Direct Converter Research Articles

A Transformer-Less Multiconverter Having Output Voltage and Frequency Regulation Characteristics, Employed with Simple Switching Algorithms

The attractive features of the direct AC-AC converters increase their use in many applications such as voltage control for a heavy-duty load that has a high time constant, AC machine drives, and heating systems based on the induction process. These converters process power in single-stage having simple circuit topologies with reduced switching devices and circuit components. These characteristics lead to the efficient power conversion process. The use of a low-frequency input transformer with multiple output tapping for the regulation of output voltage and frequency is one of the major sources of cost, size, and conversion losses. The complication in the switching algorithms is also the main concern in these converters. The preceding deficiencies lower their potency to be used in daily life. The costly controllers or processors are to be employed to realize the complex control techniques or algorithms. That increases the overall cost and circuit complication. This paper introduces the simple control techniques employed to a novel transformer less multi converter to have the various ac outputs for voltage and frequency regulation. The validation of power circuit and control schemes is tested through the simulation and practical results obtained in Simulink and practical setup respectively.

RESEARCH OF DIGITAL QUBITES FOR HETEROGENEOUS DIGITAL QUANTUM COPROCESSORS

Recently, interest is growing towards real quantum computers, which are analog and probabilistic devices by nature. Theinterest is also growing to their digital version, both software and hardware. One approach to the construction of real quantum computers is to use quantum chips. The hardware implementation of digital quantum computers involves the use offield programmable gate arrays.A digital quantum coprocessor has already been createdwhich has over a thousand digital qubitsand can perform such complex algorithms as a quantum Fourier transformation. The created and working digital quantum coprocessorcan already be used to work out various quantum algorithms, algorithms for the interaction of a classic computer and its quantum coprocessor, as well as for research various options for building digital qubits.The purpose of this work is to study the effect of the accuracy of the presentation of the state of digital qubit on the probability of obtaining the correct results of the digitalquantum coprocessor.For the study, a heterogeneous digital quantum coprocessor with thirty two digital qubits is selected, which will perform the Fourier quantum transformation. The article describes the basics of building digital quantum coprocessors.Schemes that illustrate the interaction of a classic computer and a quantum coprocessor, the architecture of the coprocessor and the possible structures of its digital qubitsare given. Two variants of the coprocessor, homogeneous one with one pseudo-random codes generator and one comparator, and heterogeneous one, with a generator and a comparator in each digital quantum cell, from which digital qubits consist, are shown.Two options for comparators are also shown -with a direct functional converter and with reverse one.In this work, the influence of the length of the qubit state codes of heterogeneous digital quantum coprocessors on the probability of the correct results formation is investigated.It was shown that the probability of obtaining the correct results at the output of the digital heterogeneous coprocessor is sharply (up to fifty percent) improved with a decrease of the qubit state code length, that is, with a decrease in the coprocessor hardware cost.With a length of a code equal to twobits, the quality of the operation of the heterogeneous coprocessor becomes commensurate with the quality of the homogeneous one. The need for additional research in this direction, including with homogeneous coprocessors, is shown.

HVDC Converter Cooling System with a Phase Change Dispersion

High voltage direct current converters require efficient cooling of thyristors via heat sinks. Currently, infrastructures use deionised water as a means of cooling the high voltage direct current converters; however, recent research has shown that other fluids have potential to offer more efficient cooling. Phase change dispersions are a new class of heat transfer fluids that employ the latent heat of phase change, thus offering isothermal cooling during melting. For cooling applications, the temperature increase during operation is thus lowered when using phase change dispersions (compared to water) and consequently, the heat sink and thyristors surface temperatures are reduced. In this investigation, a phase change dispersion with non-conductive components, high stability, high capacity and low viscosity has been developed and tested. An experimental setup of a real size heat sink has been installed and the heat transfer behaviour of both the formulated phase change dispersion and water have been investigated and a comparison has been presented. Using water as the heat transfer fluid, the temperature increase from inlet to outlet of the heat sink was 4 K and with the formulated phase change dispersion (at the same mass flow rate and heat input) the temperature increase was 2 K. The phase change dispersion caused a 50% reduction in the heat sink surface temperature. Furthermore, the global heat transfer coefficients obtained for the phase change dispersion were found to be independent of the heating input applied, unlike the trend found for water, additionally, the global heat transfer coefficients were found to be similar to those obtained for water at the same mass flow rates and reached a maximum value of 6100 W m2 K−1. Despite this, the pressure drops and viscosities obtained for the phase change dispersion were higher than for water. Overall, the current investigation demonstrates the ability of using a phase change dispersion as a cooling fluid for the cooling of electronic components, which thus far is limited to using air and water cooling and cannot reach the cooling capacity achieved by phase change dispersions.

