative braking. The converter’s steady-state and dynamic behavior are investigated, and a control strategy for regulating the power flow among the varied input energies is proposed. To develop the suggested converter, a small-signal model is modeled. MATLAB simulation and experimental findings are used for the verification of converter design and validated the performance behavior experimentally using a hardware setup.

Withdrawal: P. A. Harsha Vardhini and M. Makkena (2022), Design and Comparative Analysis of On‐Chip Sigma Delta ADC for Signal Processing Applications. Advanced Control for Applications: Engineering and Industrial Systems. Accepted Author Manuscript e82. https://doi.org/10.1002/adc2.82

Advent in VLSI technology made digital signal processing to take over analog signal processing. Analog to digital converter plays a vital role in modern digital processing applications. Sigma delta analog to digital converter architecture being digital dominant architecture is much suitable for signal processing applications. This paper presents the design of a low pass continuous time sigma delta analog to digital converter on-chip architecture suitable for signal processing applications with a very few passive components connected externally to FPGA. Schematic level architecture of high-speed comparator working at a differential swing which is not allowed by standard differential pads is designed. By applying various differential swings at the input to LVPECL, the performance and power is analyzed. High performance comparator schematic is designed for On-chip Continuous-time Sigma-delta ADC architecture. Simulations are carried out to verify the maximum input frequency for given RC values. Xilinx provided Spartan 6 I/O pad and package SPICE models are used. Power analysis is carried out with LVPECL logic family based differential buffers along with external RC circuit. The analog and digital sections simulations along with mixed signal simulations at different stages are performed. Power and performance analysis are carried out using H-Spice and Questasim simulations.

DC/DC Modular Multilevel Converters for HVDC Interconnection: A Comprehensive Review

High voltage direct current (HVDC) technology is a key component in power systems owing to huge benefits such as long-distance power transmission, lower losses, asynchronous grid interconnections, controllability, system availability, and limited short-circuit currents. HVDC transmission is a cost-effective method of transporting huge amounts of power across long distances with little loss. It can also link asynchronous alternative current (AC) networks while balancing the grid. DC/DC converters are one of the most important components for HVDC power transmission, and DC/DC modular multilevel converters (MMCs) are the backbone of HVDC grid interconnections. The DC/DC MMC is a highly regarded converter architecture for medium/high-voltage DC grid interconnection. DC/DC MMC topologies play a key role in modern HVDC networks with varying voltage levels. This paper’s fundamental aim is to offer a recent comprehensive review of HVDC topologies, current DC/DC modular multilevel converter (MMC) topologies for HVDC interconnection, and DC/DC MMC control techniques.

Design and Analysis of Partial shading of the PV System Integrated with High-Frequency Inverter and Rectifier Operation for the Electric Vehicle

Solar photovoltaic cells are in high demand for sustainable energy generation because of their capacity to provide direct power. As a result, DC-DC converters that can enhance the output voltage and do so reliably while eliminating changes in solar panel outputs are required. Inconsistencies in sun-light availability, ambient temperature, and shadows, among many other considerations, cause the fluctuations. Compared to the typical DC-DC Boost converter, the suggested converter architecture has a higher efficiency of over 95%. In a resonant inductive coupled power transmission system for an electric vehicle, this research demonstrates partial shading of a 250-W PV solar-powered interfaced with a high-frequency resonant full-bridge inverter. The suggested system’s DC input is provided by a PV panel. The ratio of DC Input sources supplied to the high-frequency inverter is 1:3. For a fixed modulation of 0.7, the step modulated for a high-frequency inverter uses a pre-calculated switching angle. Due to a very high-frequency AC connection, the suggested system is more efficient than a traditional system of 50 Hz inverter operation and multiple-output transformer architecture. Zero Voltage Switching (ZVS) is ensured in this study, which decreases switching losses. In the MATLAB/ SIMULINK environment, the suggested approach has been validated. The research aims to investigate and illustrate the effect of partial shading with and without a bypass diode on the I (V) and P (V) properties of solar panels. Hence, the suggested approach’s performance is compared to the present method in terms of parameters, and 95 percent efficiency may be attained. When compared to shaded and unshaded situations, this paper displays greater feature modifications.

Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core–shell nanostructures by pulsed laser technique

The biochemical reduction of nitrite (NO2−) ions to ammonia (NH3) requires six electrons and is catalyzed by the cytochrome c NO2− reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO3−) and NO2− in wastewater, to produce the more valuable NH3 product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO3− reduction reaction (NO3−RR), but the NO2−RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO2− to NH3 using Cu@Cu2O core–shell NPs to simultaneously treat wastewater by removing NO2− and producing valuable NH3. The Cu@Cu2O core–shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core–shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO2− and the ammonium (NH4+)−N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu2O core–shell NPs exhibited outstanding NO2−RR activity, demonstrating a maximum NO2− removal efficiency of approximately 94% and a high NH4+-N yield rate of approximately 0.03 mmol h−1.cm−2 at −1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO2−RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO2− to NH3 via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO2− to NH4+.

A Multi-Objective Co-Design Optimization Framework for Grid-Connected Hybrid Battery Energy Storage Systems: Optimal Sizing and Selection of Technology

This paper develops a multi-objective co-design optimization framework for the optimal sizing and selection of battery and power electronics in hybrid battery energy storage systems (HBESSs) connected to the grid. The co-design optimization approach is crucial for such a complex system with coupled subcomponents. To this end, a nondominated sorting genetic algorithm (NSGA-II) is used for optimal sizing and selection of technologies in the design of the HBESS, considering design parameters such as cost, efficiency, and lifetime. The interoperable framework is applied considering three first-life battery cells and one second-life battery cell for forming two independent battery packs as a hybrid battery unit and considers two power conversion architectures for interfacing the hybrid battery unit to the grid with different power stages and levels of modularity. Finally, the globally best HBESS system obtained as the output of the framework is made up of LTO first-life and LFP second-life cells and enables a total cost of ownership (TCO) reduction of 29.6% compared to the baseline.

Generalized Multivariable Grid-Forming Control Design for Power Converters

The grid-forming converter is an important unit in the future power system with more inverter-interfaced generators. However, improving its performance is still a key challenge. This paper proposes a generalized architecture of the grid-forming converter from the view of multivariable feedback control. As a result, many of the existing popular control strategies, i.e., droop control, power synchronization control, virtual synchronous generator control, matching control, dispatchable virtual oscillator control, and their improved forms are unified into a multivariable feedback control transfer matrix working on several linear and nonlinear error signals. Meanwhile, unlike the traditional assumptions of decoupling between AC and DC control, active power and reactive power control, the proposed configuration simultaneously takes all of them into consideration, which therefore can provide better performance. As an example, a new multi-input-multi-output-based grid-forming (MIMO-GFM) control is proposed based on the generalized configuration. To cope with the multivariable feedback, an optimal and structured $H_{\infty}$ synthesis is used to design the control parameters. At last, simulation and experimental results show superior performance and robustness of the proposed configuration and control.

A High-Frequency MMC for DC–DC Applications Using a Three-Winding Transformer With DC Flux Cancellation

In this article, a novel high-frequency isolated modular multilevel dc–dc converter is proposed for large step ratio, medium voltage dc–dc applications. The proposed converter is based on the recently introduced class of converters termed the current shaping modular multilevel dc–dc converter (CS-MMC). In the CS-MMC, no string inductors are required and only a fraction of the voltage source modules are switched in each fundamental ac period enabling high effective frequencies to be achieved. The proposed converter builds on this earlier work by introducing a new topology featuring galvanic isolation using only a low voltage, high-frequency, three-winding transformer, and imposing dc flux canceling within the transformer. This article describes the converter architecture, its operating principles, and a control design. Experimental results are provided from a 1250V to 145V, 50 kHz laboratory-scale prototype with a peak measured efficiency of 96.8% at 2.8 kW.

Electron Transfer at Quantum Dot-Metal Oxide Interfaces for Solar Energy Conversion.

Electron transfer at a donor–acceptor quantum dot–metal oxide interface is a process fundamentally relevant to solar energy conversion architectures as, e.g., sensitized solar cells and solar fuels schemes. As kinetic competition at these technologically relevant interfaces largely determines device performance, this Review surveys several aspects linking electron transfer dynamics and device efficiency; this correlation is done for systems aiming for efficiencies up to and above the ∼33% efficiency limit set by Shockley and Queisser for single gap devices. Furthermore, we critically comment on common pitfalls associated with the interpretation of kinetic data obtained from current methodologies and experimental approaches, and finally, we highlight works that, to our judgment, have contributed to a better understanding of the fundamentals governing electron transfer at quantum dot–metal oxide interfaces.

