Direction Of Power Flow Research Articles

Power quality monitoring system based on IEC61850

Power quality monitoring system is an important means to find and evaluate power quality problems in time. A service-oriented browser / server (B / S) mode active power quality real-time monitoring system is designed and implemented, which provides the real-time monitoring function of power quality in the process of active power distribution network absorbing distributed power generation layer by layer, and focuses on observing the impact of the change of power flow direction on the level of power quality. Based on IEC 61850 standard, the system establishes the power quality information model, and uploads the real-time monitoring data of power quality on site to the master station for analysis and storage in the real-time database through MMS. The client communicates with the server through windows communication base (WCF) service to obtain real-time monitoring data, and realizes the global real-time monitoring function of power quality of active distribution network combined with the main wiring diagram, so as to achieve the integrated display effect of data graph.

Harmonic Power Direction Method for Smart Grids

Active power flow direction is a common method used by most industries to determine the flow of harmonics in the distribution network and for data monitoring analysis. This method is integrated into most power quality analyzers and commercial software. Therefore, this paper seeks to examine the harmonic power flow direction method and quantify the size of the harmonic contribution of each harmonic source connected at the Point of Connection (PoC). A radial distribution network with harmonic loads is used and modelled in the DIgSILENT power factory. It was found that the harmonic power flow depends on the flow of harmonic current within the power system. It can be that the harmonic sources have negative power at a harmonic frequency which means it injects the harmonic current, but the dominant contribution is only from one or two harmonic sources. Thus, the load with the highest percentage of individual and total harmonic distortion is the dominant contributor to harmonics. DIgSILENT gives the contribution of each load connected at the PoC by indicating the percentage of total harmonic distortion. The active power flow direction method is the practical and commercial method to use in the industries. This gives a solution for the ongoing harmonic source detection research. It is recommended to use DIgSILENT, it shows the direction of harmonic current flow and quantifies the harmonic content within the network.

Instantaneous Frequency-Based Algorithm for Directional Relays

The looped structure of the transmission and subtransmission networks results in the bidirectional fault current passing through the protection relays. The detection of the current direction is relegated to the directional protection unit. The traditional directional overcurrent relays utilize the reference voltage phasor for the detection of the fault direction, which increases total cost due to the need for both current and voltage measurement units. In this article, a new current only directional algorithm based on the instantaneous frequency is introduced. The proposed method is robust to noise and changes in the grid parameters, such as a change in the power frequency and direction of normal power flow. To evaluate the algorithm, plenty of simulations and actual experiments are carried out in different fault conditions. Also, its performance is compared with some other directional algorithms. The results confirm that the proposed algorithm can detect fault direction with a high degree of accuracy.

Influence of FACTS Device Implementation on Performance of Distribution Network with Integrated Renewable Energy Sources

In the modern power system, Flexible Alternating Current Transmission System (FACTS) devices are widely used. An increased share of the distributed generation (DG) and the development of microgrids change the power flows in the existing distribution networks as well as a conventional power flow direction from the transmission to the distribution network level which may affect the overall stability aspects. The paper shows the FACTS devices’ implementation influence on the performance of the distribution network with integrated renewable energy sources (RES) observing the aspects of the oscillatory stability and the low-voltage motor starting. The FACTS devices, in particular the static var compensators (SVC), have been allocated according to a novel algorithm proposed in the paper. The algorithm uses an iterative process to determine an optimal location for implementation and rating power of SVC considering active power losses minimization, improvement of the voltage profile and maximizing return of investment (ROI) of FACTS devices. Novel constraints—transformer station construction constraint, SVC industrial nominal power value constraint and the constraint of distribution system operator (DSO) economic willingness to investment in the distribution network development are considered in the proposed algorithm. The analysis has been performed on 20 kV rural distribution network model in DIgSILENT PowerFactory software.

