Adaptive fuzzy control for power-frequency characteristic regulation in high-RES power systems

Future power systems control will require large-scale activation of reserves at distribution level. Despite their high potential, distributed energy resources (DER) used for frequency control pose challenges due to unpredictability, grid bottlenecks, etc. To deal with these issues, this study presents a novel strategy of power frequency characteristic dynamic adjustment based on the imbalance state. This way, the concerned operators become aware of the imbalance location but also a more accurate redistribution of responsibilities in terms of reserves activations is achieved. The proposed control is based on the concept of “cells” which are power systems with operating capabilities and responsibilities similar to control areas (CAs), but fostering the use of resources at all voltage levels, particularly distribution grids. Control autonomy of cells allows increased RES hosting. In this study, the power frequency characteristic of a cell is adjusted in real time by means of a fuzzy controller, which curtails part of the reserves, in order to avoid unnecessary deployment throughout a synchronous area, leading to a more localised activation and reducing losses, congestions and reserves exhaustion. Simulation tests in a four-cell reference power system prove that the controller significantly reduces the use of reserves without compromising the overall stability

Implementation of fuzzy logic for mitigating conflicts of frequency containment

Ever increasing shares of intermittent RES in present and future power systems pose new challenges with regard to operation, particularly balance, frequency and voltage stability. Towards effective solutions, the ELECTRA IRP project has developed a novel structure for future power systems operation, by dividing them in a number of Cells, constituting so a Web-of-Cells, and equipped with controllers addressing operation objectives. This paper deals with the Frequency Containment Control use case and, in particular, its implementation in the context of operation constraints imposed by different system conditions. To this end, a design method based on fuzzy logic for avoiding conflicts caused from these conditions or multiple control loops implemented on the same resource is proposed. Simulation results for various selected scenarios and controllers show the effectiveness of the proposed approach

Facilitating the transition to an inverter dominated power system : experimental evaluation of a non-intrusive add-on predictive controller

The transition to an inverter-dominated power system is expected with the large-scale integration of distributed energy resources (DER). To improve the dynamic response of DERs already installed within such a system, a non-intrusive add-on controller referred to as SPAACE (set point automatic adjustment with correction enabled), has been proposed in the literature. Extensive simulation-based analysis and supporting mathematical foundations have helped establish its theoretical prevalence. This paper establishes the practical real-world relevance of SPAACE via a rigorous performance evaluation utilizing a high fidelity hardware-in-the-loop systems test bed. A comprehensive methodological approach to the evaluation with several practical measures has been undertaken and the performance of SPAACE subject to representative scenarios assessed. With the evaluation undertaken, the fundamental hypothesis of SPAACE for real-world applications has been proven, i.e., improvements in dynamic performance can be achieved without access to the internal controller. Furthermore, based on the quantitative analysis, observations, and recommendations are reported. These provide guidance for future potential users of the approach in their efforts to accelerate the transition to an inverter-dominated power system

Initialization and synchronization of power hardware-in-the-loop simulations : a Great Britain network case study

The hardware under test (HUT) in a power hardware in the loop (PHIL) implementation can have a significant effect on overall system stability. In some cases, the system under investigation will actually be unstable unless the HUT is already connected and operating. Accordingly, initialization of the real-time simulation can be difficult, and may lead to abnormal parameters of frequency and voltage. Therefore, a method for initializing the simulation appropriately without the HUT is proposed in this contribution. Once the initialization is accomplished a synchronization process is also proposed. The synchronization process depends on the selected method for initialization and therefore both methods need to be compatible. In this contribution, a recommended practice for the initialization of PHIL simulations for synchronous power systems is presented. Experimental validation of the proposed method of establishing a PHIL simulation for a Great Britain network case study demonstrates the effectiveness of the approach in achieving stable operation

Load frequency control in variable inertia systems

Conventional load frequency control primarily relies on large synchronous generation units to ensure regulation of the system frequency. However, its performance deteriorates as the system parameters, including inertia and droop coefficients, deviate from original system design. This letter proposes an augmented load frequency control (ALFC) to ensure robust frequency regulation under diurnal variations in system parameters that are expected in the future, renewables-rich power system. The superior performance of ALFC is demonstrated by several case studies, and its stability is assessed by small-signal analysis

Future electricity market structure to ensure large volume of RES

The article define set of rules for future Electricity market structure, taking into account network codes, legislation and directives to ensure RES integration targets and Energy Union Dimensions in term of a fully integrated internal energy market and transition to a long lasting low-carbon society. Presented research studies are based on new way of power system operation development, namely Web-of-cell concept, of FP7 IRP ELECTRA. It’s aiming to ensure conceptual E-market design and future power system 2030+ control solutions

High-fidelity validation with smart grid modelling complexity : considerations on emerging solutions

The continued integration of increased volumes of distributed energy resources and flexibility services into power networks across the world is introducing increasing complexity into system operations. With the growing number and dimensions of complexity, modelling of smart grids for simulation is becoming more demanding. In particular, achieving high-fidelity validation of such complex cyber-physical systems is growing in importance and in scale of challenge. Coordinated real-time simulation across multiple platforms, termed geographically distributed simulations (GDS), paves a new pathway for high-fidelity validation of large-scale smart grids. Furthermore, the integration of cloud solutions enables efficient initialization of simulations and ensures secure data communications among GDS participants. This paper provides a comprehensive overview of different types of real-time simulation concepts and explains how they can best be utilized to realize GDS with enhanced computational capability. Subsequently, this paper summarizes the applicability of GDS, specifically emphasizing on cloud-based GDS, to facilitate high-fidelity validation of complex smart grids

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 (LFCs) 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 two-fold 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 Load Frequency Control (DLFC) 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 110kW

Distribution network characterization for ancillary service provision : frequency response through voltage control

The rising share of distributed generation (DG) in the power system results in reduced inertia and larger frequency deviations following power imbalance. Balancing efforts of transmission system will require increasing coordination of distribution networks. This paper analyses impact of different characteristics of Low Voltage (LV) networks on its power consumption when varying voltage at point of common coupling in order to support frequency containment of transmission system. Frequency support is delivered by adapting the LV grid voltage to shape power consumption of voltage-dependant loads. It enables the use of voltage as a trigger for active power control of 1 voltage-dependant loads without the need for additional communication and frequency measurement. The Smart Transformer allows a fast control of voltage amplitude, and consequently, power consumption of LV grid without affecting medium voltage grid. Different network characteristics were analysed to determine networks most suitable for providing frequency support through voltage control