A modified Z‐source switched‐capacitor based non‐isolated high gain DC‐DC converter for photovoltaic applications

AbstractThis work proposes a modified high gain DC‐DC converter integrated with two boost converter stages, based on a boost cell and a Z‐source (ZS) cell with a switched capacitor (SC). The proposed converter architecture is simple, with a continuous input current and a wide range of input voltage fluctuation handling capabilities. It also provides a high voltage gain while minimizing voltage stress on semiconductor components. Because of the aforementioned characteristics, the proposed converter is suitable for combining with low‐voltage DC‐sources to high‐voltage DC bus in a variety of applications such as solar photovoltaic (SPV), fuel‐cell, and LED lighting. The operational principles, thermal modeling, steady‐state, and dynamic performance analysis are meticulously carried out on a 400 W laboratory prototype of the proposed converter. The converter's performance is carefully compared with similar existing topologies in terms of total device count and size, the voltage stress on power semiconductors, voltage gain, and peak efficiency. Furthermore, experimental findings show that a 12 V input is boosted to 98.8 V at a duty ratio of 0.3, demonstrating the efficacy of the proposed converter over a comparable structure.

Combined heterostructures between Bi2S3 nanosheets and H2-treated TiO2 nanorods for enhanced photoelectrochemical water splitting

Constructing heterostructures plays a critical role in promoting separation and transfer of photo-generated carriers, which offers great potential in photoelectrochemical (PEC) water splitting. Herein, on the basis of an interesting structure–property relationship, this work provides an effective strategy to improve the photoelectrochemical performance. A hierarchical heterostructure of intercrossed Bi2S3 nanosheets on hydrogen-treated TiO2 nanorods is fabricated via a facile solvothermal method. By virtue of hydrogen treatment, H2-treated TiO2 nanorods (H-TiO2) exhibit a higher PEC performance than bare TiO2 owing to the better charge separation and narrower band gap. Moreover, boosted by the intercrossed heterostructure, the Bi2S3/H-TiO2 heterostructure achieves an optimal photocurrent density of 2.35 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE), which is 16 times that of TiO2 photoanode. PEC studies demonstrate that benefitting from the efficient electron transfer and charge separation within the novel intercrossed heterostructure, it exhibits much better photoactivity than 0D nanoparticle under visible light irradiation. Furthermore, the Z-scheme heterojunction formed between hydrogen-treated TiO2 and Bi2S3 can not only enlarge the photo-response range, but also decrease the recombination loss of photogenerated charge carriers. The synergistic effect of hydrogen treatment, intercrossed heterostructure as well as Z-scheme heterojunction ensures the excellent photoelectrochemical performance of Bi2S3/TiO2 photoanode. Based on the exciting result, this work provides a reliable strategy towards the fabrication and application of low-cost and noble-metal-free nanorod-based hierarchical architecture for solar energy conversion.

Recent Advances and Trends in Voltage-Time Domain Hybrid ADCs

The benefits of technology scaling have fueled interest in voltage-time domain hybrid ADCs. The hybrid ADCs employing combinations of successive approximation register (SAR), time-to-digital converter (TDC), and voltage-controlled oscillator (VCO) architectures have become attractive alternatives for analog intensive ADCs, owning to the merits of digital-centric nature, low-voltage tolerance, and scaling-friendly circuits. This tutorial brief aims to summarize on the advancement of voltage-time domain hybrid ADCs. The scope of this brief includes the basics and motivations behind the hybrid ADCs, followed by the survey covering the performance breakthroughs of hybrid ADC in terms of low power, high speed, and high resolution, and discuss the contributions and drawbacks of these techniques and architectures. The future trends are derived finally.

