Stability Of Power Transmission Research Articles

Синтез системного стабилизатора с применением методов нечеткой логики и нейронной сети

Power systems are large non-linear systems that are often subject to low frequency electromechanical oscillations with a frequency of 0.5–2.5 Hz. Power system stabilizers (PSS) are commonly used as effective and economically efficient means to dampen electromechanical oscillations of generators and increase the stability of power systems. PSS can increase the power transmission stability limits by adding a stabilizing signal through the channels of the automatic excitation control system. The article presents the results of training a neural network based on which a fuzzy logic PSS is obtained for increasing the stability of electric power systems. The synchronous generator rotor speed deviation and acceleration were taken as input data for the fuzzy logic controller. These variables have a significant effect on damping the rotor's electromechanical oscillations. The characteristics of the power system equipped with the proposed fuzzy logic based PSS are compared with its characteristics with a PSS with non-optimized parameters and without a PSS.

Quasi-Independent Bidirectional Communication Methods for Simultaneous Wireless Power and Information Transmission

Simultaneous wireless power and information transmission (SWPIT) is essential for power regulation, load detection, and maximum efficiency tracking in wireless power transfer (WPT) systems. To eliminate the interaction between power and information transmission, this paper proposes a novel bidirectional communication method based on differential phase shift keying (DPSK). First, the steady-state and transient models of the series–series compensated WPT system are established to analyze the characteristics of power transmission and the behavior of shared power/information channel. Second, regarding the stability of power transmission, principles of the forward and backward communication that integrated with power modulation through the full-bridge inverter and the semi-bridgeless active rectifier are elaborated. Then, the demodulator and half-duplex communication protocol are designed. Finally, the simulation is carried out and the experimental prototype is established, which shows that the proposed DPSK method is effective and the transmission of power and information is quasi-independent. Owing to the integration of power and information transmission, the complexity, cost, and volume of the SWPIT system are reduced significantly.

High-Data-Frequency-Ratio Information Transmission Method for Fast Dynamic Response SWPIT Systems Based on DASK Modulation

Integration of power and information transmission is promising for simultaneous wireless power and information transmission (SWPIT). This article presents a differential amplitude-shift keying (DASK) modulation-based high-data-frequency-ratio information transmission method for fast dynamic response integrated SWPIT systems. Modeling and analyses of the phase-shifting modulation of power converters indicate the potential of the DASK modulation for information transmission. Operation principle of the proposed modulation is established to maintain the stability of power transmission based on the modeling. Modulator, demodulator, and communication protocol are further designed. Using the dynamic analytical model of the transmission channel, the active intersymbol interference (ISI) elimination characteristics are analyzed. Due to the ISI elimination, a high-data-frequency-ratio and fast dynamic response SWPIT is realized. Interactions between power and information transmissions are evaluated, and the results show anti-interference performances. Finally, an experimental prototype rated at 200 W is built to verify the effectiveness of the method, and the data–frequency ratio reaches 0.5 bit/Hz. Complexity, cost, and response period of the method are reduced significantly, and it can be extended to other applications universally.

Integrated receiver with high misalignment tolerance used in dynamic wireless charging

Misalignments between the transmitter and receiver coils would in some cases lead to a significant decline in transmission power and efficiency in the wireless power transfer system. This study presents an integrated two-layer receiver to improve the tolerance of horizontal misalignment. On the lower layer of the integrated receiver, two coplanar spiral coils, which are decoupled and work as the auxiliary repeater, are designed to help keep a stable power transmission between transmitter coils on the track and the main receiver coil on the upper layer. Then, the optimisation model based on the Bayesian algorithm is established for the proposed receiver structure and some key parameters are optimised. A sensor-coil-based positioning approach is also proposed to achieve on–off control of the transmitter coils. The simulation results show that the system based on the optimised integrated receiver has a stable output power with a variation lower than 13.17%. Two 300 W dynamic charging prototypes based on the integrated receiver and conventional spiral receiver, respectively, have been developed to verify the effectiveness of the proposed design and the optimisation method. The experimental results match well with the simulation results.

