Direct Current Load Research Articles

How much electricity can we save by using direct current circuits in homes? Understanding the potential for electricity savings and assessing feasibility of a transition towards DC powered buildings

Advances in semiconductor-based power electronics and growing direct current loads in buildings have led researchers to reconsider whether buildings should be wired with DC circuits to reduce power conversions and facilitate a transition to efficient DC appliances. The feasibility, energy savings, and economics of such systems have been assessed and proven in data centers and commercial buildings, but the outcomes are still uncertain for the residential sector.In this work, we assess the technical and economic feasibility of DC circuits using data for 120 traditionally-wired AC homes in Austin, Texas to understand the effect of highly variable demand profiles on DC-powered residences, using appliance-level use and solar generation data, and performing a Monte Carlo simulation to quantify costs and benefits.Results show site energy savings between 9% and 20% when solar PV is distributed to all home appliances. When battery storage for excess solar energy is considered, these savings increase to 14–25%. At present DC equipment prices, converting all equipment to DC causes levelized annual costs of electricity to homeowners to roughly double. However, by converting only homes’ air conditioning condensing units to DC, the costs of direct-DC are greatly reduced and home site energy savings of 7–16% are generated.In addition to quantifying savings, we find major nontechnical barriers to implementing direct-DC in homes. These include a lack of standards for such systems, a relatively small market for DC appliances and components, utility programs designed for AC power, and a workforce unfamiliar with DC. Experience with DC is growing in other sectors, and with time this will be transitioned to a broader audience of engineers, electricians, and building inspectors to ensure that not only are the systems themselves safe, but that the image of direct current circuits becomes less foreign over time. Direct current may very well have a place in the residential sector, and research and development should continue to explore other potential benefits that might make a stronger case for a more widespread transition to what now appears a promising technology.

Simulation and characterization of a thin film Au/Ni micro hot bridge-wire ignition element under capacitor discharging

Thin film gold/nickel (Au/Ni) micro hot bridge-wire ignition elements with different bridge shapes have been proposed in this paper. They were simulated and optimized using commercial COMSOL software and a finite element (FE) model of the hot bridge-wire ignition elements with different lengths, widths and shapes was set up. Then the simulation of the bridge-wire ignition elements in firing sequence under capacitor discharging has been carried out. The temperature of the hot bridge-wire ignition elements with different lengths, widths, substrates and shapes as a function of the time has been obtained and discussed. It's indicated that the hot bridge-wire ignition element shows a quick response and can rapidly reach the maximum temperature for firing sequence under capacitor discharging. The simulated response time is 0.15 ms. However, this response speed based on the direct current load is obviously too long to meet the fast response requirement in the firing sequence system. One of the advantages of capacitor discharging current is the fast response speed. The micro hot bridge-wire element has been fabricated by surface micromachining technology and then tested using a customized circuitry. Whether the hot bridge-wire ignition element is melted or not can be used to estimate qualitatively whether its maximum temperature reaches the nickel film melting point or not. The test results show that the hot bridge-wire ignition element with zigzag shape can be fused the most easily at the same supplied voltage. It means that this structural bridge-wire element has the highest temperature under supplied capacitor discharging, which is in good agreement with the simulated results.

The performance of thermal based modified solid oxide fuel cell (SOFC) model under different DC load conditions

In this paper, a thermal-baseddynamic model of a Solid Oxide Fuel Cell under different direct current loadconditions is improved by using our previous developed fuel cell model, whichincludes ohmic, activation and concentration voltage losses, thermal dynamics,and methanol reformer. The modified SolidOxide Fuel Cell model covers restriction of fuel utilization factor. Hence, the voltage and power of the Solid OxideFuel Cell stack are limited to avoid excessive fuel flow and temperature. The SolidOxide Fuel Cell model is developed in a Matlab/Simulink environment and testedfor different direct current load conditions, which are step, ramp, random and stair-caseloads. The simulation results show that the modified Solid Oxide Fuel Cellmodel can be used to precisely follow the direct current load variations. Thisis true because reaching thesteady state of the system takes a shorter time for the ramp load, and takes a longertime for the step load. Besides, the limitation of the fuel utilizationfactor can be seen more clearly from the system with the stair-case load.

