Low-voltage Unit Research Articles

Повышение адекватности моделей электромеханотронных систем

Development of electromechanotronic systems is connected with modeling and calculation of processes of various kinds. Electromagnetic, mechanical and thermal processes are analyzed, control, regulation, protection, monitoring and diagnostics problems are solved. Systems may contain a large number of power semiconductor elements. Short-term and multi-hour processes are calculated. Taking into account mutual connections of processes of various kinds in calculations of complex systems requires inadmissibly large expenditures of machine time. The problems are solved under more or less significant assumptions, which leads to a decrease in the adequacy of the results. The methods of systems calculation are proposed, which allow to reduce machine time consumption and to use more detailed description of installations and more accurate computer models. Possibilities of calculation of processes by «smooth components» of variables, and also application of dual models, in which speed and accuracy are combined, are considered. As an example, a system with an active cascade frequency converter containing 780 transistors and diodes, parasitic inductances and snubber circuits, and a vector-controlled induction motor with ladder circuits accounting for current displacement is analyzed. The model takes into account energy losses in the converter and in the motor, as well as the distribution of losses by components. It also takes into account emergency operation modes associated with disconnection of a part of low-voltage units of the cascade converter and maintenance of power quality at its input and output by symmetrization of the main current components and suppression of parasitic components.

Intelligent Approach for Control Techniques Based on Complex Converter Structures

Hybrid frequency control strategies are used to eliminate the problem of current inversion in multilevel cascaded asymmetrical H-bridge inverters. Unfortunately, this technique results in unbalanced power at the inverter output. The improved hybrid PWM modulation strategy helps to regulate power balances within a reasonable range at high and low voltages, by adjusting the conduction angle of the cells in high frequencies. However, as the conduction angle of a high-voltage cell increases, the fundamental amplitude of the inverter output voltage decreases, since waveforms with absolute values greater than 2 E cannot be perfectly modulated. Based on mathematical models of the conduction time for each level synthesis method, a new modulation strategy is proposed to solve the problems associated with the two strategies mentioned above. This new high-frequency modulation strategy adopts a combination of pulse-width modulation (PWM) and step modulation to combine control of the high-voltage and low-voltage units. At given intervals, the control voltage signals of the low-voltage unit are exchanged. Finally, the power of each unit is balanced and the basic amplitude of the inverter output voltage is not affected. Finally, the MATLAB/Simulink simulation model and experimental platform verify the feasibility of this strategy.

Power balance modulation strategy for hybrid cascaded H-bridge multi-level inverter

Under the traditional hybrid modulation strategy, the output powers of the hybrid cascaded H-bridge inverter are not balanced between the cascaded units. With a hybrid cascaded H-bridge 13-level inverter with a DC side voltage ratio of 1:1:1:3 (referred to as III-inverter in the paper) as the research object, a hybrid modulation power equalization strategy based on carrier rotation is proposed. Under the control of which, the output voltage of inverters is formed by superposition of multiple basic voltage waveforms. Firstly, the hybrid modulation strategy is adopted to modulate the inverter so that the high- and low-voltage units, respectively, operate in the low-frequency and high-frequency states. Then, the pulse sequence within the 3/2 output voltage cycle is made to circulate among all the cascaded units by carrier rotation. Finally, the output voltage of each cascaded units is made to contain all the basic voltage waveforms, thus implementing the output power balance between all the cascaded units. Based on simulation and experiment, the effectiveness of the strategy is verified, and it is shown that under the control of this power balance modulation strategy, the output voltage waveform quality of the inverter is high, there is no current backflow, and the output power can be balanced within 3/2 cycles.

Research on Modified Hybrid Frequency Modulation Technology of Type-III Asymmetric CHB Multilevel Inverters

Asymmetric Cascaded H-bridge (ACHB) level inverters can output more voltage waveforms with fewer cascaded units while ensuring the quality of output voltage waveforms, so they have attracted more and more attention. Taking the topology of Type-III asymmetric CHB multilevel inverters as the research object, a Modified Hybrid Frequency Pulse Width Modulation (MHF-PWM) strategy is proposed in this paper. This modulation strategy overcomes the local overshoot of low-voltage unit in the presence of traditional Hybrid Frequency Pulse Width Modulation (HF-PWM), thus completely eliminating the low frequency harmonics in the output voltage waveform of Type-III ACHB nine-level inverters, and the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of PS-PWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage. At the same time, the strategy can also improve the problems of current backflow and energy feedback caused by the high-voltage unit pouring current to the low-voltage unit, thereby reducing the imbalance of the output power of the high-voltage and low-voltage units. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy.