Fault Detection on Insulated Overhead Conductors Based on DWT-LSTM and Partial Discharge

Insulated conductors can improve the stability of power transmission and reduce the construction space compared with traditional bare conductors. Therefore, insulated conductors are used more and more in overhead power transmission. However, a major challenge of using insulated overhead conductors (IOC) is that the ordinary protection devices are not able to detect the phase-to-ground faults and something, such as tree branch, hitting conductor events. This may cause an accident such as power failure or electrical fire and result in serious damage. In this paper, a new approach, which is based on Discrete Wavelet Transform (DWT) and Long Short Term Memory network (LSTM) for detecting of IOC fault according to partial discharge, is presented. Firstly, the original signal is denoised by DWT. Secondly, the denoised signal is decomposed and extracted features on different layers by DWT. Finally, IOC fault is detected by LSTM. This method can improve the detection accuracy of IOC fault which is tested on the ENET public data set and compared with other classification methods.

Improving Power Transmission System Stability in Nigerian using Statcom Device Controller

The instability of power transmission system in Nigeria is the concern of many individual and that is what this paper wants to address. The first stage was to analyze the effect of static synchronous compensator (STATCOM) on power transmission stability. In doing that, the three phase fault was introduced to the system at line 4-5. The Load flow simulation analysis was carried out according to IEEE 9 bus system. The power transmission system model was developed and simulated using MATLAB/SIMULINK software. The result of the simulation shows that Bus 5 was detected to violate the voltage limit of 0.95 < V< 1.05 p.u. having a voltage magnitude of 0.8875p.u. The per unit Voltage magnitude of power system with STATCOM and without STATCOM was calculated. From the result, the voltage magnitude without STATCOM was 0.8875p.u while that with STATCOM was 1.01p.u. The total active power Loss without STATCOM was 324.02MW while that with STATCOM was 322.53MW. Therefore the percentage of power system improvement is 0.23% when STATCOM was incorporated. Finally, Power transmission system improves when STATCOM was applied.

IPT system for tail‐free household appliances in the smart home system

Inductive power transfer (IPT) is a new power supply technology for household appliances to eliminate the effects of sparks and wires. Besides, the smart home is a popular intelligent system to connect the facilities in the home. To combine the advantages of IPT technology and smart home system perfectly, the transmission of the control signal is as important as the transmission of power for IPT system. This work proposes a method that makes the power and control signal transmission synchronously from the supply side to receiving end to achieve the wireless power supply and the intelligent control for household appliances such as televisions, air conditioners, air purifiers etc. In the proposed method, the fundamental and harmonic components of the inverter output voltage are used as the power carrier and the signal carrier, respectively. One is to supply power to household appliances and the other is to transmit a control signal to them. On the basis of this method, the features of harmonics such as low energy and high frequency are well used, which enable both stable power transmission and high-speed signal transmission. The effectiveness of the proposed method is verified by an experimental platform of kW level.

A Wireless Power and Information Simultaneous Transfer Technology Based on 2FSK Modulation Using the Dual Bands of Series–Parallel Combined Resonant Circuit

In this paper, a new wireless power and information simultaneous transfer (WPIT) technology based on binary frequency shift keying (2FSK) modulation using the dual bands of a series–parallel combined resonant circuit (SPRC), SPRC-2FSK-WPIT technology, is proposed. Conventional 2FSK-WPIT technologies commonly employ single resonant band, and due to the insufficient utilization of system resonance, they have inherent disadvantages, such as low efficiency and low system quality factor. In the proposed technology, the system employs dual resonant bands of the SPRC and both of the system carriers use the resonant frequencies, and so the disadvantages of the conventional 2FSK-WPIT technology are eliminated. Optimal design of the SPRC-2FSK-WPIT system is conducted. In the optimized system, the two carriers have similar power and information transfer characteristics, and so a high WPIT performance, including stable power transmission, is guaranteed. The proposed technology is validated by experimental results. The experimental prototype shows up to 20 kb/s of communication rate with maintaining the power transfer efficiency over 85% at the distance of 50 mm.

