Direct Current Alternating Current Research Articles

Second-Order Sliding-Mode Control Applied to Microgrids: DC & AC Buck Converters Powering Constant Power Loads

Microgrids are designed to connect different types of AC and DC loads, which require robust power controllers to achieve an efficient power transfer. However, the effects of both AC and DC disturbances in the same type of controller make achieving stability a design challenge, especially in coupled systems where disturbances affect both the upstream and downstream in the microgrid. This paper presents an analysis of a second-order sliding-mode control (SOSMC) applied to a microgrid with direct-current (DC) and alternating-current (AC) power converters. The aim is to simulate the second-order sliding-mode control with buck converters that feed constant DC–DC and DC–AC power loads. The controller was tested in consideration of a unique sliding surface facing external disturbances, such as variations in the frequency of AC converters, sudden changes in upstream voltages, and constant power loads (CPL). The influence of the gain values (K) on the controller was also analyzed. The results show that the controller is robust regarding its sensitivity to external disturbances and steady-state error. However, the importance of the constant “K” in the model states that there exist K-limit values where if “K” is too low, a slowdown is presented, and the response against disturbances can be critical, and if is too high, an overshoot is presented in the output voltage.

Assessing the Discriminatory Capabilities of iEK Devices under DC and DC-Biased AC Stimulation Potentials.

There is a rising need for rapid and reliable analytical methods for separating microorganisms in clinical and biomedical applications. Microscale-insulator-based electrokinetic (iEK) systems have proven to be robust platforms for assessing a wide variety of microorganisms. Traditionally, iEK systems are usually stimulated with direct-current (DC) potentials. This work presents a comparison between using DC potentials and using DC-biased alternating-current (AC) potentials in iEK systems for the separation of microorganisms. The present study, which includes mathematical modeling and experimentation, compares the separation of bacterial and yeast cells in two distinct modes by using DC and DC-biased AC potentials. The quality of both separations, assessed in terms of separation resolution (Rs), showed a complete separation (Rs = 1.51) with the application of a DC-biased low-frequency AC signal but an incomplete separation (Rs = 0.55) with the application of an RMS-equivalent DC signal. Good reproducibility between experimental repetitions (<10%) was obtained, and good agreement (~18% deviation) was observed between modeling and experimental retention times. The present study demonstrates the potential of extending the limits of iEK systems by employing DC-biased AC potentials to perform discriminatory separations of microorganisms that are difficult to separate with the application of DC potentials.

Inverter Control Design for the optimal management of electrical Microgrids

Nowadays, the promotion of renewable energy sources is a necessity. Technically, the increase of the renewable penetration in the power system (PS) is a challenge. One solution for this problem is the use of self-controlled microgrids (smartgrid, SG). In this work, the design of an algorithm to optimal manage the SG energy through the power inverter control in the SG is presented. In general, a SG consists of renewable energy sources, electrical loads and storage systems. In an isolated SG (no connected to the power system), a DC/AC (direct current / alternating current) converter (power inverter, PInv) is necessary to provide an alternating voltage to supply the loads. If the SG is connected to the PS, the PInv is used to inject the active power from the renewable energy sources.

Parametric resonance of multi-frequency excited MEMS based on homotopy analysis method

The nonlinear dynamics and control of micro electromechanical systems (MEMS) is an important topic at present and homotopy analysis method (HAM) is an effective semi-numerical and semi-analytical method for solving strongly nonlinear problems. In this paper, the parametric resonance of MEMS with multi-frequency excitation is studied by HAM. Firstly, the differential equation of electrostatically driven microbeam is processed by Taylor expansion, and it is transformed into the parametric motion model with multi-frequency excitation. Then, the approximate solution and amplitude–frequency response equation of the system are obtained by HAM, and compared with the numerical solution. Finally, the influence of direct current (DC) and alternating current (AC) on principal parametric resonance and superharmonic resonance is discussed. The results show that HAM is an effective method to analyze the parametric vibration of multi-frequency excitation system, and the amplitude–frequency response curve of microbeam about parametric motion depends on the time scale in high DC and high AC state. This study effectively extends the application of HAM in parametric resonance, which is of great significance to the study of nonlinear vibration of MEMS.