Enhancing the Performance of Eskom’s Cahora Bassa HVDC Scheme and Harmonic Distortion Minimization of LCC-HVDC Scheme Using the VSC-HVDC Link

Cahora Bassa, a thyristor-based High Voltage Direct (HVDC) link, transmits 1920 MW of power from a hydro-power plant in Zambezi River, north of Mozambique, to Apollo Substation in Johannesburg, South Africa. The high degree of harmonics distortion that is transferred into the AC side of the transmission network and the continuous increase in the rate at which commutation failure occurs during systems disturbance are both flaws in the utilization of this HVDC converter technology. AC and DC filters with rugged controllers are often used to minimize this effect but are limited in scope. Modern converter technology, such as the Voltage Source Converter (VSC), was proposed in this study to reduce harmonics content level, increase power transfer capabilities, enhance network stability, and reduce the rate of commutation failure occurrence. This paper, therefore, evaluates the performance analysis of the Cahora Bassa HVDC link and its level of harmonic distortion in the line commutated converters. A proposed method of utilizing VSC HVDC is provided as a suitable solution using three modular-level voltage source converter technology. Current and voltage waveform characteristics during a three-phase short circuits fault were analyzed, and the latest developments in the area of VSC HVDC were discussed. The results show a lower total harmonics distortion with the usage of VSC HVDC converter technology at the inverter station. The continuous occurrence of commutation failure was minimized by implementing a new converter architecture. The network simulation and analysis were carried out using the DIgSILENT PowerFactory engineering software tool.

Deep Learning-Based Channel Estimation for mmWave Massive MIMO Systems in Mixed-ADC Architecture.

Millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems can significantly reduce the number of radio frequency (RF) chains by using lens antenna arrays, because it is usually the case that the number of RF chains is often much smaller than the number of antennas, so channel estimation becomes very challenging in practical wireless communication. In this paper, we investigated channel estimation for mmWave massive MIMO system with lens antenna array, in which we use a mixed (low/high) resolution analog-to-digital converter (ADC) architecture to trade-off the power consumption and performance of the system. Specifically, most antennas are equipped with low-resolution ADC and the rest of the antennas use high-resolution ADC. By utilizing the sparsity of the mmWave channel, the beamspace channel estimation can be expressed as a sparse signal recovery problem, and the channel can be recovered by the algorithm based on compressed sensing. We compare the traditional channel estimation scheme with the deep learning channel-estimation scheme, which has a better advantage, such as that the estimation scheme based on deep neural network is significantly better than the traditional channel-estimation algorithm.

On-Line Diagnostics of Electrolytic Capacitors in Fault-Tolerant LED Lighting Systems

As technology advances, the utilization of lighting systems based on light-emitting diode (LED) technology is becoming increasingly essential, given its benefits in terms of efficiency, reliability, and lifespan. Unfortunately, the power electronic components required to drive LEDs are unable to compete with LED devices in terms of lifetime. Aluminum electrolytic capacitor (AEC) failures represent the root cause of power electronic equipment breakdown, mainly through both aging and temperature effects. This highlights the importance of designing robust power converter architectures and control methods that allow the evaluation of the condition of electrolytic capacitors while maintaining the performance of converter controllers, even in the presence of capacitor failure. On this basis, this work proposes a novel condition-monitoring system for the diagnosis of capacitor faults on a fault-tolerant LED driver, which is able to deal with the specific architecture and low ratings of the most recent LED lighting systems. The fault-detection task applies the short time least square Prony’s (STLSP) approach to perform an online estimation of the ESR and C parameters, allowing the continuous evaluation of the electrolytic capacitor’s condition and, as a result, the prevention of total system failure. With regard to capacitor failure, the experimental results suggest that the condition-monitoring task is extremely effective, even when considering a limited number of data samples.

