M. Invernizzi

Multiobjective optimization for pricing system security in electricity markets

This paper proposes a novel technique for representing system security in the operations of decentralized electricity markets, with special emphasis on voltage stability. An interior point method is used to solve the optimal power flow problem with a multiobjective function for maximizing both social benefit and the distance to maximum loading conditions. A six-bus system with both supply and demand-side bidding is used to illustrate the proposed technique for both elastic and inelastic demand, and a 129-bus test system that models the Italian HV transmission network is used for testing the practical applicability of the proposed method. The results obtained show that the proposed technique is able to improve system security while yielding better market conditions through increased transaction levels and improved locational marginal prices throughout the system.

An integrated active and reactive power control scheme for grid-connected photovoltaic production systems

The paper presents an advanced control scheme for a photovoltaic unit (PV) to suitably drive the injection of both active and reactive power into a MV radial distribution grid. Such algorithm allows a decoupled control of active and reactive power by properly adjusting the modulating signals of the PWM interface converter with the grid. A closed loop regulation scheme has been derived and guidelines for the design of the regulators are provided. The control algorithm has been applied to a real MV grid-connected PV power plant and several simulations have been performed in order to analyze the behavior of the system and to verify the effectiveness of the adopted regulation. The positive effect of reactive power support has been highlighted showing benefits on grid current and voltage profiles with respect to the typical case of the sole active power production.

Criteria for the equivalent modeling of large photovoltaic power plants

The aim of the present article is to propose an innovative simplified approach for the evaluation of active and reactive power losses for large photovoltaic plants. This methodology can be then employed in the design phase of large photovoltaic plants in order to have a preliminary evaluation of the system efficiency and of the capability of reactive power exchange with the electricity system operators (TSOs and DSOs). This necessity is strictly related to the increasing number of TSOs and DSOs that require photovoltaic plants to provide ancillary services, such as the supply of reactive power and the participation in voltage regulation.

A Feedback Linearization Scheme for the Control of Synchronous Generators

Abstract This article proposes an advanced non-linear control algorithm to manage active power and voltage provided by a synchronous generator. The algorithm is based on the so-called feedback linearization theory, which relies on the central concept to algebraically transform non-linear systems dynamics into fully or partly linear ones, so that linear control techniques can be applied. Starting from the basic (electrical, magnetic, and mechanical) machine equations, a suitable state transformation is introduced in order to apply the feedback linearization block to the generator model. A regulation scheme is then derived, which receives as inputs the measure and reference signals of both the electric power and the voltage at the generator side and produces as outputs the physical inputs of the machine, i.e., the mechanical torque and the field voltage. Particular attention is devoted to both the linearization process, where internal dynamics and stability studies play an important role, and to the design of the two (power and voltage) decoupled regulators. Several simulations are finally performed in order to verify the effectiveness of the proposed approach and to highlight its main advantages and drawbacks with respect to the traditional P-V synchronous generator control strategy.

A technique for the optimal control and operation of grid-connected photovoltaic production units

The strong and intense increase of the number of Photovoltaic production plants has slowly changed the asset and the operation conditions of the electric system. The aim of the present work is to introduce an innovative optimized control strategy to exploit the reactive power resource generated by photovoltaic plants in order to improve the quality and efficiency of the low/medium voltage distribution network. Here, a methodology to define the optimal reactive power reference for every photovoltaic unit of the network is presented in order to pursue a well-defined goal, such as the minimization of the Joule losses or the voltage support. Such reference signals are then provided to the photovoltaic control systems that will guarantee the decoupling between the reactive power channel and the active power one, thanks to the use of the FeedBack Linearization (FBL) control technique. The problem is here formulated in a general way, therefore it can be extended to any possible grid configuration and test case scenario.

A control algorithm for the maximum power point tracking and the reactive power injection from grid-connected PV systems

This paper deals with the use of large-size Photovoltaic (PV) units as providers of the reactive power compensation ancillary service. To do this, a suitable control scheme has been developed, which is based on an advanced control theory, called FeedBack Linearization (FBL), widely employed in the robotics field but still not so popular in power systems engineering. This allows to regulate both the injection of reactive power and the PV voltage, which is fixed to the value corresponding to the maximum power extraction from the PV unit, thanks to the implementation of an efficient MPPT algorithm, whose main features are described in detail. Several simulations are performed in the PSCAD-EMTDC electromagnetic environment to validate the proposed approach.

A methodology to quantify the impact of a renewed T&D infrastructure on EU 2020 goals

This paper addresses the issue of the evaluation of how modern and restructured Transmission and Distribution (T&D) infrastructures help accomplish the so-called EU 2020 targets, in terms of efficiency increase, CO2 reduction and a wider employ of renewable energy resources. A methodology is proposed in order to quantify the possible environmental benefits as well as the power quality improvement provided by the application of modern T&D products and systems on the power grids. Such methodology is based both on the identification of suitable “performance (technical) indices” to be used to rank the benefits brought by the different grid upgrading measures and on the definition of suitable “test networks”, which can be employed as benchmarks to perform the numerical evaluation of the introduced indices. Then, a procedure is presented in order to determine and compare the quantitative effect of each single corrective action on T&D power grids. Finally, some considerations on possible side effects and advices on strategies for the implementation of the corrective measures are discussed.

Improving power grids transient stability via Model Predictive Control

This paper proposes the application of Model Predictive Control (MPC) to ensure the stability of an electric grid following fault conditions. The technique is firstly described as a general tool; subsequently, the chosen model of the power system is detailed together with the specific requirements to be met by the control algorithm. Finally, the application of MPC strategy to a WECC (Western Electricity Coordinating Council) test case network shows that the effects of a contingency, that would bring the system to instability without any external action, are mitigated by the control action, leading the network to a new working point, as close as possible to the previous one and, most of all, without exceeding the stability limits.

Enhanced economic dispatching in competitive electricity market by optimal location and setting of angle compensation devices

The paper discusses the evolution of the economic dispatching in a deregulated environment, and the following impact on the scheduling of power transactions. The benefit of additional degrees of freedom introduced by advanced compensation devices properly located, useful both for transmission planners and system operators, is then analysed.

Voltage regulation via automatic load tap changing transformers: Evaluation of voltage stability conditions

Abstract The paper shows the role played by load tap changing (LTC) transformers, equipped with tap automatic control, in the analysis of voltage stability at the receiving end of transmission links. Owing to the slow nature of the process, voltage stability at load nodes is investigated with regard to the mid-term dynamics of synchronous generators and to the secondary voltage regulation. The importance of load models is also recognized so that voltage and frequency load characteristics are introduced and their effects on the voltage stability conditions are evaluated and discussed.