Single Phase MOSFET Inverter Using PWM Technique

Abstract: Electricity has two types which are DC (Direct Current) electricity and AC (Alternating Current) electricity. Electricity which generally used for household components is utilized AC electricity. AC power can be generated from DC electricity by using an inverter tool. The inverter has various methods of converting DC power to AC power. In this research, inverter built using full bridge configuration. Using the full bridge configuration, it is obtained more efficient results by using other configurations. The inverter designed using voltage source 12 volt battery with a capacity of 7.5 Ah. The maximum power capacity which generated by the inverter is 100 watts. To control this inverter, Arduino uno R3 microcontroller is used.

Preparation of X5R type Ni-MLCCs and capacitance response to combined out-field variations

With the continuous development of electronic devices, miniaturization and high capacitance have become important factors in the fabrication of multilayer ceramic capacitors (MLCCs) with a Ni internal electrode (Ni-MLCCs). The typical thickness of the dielectric layer of commercial MLCCs is less than 1 μm, which implies a higher capacitance compared to MLCCs with a thicker dielectric layer. In this study, 1210-type Ni-MLCCs were prepared via a tape casting method using a BaTiO3 powder chemically coated with Dy and Ho additives. The high capacitance (390 nF) Ni-MLCC sintered at 1220 °C exhibited a low dielectric loss (tan δ < 2%), high insulation resistance (>9000 MΩ), and temperature stability comparable to that of the EIA X5R standard (capacitance-temperature coefficient (TCC) = ΔC/C25 °C ≤ ±15%, between -55–85 °C). Relaxation behavior was observed between 1 Hz and 10 kHz, following the modified Curie–Weiss law and the Vogel–Fulcher relationship. The capacitive temperature stability of Ni-MLCC is closely related to the applied direct current (DC) bias field. The EIA X7R stability (TCC ≤ ±15%, between -55–125 °C) of the Ni-MLCCs at 1220 °C was gained under dc-bias field 3 and 5 V/μm. The capacitance varied as alternating current (AC) electric fields were applied. The grain shell was sensitive to both the DC bias and AC fields, but the grain core was more sensitive to the DC bias electrical field than the AC field. Furthermore, the ferroelectric response in MLCC decreases with rising temperature.

Investigation of integrated converter circuit and enriched error tolerant fuzzy logic controller based control approach for solar powered EV system

PurposeThis study aims to extend the driving range by on-board charging with use of photovoltaic (PV) source, avoiding the dependency on the grid supply and energy storage system in addition to that reduce the conversion complexity influenced on converter section of electric vehicle (EV) system.Design/methodology/approachThis paper proposed a PV fed integrated converter topology called integrated single-input multi-output (I-SIMO) converter with enriched error tolerant fuzzy logic controller (EET-FLC) based control technique to regulate the speed of brushless direct current motor drive. I-SIMO converter provides both direct current (DC) and alternating current (AC) outputs from a single DC input source depending on the operation mode. It comprises two modes of operation, act as DC–DC converter in vehicle standby mode and DC–AC converter in vehicles driving mode.FindingsThe use of PV panels in the vehicle helps to reduce dependence of grid supply as well as vehicle’s batteries. The proposed topology has to remove the multiple power conversion stages in EV system, reduce components count and provide dual outputs for enhancement of performance of EV system.Originality/valueThe proposed topology leads to reduction of switching losses and stresses across the components of the converter and provides reduction in system complexity and overall expenditure. So, it enhances the converter reliability and also improves the efficiency. The converter provides ripple-free output voltage under dynamic load condition. The performance of EET-FLC is studied by taking various performance measures such as rise time, peak time, settling time and peak overshoot and compared with conventional control designs.

High-quality restoration image encryption using DCT frequency-domain compression coding and chaos