Grid to vehicle wireless power supply using single-phase matrix converter

This paper presents the computer simulation model of a grid to vehicle (G2V) wireless power supply using a single-phase matrix converter (SPMC). The proposed system uses the SPMC that operates as a direct AC-AC converter to convert the supply frequency of 50 Hz to reach 20 kHz output frequency. The use of 20 kHz frequency is suitable for wireless power transfer (WPT) operation in order to obtain higher power transfer efficiency between the transmitter and the receiver parts. An advanced of the proposed circuit topology can solve the conventional system for G2V circuit topology that uses multiple stages of power conversion system, resulting in high power semiconductor losses that could lead to low efficiency. In this work, multiple stages of the conventional "AC-DC-AC" circuits have been reduced to a single power conversion stage by using the SPMC circuit topology. The use of the proposed circuit topology can reduce the number of devices, thus reduce the semiconductor losses. A part of reducing the semiconductor losses, the proposed circuit topology could also improve the power density and efficiency of the power supply system. A computer simulation model using MATLAB/Simulink has been developed to investigate the behavior of the proposed system. Selected simulation results are presented to verify the functionality of the proposed system.

Switching Regulation in the Control of 5-Phase Permanent Magnet Synchronous Motor Fed by 3×5 Direct Matrix Converter

Matrix converter is an AC-AC direct power converter comprising of an array of bi-directional switches. It does not require an intermediate DC-link and allows sinusoidal output waveforms with varying amplitudes and frequencies. The configuration of these bi-directional switches decides the number of inputs and outputs of the matrix converter. This research uses a direct matrix converter (DMC) as a phase-changing device that can convert a three-phase AC voltage into a 5-phase AC voltage. The DMC is modulated with the model predictive control algorithm. The output of DMC is fed to a five-phase permanent magnet synchronous motor (PMSM). The model predictive current control technique for DMC is carried out by developing a mathematical model of an input filter and PM motor used as a load. The predictive control of DMC results in sinusoidal output current, and it also enables the frequency variation in the output current. This frequency variation is useful in controlling the speed of the motor connected to the load. After controlling the 5-phase motor, the switching frequency regulation is done to observe its effect on the motor's stator current waveforms. Switching frequency regulation helps to limit the unnecessary switching of DMC. We developed a MATLAB-based Simulink model to study PMSM, and detailed results are presented. The results show that switching regulation can significantly reduce the switching frequency without compromising the current waveform quality.

Kendali Tegangan Output Buck Converter Menggunakan Arduino Berbasis Simulink Matlab

The rapid development of technology to date has made many electrical and electronic equipment that require a direct current (dc) voltage source whose output voltage can be adjusted to the needs of the user. There are several direct voltage levels that are commonly used by electrical and electronic equipment. To get a direct voltage that can be used for various equipment, a direct voltage source that can be varied according to need is required. One way to convert a dc voltage source to a lower dc voltage source is by using a buck converter circuit. This study proposes a buck type direct current converter is porposed to use the Arduino uno as a PWM signal generator circuit to control to control the 24 volt input voltage. The converter output voltage regulation is implemented through a potentiometer and Arduino programming using the simulink Matlab. In this research, a buck converter is tested with output voltage feedback so that the output voltage remains stable. The result of the test that have been carried out show that the buck converter designed in this study has worked well in accordance with objectives. This can be seen from the buck converter output voltage that is in accordance with the reference voltage using a potentiometer that is included in the simulink Matlab program.