A control scheme with performance prediction for a PV fed water pumping system

This paper focuses on modeling and performance predetermination of a photovoltaic (PV) system with a boost converter fed permanent magnet direct current (PMDC) motor-centrifugal pump load, taking the converter losses into account. Sizing is done based on the maximum power generated by the PV array at the average irradiation. Hence optimum sizing of the PV array for the given irradiation at the geographical location of interest is obtained using the predetermined values. The analysis presented here involves systems employing maximum power point tracking (MPPT) as they are more efficient than directly coupled systems. However, the voltage and power of the motor might rise above rated values for irradiations greater than the average when employing MPPT, hence a control scheme has been proposed to protect the PMDC motor from being damaged during these conditions. This control scheme appropriately chooses the optimum operating point of the system, ensuring long-term sustained operation. The numerical simulation of the system is performed in Matlab/Simulink and is validated with experimental results obtained from a 180 V, 0.5 hp PMDC motor coupled to a centrifugal pump. The operation of the system with the proposed control scheme is verified by varying the irradiation levels and the relevant results are presented.

Optimal design of mixed AC–DC distribution systems for commercial buildings: A Nonconvex Generalized Benders Decomposition approach

• We develop an MINLP model which determines the optimal design of a mixed AC–DC building electrical distribution system. • We develop a tailored global optimization algorithm, based on Nonconvex Generalized Benders Decomposition. • We provide a case study, including a medium office building. Direct current (DC) electricity distribution systems have been proposed as an alternative to traditional, alternating current (AC) distribution systems for commercial buildings. Partial replacement of AC distribution with DC distribution can improve service to DC loads and overall building energy efficiency. This article develops (i) a mixed-integer, nonlinear, nonconvex mathematical programming problem to determine maximally energy efficient designs for mixed AC–DC electricity distribution systems in commercial buildings, and (ii) describes a tailored global optimization algorithm based on Nonconvex Generalized Benders Decomposition. The results of three case studies demonstrate the strength of the decomposition approach compared to state-of-the-art general-purpose global solvers.

Design of a Simulating Control System for Hybrid Wind/PV Power Generation

A system based on STM32F103 chip is designed to simulate the hybrid wind and PV wind power generation control process. The simulation system consists an electric motor with stepless rotational speed regulating feature to simulate wind turbine power generation, a light intensity sensor to simulate PV power generation with its measure results, the electrical source of chip microcomputer to simulate the current output from storage batteries, and two electric motors with different power to simulate the direct-current loads. The control strategy and the corresponding programs are developed based on certain hardware composition and the control system is implemented and operates well.

Passivity-Based Control by Series/Parallel Damping of Single-Phase PWM Voltage Source Converter

This paper describes a detailed design procedure for passivity-based controllers developed using the Brayton–Moser (BM) framework. Several passivity-based feedback designs are presented for the voltage-source converter, specifically for the H-bridge converter, since nowadays it is one of the preferred solutions to connect direct current (dc) loads or distributed sources to the alternating current (ac) grid. Independent of the operating mode, namely, the rectifier and regenerative operating mode, the achieved control aims are: high power factor correction in the ac-side and optimal dc voltage regulation capability in the dc-side. The proposed controllers can use series or parallel damping-based solutions for the error dynamics, naturally providing the conditions for stability and tuning of control parameters. In addition, the BM structure facilitates the addition of virtual resistance-inductance-capacitance (RLC) filter circuits to the control design for the rejection of low frequency harmonics. The effectiveness of series/parallel damping is investigated in case of abrupt changes in the load, using conductance estimators. Simulation and experimental results validate the analysis.

Exploring design of universal propeller simulator for airship propulsion system’s driving motor

Rare earth permanent magnet brushless direct current motor is the energy conversion device between power system and propeller of high-altitude airship. Its performance has a profound effect on the overall performance of the high-altitude airship. Limited by the output torque of the permanent magnet brushless direct current motor, propeller on the ground cannot reach the rated angular speed when propeller works at high altitude, so it is difficult to carry on rotation test on the ground. In addition, performances of the permanent magnet brushless direct current motor system such as control accuracy, reliability and efficiency cannot be tested. The functional level of the motor load simulator is proposed considering the dynamic properties of the propeller and the basic functions of the propulsion system. Different loading actuators are evaluated and the conceptual design of the load simulator is accomplished. Inertia is realized by relatively small flywheel and inertia electrical emulation method. Torque is simulated by servo motor that can work at braking state and thrust is exerted on the motor by hydraulic servo valve control system. Finally, depending on the proposed scheme and design parameters, co-simulation model of the load simulator is established utilizing software MATLAB/Simulink and AMESim. After comparing co-simulation results with real propeller properties, the feasibility of the conceptual design of permanent magnet brushless direct current motor load simulator is proved, and what is more, the effectiveness of control strategies and the rationality of parameters settings for co-simulation are testified.

