Stefano Massucco

Short-Term Scheduling and Control of Active Distribution Systems With High Penetration of Renewable Resources

Among the innovative contributions to electric distribution systems, one of the most promising and qualified is the possibility to manage and control distributed generation. Therefore, the latest distribution management systems tend to incorporate optimization functions for the short-term scheduling of the various energy and control resources available in the network (e.g., embedded generators, reactive power compensators and transformers equipped with on-load tap changers). The short-term scheduling procedure adopted in the paper is composed by two stages: a day-ahead scheduler for the optimization of distributed resources production during the following day, an intra-day scheduler that every 15 min adjusts the scheduling in order to take into account the operation requirements and constraints of the distribution network. The intra-day scheduler solves a non-linear multi-objective optimization problem by iteratively applying a mixed-integer linear programming (MILP) algorithm. The linearization of the optimization function and the constraints is achieved by the use of sensitivity coefficients obtained from the results of a three-phase power flow calculation. The paper shows the application of the proposed approach to a medium-voltage 120 buses network with five wind plants, one photovoltaic field, ten dispatchable generators, and two transformers equipped with on-load tap changers.

Optimal Management Strategy of a Battery-Based Storage System to Improve Renewable Energy Integration in Distribution Networks

The paper proposes the modeling and the optimal management of a hot-temperature (sodium nickel chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge, temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a forward dynamic programming algorithm, specifically developed to exploit the energy price arbitrage along the optimization time horizon (“generation shifting”). Taking advantage of this strategy wind generation performances can be enhanced and adapted to load demand, obtaining an increased economic gain measured by the difference between the economic revenue obtained with and without the proposed generation shifting policy.

A Gas Turbine Model for Studies on Distributed Generation Penetration Into Distribution Networks

The paper proposes a detailed model of a gas turbine for a combined heat and power (CHP) plant. The prime mover is endowed with several controls: first of all, a speed control which can be either droop type or isochronous type according to the status of connection to the distribution grid. An acceleration limiter and an exhaust gases temperature limiter intervene to cut the fuel request, respectively, in case of an excessive rotor acceleration and of a too high temperature of the exhaust gases. A further control regulates inlet guide vanes (IGV) in order to keep the exhaust temperature almost constant. This is important in a cogeneration plant where the heat recovery from the exhaust gases is used to satisfy the demand of the thermal load. Some validation simulations on a model of cogeneration plant connected to a MV distribution grid are carried out and commented.

Microturbine Control Modeling to Investigate the Effects of Distributed Generation in Electric Energy Networks

The great attention of research initiatives to sustainable energy systems calls for contributions in modeling new small size generation plants exploiting innovative technologies. In such a context, the paper presents detailed models of the components and controls forming the thermo-mechanical and electric subsystems of a microturbine power plantP. The modeled thermo-mechanical subsystem includes different control loops: a speed controller for primary frequency control (droop control), an acceleration control loop, which limits the rotor acceleration in case of sudden loss of load or in case of start-up, and a controller to limit the temperature of the exhaust gases below the maximum admissible temperature. The modeling of control schemes in the electric subsystem is another key issue of the paper in view of providing efficient energy production from distributed generation: an active power-voltage (PV) control is adopted for the inverter in case of the operation of a microturbine connected to the grid. This control scheme provides an innovative contribution with respect to the usually adopted active power-reactive power (PQ) control scheme. The adoption of the PV control scheme allows to evaluate the contribution of micro-turbines to voltage support in electric distribution grids. In case of isolated operation of the generation source a voltage-frequency (VF) control scheme is proposed. A test grid is set up for model validation and the simulation results are described and discussed.

An Energy Resource Scheduler Implemented in the Automatic Management System of a Microgrid Test Facility

The paper deals with a microgrid test facility, settled at the CESI RICERCA laboratories, equipped with various distributed energy resources (DERs) and connected to a LV network. The operation of such a microgrid is supervised by a central automatic microgrid management system (MMS). The paper first reports and discusses some experimental results carried out for the assessment of DERs performance and for the implementation of specific MMS functions. Then, it describes the functions of the energy resources scheduler (ERS) implemented in the MMS. The scheduler periodically updates the set points of DERs regulators in order to achieve economic, reliability and power quality objectives, starting form the load and renewable production forecasts and from the results of the system state estimation. The ERS is composed by two main parts, namely: a day-ahead economic scheduler of active power set points during the following day for the minimization of the overall costs, and an intra-day scheduler that every 15 minutes settles the set points of the DERs regulators to optimize the voltage profile at the grid buses, taking into account both technical constraints and the day-ahead economic schedules.