A Cost-Effective Passive/Active Hybrid Equalizer Circuit Design

This paper proposes a novel hybrid equalizer circuit (HEC) for a battery management system (BMS) to implement the passive HEC (P-HEC), active HEC (A-HEC), or active/passive (AP-HEC) with the same equalizer circuit architecture. The advantages of an HEC are that it is simple, cost-effective, highly energy efficient, and fail safe. The P-HEC can further use a cooling fan or heater instead of a conventional resistor as a power dissipation element to convert the energy of the waste heat generated by the resistor to adjust the battery temperature. Even if the P-HEC uses the resistor to consume energy as in conventional methods, the P-HEC still dramatically improves the component lifetime and reliability of the BMS because the waste heat generated by the equalizer resistor is outside of the BMS board. Three significant advantages of an A-HEC are its (1) low cost, (2) small volume, and (3) higher energy efficiency than the conventional active equalizer circuits (AECs). In the HEC design, the MOSFETs of the switch array do not need high-speed switching to transfer energy as conventional AECs with DC/DC converter architecture because the A-HEC uses an isolated battery charger to charge the string cell. Therefore, the switch array is equal to a cell selector with a simple ON/OFF function. In summary, the HEC provides a small volume, cost-effective, high efficiency, and fail-safe equalizer circuit design to satisfy cell balancing demands for all kinds of electric vehicles (EVs) and energy storage systems (ESSs).

Metal-organic framework-derived cobalt oxide and sulfide having nanoflowers architecture for efficient energy conversion and storage

Water electrolyzers coupled with fuel cells offer a close loop of sustainable energy, requiring supercapacitors as energy storage devices; however, the performance of such devices largely depends on corresponding electrode materials. Metal oxides and sulfides containing Fe, Co, and Ni metals, in particular, have created significant interest due to their tunable and high theoretical energy performance for such devices. Herein, metal-organic framework (MOF) derived cobalt oxide (MOF-Co3O4) and sulfide (MOF-Co9S8) have been synthesized using solvothermal and hydrothermal strategies. The MOF-Co3O4 exhibited an overpotential of 375 and 213 mV for OER and HER, whereas, MOF-Co9S8 being a better electrocatalyst, displayed an overpotential of 278 and 212 mV for the same, respectively, at 10 mA/cm2. The theoretical evaluation suggested that incorporation of S-atoms with Co active sites in MOF-Co9S8 significantly reduced the energy barriers for crucial elementary processes of OER and HER, endowing its electrocatalytic activity. In addition, MOF-Co9S8 with a specific capacitance of 2831 F/g was found to have over four times higher energy storage capacity than MOF-Co3O4 with a 674 F/g specific capacitance @1 mA/cm2.

Evaluating Piezoelectric Materials and Vibration Modes for Power Conversion

Piezoelectric components offer several potential advantages to power conversion including high power density and efficiency capabilities compared to magnetics at small scales. Converter architectures have been developed for efficient utilization of piezoelectrics, but without fundamental criteria for designing the piezoelectric components themselves. In this article, we derive figures of merit for the achievable efficiencies and power handling densities of piezoelectric materials and vibration modes based on realistic utilization in a power converter. These figures of merit are likewise accompanied by geometry conditions that serve as guidelines for high-efficiency high-power-density piezoelectric resonator design. We demonstrate use of these metrics to evaluate commercially available PZT and lithium niobate materials across seven vibration modes, and we validate the figures of merit and geometry conditions with numerical solutions of converter operation and experimental results. The proposed figures of merit are concluded to be highly representative metrics for the capabilities of piezoelectrics in power conversion, and these capabilities are shown to have favorable scaling properties for converter miniaturization.

A 0.5 V 10 b 3 MS/s 2-Then-1b/Cycle SAR ADC With Digital-Based Time-Domain Reference and Dual-Mode Comparator

This paper presents a low-power asynchronous 10-bit 2-then-1b/cycle successive approximation register (SAR) analog-to-digital converter (ADC). With partial adoption of 2b/cycle mode only for higher-order bit conversions, additional area and power consumption could be minimized while maintaining fast conversion rate. Moreover, unlike the previous 2b/cycle conversion architecture, where two capacitive digital-to-analog converters (C-DACs) and multiple analog comparators are unavoidable, the proposed 2-then-1b/cycle conversion is implemented with only one C-DAC and one analog comparator by utilizing a digital-based time-domain reference. The speed of 1b/cycle conversion for lower-order bits is improved with a dual-mode comparator. With the aforementioned techniques, the prototype 10-bit SAR ADC is fabricated in 65 nm CMOS process. The ADC core occupies an active area of 0.0142 mm2 and consumes power of 3.8 μW at 0.5 V supply voltage and 3 MS/s conversion rate. The SNDR measured at a Nyquist-rate input frequency is 56.41 dB, resulting in a figure of merit (FoM) is 2.33 fJ/c.-s.