The Case against Carbon Prices

Professor Dr. Anthony Patt is head of the Climate Policy Group in the Department of Environmental Systems Science at ETH Zurich, Switzerland. His research focus is on technological pathways and public policies for climate change mitigation and adaptation. He is a Coordinating Lead Author in Working Group III of the Intergovernmental Panel on Climate Change. He obtained his PhD at Harvard University's Kennedy School of Government. He is the author of “Transforming Energy: Solving Climate Change with Technology Policy” (Cambridge University Press, 2015). Download : Download high-res image (204KB) Download : Download full-size image Professor Dr. Johan Lilliestam is head of the Renewable Energy Policy Group in the Department of Environmental Systems Science at ETH Zurich, Switzerland. His research focus is policies and strategies for a transition to a completely renewable energy system, including the effects of interactions between different energy policies. He obtained his PhD at the Central European University in Budapest, Hungary. Before joining the ETH, he worked at the Potsdam Institute for Climate Impact Research (PIK) in Potsdam, Germany, and the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria. He currently holds a grant from the European Research Council for his work on policy interactions. Download : Download high-res image (202KB) Download : Download full-size image

Synthetic electric field calculation method of three-coil structure to resist the seawater flow vibration

In the marine environment, the inductive power transfer (IPT) technology offers many benefits such as increased flexibility and complete rejection of the winding problem. However, for underwater vehicles, the impact of seawater flow vibration will affect the stability of the power transmission. In this paper, a symmetrical double coil structure named 1×1×1 system is proposed to reduce the eddy current loss (ECL) and enhance the power transmission stability of the system under the impact of seawater flow vibration. Firstly, based on the discretization of the electric fields excited by each turn of two transmitting coils, the novel calculation method proposed is that the synthetic electric field at each discrete point is the sum of the electric field vector. Then the synthetic electric field and induced voltage of the 1×1×1 system are simulated by the finite element simulation software COMSOL to verify the calculated results. Finally, experiments are conducted to illustrate that the 1×1×1 system has good ability to resist Z-axial interference and reduce the impact of the seawater flow vibration.

Summarization of busbar protection principle

Safe bus operation is an important requirement for stable power transmission of a power system. Further, bus protection is also an important part of relay protection. Regarding the former, a variety of different protection principles have been proposed. Based on the amount of protection used in different protection principles, this paper describes the advantages and disadvantages of power frequency protection, transient parameters protection, and full-waveform protection. Finally, the paper summarizes the problems to be solved by current bus protection and formulates its future research direction.

Novel Dual-Phase-Shift Control With Bidirectional Inner Phase Shifts for a Dual-Active-Bridge Converter Having Low Surge Current and Stable Power Control

To transmit constant powers particularly at light load, the isolated dual active bridge (DAB) with conventional dual-phase-shift (DPS) control exhibits large variations of currents, losses, and efficiencies if there is a small change of outer phase shift ratio, which is caused by the change of command to adjust power transmission. This is mainly because of the narrow operation region of outer phase shift ratio if the conventional DPS modulation is used. To solve this problem, a novel DPS control with bidirectional inner phase shifts for the DAB is developed to reduce the current surge in the high-frequency transformer, which can stabilize the output power with high efficiency. From the analysis of operation modes and power characteristics of the proposed DPS control, it is shown that due to wider operation region of outer phase shift ratios compared with the conventional DPS control in which the inner phase shifts of both the primary and secondary H-bridges are in the same direction, lower surge current can be obtained in the change of phase shift command, which results in stable power transmission particularly at light load without scarifying the efficiency. Moreover, the DAB of using the proposed DPS control can transmit bidirectional energy with the inner and outer shift ratios of 0-1. For experimental verifications, the test results are also presented in this paper.

