Michel M.N. Rezkalla

Identification of requirements for distribution management systems in the smart grid context

The integration of significant volumes of distributed and renewable energy resources directly connected to the distribution network raises new requirement to maintain and operate the power system in secure state. Thus the Distribution Management System (DMS) needs to be updated and integrated with new functionality to provide effective support for the operators. The DMS is a control center solution that provides the needed functionality for the management of medium and low voltage distribution networks. This paper aims to provide an overview of the main functions present in todays DMS platforms and to identify the new requirements to better serve in a smart grid context.

The Pan-European reference grid developed in ELECTRA for deriving innovative observability concepts in the Web-of-Cells framework

In the ELECTRA EU project, an innovative approach for frequency and voltage control is investigated, with reference to future power system scenarios characterized by massive amounts of distributed energy resources. A control architecture based on dividing the power system into a web of subsystems, the so-called cells, is proposed. Cells are individual control entities but also need to be coordinated together at system-wide level, in order to ensure secure and reliable overall operation (at Pan-European level). Task 5.4 in the ELECTRA project focuses on deriving novel observability concepts at system-wide scale. The methodology proposed in the task analyzes the system performance by investigating typical phenomena peculiar to each stability type and by developing observables necessary for the novel Web-of-Cells based control methods to operate properly at cell- and inter-cell level. Crucial aspects of angle, frequency and voltage stability are considered, according to the stability classification by CIGRÉ. In order to carry out the evaluations, a suitable test multi-cell grid model is developed. The paper aims at describing this reference model and at presenting the approach used in the task for assessing system stability in the developed WoC framework.

Voltage estimation in active distribution grids using neural networks

The power flow in distribution grids is becoming more complicated as reverse power flows and undesired voltage rises might occur under particular circumstances due to integration of renewable energy sources, increasing the occurrence of critical bus voltages. To identify these critical feeders the observability of distribution systems has to be improved. To increase the situational awareness of the power system operator data driven methods can be employed. These methods benefit from newly available data sources such as smart meters. This paper presents a voltage estimation method based on neural networks which is robust under complex load and in-feeder generation situations. A major advantage of the proposed method is that the power system does not have to be explicitly modeled.

Grid frequency support by single-phase electric vehicles employing an innovative virtual inertia controller

The displacement of conventional generation by converter connected resources reduces the available rotational inertia in the power system, which leads to faster frequency dynamics and consequently a less stable frequency behavior. Virtual inertia, employing energy storage systems, could be used to limit the rate of change of frequency of power systems, thus, improving frequency dynamics. Electric vehicles (EVs) can represent a reliable solution to enhance frequency stability due to their fast response and capability to provide a large amount of aggregated power. On one hand, EVs are capable of adjusting the battery charging process (i.e., power flow) according to pre-defined algorithms. On the other hand, in case of islanded operation (i.e., low inertia), some of the EVs technical constraints might cause oscillations. This study presents two control algorithms which show that the EVs are capable of providing virtual inertia support. The first controller employs a traditional droop control, while the second one is equipped with an innovative control algorithm to eliminate likely oscillations. It is shown that, the proposed innovative control algorithm compared to the traditional droop control, assures same effects in terms of frequency but reducing significantly the number of variation of the EVs current set-point.

Tuningless Load Frequency Control Through Active Engagement of Distributed Resources

The increasing share of volatile and inverter-based energy sources render electric power grids increasingly susceptible to disturbances. Established Load Frequency Controls (LFC) schemes are rigid and require careful tuning, making them unsuitable for dynamically changing environments. In this paper, we present a fast and tuningless frequency control approach that tackles these shortcomings by means of modern grid monitoring and communications infrastructures in a twofold concurrent process. First, direct observation of supply and demand enables fast power balancing decoupled from the total system dynamics. Second, primary resources are actively involved in frequency restoration by systematic adjustment of their frequency reference setpoints. In contrast to the commonly used Automatic Generation Control (AGC), the proposed direct LFC does not require an integrator for frequency control in the closed loop even under partial grid observability. The approach is Lyapunov-stable for a wide range of system parameters, including ramping limits of controlled resources. A performance study against AGC has been conducted on a three-area power system in simulations as well as in a real-laboratory grid with an installed generation capacity of 110 kW.

Grid frequency support by single-phase electric vehicles: Fast primary control enhanced by a stabilizer algorithm

Electric vehicles are growing in popularity as a zero emission and efficient mode of transport against traditional internal combustion engine-based vehicles. Considerable as flexible distributed energy storage systems, by adjusting the battery charging process they can potentially provide different ancillary services for supporting the power grid. This paper presents modeling and analysis of the benefits of primary frequency regulation by electric vehicles in a microgrid. An innovative control logic algorithm is introduced, with the purpose of curtailing the number of current set-point variations that the battery needs to perform during the regulation process. It is shown that, compared to traditional droop-control approaches, the proposed solution assures same effects in terms of frequency containment, by employing a considerably lower number of variations of battery current set-point. The modeled low voltage microgrid is built to reproduce a real configuration of the experimental facility SYSLAB-PowerLabDK. Root-mean-square simulation studies have been carried out in DIgSILENT PowerFactory environment for the validation of the controller.