Electric Vehicles Charging Technology Review and Optimal Size Estimation

Many different types of electric vehicle (EV) charging technologies are described in literature and implemented in practical applications. This paper presents an overview of the existing and proposed EV charging technologies in terms of converter topologies, power levels, power flow directions and charging control strategies. An overview of the main charging methods is presented as well, particularly the goal is to highlight an effective and fast charging technique for lithium ions batteries concerning prolonging cell cycle life and retaining high charging efficiency. Once presented the main important aspects of charging technologies and strategies, in the last part of this paper, through the use of genetic algorithm, the optimal size of the charging systems is estimated and, on the base of a sensitive analysis, the possible future trends in this field are finally valued.

Analysis and Transition Techniques for a Bidirectional DC–DC Converter

This article proposes two new pulsewidth modulation (PWM) schemes, namely, asynchronous PWM scheme (APS) and synchronous PWM scheme (SPS), for a nonisolated fourth-order bidirectional dc-dc converter (FOBDC), which are implemented to achieve a smooth start-up operation and mode transition to reverse the direction of power flow. The presented FOBDC is reported already in the literature as a unidirectional boost converter, the functionality of which is modified in this work, to enable bidirectional power flow. The FOBDC can operate in either discharging (Mode-I) or charging (Mode-II) mode. The overshoot/undershoot of inductor currents in the FOBDC occur during converter start-up operation in either of the modes and while transitioning modes (from charging to discharging and vice-versa). To eliminate the overshoot/undershoot of inductor current, two effective transition techniques are developed for smooth start-up operation and mode transition, thereby reducing the delay time significantly. The FOBDC is modeled using the state-space modeling technique, and duty ratio-to-inductor current transfer function is derived, which is validated for resistive load and battery load. Two different compensators are designed for these two transfer functions to achieve an average current-mode control (ACMC) during the charging and discharging modes of operation. The performance of the compensators is evaluated by introducing perturbations. A 12-48-V FOBDC converter, controlled by these PWM techniques with the aforementioned features, is designed, analyzed, and experimentally verified for low-power applications.

Bidirectional Soft-Switching Converter With Reduced Current Ripple at Low-Voltage Side

Bidirectional dc–dc converters with storage devices and high-voltage conversion ratio are widely utilized in renewable energy systems in order to manage power flow between renewable sources, storage devices, and load. One of the most important parameters in these converters, which affects the lifetime of storage devices, is the pulsating current flowing through them. This article presents a bidirectional buck/boost converter that employs a coupled inductors technique to increase the voltage conversion ratio while the current in low-side voltage source is continuous. Furthermore, only an active clamp circuit, including a clamp capacitor and an auxiliary active switch, is utilized to create soft-switching conditions for the main switches and absorb the leakage inductance energy of coupled inductors for both high step-up/step-down operating states. In this converter, the soft-switching condition is provided for all switches without any extra element in the power flow direction. Also, all diodes turn off at the ZCS condition, which removes the reverse recovery problem. A low number of elements and fully soft-switching condition for all semiconductor devices have contributed to the converter efficiency. Theoretical analysis of the proposed converter in both operating states is presented in detail, and a 500-W prototype circuit is implemented to verify the validity of the theoretical analysis and converter performance.

Power Distribution Algorithm and Steady-State Operation Analysis of a Modular Multiactive Bridge Converter

Electrical distribution systems comprising different power sources and loads, such as electric vehicles, aircraft electrical distribution systems, and residential microgrids, need new power conversion architectures. Multiport converters are an alternative to conventional multiconverter systems. This work studies a modular multiactive bridge (MMAB) converter, which is a multiport converter based on the connection of active bridges and independent transformers. The converter is bidirectional, fully modular, and scalable. It allows the connection of multiple power sources and loads that may change its power flow direction, allowing hot connection and disconnection of modules. The control of the power flow in each port depends on the relative phase shift among the control pulses of the other active bridges. An iterative algorithm is developed and implemented in a digital device to control the converter in real time. Besides theoretical analysis, the main characteristics of the converter have been validated in a lab prototype with five modules. The experimental results validate the theoretical predictions. Power distribution among the modules has been kept under 9% of error with respect to the desired value, considering an open-loop control.