Performance Analysis of PEM Fuel Cells with Different Electrical Loads

AbstractOne of the most outstanding products of fuel cells is electrical power but, currently, there is a reduced number of publications that provide experimental data about the performance of fuel cells when used for supplying Alternating Current (AC) loads. Most of the existing publications provide experimental data only with direct current (DC) loads, or analyze the performance with AC loads using simulation models. For this reason, this paper analyses experimentally the behavior of a proton exchange membrane fuel cell (PEMFC) system when feeding different electrical loads. The system tested is constituted by a PEM fuel cell, a storage battery, electronic converters and electrical loads. In the tests, the fuel cell system supplies power to three different loads: DC, single‐phase AC and three‐phase AC. For these cases, voltage, current, power, power factor and efficiency data are shown, at different load levels. From those parameters, efficiency of the global system is estimated. Finally, as the power quality concept is a topic of increasing importance when supplying electricity, the total harmonic distortion (THD) of the electric signals has also been analyzed.

Modeling of Control and Power Management of a Hybrid Wind-Solar System Using Optimization Technique

A probabilistic methodology is described in this paper to determine an optimal design and implementation of a multi source hybrid like Wind, Photovoltaic (PV) stand alone system with energy management strategy. Hybrid energy system is an excellent solution for electrification of remote rural areas where the grid extension is difficult and not economical. Hybrid (Wind-PV) system are highly efficient and requires very low maintenance. An average model of a hybrid Wind-PV generating system is presented. The Model is important for synthesizing the control strategy and analyzing the dynamic behavior of the system. The main objective is to provide 24 hours demand quality power in remote communities. The method of investigation concerns with the definition of the system topology, interconnection of the various sources with maximum energy transfer, optimum control and energy management. The proposed energy management strategy is simulated for Very Low Voltage (VLV) node connection and its coupled with DC loads in MATLAB/Simulink using the Fuzzy Logic Controller (FLC). The FLC takes the input from Solar (irradiation), Wind (speed) and the battery and controls the respective subsystem which formulates into different operational modes of energy management. The role of Fuzzy threshold controller is to adjust continuously the threshold value for optimal performance based on expected wind, solar conditions and batter voltage. It is shown that, when the Fuzzy Logic Controller is used.The proposed Direct Current (DC) bus voltage regulation strategy with different modes of operation has fast response and efficient operation which leads to a reduced operating cost. The optimal power transfer from the source to load is based on mechanism which are used to control power, voltage and current and these parameters are used to regulate the DC bus voltage to a fixed value. The various models with the output waveforms are represented and discussed. Finally, simulation results are presented to verify the effectiveness and accuracy of the proposed system.

Indium–tin-oxide coatings for applications in photovoltaics and displays deposited using rotary ceramic targets: Recent insights regarding process stability and doping level

Several aspects related to high power sputtering with industrial scale sintered ceramic rotary indium–tin-oxide (ITO) targets are presented in the first part of this paper. In particular, the process stability and target integrity upon sputtering with ≥20kW/m power load and the influence of the gap size between cylindrical segments are discussed. Results show that, in order to avoid nodule formation and deposition rate fluctuations, direct current (DC) power load needs to be limited well below 20kW/m over long sputter runs. Additional work demonstrates that at a gap size at or below 0.15mm, strongly adhering deposits form readily between cylindrical segments which are not observed with standard 0.35mm gaps.The influence of Sn doping level on electro-optical properties of thin films targeting an application such as hetero-junction c-Si solar cells is also investigated. Again, rotary targets operated at high power (10kW/m) are used, including standard grade ITO containing 10wt.% SnO2 and another composition with only 3wt.% SnO2. The influence of H2 and different concentrations of O2 in the sputter gas is analysed for both target materials. Results indicate that although coatings derived from the lower-doped ITO exhibit considerably less absorption in the NIR due to lower carrier concentrations, their resistivity is nearly 30% higher than that from the standard ITO coating.