With the arrival of the age of big data, the amount and types of data in the process of information transmission have increased significantly, and the full-disk encryption mode used by traditional encryption algorithms has certain limitations of the times. In order to further improve the bandwidth efficiency of digital images in the transmission process and the information effectiveness of digital image transmission, this paper proposes an algorithm of high-quality restoration image encryption using DCT frequency-domain compression coding and chaos. Firstly, the image hash value is used for the generation of an encryption key with plaintext correlation, then lightweight chaos is generated based on the key to obtain a pseudo-random sequence. Secondly, the image is partitioned into subblock, and converted from time domain into frequency domain by employing Discrete Cosine Transform (DCT) on each block, then perform quantization operation based on frequency domain information to obtain DCT coefficient matrix. Thirdly, the direct current (DC) coefficients and alternating current (AC) coefficients are extracted in the DCT coefficient matrix and compressed by different encoding methods to obtain two sets of bitstream containing DC coefficient and AC coefficient information. Fourthly, permute the DC coefficient bit stream by the chaotic sequence, and reconstruct it with the AC coefficient bit stream to obtain the frequency domain ciphertext image. Finally, the chaotic sequence is used to diffuse ciphertext, and the processed hash value is hidden in the ciphertext to obtain the final ciphertext. The theoretical and experimental analysis showed that the key length reaches 341 bits, and the PSNR value of the restored image is close to 60, all of which satisfy the theoretical value. Therefore, the algorithm has the characteristics of high compression rate, high-quality image restoration large key space, strong plaintext sensitivity, strong key sensitivity and so on. Our method proposed in this paper is expected to provide a new idea for confidential and secure communication in the age of big data.

The Measurement and SPICE Modelling of Schottky Barrier Diodes Appropriate for Use as Bypass Diodes within Photovoltaic Modules

The modelling of surges within PV (photovoltaic) installations has been the subject of much research in recent years. However, accurate simulations cannot be performed unless each and every component within a PV installation is modelled in sufficient detail. The bypass diodes within a PV module are frequently omitted from such simulations. When included, they are often represented by oversimplified models. This article addresses this need by presenting SPICE (Simulation Program with Integrated Circuit Emphasis) models for three Schottky diodes, chosen due to their suitability for use as bypass diodes. These models are the combination of DC (direct current) large-signal and AC (alternating current) small-signal sub-models, which are integrated such that the resulting full circuital models allow for accurate simulations involving large-signal transient stimuli. Two types of experimental setups, one incorporating a DC current–voltage curve sweep, and the other involving VNA-based (vector network analyser) AC small-signal impedance measurements, allow for the acquisition of the necessary model parameters at multiple operating points. The AC small-signal measurements cover a wide bandwidth of 100 Hz to 50 MHz. Multiple configurations of the measurement setups are employed in order to achieve the required dynamic range and sensitivity.

Short and open circuit faults study in the PV system inverter

&lt;p&gt;The inverter is the principal part of the photovoltaic (PV) systems that assures the direct current/alternating current (DC/AC) conversion (PV array is connected directly to an inverter that converts the DC energy produced by the PV array into AC energy that is directly connected to the electric utility). In this paper, we present a simple method for detecting faults that occurred during the operation of the inverter. These types of faults or faults affect the efficiency and cost-effectiveness of the photovoltaic system, especially the inverter, which is the main component responsible for the conversion. Hence, we have shown first the faults obtained in the case of the short circuit. Second, the open circuit failure is studied. The results demonstrate the efficacy of the proposed method. Good monitoring and detection of faults in the inverter can increase the system's reliability and decrease the undesirable faults that appeared in the PV system. The system behavior is tested under variable parameters and conditions using MATLAB/Simulink.&lt;/p&gt;

Robust Tracker of Hybrid Microgrids by the Invariant-Ellipsoid Set

This paper introduces a new ellipsoidal-based tracker design to control a grid-connected hybrid direct current/alternating current (DC/AC) microgrid (MG). The proposed controller is robust against both parameters and load variations. The studied hybrid MG is modelled as a nonlinear dynamical system. A linearized model around an operating point is developed. The parameter changes are modelled as norm-bounded uncertainties. We apply the new extended version of the attractive (or invariant) ellipsoid for this tracking problem. Convex optimization is used to obtain the region’s minimal size where the tracking error between the state trajectories and the reference states converges. The sufficient conditions for stability are derived and solved based on linear matrix inequalities (LMIs). The proposed controller’s validity is shown via simulating the hybrid MG with various operational scenarios. In each scenario, the performance of the controller is compared with a recently proposed sliding mode controller. The comparison clearly illustrates the superiority of the developed controller in terms of transient and steady-state responses.