Optimization techniques using DWT-differentiation algorithms for fault detection and relay coordination in microgrid

Moreover, optimizing the power allocation coefficients is seen as of the most extreme significance to amplify the exhibition of the framework and coordination between defensive devices. The fault clearing times and relay coordination stability are essential to avoid nuisance tripping. The forward and reverse way operating relay security design for microgrids with the network-associated and islanded ability is utilized. The microgrid distribution frameworks, sporadic framework, fault attributes (regarding grid-associated mode) and the fluctuation of intensity in the power flow direction present difficulties. To build up robust and reliable protection conspire that will have a strong reaction in both grid-associated and grid-disconnected modes, this research work exhibits the novel optimization-based smart; discrete evolution algorithm protection conspires for the microgrid. The suggested system preprocesses the short-circuit current signal waveform utilizing discrete wavelet transform and gauges the most influenced delicate attributes. These are being used to fabricate the choice differential evolution algorithm for enlisting the right relay choice. The broad test outcomes demonstrate that the recommended canny differential transferring plan can be significantly better in giving a compelling protection measure to the safe and anchored microgrid operation. About this research, output signals from differential evolution algorithms are led to decide the viability of the given arrangement in securing overall microgrid while working with grid-connected or grid-disconnected modes. Time–space shown for endorsement purposes is managed using an existing microgrid network in the MATLAB Simulink programming environment. Moreover, it accomplishes the astounding decrease in both the essential and secondary transfer working occasions, which results in a decrease in the all-out relay working time.

A phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines

AbstractThis paper presents a phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines. Detection and classification of faulty phase(s) have been carried out by deriving indices from the change in phasor values of current with a distance of one cycle. The derived indices have zero values during normal operating conditions whereas the index corresponding to the faulty phase exceeds the pre-defined threshold in case of occurrence of a fault. A separate ground detection algorithm has been utilized for the identification of involvement of ground in a faulty situation. The performance of the proposed technique has been evaluated for intra-circuit, inter-circuit and simultaneous faults with wide variations in system and fault conditions. The suggested technique has been evaluated for over 23,000 diversified simulated fault cases as well as 14 recorded real fault events. The performance of the proposed technique remains consistent under Current Transformer (CT) saturation as well as different amount and direction of power flow. Moreover, suitability to different power system network has also been studied. Also, faults having fault current less than pre-fault conditions have been detected accurately. The results obtained suggest that it is able to detect faulty phases as well as classify faults within quarter-cycle from the inception of fault with impeccable accuracy. Besides, as modern digital relays have been already equipped with phasor computation facility, phasor-based technique can be easily incorporated with relative ease. At last, a comparative evaluation suggests its superiority in terms of fault classification accuracy, fault detection time, diversify fault scenarios and computational requirement among other existing techniques.

Research on Transmission Characteristics of Hydromechanical Continuously Variable Transmission of Tractor

This paper proposes a new transmission scheme of hydromechanical continuously variable transmission (HMCVT) for tractors. The HMCVT has 4 working ranges in each of the front and rear directions. The speed characteristic and the torque characteristic of HMCVT are theoretically derived. On the basis of HMCVT power flow direction, the Крейнeс formula is used to calculate the transmission efficiency. Then, the image analysis method is used to study the influence of parameters on the transmission efficiency of HMCVT, and the main influencing factors are found. The results of theoretical derivation demonstrate that, by coordinating control of the HST displacement ratio and the engagement conditions of shifting clutches, the stepless speed regulation of HMCVT at the tractor speed of 0–50 km/h can be realized. The proposed HMCVT has the ability to continuously transmit and change torque over all working ranges. The overall transmission efficiency of HMCVT is at a high level. To verify the theoretical derivation, Amesim simulation software is used for the modeling and simulation of HMCVT. The simulation results are consistent with the theoretical analysis results. Therefore, the HMCVT proposed in this paper has the advantages of compact structure and high transmission efficiency, and it is suitable for matching tractors.