Random vibration analysis of an offshore flexible direct current converter valve

With the rapid development of the direct-current grid technology and construction, the flexible direct-current transmission technology has been widely used in many aspects, such as long-distance large-capacity power transmissions, offshore platforms and island power supplies. The offshore flexible direct current converter valve will encounter a variety of unfavorable loads during the marine transportation and the long-term operation on the sea. The safety requirements of the offshore flexible direct current converter valve are higher as a result. Based on the structural characteristics of the converter valve, the converter valve is calculated by finite element method. Under two working conditions of the marine transportation and the long-term operation on the sea, this paper carries out modal analysis and random vibration analysis of the converter valve tower respectively. This paper gives the unfavorable position of the force from the calculation results, and provides a reference for the design and selection of the flexible direct current converter valve to meet the needs of the offshore converter station’s construction.

Comparison of Energy Indicators of the Electric Lift Drive of the Ekg-5 Excavator with Different Power Converters

The energy indicators of the EKG-5 excavator lifting electric drive with thyristor power circuits have been determined according to the systems thyristor direct frequency converter - two-phase asynchronous electric motor, converter-DC motor and direct frequency converter - three-phase asynchronous electric motor. Losses in electric motors and converters have been determined, taking into account the specifics of their joint work in theefficiency for the excavation cycle were determined based on the results of calculating the simulation model, the initial data for which were the parameters of the excavation cycle of the lift drive of a real excavator. Distortion coefficients of the mains current were determined for two cases: during digging and during accelerated lowering of an empty bucket. For comparison, the energy indicators of the selected electric drives with a filter-compensating device were calculated. The analysis of energy indicators is made.

Development of Power Electronic Practicum Units for Vocational Education

The purpose of this research is to develop a Power Electronics practicum unit in the Department of Electrical Engineering Education, Faculty of Engineering, YSU, so that it is suitable and feasible to be applied in vocational education learning by considering the safety aspects of the components and their users. The development includes a three-phase AC source voltage drop from 45 volts to 24 volts per phase, load replacement, the use of up and down voltage converters with greater current capability, and a direct voltage power supply without a transformer switching model. The method used is research & development with technical tests for each part of the module according to the purpose of setting up the practicum unit. The research results were obtained; the power supply with a 24 volt AC source is able to supply a current of 3.63 amperes at a direct voltage of 20 volts with a voltage drop of 0.5 volts, a direct voltage lowering converter is able to change the voltage from 15 volts to 6 volts at a current of 3.66 amperes, with a voltage drop of 0.13 volts. A direct voltage booster converter is able to convert a voltage of 15 volts from 1.78 amperes to 25 volts with a voltage drop of 0.1 volts. The four-pole three-phase motor can be controlled via the TRIAC from zero rotation to maximum rotation, the protection system is capable of breaking the fuse instantaneously in the event of a faulty connection from phase-neutral to phase, followed by disconnection of the 24-volt three-phase AC power source within one second.

An Improved Bipolar Voltage Boost AC Voltage Controller With Reduced Switching Transistors

Single-stage power conversion with simple circuit arrangement is one of the attractive features of direct bipolar voltage ac-ac converters. This increases their potency in various applications that require voltage and frequency regulation. The grid voltage compensators, direct variable speed ac-ac drives, and induction heating systems require inverting and non-inverting operation of the input voltage. Their size, cost, and circuit complexity directly depend on the number of switching transistors, as the operation of each transistor requires the use of one gate drive circuit (GDC) and one isolated dc power supply (IDCPS). The size and cost of GDC and IDCPS are much larger than that of switching transistors. The use of fewer switching transistors also ensures low conversion losses and simplifies the switching schemes. Therefore, this research proposes a new ac-ac converter that is realized as a bipolar boost ac voltage controller having a low count of switching transistors. The suggested topology also eliminates the shoot-through of the input source or output filtering capacitor. The characteristics of the proposed circuit are explored through simulation results obtained through the Simulink platform. The confirmation of the simulation results is validated through the laboratory prototype.

Comparative analysis of voltage controllers for a single stage AC-AC converter for Aircraft Ground power unit application

In this paper, analysis and comparison of various voltage controllers for a direct AC-AC converter suitable for Aircraft Ground power Unit (AGPU) system is discussed. Simulation of the proposed converter is executed and behaviour of the system is studied for various load conditions. A source disturbance is created to check the capability of the system to cope with change in input. By using the open loop simulation parameters, a voltage control loop using P, PI and PID controller is designed and simulated. The expediency of the controller is tested by observing the converter’s response to changes in input parameters.