Modified Modulation Strategy of 1: 1: 2 Asymmetric Nine-Level Inverter and Its Power Balance Method

The three unit nine-level inverter can output more voltage levels with fewer h-bridge units, while having better output waveform quality. However, in the conventional hybrid frequency modulation strategy, only one low-voltage unit adopts pulse width modulation (PWM), which causes the problem of switching loss and uneven heat distribution between the two low-voltage units. At the same time, the output power of the conventional modulation strategy is unbalanced. Aiming to resolve the above problems, a modified hybrid modulation strategy and a power balance control method under the strategy is proposed in this paper. The modulation strategy achieves output power balance between the three units and an even distribution of switching losses between the two low voltage units while maintaining the same output power quality. Simulation and experimental results verify the feasibility of the modulation strategy.

Effect of inductor parasitic resistances on the voltage gain of high step‐up DC–DC converters for electric vehicle applications

Reconfiguration, sizing and downsizing of the storage unit, in electrically propelled vehicles, are techniques that have been reported effective to improve the shelf life and performance of the storage cells. However, these solutions might decrease the rated voltage of the storage unit and therefore DC-DC converters with high voltage gain are suitable solutions to connect these low-voltage units to the motor drive, keeping a good performance of the vehicle. Moreover, parasitic resistances presented in the components of these converters have proved to influence the efficiency and the voltage gain of the converter. The ideal voltage gain of four high step-up converters is analysed, derived, and compared. These converters were selected because of their potential to be applied in electric mobility and their similarity in the techniques that use to achieve high voltage gain: interleaving phases and magnetic integration. One of the analysed topologies is proposed by the authors. Afterwards, the parasitic resistance effect is analysed to obtain the non-ideal voltage gain and the efficiency of these four topologies. Finally, the topology that presents the best trade-off between the non-ideal voltage gain and the efficiency is experimentally tested with a 100 W prototype.

Understanding energy loss in parallelly connected microbial fuel cells: Non-Faradaic current

In this work, the mechanisms of energy loss in parallel connection of microbial fuel cells (MFCs) is explored using two MFC units producing different open circuit voltage (OCV) and current. In open circuit mode, non-Faradaic current flows in low OCV unit, implying energy loss caused by different OCVs in parallelly stacked MFCs. In a stacked MFC in parallel under close circuit mode, it is confirmed that energy loss occurs until the working voltage in high OCV unit becomes identical to the other unit having low OCV. This result indicates that different voltage between individual MFC units can cause energy loss due to both non-Faradic and Faradaic current that flow from high voltage unit to low voltage unit even in parallelly stacked MFCs.

Low-voltage arithmetic units based on fully depleted SOI CMOS nanotransistors

Approaches to the development of low-voltage low-power-demand arithmetic units on the basis of silicon-on-insulator nanotransistors are considered. The characteristics of physical models of one- and eight-bit adders based on fully depleted silicon-on-insulator complementary metal-oxide-semiconductor nanotransistors with different topological parameters are numerically analyzed. For some selected elements, the dependences of the delay time and switching power on supply voltage below 1 V are studied for different voltages at the back gate of the transistor.

One Mill's Response to a Specific Type of Arc Flash Problem

It is sometimes a difficult concept to get across to those most affected, but the greatest arc flash hazards in a mill's electrical distribution system often do not occur at the highest voltages. In fact, they often occur at much lower voltages, such as 480 or 575 V, on the secondary bushings and bus of low-voltage unit substations. This paper describes one mill's response to this challenge.

70.2: Low-Voltage White Tandem Structures for Fabricating RGBW AMOLED Displays

We recently demonstrated full-color RGBW AMOLED displays based on white-emitting OLED structures optimized for a D65 white point. The efficiency of the white formulation has been improved by the use of tandem structures with two or three lowvoltage white-emitting units connected by organic “PN”-type connectors. It has been found that the separation between emitting units is critical to the efficiency and the white point of the tandem structure. Optimized two- and three-EL unit structures exhibit efficiencies of 17.4 cd/A and 24.6 cd/A, respectively, compared to 10.7 cd/A for the single-EL unit control. The tandem structures demonstrate excellent operational stability, with extrapolated half-life times for one-, two-, and three-unit test devices of about 50,000 h, 70,000 h, and 110,000 h, respectively, at 1000 cd/m2. We have also fabricated advanced white tandem structures where the color gamut (NTSC x,y ratio) has been improved to greater than 70% using standard color filters.