Compensation of distortions in VSC-based DC–AC power systems using a modified vector control method

Offshore wind farms are always connected to onshore alternating current (AC) power systems using direct current (DC) submarine cables through a DC–AC voltage source converter station. In most cases, nonlinear loads are located on the AC side of the station. The distortion caused by such loads tends to flow into the AC system due to its low impedance, negatively impacting power quality and raising the power losses. This paper presents a novel vector control method (VCM) for the DC–AC station to simultaneously deliver the power demanded by the AC side and act as a shunt active power filter to suppress distortions. In this scope, the conventional VCM is further modified by developing several control loops with proper control and power parameters to obtain a sufficiently wide bandwidth. Additionally, the performance of three different types of low pass filters (LPF) is investigated due to the significant role of LPF in the success of the proposed method. Simulation and experimental outcomes are provided to validate the effectiveness of the proposed method

Identification of Environmental and Experimental Factors Influencing Human Perception of DC and AC Electric Fields.

As part of the energy transition in Germany, high-voltage direct current (HVDC) lines producing DC electric fields (EF) are in planning. Since the human perception of DC EF was rarely investigated in the past, we aimed to identify environmental and experimental factors influencing the human perception of direct current (DC) EF, alternating current (AC) EF, and the co-exposure of DC EF and AC EF (hybrid EF) under whole-body exposure. Additionally, first estimates of DC EF and AC EF perception thresholdsas well as differences in human perception of DC EF and AC EF concerning the type of sensation experienced and the affected body part were evaluated. A highly sophisticated exposure lab was built to expose participants to various EF strengths and ask for their assessment concerning the presence of an EF. To estimate the individual perception thresholds of 11 participants, the signal detection theory as well as the single-interval-adjustment matrix procedure were applied. Relative humidity could be identified as an environmental factor influencing the perception of AC EF and DC EF in different ways. An appropriate ramp slope and an exposure duration for future studies could be elaborated. Additionally, perception thresholds were lower under hybrid EF exposure than under DC EF or AC EF exposure alone. Cutaneous sensations evoked under DC EF and AC EF exposure were individually different and attributed to various parts of the body. Several environmental and experimental factors influencing the human perception of EF could be identified and provide an essential basis for a large-scale study. © 2021 Bioelectromagnetics Society.

Reliability Analysis and Repair Activity for the Components of 350 kW Inverters in a Large Scale Grid-Connected Photovoltaic System

The reliability of photovoltaic (PV) generators is strongly affected by the performance of Direct Current/Alternating Current (DC/AC) converters, being the major source of PV underperformance. However, generally, their reliability is not investigated at component level: thus, the present work presents a reliability analysis and the repair activity for the components of full bridge DC/AC converters. In the first part of the paper, a reliability analysis using failure rates from literature is carried out for 132 inverters (AC rated power of 350 kW each) with global AC power of 46 MW in a large scale grid-connected PV plant. Then, in the second part of the work, results from literature are compared with data obtained by analyzing industrial maintenance reports in the years 2015–2017. In conclusion, the yearly energy losses involved in the downtime are quantified, as well as their availability.

Research on Coordinated Control Strategy of AC-DC Hybrid Microgrid Bidirectional Converter

Based on the improved droop control of the bidirectional converter controlled by the DC (direct current) side power quantity, a coordinated control scheme with energy storage is proposed. Not only can the two-way converter automatically and smoothly switch in the rectification, inverter, and idle modes, but also the energy storage device can perform coordinated control in the DC side idle mode to maintain the DC bus voltage stability. Using DC side power control, there is no need to switch control strategies to meet islanding and grid-connected modes. The simulation results show that improved droop control can reduce frequent actions of power electronic devices caused by small-range fluctuations in DC bus voltage and AC (alternating current) frequency. Coordinated control can make the DC bus voltage more stable, ensure stable operation of the AC and DC hybrid microgrid, and improve system reliability.

Improved Predictive Control for an Asymmetric Multilevel Converter for Photovoltaic Energy

This article proposes a 27-level asymmetric cascade H-bridge multilevel topology for photovoltaic applications, which considers a predictive control strategy that allows minimization of the commutations of the converter. This proposal ensures a highly sinusoidal and stable photovoltaic injection when there are solar irradiance disturbances, generating a low distortion in the current waveform and low switching losses. To validate the performance of the control and the proposed topology, the dynamic model of the alternating current (AC) and direct current (DC) side system is first obtained, which is checked by computational simulations. Subsequently, the implementation of a master–slave control is carried out, focused on the control of DC voltage and AC current. The proposal is simulated, and the total harmonic distortion (THD) is obtained in the voltage and current waveforms. Undesired commutations, typical of the predictive control, are eliminated in the AC voltage waveform, and a proper DC voltage tracking is achieved for the high-power cell. In order to demonstrate the performance of the proposed control strategy, a low-power proof-of-concept prototype is implemented, in which the energy is injected to the grid, under the event of solar irradiance disturbances (with DC control).Then, the undesired switching in the main cell is eliminated, generating THDs in the voltage and current signal of 7.76% and 2.65%, respectively.