Design and Implementation of a SiC-Based VRFB Power Conditioning System.

An energy storage system using secondary batteries combined with advanced power control schemes is considered the key technology for the sustainable development of renewable energy-based power generation and smart micro-grids. The performance of energy storage systems in practical application mainly depends on their power conditioning systems. This paper proposes a silicon carbide-based multifunctional power conditioning system for the vanadium redox flow battery. The proposed system is a two-stage circuit topology, including a three-phase grid-tie inverter that can perform four-quadrant control of active and reactive power and a bi-directional multi-channel direct current converter that is responsible for the fast charging and discharging control of the battery. To achieve the design objectives, i.e., high reliability, high efficiency, and high operational flexibility, silicon carbide-based switching devices, and advanced digital control schemes are used in the construction of a power conditioning system for the vanadium redox flow battery. This paper first describes the proposed system topologies and controller configurations and the design methods of controllers for each converter in detail, and then results from both simulation analyses and experimental tests on a 5 kVA hardware prototype are presented to verify the feasibility and effectiveness of the proposed system and the designed controllers.

Multiband asymmetric radio frequency to direct current converter circuit for wireless power transfer

AbstractThis article presents the multiband asymmetric radio frequency (RF) to direct current (DC) converter circuit for the wireless power transfer (WPT) applications. The proposed circuit is composed of a power divider, novel asymmetric multiband matching circuit and RF Schottky diode quadrupler voltage rectifier circuit. Unlike the conventional narrow band quadrupler using two Greinacher cells with opposite polarities, the proposed circuit aims to cover the multifrequency bands, which are the cell phone 1.8–2.1 GHz, the industrial, scientific, and medical (ISM) bands 2.4–2.5 GHz and 5.725–5.875 GHz. The interested RF input power range of −10 to 20 dBm for the WPT application is focused. The measured RF‐to‐DC conversion efficiency (η) of 50–65% at 1.8–2.1 GHz, 65% at 2.45 GHz and 16% at 5.8 GHz are obtained at 10 dBm optimal input power.

Developed owl search algorithm for parameter estimation of PEMFCs

In recent years, the application of renewable energy has been increasingly paid attention to keep environmental clear. One of the key components of this project is the fuel cell industry, which is considered as an environmentally friendly industry. They are, in fact, direct converters of chemical energy to electricity through an electrochemical reaction without the need for any mechanical parts. In this paper, an optimal methodology has been proposed for parameters estimation of a proton exchange membrane fuel cell (PEMFC). The main idea is to develop a modified model of Owl Search Algorithm (DOSA) based on mutation and self-learning mechanisms to enhance the algorithm diversity and resolving its premature convergence. To analyse the efficiency of the method, it is verified by two experimental PEMFC case studies, NedStack PS6 and BCS 500-W and the results are compared by different metaheuristics. The results indicated the superiority of the proposed algorithm toward the others.

(Invited) Improvement of Durability of NiCo-Dispersed SDC Hydrogen Electrodes via Reversible Cycling Operation Between SOEC and SOFC-Modes