High-Gain Bidirectional Quadratic DC–DC Converter Based on Coupled Inductor With Current Ripple Reduction Capability

In this article, a high-gain bidirectional quadratic dc-dc converter is proposed. This converter is studied under step-up and step-down modes. In each power flow direction, two switches and two antiparallel diodes of the other switches operate. Therefore, the switching losses depend only on the operation of two switches in each direction. The use of coupled inductor in the proposed converter significantly reduces the input and output current ripples of the step-up and step-down modes, respectively, at all operating points of continuous and discontinuous conduction modes (CCM and DCM). The voltage gain of the proposed converter in the step-up mode is as high as that of the cascaded boost converter, and in the step-down mode, the converter voltage gain is similar to that of the cascaded buck converter. Thus, the high-voltage conversion ratio with an appropriate duty-cycle in both power flow directions can be achieved. The operating principles and steady-state analysis of the proposed converter in CCM, DCM, and the boundary-conditions between these modes are discussed in detail. Finally, a prototype of the converter is implemented in the laboratory and the experimental results are presented to validate the effectiveness of the proposed converter.

Protection strategy for fault detection in inverter-dominated low voltage AC microgrid

This paper presents a protection strategy based on active power flow direction, current magnitude and voltage sags to determine the existence of low impedance faults in inverter-dominated low voltage AC microgrids. Different fault situations are considered, concerning each element of the microgrid (line section, load, node and energy sources). Simulation is done in MATLAB/Simulink software. Microgrid was modelled based on CIGRE benchmark for network integration of renewable and distributed energy resources, considering the low voltage european distribution network characteristics. Inverter-based distributed generation units were modelled considering a control scheme composed by natural reference frame control and RMS current limiter. The results obtained from simulations indicate that the proposed strategy is able to protect the microgrid in any topology configuration or mode of operation, for all type of low impedance faults.

Research on Transmission Performance of A Seven-gear Three-degree-of-freedom Planetary Gear Automatic Transmission Based on Graph Theory and Matrix Equation

The transmission performance analysis of planetary gear automatic transmission is helpful for the following structural size optimization, hydraulic design and electric control design. The current graphic method has the disadvantages of low calculation accuracy and lack of intuition in numerical analysis method. This paper proposes a method to analyze the transmission performance based on graph theory and matrix equation. Firstly, a graph theory analysis model is established for the self-designed seven-gear three-degree-of-freedom planetary gear automatic transmission, and the structural characteristics of the transmission are analyzed. Then, on the basis of analyzing the shift actuator worksheet, the motion analysis model and torque analysis model of typical gears are designed by taking the first gear and the reverse gear as examples, and the speed and torque values of all gears of the transmission are calculated by using the corresponding matrix equation. Finally, the power flow diagram of the typical gear is established by taking the first gear and the fourth gear as examples, and the direction and numerical value of power flow are identified on the diagram. The results show that the method can realize the combination of qualitative and quantitative analysis for the transmission performance analysis of the planetary gear automatic transmission with multiple gears and multiple degrees of freedom, which is more intuitive, accurate and efficient.

Analysis of potential low frequency resonance between a 1GW MMC HVDC and a nearby nuclear generator

This paper presents a comprehensive analytical eigenvalue stability study of subsynchronous torsional interactions between the 1 GW Eleclink MMC HVDC and the 1.12 GW Gravelines turbine-generator in north France. It revalidates the conclusions of previous studies on VSC-based HVDC systems by showing that the risk of SSTI may be of significance when the HVDC is based on the MMC and not the two level VSC technology. The study demonstrates that in the case of the weak French grid and the rated HVDC power flow from France to England, the HVDC can destabilize the dominant low frequency, 6.3 Hz, torsional mode. The analysis also expands the work of previous studies on MMC and reveals that the case of the HVDC power flow from the English to the French grid may also introduce the risk of destabilizing the lower frequency mode. Furthermore, it also reveals a noticeable impact of the PLL and that increasing the gains has an opposite effect on the two HVDC power flow directions. Moreover, participation factors are analyzed for the 6.3 Hz mode indicating that the main cause of the torsional interactions is the HVDC power control loop. The main findings are verified on the detailed EMTP model.