Nonlinear Voltage Control for Three-Phase DC-AC Converters in Hybrid Systems: An Application of the PI-PBC Method

In this paper, a proportional-integral passivity-based controller (PI-PBC) is proposed to regulate the amplitude and frequency of the three-phase output voltage in a direct-current alternating-current (DC-AC) converter with an LC filter. This converter is used to supply energy to AC loads in hybrid renewable based systems. The proposed strategy uses the well-known proportional-integral (PI) actions and guarantees the stability of the system by means of the Lyapunov theory. The proposed controller continues to maintain the simplicity and robustness of the PI controls using the Hamiltonian representation of the system, thereby ensuring stability and producing improvements in the performance. The performance of the proposed controller was validated based on simulation and experimental results after considering parametric variations and comparing them with classical approaches.

Review of GaN HEMT Applications in Power Converters over 500 W

Because of the global trends of energy demand increase and decarbonization, developing green energy sources and increasing energy conversion efficiency are recently two of the most urgent topics in energy fields. The requirements for power level and performance of converter systems are continuously growing for the fast development of modern technologies such as the Internet of things (IoT) and Industry 4.0. In this regard, power switching devices based on wide-bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) are fast maturing and expected to greatly benefit power converters with complex switching schemes. In low- and medium-voltage applications, GaN-based high-electron-mobility transistors (HEMTs) are superior to conventional silicon (Si)-based devices in terms of switching frequency, power rating, thermal capability, and efficiency, which are crucial factors to enhance the performance of advanced power converters. Previously published review papers on GaN HEMT technology mainly focused on fabrication, device characteristics, and general applications. To realize the future development trend and potential of applying GaN technology in various converter designs, this paper reviews a total of 162 research papers focusing on GaN HEMT applications in mid- to high-power (over 500 W) converters. Different types of converters including direct current (DC)–DC, alternating current (AC)–DC, and DC–AC conversions with various configurations, switching frequencies, power densities, and system efficiencies are reviewed.

Coordinated control for medium voltage DC distribution centers with flexibly interlinked multiple microgrids

From flexible interconnection among feeders to hybrid alternating current (AC) and direct current (DC) distribution structures of future smart distribution systems, medium-voltage DC distribution centers with flexibly interlinked multiple microgrids (MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.

Study and Application of Intelligent Sliding Mode Control for Voltage Source Inverters

In this paper, an intelligent sliding mode controlled voltage source inverter (VSI) is developed to achieve not only quick transient behavior, but satisfactory steady-state response. The presented approach combines the respective merits of a nonsingular fast terminal attractor (NFTA) as well as an adaptive neuro-fuzzy inference system (ANFIS). The NFTA allows no singularity and error states to be converged to the equilibrium within a finite time, while conventional sliding mode control (SMC) leads to long-term (infinite) convergent behavior. However, there is the likelihood of chattering or steady-state error occurring in NFTA due to the overestimation or underestimation of system uncertainty bound. The ANFIS with accurate estimation and the ease of implementation is employed in NFTA for suppressing the chatter or steady-state error so as to improve the system’s robustness against uncertain disturbances. Simulation results display that this described approach yields low distorted output wave shapes and quick transience in the presence of capacitor input rectifier loading as well as abrupt connection of linear loads. Experimental results conducted on a 1 kW VSI prototype with control algorithm implementation in Texas Instruments DSP (digital signal processor) support the theoretic analysis and reaffirm the robust performance of the developed VSI. Because the proposed VSI yields remarkable benefits over conventional terminal attractor VSIs on the basis of computational quickness and unsophisticated realization, the presented approach is a noteworthy referral to the designers of correlated VSI applications in future, such as DC (direct current) microgrids and AC (alternating current) microgrids, or even hybrid AC/DC microgrids.