Renewable Energy Sources (RESs) such as wind and photovoltaic are environment-friendly energy sources for power generation. However, the largely varying output energy of RESs is a major obstacle to their integration into the power grid. In addition, variations in consumer activity increase the risks of power fluctuations. The ability of power systems to deal with power fluctuations caused by renewable sources and dynamic demand has to be improved to keep the stable operation of a power system. This paper proposes a novel robust energy balancing concept to reduce energy imbalance due to the mismatch between fluctuating generation and demand. The proposed concept targets the long-term operation of a power system and aims to guarantee its safe operation under any dynamic fluctuations of RESs and demands. The key ideas behind this concept include the periodic power level patterns of fluctuating sources and loads, and their upper bound envelops and lower bound envelops, which enable us to analyze the long-term system behavior by the analysis of one cycle operation. The extracted non-trivial upper bound envelops and lower bound envelops provide us with a novel interpretation of the collaboration between storage systems and controllable sources/loads in power balancing, as well as their minimum sizes.
This paper presents an optimisation method for the direct energy exchange between two electric vehicle (EV) charging stations located in the UK. Each EV charging station consists of solar panels, hydrogen and battery energy storage systems (SHBS). The stations are interconnected through a energy exchange system that enables the transfer of excess energy from one station to the other. The objective function of SHBS charging stations is to minimize the capital and operation and maintenance costs of the stations. The system constraints are the power output of individual components, as well as the power balance between SHBS charging stations and EV charging demand. Genetic Algorithm is used to optimize the system, considering various factors such as the size of the solar panels and hydrogen storage tanks, the capacity of the electric vehicle chargers, and the amount of energy exchanged between the two stations. The optimized system yields substantial cost savings.
The high penetration of converter-interfaced renewable energy sources reduces the inertia levels of modern power systems, jeopardizing grid stability. Therefore, to ensure the safe and reliable operation of their grids, power system operators shall monitor close to real-time the overall inertia levels. Towards this objective, in this paper an inertia estimation technique, based on the modal sensitivity concept, is formulated and validated on heterogeneous multi-machine power systems. Several cases are considered and examined to demonstrate the applicability range of the developed method.
The availability of realistic grid topologies is of central importance for the usability of grid models in calculations. However, especially in distribution grids, poor documentation, limited digitization and insufficient data quality can lead to faulty topologies, which result in errors in subsequent calculations. Methods of topology identification (TI) offer possibilities to use measurement data of grid quantities such as voltages to validate and, if necessary, correct the topology used for calculations. This paper presents robust methods for TI in medium voltage networks based on an adapted form of Prim's algorithm, which is based on measurements of node voltage magnitudes. Methods to include spatial priors in the process are investigated. The developed method is applied to realistic models of medium-voltage networks and its robustness to unadapted graph-based methods is shown. The correlation of injection correlations, as well as noise on the measured data, is addressed to show that the proposed methods can handle these conditions.
This study deals with the implementation of recorded lightning current waveforms in ATP-EMTP. These can be employed as excitation in fast-front transient simulations. A generalized code is developed in MODELS language to import arbitrary waveforms expressed in the form (time, voltage/current) pairs. An investigation is presented on the influence of the time interval used for digitizing recorded lightning current waveforms and of the interpolation method applied between points. ATP-EMTP simulations of direct lightning strikes to 150 kV overhead transmission lines are performed. Fast-front overvoltages are computed across line insulators and the minimum backflashover currents are determined. Cases with Line Surge Arresters (LSAs) are also treated and the energy stressing the LSAs is computed. It is shown that the digitization time interval is not important as long as it reproduces the main features of the recorded waveforms. This applies also for the interpolation method.