Impact of climate change on water availability and its propagation through the Western U.S. power grid

Climate change is expected to affect the availability of water for electricity generation, yet the propagation of climate impacts across a large and diverse power grid remains unexplored. In this study, we evaluate how projected changes in water availability affect electricity generation at hydroelectric and thermal power plants and how the coincident impacts propagate locally and throughout the interconnected power grid of western United States. We also evaluate whether the prospect of climate-driven change could affect regional power dependencies. Hydrologic simulations derived from three Global Circulation Models (CCSM4, INMCM4, and GFDL-CM3), two radiative scenarios (RCP4.5 and RCP8.5) and the VIC hydrology model are used to force a large-scale, distributed water management model (MOSART-WM), which translates water availability into power generation constraints at hydropower plants and water-dependent thermoelectric plants. Power system dynamics are evaluated using the production cost model PLEXOS. We find that the interregional connections across the contemporary Western U.S. electricity infrastructure play an essential role in managing variations in regional generation due to hydrological variability. Projected WECC-scale changes in mean annual precipitation ranging from −3.8% to +17% are moderated to −6% to +4% in mean annual production cost changes. Climate change impacts on water availability in the Northwest drive future changes in other regions’ generation and in regional power flows. Northwest total generation influences interannual variability in other regions’ net generation, explaining about 40%, 50%, and 35% of the variability in Southwest, Rockies, and Southern California regions respectively. The propagation of Northwest climate change impact throughout the grid is exacerbated by the occurrence of dry years in Northern California. Generation from the Desert Southwest emerges as a critical resource to compensate for variations in water availability, and generation, in these regions. Though the regional power flow directions seem insensitive to long-term variations in water availability, our analysis highlights the need to consider other compounding regional factors, such as changes in Southern California’s net load and changes in regional fuel prices.

Modelling of phase‐shift modulated bidirectional CLLC resonant converter

The study proposes the application of two modelling techniques for analysis of bidirectional CLLC resonant converters. The state-variable and cyclic-averaging techniques are applied for converters operating under two types of phase-shift modulation: single-phase-shift and pulse-phase modulation. The converter is analysed considering forward and reverse power flow directions and a state-variable equation description is obtained for both modes. The models are first validated through simulation, comparing the state-variable and cyclic-averaging results to a simulation program with integrated circuit emphasis (SPICE)-based simulation. Additionally, a low power prototype is built, experimental results are presented and the influence of parasitic elements and system delays is discussed. Simulation and experimental results show the models can accurately represent the behaviour of CLLC converters for both types of phase-shift modulation. In addition, using the cyclic-averaging technique results in a considerably faster execution compared to state-variable and SPICE-based models.

An Accurate Non-Pilot Scheme for Accelerated Trip of Distance Relay Zone-2 Faults

The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions.

A Simplified Algorithm for Detecting Power Recirculation within 1-Dof Multi-Entity Planetary Gear Trains

Because there is power recirculation around internal loops in many transmissions, an undesirable increase in tooth meshing loss can arise in the system which results in lower efficiency. A single graph is used to illustrate the power flow magnitudes and directions. A simple formula for detecting power circulation in one degree of freedom multi-entity parallel-connected planetary gear trains is developed. In the absence of friction, power recirculation mainly depends on the speed ratios of the individual entities that constitute the PGT. The main novelty of the current method is in its extreme simplicity.

A pilot protection algorithm for TCSC compensated transmission line with accurate fault location capability

This paper introduces a communication-aided scheme to enhance the fault detection, and fault location calculation for a thyristor-controlled series capacitor (TCSC) compensated transmission lines. In the proposed method only the current data at the remote-end should be synchronously sent to the local-end. Since the remote-end voltage data do not use in local-end, compared with the conventional pilot impedance-based protection schemes, the proposed method significantly reduces the requirement of data transmission bandwidth. The proposed algorithm is independent of fault resistance, power flow direction, and pre-fault condition. In the proposed method the TCSC parameters are not utilized in the derived fault location formula and as a result, the performance of the proposed method is not impacted due to variations in TCSC parameters. Several major factors are taken to investigate the accuracy of the proposed method, including measurement errors and power swing conditions. The simulation results prove the high accuracy and acceleration of the proposed scheme during all fault cases.