An Optimal Model-Based Control Technique to Improve Wind Farm Participation to Frequency Regulation

Summary form only given. This paper presents a model-based control technique to provide the contribution of wind power generators to primary frequency regulation in electric power systems. Models of individual wind power generators and wind farm (WF) as a whole are presented and the proposed control strategy is detailed. It consists of a central controller, a central Kalman filter (KF), and some local KFs, one for each wind turbine. The central controller is disabled in normal operation conditions and its task is to set the power reference for each wind turbine, overwriting the local reference, when a disturbance occurs. Central KF is in charge of estimating the external load variation, while each local KF estimates wind speed and the wind turbines dynamical state. The key feature of this approach is that each wind turbine can react to grid disturbances in a different way, which depends on wind speed as seen by the wind turbine itself and by its dynamical conditions. Real wind data and a large WF connected to the grid in a dedicated simulation environment have been used to test the effectiveness of the proposed control strategy.

An Integrated Platform for Power System Security Assessment Implementing Probabilistic and Deterministic Methodologies

Power system security assessment both for planning (off-line) studies and for operational (on-line) applications is performed by various analysis methods which highlight different phenomena (steady-state violations, angle stability, voltage stability, etc.) in order to retrieve an exhaustive vision of the problems. Besides traditional deterministic tools, recently proposed probabilistic tools may highlight new interesting security aspects by introducing the concepts of probability and quantifying the risk associated with the contingencies. This paper proposes the overall architecture of a security assessment platform which integrates both probabilistic and deterministic methodologies in a simple environment.

Power and energy control strategies for a Vanadium Redox Flow Battery and wind farm combined system

The paper aims at describing two different control strategies for a combined system composed by a Vanadium Redox Flow Battery and a wind farm. A brief overview of the dynamic models used at describing the storage system and the wind turbines is presented. The focus is then devoted to the description of the two controllers, which task is to grant the desired power output at the point of connection of the system to the main network. The two control strategies called respectively Power Control and Energy Control are analyzed and their effectiveness is tested. The wind turbines are, in fact, fed with turbulent winds and the storage is controlled to perform a series of charges and discharges in order to have the desired global output. Their implementation and the dynamic simulations are performed in the Matlab-Simulink environment.

Operational Risk Assessment and control: A probabilistic approach

Probabilistic Risk Assessment (PRA) techniques are raising more and more interest in the context of the operation of high voltage transmission networks because they represent a new approach to the security assessment in power system operation. The classical deterministic methods, which compare the power system performance to a predefined set of requirements (e.g. no current and voltage violations, no stability problems), do not take into account the probability of occurrence and the magnitude of events and do not perform a quantitative characterization of the impact of the contingencies. The fulfillment of the security requirements also for the most critical contingencies determines large security margins, thus higher operational and planning costs. On the other hand the risk of other contingencies may be underestimated. The paper starts by illustrating a methodology to assess the risk of loss of load caused by conventional (N-1) or multiple dependent contingencies resulting into a cascading process. A control strategy is then introduced, aimed to reduce operational risk by optimal preventive redispatching of conventional generators. Simulation results of the application of the approach to an IEEE test system and to a model of the Italian EHV transmission grid are illustrated and discussed.

Evaluation of some indices for voltage stability assessment

The liberalization of the electricity markets causes power systems to work closer and closer to their limits. The online assessment of system security becomes a topic of paramount importance in control centers. In this context fast indices to quickly assess system security are fundamental in an on-line DSA session. This paper considers three voltage stability indices recently proposed in literature and carries out some comparisons. In the first part the authors briefly describe the theoretical background of each index. The second part is devoted to two comparisons: at first, the three indices are compared by using an IEEE test system. Secondly, the FVSI (Fast Voltage Stability Index) and the VCI (Voltage Collapse Index) are compared by adopting a model of the Italian HV transmission grid. The comparisons will show the peculiar information provided by each of the considered indices and will assess the performance of these indices also on a realistic power system. Final remarks are reported and discussed.