Search

The opening up of the railway to competition in Europe has been accompanied by many technical challenges never before seen in the railway field. One of these challenges concerns precise energy metering. As European railways have been a monopoly until now, the current systems can only measure the energy consumption of a single operator. In accordance with European law, the installation of an energy meter has been mandatory in new or refurbished rolling stocks since 2014. Nevertheless, these energy meters are still not fully reliable, with misreadings and missing readings being common occurrences. To address the problem of energy metering data reliability, this paper presents a method for validating the reading measurement based on a physical model and validates it in two different case studies. For the issue of energy metering data availability, different estimators are developed, and their performance are shown with the aim of calculating the missing consumptions for both case studies. Finally, the paper suggests how these methods may be implemented in other types of trains. [ABSTRACT FROM AUTHOR]

The paper addresses a real-time optimization-based reference calculation integrated with a control structure for Modular Multilevel Converters (MMC) operating under normal and constrained situations (where it has reached current and/or voltage limitations, as it may occur during system faults). Firstly, a nonlinear optimization problem has been developed in which it prioritizes to satisfy the AC grid current set-points imposed by the transmission System Operator (TSO). The constrained nonlinear optimization problem is formulated based on the steady-state model of the MMC, whereby the prioritization is achieved through distinct weights defined in the Objective Function’s (OF) terms. The resultant optimization problem, however, is highly nonlinear requiring high computation burden to be solved in real-time. To cope with this issue, this paper applies a Linear Time-Varying (LTV) approximation, which permits to represent the nonlinear dynamics of the system as constant parameters, while a Linear Time-Invariant (LTI) system is used to formulate the optimization constraints. The converter’s current references are determined in real-time by solving a constrained linearized optimization problem at each control time step, which considers the TSO’s demands, the current MMC operating point and its physical limitations. Theoretical analyses comparing the responses of the linear and nonlinear optimization problems are performed to validate the accuracy of the LTV approximation. Finally, the linearized-optimization problem is integrated with the MMC controllers, evaluated under different AC and DC network conditions and compared with conventional control strategies, where it is shown that the presented method can be potentially employed to obtain the MMC current references for distinct network scenarios. [ABSTRACT FROM AUTHOR]

The concept of segmented AC power systems interconnected by means of HVDC is becoming more and more significant for many cases worldwide. Such systems already exist and will become more complex with the increasing emergence of HVDC links and grids. The concept of a grid composed of multiple subgrids motivates the need to define the governing roles of Interconnecting Power Converters (IPC) which connect the different subgrids. Such IPC can have various operation modes which are presented and analyzed in this paper. In addition, the principles of operation needed for each individual subgrid and for the overall system are introduced and discussed. The resulting fundamental equations are outlined and combined in a power flow formulation of the overall system. A simple case study is presented to illustrate the power flow formulation in a grid of multiple subgrids, also introducing example dynamic simulations of transitions between different operating points. [ABSTRACT FROM AUTHOR]

Voltage-source-converter (VSC) technologies present a bright opportunity in a variety of fields within the power system industry. New modular multilevel converters (MMCs) are expected to supersede two- and three-level VSC-based technologies for HVDC applications due to their recognized advantages in terms of scalability, performance, and efficiency. The computational burden introduced by detailed modeling of MMC-HVDC systems in electromagnetic-transients (EMT)-type programs complicates the study of transients especially when these systems are integrated into a large network. This paper presents a novel average-value model (AVM) for efficient and accurate representation of a detailed MMC–HVDC system. It also develops a detailed 401-level MMC-HVDC model for validating the AVM and studies the performance of both models when integrated into a large 400-kV transmission system in Europe. The results show that the AVM is significantly more efficient while maintaining its accuracy for the dynamic response of the overall system. [ABSTRACT FROM AUTHOR]

As a result of many factors, including the European Union's aim to increase the share of electrical energy from renewable sources, the number of distributed-generation (DG) devices in Europe is significantly increasing. Increasing numbers of DG units may cause problems with power quality (PQ). In this paper, a PQ-management algorithm is presented that reduces or even solves this problem in low-voltage grids. This algorithm will be implemented as one of several software modules in a system for distributed power operation and PQ management in low-voltage grids. PQ management in this context means maintaining PQ within prescribed limits by optimizing the control of generators, storage units, and controllable loads. Significant advantages of the presented approach are that the algorithm is universal and that it adapts its control variables automatically. Therefore, a detailed analysis of the grid in advance is not necessary. Furthermore, local PQ control of distributed resources can work autonomously and continuously without triggering by external signals, which is advantageous in the case of loss of communications. Various simulations to validate the effectiveness and stable operation of the algorithm were performed and results presented that show a marked improvement in PQ. [ABSTRACT FROM AUTHOR]

Part I. Identifies the occurrence of channel impairment in domestic powerline in Europe. Properties of attenuation and noise in the power system; Linear impairment of electric channel; Cyclic process of noise intensity.

Part II. Determines the multiplicative signal fading and modulation schemes of narrowband in domestic powerline in Europe. Distortion process of signal fading; Advantages of orthogonal frequency division modulation; Characterization of the electric noise process.

For the connection of remote energy sources, HVDC offers higher efficiency and flexibility compared to conventional HVAC. As the acceptance for overhead lines in Europe is often low, the detailed understanding of its environmental effects, such as audible noise is of crucial importance. Still, only few experimental studies have investigated HVDC corona. Recent publications have demonstrated, that existing prediction models for DC audible noise show strong deviations when extrapolated for higher surface gradients. While audible noise is considered negligible in rain, research has shown that the discharge amplitudes increase significantly during transitions from dry to wet weather and vice-versa. In this study, the corona current and audible noise are investigated for a large range of surface gradients and rain rates. A special focus is set on the behavior during rain onset and dry-off. While the corona current increased during rain, the measured audible noise was significantly higher during the transitions before and after the steady state. The duration of these transition periods varied with rain rate and surface gradient. The observed effects are explained using corona pulse patterns and UV data. Compared to these measurements, existing audible noise prediction models were found to overestimate the sensitivity regarding the electric field. [ABSTRACT FROM AUTHOR]

It has been suggested that the recommended flicker planning levels provided in IEC 61000 3-7 and IEEE 1453 are too restrictive for high-voltage and extra-high-voltage networks. The premise of this argument is based on a perceived increase in low-voltage (LV) flicker compatibility level. Some believe that flicker measurements made in Europe over a period of several years support the notion of an increased LV compatibility level; however, measurements performed by the authors in North America indicate otherwise. Analysis of authors' measurements suggests that the lack of customer complaints is due primarily to the effect of flicker transfer coefficients, rather than a presumed increase in LV compatibility level, and supports the continued use of Pst95\%=1.0 as the LV flicker compatibility level. [ABSTRACT FROM AUTHOR]