A dynamic model for solid oxide fuel cell system and analyzing of its performance for direct current and alternating current operation conditions

SUMMARY This paper presents a dynamic model of a solid oxide fuel cell (SOFC) and its performance test under direct current (DC) and alternating current (AC) operation conditions. The proposed fuel cell model involves all voltage losses, thermal dynamics and methanol reformer. SOFC model is developed on Matlab/Simulink environment. First, DC load following capability of proposed SOFC dynamic model is examined. Then, the SOFC dynamic model is connected to single-machine infinite bus through a transmission line. To connect the proposed SOFC dynamic model to AC bus, a basic power conditioner unit (PCU) is designed. A PCU, which consists of a DC–DC boost converter, a DC–AC inverter, their controller, transformer and filter, is designed. Finally, the proposed SOFC model is also simulated for an AC power system that has sinusoidal voltage of 400 V, frequency of 50 Hz and resistive load of 200 W. The simulation results show that the proposed SOFC dynamic model has followed fairly DC load variations. Also, the output voltage of fuel cell system under maximum DC load conditions is obtained as 280 V. The designed power conditioning unit is suitable for studying AC power system applications. Copyright © 2012 John Wiley & Sons, Ltd.

Coordinated control of series‐connected offshore wind park based on matrix converters

ABSTRACTOptimization and reliability are two important aspects in design and operation of wind parks either for offshore as for onland emplacements. However, offshore locations demand conscientious effort in optimizing the size and the weight of each component in the energy conversion system because of the high investment and maintenance costs related with the supporting structures and transportation respectively. Achieving these two objectives requires the combination of different optimization stages, which consider a suitable design of the entire conversion system with innovative and more efficient power electronic devices, optimized topology of the offshore grid and customized control strategies for optimizing the operation of the park.This paper presents an energy conversion concept for wind turbines on the basis of a reduced matrix converter (RMC) that will enable series direct current architecture in offshore wind parks thus preventing the need for offshore platforms. The RMC is built with bidirectional semiconductors that give reduced losses because of both superior topology and more efficient semiconductors. The proposed conversion topology is tested in stationary state and transient operation. In addition to operational features of the concept, control and operation of a wind park with several turbines are presented.Dynamic operation of the turbine as well as the high‐voltage direct current transmission line effects are considered. Three types of models are therefore developed. First, an accurate and detailed model for analyzing one single turbine with the converter operated at high‐frequency switching is presented. This model considers a new modulation for the RMC. A second and simplified model is used for small signal analysis. This model permits to simulate several series‐connected cluster during transient. Finally, an optimal direct current load flow model is used for evaluating stationary state operation.Results show the technical feasibility of the proposed concept and their advantages over conventional topologies. The paper also discusses the technological challenges that this type of offshore grid architecture will bring. Copyright © 2011 John Wiley & Sons, Ltd.

PEM fuel cells analysis for grid connected applications

Polymer electrolyte fuel cells (PEFCs) fed by hydrogen were investigated with the aim of highlighting their behaviour during grid connected (GC) operation. Starting from the analysis of the systems working under practical conditions on the utility grid, the study was addressed to the materials degradation during GC applications. Endurance tests on 5 kW pre-commercial PEFC fuel cell systems were carried out at direct current constant load and in GC configuration. An evidence of disturbance on the FC system power output was observed. The study was focused on Low Frequency (LF) 100 Hz noise (current ripple) that can mainly affect the fuel cell performance and lifetime. In order to evaluate the issues that occurred on the active components of a PEMFC, when subjected to a current ripple, electrochemical characterizations were performed on single cells of 5 cm 2 subjected to a dynamic load. Post mortem physico-chemical analyses showed materials degradation on the cathode catalyst associated to the current ripple.

Influence of Voltage on Arc Characteristics and Electrode Mass Change of AgNi Contacts for Electromagnetic Contactors

Recently, photovoltaic power systems and electric vehicles have been commonly used. Therefore, the importance of DC (direct current) switching is expected to increase in the near future. The authors have been examining a method of evaluating the electrode loss of AgNi contacts for an electromagnetic contactor with a medium DC load current at a resistive circuit. In this study, the arc energy and electrode mass changes were investigated in more detail. We carried out experiments of 100,000 operations for an electromagnetic contactor at a load current of 5A constant with a source voltage change from 100 to 160V. The arc duration, contact resistance, arc energy, and electrode mass changes were measured. As a result, the arc duration was found out increase with the source voltage. In addition, the stationary cathode mass change (loss) increased proportion only to the total arc energy. However, the stationary cathode loss per unit arc energy decreased at the highest source voltage.