A reversible solid oxide cell (R-SOC, operating as SOEC and SOFC) is a promising direct energy converter between hydrogen and electricity (1). We have engaged in the research and development of high-performance, durable electrodes with novel architecture for the R-SOC (2-12). We used an oxygen electrode consisting of a composite of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and samaria-doped ceria (CeO2)0.8(SmO1.5)0.2 (SDC) with SDC interlayer (5, 7-11) and a double-layer (DL) hydrogen electrode consisting of porous SDC with highly dispersed Ni0.9Co0.1 catalyst as a catalyst layer (CL) and a Ni-SDC or Ni-YSZ cermet attached as a current-collecting layer (CCL) (4, 7, 10-12). This presentation focuses on a significant improvement of the durability of our hydrogen electrodes via a reversible cycling operation. We prepared a coin-size cell with an air reference electrode (ARE):DL-H2 electrode│YSZ (0.5 mm)│SDC interlayer│LSCF–SDC O2 electrodeThe preparation method of the cell was similar to that described previously (7, 10, 11). For the DL-H2 electrode, 7.2 vol.% Ni0.9Co0.1 nanocatalyst was dispersed on SDC scaffold in the CL with addition of 10 vol.% three-dimensionally-connected Ni or Ni0.8Co0.2 (11, 12), and 60 vol.% Ni‒YSZ CCL was prepared on the CL. Figure 1 shows the time course of the IR-free potential E (vs. ARE) of each electrode and the ohmic resistance R ohm of the oxygen and hydrogen electrode sides (R O2-side and R H2-side) during two operation protocols: a constant current density operation at −0.50 A cm−2 (SOEC mode only) and a reversible cycling operation between −0.50 A cm−2 (SOEC mode for 11 h) and 0.50 A cm−2 (SOFC mode for 11 h). As reported previously (11, 12), the DL-hydrogen electrode showed appreciable degradation in the SOEC mode only (j = −0.50 A cm−2), specifically, an increase in the R H2-side with time. During the initial 100 h, the degradation rate of R H2-side was rapid, and the cathode potential shifted in the negative direction (increase in overpotential). On the other hand, it is striking that the durability of the DL-hydrogen electrode was improved greatly via the reversible cycling operation. Even though the actual operation time in the SOEC was nearly half that with the constant current operation, the degradation rate of R H2-side was very low. The cathode potential in the SOEC mode (red circles) shifted in the positive direction, and the anode potential (blue circles) shifted in the negative direction during the initial 400 h, i.e., the performances were improved via the cycling operation. Graves et al. have reported a remarkable improvement of the durability of an Sr-doped LaMnO3 oxygen electrode via a cycling operation (13). In contrast, our LSCF‒SDC oxygen electrode exhibited very stable operation, irrespective of the operation protocol. Thus, an improved durability of the H2 electrode via the cycling operation has been demonstrated for the first time. Research on the mechanism of the suppression of degradation of the DL-H2 electrodes is in progress in our laboratory. References S. D. Ebbesen, S. H. Jensen, A. Hauch, and M. B. Mogensen, Chem. Rev., 114, 10697 (2014).H. Uchida, N. Osada, and M. Watanabe, Electrochem. Solid-State Lett., 7, A500 (2004).N. Osada, H. Uchida, and M. Watanabe, J. Electrochem. Soc., 153, A816 (2006).H. Uchida, S. Watanabe, Y. Tao, N. Osada, and M. Watanabe, ECS Trans., 7 (1), 365 (2007).Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta, 54, 3309 (2009).R. Nishida, P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, RSC Adv., 4, 16260 (2014).H. Uchida, P. Puengjinda, K. Miyano, K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and M. Watanabe, ECS Trans., 68 (1), 3307 (2015).K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, Electrochim. Acta, 225, 114 (2017).K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, J. Ceram. Soc. Jpn., 125, 218 (2017).P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, J. Electrochem. Soc., 164, F889 (2017).H. Uchida, P. Puengjinda, K. Shimura, H. Nishino, K. Kakinuma, and M. E. Brito, ECS Trans., 78 (1), 3189 (2017).H. Uchida, H. Nishino, K. Kakinuma, and M. E. Brito, ECS Trans., 91 (1), 2379 (2019).13.C. Graves, S. D. Ebbesen, S. H. Jensen, S. B. Simonsen, and M. B. Mogensen, Nat. Mater., 14, 239 (2015). Figure 1

Bang-Bang control over a direct current to direct current converter

The following document presents an optimal control technique to control power converters direct current to direct current using the Bang-Bang control technique, for example a Buck power reducing converter will be shown, Subsequently and using an approach based on the principle of the maximum of Pontryagin, an optimized switched control technique (bang-bang) is designed and implemented that allows to obtain a performance comparable to the on-off action in terms of dynamic characteristics. Additional tests allow quantifying the optimality of the proposed technique and verifying the performance of the controlled system in energy terms, showing that an optimal switched control has, in addition to the minimization of the functional cost (minimum error energy), a lower incidence in the generation of high frequency switching noise, compared to conventional technique. As one of the most important aspects highlighted in the results corresponds to the simplicity of design and the high efficiency of the Bang-Bang controllers, making the output voltage practically no ripples.

