Search

The actions for limiting the climate change are significantly affecting the electrical power system. Indeed, the increase in renewable power sources and the progressive shut off of coal-fired power plants are transitioning the generation from a centralized to a decentralized paradigm. The latter may cause issues in a grid that was originally designed taking as granted the presence of several big power plants to be used as actuators for the system control. Considering voltage control, the actual control architecture is based on a hierarchical structure applied to a given set of rigidly subdivided control areas. Although such architecture is currently capable of maintain voltage control on the grid, the increase in converter interfaced generators (due to renewables exploitation) and the decrease of the buses short circuit powers (due to high power plants shut-off) may decrease its effectiveness in the future. To this aim, in this paper a coordinated decoupling voltage control is proposed, capable of using all the available reactive power sources on the grid as actuators. The issue of controlling a system with a variable number of actuators (due to generators connection and disconnection) is taken into account, proposing a suitable solution for avoiding transients during the switch between controllers having different output dimension. A brief discussion about communication (among actuators and controller) performances required for implementing the proposed control in the power system is also given.

This paper analyzes innovative devices to optimize the energy flows transmission on existing overhead lines. Indeed sometimes the structural asset isn’t adequate to manage energy generated by Renewable Energy Source (RES) in particular operating conditions. In addiction the outage of primary substations on the grid and the increase of consumptions have caused growing load currents. In order to satisfy these needs, TSOs have adopted new measures on existing power lines and N-1 criteria to ensures the electrical grid security. These particular devices are Dynamic Rating systems. After introducing thermal resistant conductors and Dynamic Rating (DR) solutions, paper reports two different applications used by TERNA Italian TSO. These systems are already installed on lines and they are contributing to increase power flows thanks to raise by 10-30% of the real time dynamic ratings than the static evaluations. Advantages for electrical systems are many such energy vectors optimizations, congestions reductions, reliability increasing, cross-border power flows increasing, smart grid development.

The forced switching converters are the kernel of the modern paradigm of VSC-HVDC system. It is widely recognized that appropriate control laws make these converters more advantageous than the traditional line commutated ones. They can play a versatile role by properly controlling active and reactive powers between electrical networks, improving the dynamic performances of the whole system. Besides this is more and more motivated by the wide spreading penetration of renewable resources. In this paper after a few references to basic concepts, a possible control strategy of VSC-HVDC transmission system is discussed. With respect to a two-area system with AC-DC link, a combined control law is investigated for improving inertial and primary frequency response. The control law is based upon the equivalent HVDC tie link synchronization coefficient which allows determining the reference value of the AC voltage reference angles of the converters. A damping action is further added for improving the power swings damping. The simulations performed with a simple but quite general case study permit to confirm the validity and the goodness of the proposed control strategy.

The paper deals with a novel method for the analysis of low-frequency inter-area oscillations, a harmful phenomenon that can be more and more frequent in electrical power systems due to the expansion of interconnected power grid. In particular, inter-area oscillations are electromechanical oscillations involving groups of generators geographically far from each other; correctly and timely estimating their parameters is a fundamental task to preserve the stability of the electrical power system. Phasor Measurement Unit (PMU) technology has become the key element in Monitoring and Control systems of Transmission System Operators offering new opportunities for improving their situational awareness. Proposed method processes measures provided by the PMUs to extract the oscillating components and, for each of them, estimates characteristic parameters such as frequency and damping. To this aim, the method exploits a combination of the Hilbert Transform and some optimization algorithms, thus gaining the following improvements: (a) enhanced capability of separating oscillatory components, thanks to a new strategy for the choice of bisecting frequency, (b) possibility of separating components characterized by frequency difference lower than the spectral resolution, (c) remarkable accuracy associated with the damping estimates of each oscillation and (d) robustness to the noise affecting the input signal. Results obtained in tests involving either synthesized signals or simulated electrical systems finally assessed the promising performance of the proposed method.

This paper presents a novel approach for the optimal design of the control system for battery energy storage systems adopted in power systems in the framework of the primary frequency control. The challenge issued by the use of batteries for frequency control in modern power systems is related to the need of the repeatedly deep charge and discharge phases. The presence of intermittent loads and generators, in fact, imposes very stressful power profiles to the battery which imply high rate of degradation to its lifetime. Based on the stress model of the battery, the proposed approach aims to design a control system which allows for containing the state of charge time variation within intervals able to match the requirements of frequency profile improvements and lifetime preservation. At this aim, the typical control scheme for batteries adopted for primary frequency control is analyzed and elaborated to address stable dynamic behavior of the regulator. Moreover, starting from the observation of the statistical nature of the power request for the pure frequency regulation service, a statistical study is conducted to perform an optimal design of the regulator in terms of both lifetime duration and primary frequency regulation service.

Large-scale penetration of renewable energy sources in power systems is essentially related to the need of reducing the environmental impact caused by the fossil-fuel. As well known, the interface between the power grid and this kind of energy resource is achieved by power converters, with a consequent dynamic behavior quite different from the synchronous generators. This matter involves negative impacts on the operating conditions of power systems. In this context, it is crucial to individuate estimation techniques able to predict promptly critical conditions which could, in extreme cases, compromise the stability of whole system. In this paper the authors employ an auto-regressive model which can describe the dynamic evolution of the power system inertia. The core of the procedure relies on an inertia model conceived as the sum of a periodic component and a noise stochastic process distributed according a Logistic model. The robustness of a novel estimation procedure, able to capture the dynamic evolution of the inertia, is investigated by testing two scenarios of Italian Transmission Network. The assumptions in terms of the obtained numerical results show the validity of the estimation technique and of the probabilistic characterization of the noise.

Global warming, also referred to as climate change, is the observed century-scale rise in the average temperature of the Earth and its related effects. Many scientific studies show that the climate system is warming. Considering the increase in extreme meteorological events related to this global warming, climate change is likely to make the national energy infrastructure increasingly vulnerable - especially in the absence of preventive actions. In recent years, the Italian transmission grid faced unusually severe weather events. Climate change is expected to worsen these extreme events such as snow blizzards and windstorms. This potentially increases the probability of damaging HV overhead lines and hindering the safety of the supply in the mountainous areas of the Alps and Apennines. In addition to the network infrastructure developments, Terna is improving operational procedures in order to manage extreme weather situations in real time. Real time control room operators can adopt preventative dispatching measures to increase the current on the critical lines and avoid the risk of ice sleeves (Joule effect). One of the possible preventive anti-icing measures is to create a reactive loop on the network. Where possible, the position of the on load tap changers of the autotransformers can be adjusted to create voltage differences and increase the reactive power flows on the critical lines. This article describes a real application of this approach in a portion of High Voltage network across the Apennines Mountains and Dolomites Alps.

The increase of Renewable Energy Sources (RES) production units has caused significant changes in the electrical system configuration. The existing structural asset isn't adequate to dispatch these new power flows that, at same time, should be favorite by various TSOs in order to obtain incentives. The outage of primary substations on the grid and the increase of consumptions have caused growing load currents on existing overhead line. This paper, after introducing thermal resistant conductors and Dynamic Rating (DR) solutions, reports an applications used by TERNA Group S.p.A. (Italian TSO). These systems are already installed on lines and they are contributing to increase power flows thanks to raise by 10-30% of the real time dynamic ratings than the static evaluations. Advantages for electrical systems are many such energy vectors optimizations, congestions reductions, reliability increasing, cross-border power flows increasing, smart grid development.