The power transmission stability and efficiency of V-belts

The V-belt drive is a rather popular, widely used form of power transmission in agricultural and food industry engineering. At the same time, its stability, the lifetime of V-belt is influenced by several environmental factors, namely in the food industry by the contamination affecting the belt sides, the ambient temperature, humidity and the occasionally aggressive (acidic, alkaline air, air saturated with gases, etc.) medium. In the case of agricultural machinery, the vibration caused by uncertainly oriented pulleys with bearing in different plate structures (often being shaken in the fields) as well as alignment adjustment inaccuracies jeopardize the reliability of the parameters of the drive. Furthermore, the efficiency is determined by several factors together: the slippage occurring during drive transmission, the hysteresis loss resulting from the external and internal friction occurring with the belt entering and exiting the pulley. Experimental equipment and calculation methods were developed to determine the dynamics of temperature increase generated by the belt and pulley relationship. The temperature generated in the V-belt was measured as a function of pretension, pulley diameter and bending frequency. The so-called damping factor characterizing the contact with the pulley (the external friction when entering and exiting the groove) and the hysteresis loss (inner friction) are also determined. On the basis of the damping factor (ζ ≈ 400 Ns/m2) of the V-belt involved in the experiments the other losses (Poth) occurring from the pulley—V-belt contact and internal friction may be estimated. The drive parameters may be optimized with the mathematical model describing the effect of the pulley diameter and belt frequency on the increase in temperature. A standardized calculation method as well as design factors valid for the properly adjusted drive and normal operating conditions determined through empirical and laboratory experiments are used for the sizing of V-belt drives. The lifetime of V-belt drives designed in this way, used in extreme conditions typical of agricultural machinery will not be appropriate and will not provide clear, predictable information for maintenance planning. In such cases the results of our own many lifetime tests conducted in the given circumstances can be safely relied on. The agricultural harvesting machines are large plate-body self-propelled structures on which most of the power supply of the (threshing, cleaning, moving, etc.) machine units handling the crop is realized via belt drives. The distance and angular displacement of the axes involved in the drive can vary within wide limits. The misalignment and angular displacement of the pulleys can be the result of installation instability — due to the plate structure — and the deformation of the plate structure occurring during the operation as well. V-belt drives operate satisfactorily under such conditions as well, however these faults are unfavourable in terms of belt lifetime and result in the reduction of drive efficiency. A further aim of our research is to examine through experiments the lifetime and efficiency of V-belts used in agricultural machines as a function of drive adjustment errors. According to the results of the measurements of the geometrical adjustment errors of V-belt drives performed in the field, the pulleys of agricultural equipment are not always positioned in the medium plane of the drive. In our experiments these data served as independent variables. Figure 1 shows the arrangement of a V-belt drive in a grain harvester with the laser pulley alignment measuring instrument installed as an accessory. In the case of many machine types in 80% of the tested drives three times the permissible error was measured, and because of off-road use, due to dynamic load these errors further increased as a result of the frame deformation. The results of both the belt bending testing and the geometrical adjustment testing of the drive offer great help in the design of belt drives. At the same time they can be the source of lifetime and efficiency forecasts.

Hierarchical Direct Power Control of Modular Multilevel Converter for Tundish Heating

In this paper, the full bridge-based modular multilevel converter (MMC) is discussed for the application of tundish induction heating power supply (TIHPS). TIHPS features three-phase to single-phase ac/ac conversion and variable output frequency, and has intense demand for the power transmission stability and output current control precision. MMC is suitable for this application and especially the bulky and costly transformer and ac filter in the conventional topology can be dispensable. Therefore, it is interesting to investigate the applicable control method for MMC-TIHPS. According to the instantaneous power theory, a hierarchical direct power control based on the improved deadbeat current control is presented to assure the energy balance inside and outside MMC-TIHPS and reduce the sensitiveness of the current controller to parameter uncertainties. The proposed control strategy dispenses with the phase-locked loop, and does not exist the coupling among control variables of internal and external currents. Then, parameters design of energy controller is studied for stability analysis. Finally, MMC-TIHPS and proposed control method are verified by experimental results of a down-scaled physical prototype.

Improvement of Power System Stability Using FACTS Device

This paper describes the impact of the Flexible AC Transmission System (FACTS) controller, namely Thyristor Controlled Series Capacitor (TCSC), on the transient stability of power transmission. For demonstration of the impact of TCSC on transient stability of a power system, a model of the Slovak power system was used. The devices with a suitable controller can also be used for many other purposes than those for which they were designed.

New Control of PV Solar Farm as STATCOM (PV-STATCOM) for Increasing Grid Power Transmission Limits During Night and Day

This paper presents a novel concept of utilizing a photovoltaic (PV) solar farm inverter as STATCOM, called PV-STATCOM, for improving stable power transfer limits of the interconnected transmission system. The entire inverter rating of the PV solar farm, which remains dormant during nighttime, is utilized with voltage and damping controls to enhance stable power transmission limits. During daytime, the inverter capacity left after real power production is used to accomplish the aforementioned objective. Transient stability studies are conducted on a realistic single machine infinite bus power system having a midpoint located PV-STATCOM using EMTDC/PSCAD simulation software. The PV-STATCOM improves the stable transmission limits substantially in the night and in the day even while generating large amounts of real power. Power transfer increases are also demonstrated in the same power system for: 1) two solar farms operating as PV-STATCOMs and 2) a solar farm as PV-STATCOM and an inverter-based wind farm with similar STATCOM controls. This novel utilization of a PV solar farm asset can thus improve power transmission limits which would have otherwise required expensive additional equipment, such as series/shunt capacitors or separate flexible ac transmission system controllers.