Effects of electrical stimulation, followed by moderate cooling, on meat quality characteristics of veal Longissimus dorsi

Three groups of male Friesian veal calves (in total, 92) were slaughtered in separate series. Within each group, a subgroup (selected on the basis of blood characteristics determined 1 week ante mortem) was electrically stimulated immediately after bleeding (64 s-Mitab® Low voltage unit). Carcasses were transferred ca. 25 min post mortem (pm) to a cooler at 6°C and ca 2 h pm to a cooler at 3°C. Electrical stimulation (ES) increased brightness and, to a lesser extent, yellowness, of the freshly cut surface (6th rib Longissimus dorsi, 24 h pm) but resulted also in a diminished water-holding capacity (WHC) of the veal meat. The effect of ES on tenderness (Warner-Bratzler shear force, 48 h pm) is positive for two of the three groups but negative for the third. This indicates that ES probably results in two opposite effects on tenderness—‘toughening’, as a result of the sarcomere shortening which occurred in all three groups, and ‘tenderizing’, as a result of microscopical fibre disruption. Our data indicate that disadvantages of ES may outweigh advantages when followed by moderate cooling.

Small anal tumors irradiated via rectoscope

An intracavitary radiation device that can slip inside a rectoscope and quell small, localized rectal tumors into submission is providing a safe and effective alternative for patients in whom anorectal surgery may be contraindicated. The device, a low-voltage contact unit that keeps 80% to 90% of the x-ray beams to within 2 cm of the target tissue, has yielded an 85% complete tumor regression rate in patients treated for small, well-defined rectal carcinomas at the Cleveland Clinic Foundation. Gwynn L. Jelden, MD, staff physician in the foundation's department of radiation therapy, told the recent meeting of the American Society of Therapeutic Radiologists in Miami Beach that the intracavitary regimen should be considered only for carefully selected patients with small cancers of not more than 3 cm in diameter and a low probability of lymph node involvement. Additional reasons for assigning patients to the treatment may be advanced age, cardiac or

Sintered constructional conducting copper parts for low-voltage units

A process has been developed for the manufacture of copper conducting constructional parts of complex configuration by the powder metallurgy technique. The electrical resistivity of such sintered copper parts is virtually no different from that of parts from rolled copper. The operating characteristics of parts produced by this process are markedly superior to those of parts made from copper rolled stock.

A New Approach to Tubal Sterilization by Laparoscopy

Laparoscopic tubal sterilization has been rapidly gaining acceptance as a nonpuerperal method of permanent fertility control. A number of problems have nonetheless been associated with this technique. For example, tubal destruction often exceeds that necessary for tubal occlusions, increasing the danger of thermal injuries and possibly such dysfunctional disorders as abnormal uterine bleeding and dysmenorrhea. Furthermore, excessive destruction precludes any possibility of later tubal reconstruction. In an attempt to avoid these problems, a new low-voltage unit with a rechargeable battery was evaluated. With this unit, cautery is provided under laparoscopic view with a spring-activated hook which retracts the fallopian tube into a Teflon shield, where it is coagulated and transected. Histopathologic studies of the healthy fallopian tubes of four women in their reproductive years treated by this method while the abdomen was open prior to an elective hysterectomy demonstrated minimal destruction of the mesosalpinx, with complete tubal occlusion and a coagulated area 10 mm in length. One hundred and sixty-five patients have been sterilized successfully by this method. Indications are that it may provide safe tubal occlusion without unnecessary destruction of the fallopian tubes and surrounding vasculature.

A new concept in station arrester design

In 1968 Matsushita Electric Industrial Co. of Osaka, Japan announced a new improved non-linear resistance material based on zinc oxide. The original devices were small low voltage units applicable for use in the electronics industry. In 1970 work was performed by the General Electric Co., and is continuing, using its own funds and technical resources, to develop larger devices for use as a substitute for silicon carbide valve blocks in surge arresters. Development has now progressed to the point where this material, with non-linearity characteristics far superior to silicon carbide, can be used to manufacture station type arresters which do not employ series gaps. The purpose of this paper is to outline some of the characteristics made possible by the new material which is becoming increasingly important to the electrical industry.

What to Look for in a Low-Voltage Unit Substation

Many considerations from location to breaker selection in the application of low-voltage unit substations in the cement industry are presented. Five basic topics are covered in the following order: general considerations, high-voltage section, transformer section, breaker section, and device coordination. Features of the new solid-state trip device now available on low-voltage circuit breakers plus coordination aspects of fault protection are also discussed. The material is presented in such a manner that it can be used as a check list when specifying low-voltage unit substations.