Determination of optimum generation level in DTEP using a GA-based quadratic programming

In this paper, a new approach by accomplishing dynamic transmission expansion planning (DTEP) problem, the optimum generation level of generators is determined for annual load peak using a genetic algorithm (GA) based quadratic programming (QP) method. This study is carried out in order to achieve a better prospect from the generation network and consequently the suitable planning for its future expansion. Another important aspect of this paper is taking the advantage of line outage distribution factors (LODFs) or sensitivity analysis for the evaluation of network reliability instead of the direct current load flow (DCLF), that the computations and performance of DTEP problem considerably speeds up in comparison with previous researches. Also, the applied coding for problem solution using GA is more flexible and is significantly improved the performance of the proposed method. The proposed method is successively applied to a realistic system of the 18-buses Azerbaijan regional electric network, which is located in the northwest of Iran, and the results are extensively analyzed. The results evaluation reveals that the generators with high capacity operated in full capacity almost the whole of the planning period, because the generation cost coefficients is decreased as the generator capacity increased and vice versa.

Experimental investigations on triggering characteristic of TVS under DC and AC load

Triggered vacuum switches (TVSs) have fast growing applications in the field of power system and pulse power. The relation between triggering parameters of triggering system, such as triggering voltage and triggering power, between the triggering time delay and its scatter of TVS had been obtained through series of experiments. The result can be adopted as the steering for high-power controller design and application of TVS. A steepened high-voltage triggering pulse is introduced in the main high-voltage generating circuit. As a result, the triggering time delay and its scatter can be decreased remarkably. Synchronous switch technology is imported to control the triggering phase at the crest of applied voltage on TVS. The Triggering characteristic of TVS under alternating current (AC) and direct current (DC) load has been investigated emphatically. Given the identical triggering parameter of triggering system, DC condition is prior to AC on the triggering probability and stability markedly. Such conclusion can be drawn, for AC condition, TVS would require much for the triggering system.

Case Studies: Enhancing Reliability and E fficiency Using Locally Generated DC Power— The Hybrid Building

Since Edison’s day alternating current (AC) and direct current (DC)have co-existed by necessity: AC to make the trip from the generatingplant and DC to power electronic loads. This has resulted in billions ofelectrical compromises in the form of the ubiquitous power supply, ora rectifier, that must stand in front of DC loads to convert AC to DC.As Arthur Rosenfeld a California Energy Commissioner calls them, our“Energy Vampires.”But now, many buildings are generating power of their own, usu-ally direct current energy. Is this wasteful back-and-forth conversionreally necessary? Just as the automobile industry has advanced to thehybrid car, buildings can use multiple sources of power to achieve dra-matic increases in ef ficiency

Case Studies: Enhancing Reliability and Efficiency Using Locally Generated DC Power—The Hybrid Building

ABSTRACT Since Edison's day alternating current (AC) and direct current (DC) have co-existed by necessity: AC to make the trip from the generating plant and DC to power electronic loads. This has resulted in billions of electrical compromises in the form of the ubiquitous power supply, or a rectifier, that must stand in front of DC loads to convert AC to DC. As Arthur Rosenfeld a California Energy Commissioner calls them, our “Energy Vampires.” But now, many buildings are generating power of their own, usually direct current energy. Is this wasteful back-and-forth conversion really necessary? Just as the automobile industry has advanced to the hybrid car, buildings can use multiple sources of power to achieve dramatic increases in efficiency.

A new iterative method for the global simulation of power electronic multi-converter systems

Power electronic converters generate harmonic currents that can disturb the network. To study the perturbations on the power line, it is necessary to perform a functional analysis via a global simulation. However, when the plant contains several static power converters feeding direct-current loads, global simulation becomes difficult, even impossible, because of the limitations of the software or the microcomputer used. There are no simulation tools that allow the quantitative evaluation of harmonic voltages and currents generated by a multistatic converter system. To fulfil this goal, the authors propose a new iterative analysis method for such systems and a new model for electronic power converters in terms of nonlinear current sources. This methodology has been included in a modified version of the ATOSECS software, renamed ATOSECM. The methodology is illustrated with an example of the use of ATOSECM on a personal computer for the study of two single-phase power converters connected to the same power line. A comparative analysis between global simulation (ATOSECS) and the new method of simulation (ATOSECM) is also presented for the case of two three-phase full-wave thyristor converters, with different firing angles and loads.