TECHNICAL MEANS FOR SUPPRESSION OF RESONANCE PHENOMENA IN ELECTRICAL NETWORKS

The self-excitation phenomenon of generators connected to an unloaded power line is considered. Accordingly, the selected values of the conductivity of the controlled shunt reactors, following the control range (especially in the overload mode), avoid the occurrence of self-excitation of the generators. The physical analysis of the processes occurring at self-excitation of the synchronous generator is given, and the calculated models are developed. It is established that in the case of artificial support along the entire length of the voltage line at the nominal value using controlled compensating devices, the transmission will have properties characteristic of relatively short lines (up to 500 km) regardless of its geometric length. It is determined that the length of the line section at the ends of which the DC voltage is maintained is much less than 500 km. Therefore, less than the natural voltage along the section length will exceed the nominal value at the transmitted power, and the line will have excess reactive power. Consumption in intermediate compensation devices (compensation current must be inductive). Ref.8, fig. 4, tables 4.

Implementation Mixed Wireless Network with Lower Number of Wi-Fi Routers for Optimal Coverage

With the development of various wireless communication networks, Wi-Fi Router positioning and deployment systems have become widely popular in recent years to improve coverage in various environments. In this paper, we present an appropriate mechanism for defining the deployment of Wi-Fi Routers to improve coverage in the Oxford Languages Institute (OLI) environment. In addition, the institute's environment was simulated using the Wireless InSite (WI) Package. In this work, two types of Wi-Fi Routers are used. The first is the TP-Link, while the second is the Rocket. These two devices operate at 2.4 and 5 GHz frequencies. There are two objectives in this work. The first aim is to determine the best location to cover the simulated scene environment in a better way. The second aim is to compare Wi-Fi Routers to find out which Wi-Fi Router is better and find out how many Wi-Fi Routers we need to cover the institute's environment. The comparison between Wi-Fi Routers was based on basic parameters to measure the performance of wireless networks, the most important of which are Coverage Rate (CR) Percentage, Signal Quality Rate (SQR), and Received Power Rate (RPR). According to the results that were shown on the Graphical User Interface (GUI) using MATLAB Software. We noticed that the CR, SQR, and RPR of the Rocket are 83.9080%, 97.0082%, and -35.2337 dBm respectively, and these results are better than the results provided by the TP-Link, as it gave the CR, SQR, and RPR are 32.1839%, 77.8690%, and -58.1685 dBm, respectively. Finally, we conclude that CR using the Rocket is good and we need one device to cover the institute’s environment. While CR using the TP-Link is bad and we need five devices to reach the coverage provided by the Rocket because the Rocket has high transmitted power and gain capacity.

Enhancing performance of grid-connected photovoltaic systems based on three-phase five-level cascaded inverter

<span lang="EN-US">Multilevel inverters play an important role in power converters due to their good advantages. The cascaded H-bridge inverter is one of the most prominent and most suitable multilevel inverters in PV systems. Each H-bridge has a separate photovoltaic (PV) array as an independent direct current (DC) source. This paper introduces a three-phase cascaded H-bridge inverter with five levels connected to the grid to improve the performance and efficiency of the photovoltaic system. In the proposed system, each PV group has MPPT to extract the maximum power point from the PV group at certain irradiation and temperature and also to mitigate the mismatch that causes in the imbalance transmitted power from inverter to the main grid. The proposed control scheme with modulation compensation was used, and the system was simulated in MATLAB/Simulink with two different scenarios. The simulation results demonstrate the effectiveness of the proposed connection in minimizing the total harmonic distortion (THD) to acceptable limit, low overshoot, and fast-tracking to the desired value.</span>

Validation of a Monte Carlo Modelling Based Dosimetry of Extraoral Photobiomodulation

An in vivo validation study was performed to confirm the accuracy of extraoral photobiomodulation therapy (PBMT) dosimetry determined by modelling. The Monte Carlo technique was utilized to calculate the fluence rate and absorbed power of light delivered through multi-layered tissue. Optical properties used during Monte Carlo simulations were taken from the literature. Morphological data of four study volunteers were acquired using magnetic resonance imaging (MRI) scans. Light emitting diode (LED) coupled to a power meter were utilized to measure transmitted power through each volunteer’s cheek, in vivo. The transmitted power determined by Monte Carlo modelling was compared to the in vivo measurements to determine the accuracy of the simulations. Experimental and simulation results were in good agreement for all four subjects. The difference between the mean values of the measured transmission was within 12% from the respective transmission obtained using Monte Carlo simulations. The results of the study indicate that Monte Carlo modelling is a robust and reliable method for light dosimetry.

