Transmission network voltage regulation through coordinated automatic control of reactive powers is now becoming a challenging objective for many utilities and system operators (ISO or TSO) to achieve significant improvements in the security, quality, and efficiency of power system operation. This survey paper is concerned with application of Secondary and Tertiary Voltage Regulations (SVR and TVR), already operating in the Italian transmission network. The basic concepts behind SVR and TVR and the related hierarchical control system are first described in terms of system characteristics, main functions and design requirements. Cost/benefit analysis and comparison with alternative voltage control solutions are also provided in relation to the influence of power system restructuring process on the voltage ancillary service. More details about control system apparatuses and their field test results are provided in Part II.

Closure of "The coordinated automatic voltage control of the Italian transmission grid - part I: reasons of the choice and overview of the consolidated hierarchical system"

Emergency voltage control using search and predictive control

The power industry in China has grown significantly over the past decade, spurring the adoption of system-wide automatic voltage control (AVC) technology to meet stricter requirements for security and economical power system operation. To cope with the rapidly developing and frequently changing Chinese power grid, an AVC scheme based on adaptive zone division is introduced in this paper. Logically, this type of system has a three-level hierarchical structure, but, here, both secondary voltage control (SVC) and tertiary voltage control (TVC) are implemented via software at the same control center. The control zones are no longer fixed but are reconfigured online and updated in accordance with variations in the grid structure. The technical details of these procedures are presented here. The implementation of TVC (which is based on an online reactive optimal power flow) and SVC are also discussed, together with some technical details on improvements to their reliability and robustness. Some results obtained from field-site applications based on similar-days testing rather than simulations are employed to evaluate the performance and improvements of the AVC system. This system has been installed at over 20 control centers in China.

An Adaptive Zone-Division-Based Automatic Voltage Control System With Applications in China

This thesis deals with various aspects of coordinated voltage control in electric power systems. It consists of an introduction and six papers. The introduction contains a summary of the thesis and tutorials on voltage control and the search methods that have been applied.

The first part deals with the coordination of cascaded tap changers in radial distribution feeders. A tuning rule for the conventional (local) controllers as well as two new (centralized) schemes are proposed: firstly, an optimal controller based on on-line optimization and secondly, a rule based controller based on a fuzzy inference system. A prototype of the fuzzy-rule based controller has been installed and successfully tested in a distribution feeder in the south of Sweden.

The second part of the thesis describes a coordinated system protection scheme (SPS) against voltage collapse based on model predictive control. Using combinatorial optimization and predictions of the system's future behaviour, the SPS optimally coordinates dissimilar and discrete controls such as generator, tap changer and load shedding controls in presence of load dynamics and constraints on controls as well as voltages and currents in the network.

Modelling of power systems has also been addressed. The third part describes a freely available power system library called ObjectStab intended for voltage and transient stability analysis and simulation written in Modelica--a general-purpose object-oriented modelling language. All component models are transparent and can be modified or extended. Power system topology and parameter data are entered in one-line diagram form using a graphical editor. The component library has been validated using comparative simulations with Eurostag.

Coordinated Voltage Control in Electric Power Systems

An approach of big data characterization for smart grids (SGs) and its applications in fault detection, identification, and causal impact analysis is proposed in this paper, which aims to provide substantial data volume reduction while keeping comprehensive information from synchrophasor measurements in spatial and temporal domains. Especially, based on secondary voltage control (SVC) and local SG observation algorithm, a two-layer dynamic optimal synchrophasor measurement devices selection algorithm (OSMDSA) is proposed to determine SVC zones, their corresponding pilot buses, and the optimal synchrophasor measurement devices. Combining the two-layer dynamic OSMDSA and matching pursuit decomposition, the synchrophasor data is completely characterized in the spatial-temporal domain. To demonstrate the effectiveness of the proposed characterization approach, SG situational awareness is investigated based on hidden Markov model based fault detection and identification using the spatial-temporal characteristics generated from the reduced data. To identify the major impact buses, the weighted Granger causality for SGs is proposed to investigate the causal relationship of buses during system disturbance. The IEEE 39-bus system and IEEE 118-bus system are employed to validate and evaluate the proposed approach.

Spatial-Temporal Synchrophasor Data Characterization and Analytics in Smart Grid Fault Detection, Identification, and Impact Causal Analysis

Secondary voltage control was introduced in some European countries as a means to improve voltage security and operation. It is a closed loop system dedicated to keep the voltage of some load buses called pilot buses constant. In this paper, a new approach covering all the main aspects of secondary voltage control; pilot buses and control generators selection, the control law and the decentralization problem, is presented. This approach has been applied to the Spanish power system. Some of the results obtained are also presented.

A. Cortes

Papers

Secondary voltage control: analysis, solutions and simulation results for the Spanish transmission system