Performance Analysis of a High Voltage DC (HVDC) Transmission System under Steady State and Faulted Conditions

The modern High Voltage Direct Current (HVDC) transmission technology depends on the development of power electronics based on the semiconductor devices. This paper represents a simple model of HVDC transmission system in which the converter and filter have been designed to increase stability of power transmission. The HVDC transmission system has been proposed on the basis of simulation studies using MATLAB software package (Simulink Model). Using this model, current - voltage (C-V) characteristics have been simulated for steady state condition. It has also been studied for different fault conditions. With the proposed strategy the HVDC system can provide useful and economical way to transmit electric power over the long distance, thereby improving the bulk transmission of electric power and power system stability.

Parameters optimization for magnetic resonance coupling wireless power transmission.

Taking maximum power transmission and power stable transmission as research objectives, optimal design for the wireless power transmission system based on magnetic resonance coupling is carried out in this paper. Firstly, based on the mutual coupling model, mathematical expressions of optimal coupling coefficients for the maximum power transmission target are deduced. Whereafter, methods of enhancing power transmission stability based on parameters optimal design are investigated. It is found that the sensitivity of the load power to the transmission parameters can be reduced and the power transmission stability can be enhanced by improving the system resonance frequency or coupling coefficient between the driving/pick-up coil and the transmission/receiving coil. Experiment results are well conformed to the theoretical analysis conclusions.

1.7MHz, 25W급 자기공명 무선전력 전송 시스템 구현

본 논문에서는 자기공명 방식을 이용한 25W급 무선전력 전송 시스템을 설계 및 구현하는 것을 제안하고 있다. 본 논문에서 제안하는 자기공명 방식 무선전력 전송 시스템은 100W급 Class-F 송신기, 1.7MHz대역의 송수신 공진기, 40W급 Full-bridge 다이오드 수신기로 구성되어 있다. 특히 제안된 시스템은 수신기에 전달되는 전력이 부하를 구동할 수 있는 적정레벨로 유지될 수 있도록 송신기와 수신기 사이의 통신을 이용한 송신전력제어 기능을 구현하여 송신기가 최적의 전력을 송신하여 불필요한 전력 낭비를 줄일 수 있도록 구현되었다. 본 논문에서 제안된 시스템 및 송신전력 제어기능을 기반으로 다양한 기기에 동일한 기능의 적용이 가능하며 상용화에 보다 근접할 수 있을 것이다. In this paper, 25W wireless power transmission(WPT) system using the coupled magnetic resonance is presented. The WPT system consists of a 100W class-F power transmitter, 1.7MHz magnetic resonators and a 40W full-bridge receiver using diodes. Especially, the transmit power control function using the 400MHz FSK communication between the transmitter and the receiver is adopted in the proposed system for the stable power transmission. Using the system and the power control function, the WPT system can be adopted in the various electronic devices and the commercialization of WPT system can be moved forward.

The optimization of wireless power transmission: design and realization

A wireless power transmission system is regarded as a practical way of solving power-shortage problems in multifunctional active capsule endoscopes. The uniformity of magnetic flux density, frequency stability and orientation stability are used to evaluate power transmission stability, taking into consideration size and safety constraints. Magnetic field safety and temperature rise are also considered. Test benches are designed to measure the relevent parameters. Finally, a mathematical programming model in which these constraints are considered is proposed to improve transmission efficiency. To verify the feasibility of the proposed method, various systems for a wireless active capsule endoscope are designed and evaluated. The optimal power transmission system has the capability to supply continuously at least 500 mW of power with a transmission efficiency of 4.08%. The example validates the feasibility of the proposed method. Introduction of novel designs enables further improvement of this method.