Linearized Sigma–Delta-Based Direct Digital Converter for GMR Sensors

A direct digital converter, based on the sigma-delta modulation principle, is proposed in this article for giant magnetoresistance (GMR) sensors. The proposed converter intelligently integrates the GMR sensors with an improved sigma-delta modulator and provides a linear digital indication of the input magnetic field. The digital output is obtained directly, without using any analog-to-digital converter modules. Some additional merits of the proposed interface are: 1) requirement of a single reference voltage; 2) easy-to-use facility to tune/enhance the overall sensitivity; 3) low conversion time etc. The modulator circuit is followed by a digital filter and decimation circuit, implemented in a microcontroller unit. This sigma-delta converter is validated extensively using simulation and emulation studies. The results from these studies corroborate well, and the maximum nonlinearity is found to be less than 0.12%. Finally, an experimental prototype is developed with a GMR sensor, and the functionality of the converter is tested for static and time-varying field inputs. The experimental nonlinearity of 0.69% shows the better performance of the proposed scheme with respect to other digital digitizer circuits present in the literature.

Coupling model of AC filter branch in SF6 circuit breaker during the break process

In this paper, a coupling model of the AC filter branch circuit with the arc plasma in the circuit breaker was built to investigate the arcing process considering the harmonic current. The comparisons among the current at power frequency (50 Hz), power frequency combining the 11th harmonic and power frequency combining the 24th harmonic show that the high-order harmonic current would lead to higher decreasing rate of current before current-zero period. In addition, the influence of arc on the amplitude of high-order harmonic current is not negligible. Thus, the coupling of arc with AC filter branch circuit is quite necessary in the numerical modeling of the circuit breaker in the AC filter branch at the high voltage direct current converter station.

Analysis of the Behavior of an Air Conditioning System Based on the Solar Energy Natural Regulation in Amazonian Climatic Conditions

Abstract Air conditioning systems (ACSs) represent one of the main demands for electricity in residential, commercial, and industrial buildings. The use of a photovoltaic air conditioning unit (PVACU) represents an attractive application to this demand for reasons such as environmental concerns and the match between diurnal cooling load and solar resource. A PVACU consists of a photovoltaic generator (PVG) that supply an ACS through direct current to direct current and frequency converters, without energy storage. This system considers the natural adjustment of the ACS cooling capacity according to the PVG power. Modeling the ACS, the PVG, and the thermal load (TL) makes possible to evaluate PVACU performance. For this, a small library’s TL and an ACS supplied by a PVG were used as case study. The PVG installed capacity assumes values of 700, 1000, and 1400 Wp. The simulation results show that the PVACU with a 1400 Wp PVG would be sufficient to regulate internal temperature within international comfort standards in the range of 20 °C to 24 °C. According to the data obtained in the simulations, it was possible to conclude that the PVACU has a large potential to be used in air conditioning of other environments in regions with Amazonian climatic conditions.

Heat dissipation characteristics of anode saturable reactors with high thermal conductivity epoxy resin used for ultra‐high‐voltage direct current converter valves

A saturable reactor is one of the important components of converter valves in high-voltage direct current transmission systems. With the ever-increasing capacities of converter valves, the heat losses generated by saturable reactors are also increasing. Thus, a thermal–fluid mechanics coupled heat dissipation model for saturable reactors is proposed. In order to study the factors affecting the thermal dissipation in the saturable reactor, the epoxy resin insulating layers with different thermal conductivity were considered in this work. The simulation results showed that the hot spots in the saturable reactor are on the iron core and close to the pipe inlet that most of the generated heat can be extracted by a cooling pipe and that the effect of heat dissipation can be improved by raising the thermal conductivity of the epoxy resin. The thermal conductivities of the epoxy resin used in the two reactors were 0.8 and 1.2 W/mK, respectively. The time dependence of the iron core temperature was in accordance with the simulation results and the maximum temperatures of the saturable reactor were also consistent with the simulation results. By increasing the thermal conductivity of the epoxy insulation layer, the temperature of the iron core could be significantly reduced.