Improving the Quality of the Underwater Robot’s Contactless Battery Charging System

A special feature of the contactless battery charging system of an autonomous underwater robot is the use of a transformer with separating primary and secondary windings. As a result, a non-magnetic gap arises, which leads to the need to increase the primary current and the output current of the autonomous inverter. One of the ways to improve the quality of the system is the use of a resonant circuit at the inverter output in combination with the "soft switching" mode of its power switches. The use of resonance on the transformer secondary side also allows you to equalize the current loads of the primary and secondary windings. In this way, a minimum of losses in the inverter is achieved and the power transformer of the system is optimized. This allows you to reduce the size of the system while maintaining the transmitted power, or increase the transmitted power while maintaining the dimensions. The problem solved by using mathematical modelling with verification of the solution adequacy in a full-scale experiment.

Joint Power and Channel Optimization of Agricultural Wireless Sensor Networks Based on Hybrid Deep Reinforcement Learning

The reduction of maintenance costs in agricultural wireless sensor networks (WSNs) requires reducing energy consumption. At the same time, care should be taken not to affect communication quality and network lifetime. This paper studies a joint optimization algorithm for transmitted power and channel allocation based on deep reinforcement learning. First, an optimization model to measure network reward was established under the constraint of the signal-to-interference plus-noise-ratio (SINR) threshold, which includes continuous power variables and discrete channel variables. Secondly, considering the dynamic changes of agricultural WSNs, the network control is described as a Markov decision process with continuous state and action space. A deep deterministic policy gradient (DDPG) reinforcement learning scheme suitable for mixed variables was designed. This method could obtain a control scheme that maximizes network reward by means of black-box optimization for continuous transmitted power and discrete channel allocation. Experimental results indicated that the studied algorithm has stable convergence. Compared with traditional protocols, it can better control the transmitted power and allocate channels. The joint power and channel optimization provides a reference solution for constructing an energy-balanced network.

Features of choosing functionally-oriented manufacturing processes of gear pairs for continuous-drive transmissions

The results of studying the features of manufacturing gear pairs for continuous-drive transmissions are presented. It is shown that due to the peculiarities of gear functional and operational properties while switching without breaking the kinematic chain and without interrupting the flow of transmitted power, it is necessary to provide additional surface treatment of drive gear teeth and block shaft driven wheels in the zones involved in the actual transmission shift.

Structure and circuit solution of a wireless power transfer system for application in mobile robotic systems

This paper presents the development of a medium-power wireless power transmission system for use in robotics and other applications. The presented system can be used to power devices or charge batteries. The system is based on the principle of inductive power transmission. A feature of the system is the use of a resonant self-oscillator, for which the transmitting LC circuit of the system is a frequency setting. The use of identical receiving and transmitting resonant circuits makes it possible to refuse additional frequency control devices in the receiving part of the system. The presented circuitry solution of the wireless power transmission system ensures operation in the resonance mode in the receiving and transmitting circuits, where the receiving and transmitting coils are at various positions relative each other, while not requiring a dedicated monitoring and control system for this. Experimental verification of the proposed solution was carried out on a prototype of a system with shell elements, shielding from magnetic fields, while the maximum level of efficiency of the system without an output stabilizer in the receiving part was 80.41%, with a transmitted power of 131.5 W, at a transmission distance of 15 mm. The dependency curves of the efficiency and the transmitted power were obtained for three distances of energy transfer — 0 mm, 15 mm and 30 mm. With distances between the coils up to 30 mm, the efficiency of the system is above 70% with a transmitted power of more than 55 W. Key words Wireless charging system, wireless power transmission, resonant oscillator, wireless power transmission efficiency. Acknowledgements This research is supported by the RFBR, project no.19-08-01215_А.