A Model Predictive Control Strategy for Distribution Grids: Voltage and Frequency Regulation for Islanded Mode Operation

Giulio Ferro,Michela Robba,Roberto Sacile

doi:10.3390/en13102637

Abstract

In the last few years, one of the most important challenges of power technologies has been the integration of traditional energy production systems and distributed energy resources. Large-scale photovoltaic systems and wind farms may decrease the quality of the electrical grid service, mainly due to voltage and frequency peaks and fluctuations. Besides, new functionalities, such as the operation in islanded mode of some portions of the medium-voltage grid, are more and more required. In this respect, a model predictive control for voltage and frequency regulation in interconnected local distribution systems is presented. In the proposed model, each local system represents a collection of intelligent buildings and microgrids with a large capacity in active and reactive power regulation. The related model formalization includes a linear approximation of the power flow equations, based on stochastic variables related to the electrical load and to the production from renewable sources. A model predictive control problem is formalized, and a closed-loop linear control law has been obtained. In the results section, the proposed approach has been tested on the Institute of Electrical and Electronics Engineers(IEEE) 5 bus system, considering multiple loads and renewable sources variations on each local system.

Highlights

The increase of intermittent renewable energy sources (RES) has created instability issues, requiring new controllers for modern smart microgrids [1,2,3]
The control scheme is fully distributed, and necessary and sufficient conditions for convergence and stability of the whole system are described. We model both active and reactive power, but providing a control strategy for the whole optimization problem that can be used under a model predictive control (MPC) scheme
Without any upper-level controller but only with the damping given by each local system, the generators could not be able to efficiently compensate the given power variation, causing frequency and voltage variations

Summary

Introduction

The increase of intermittent renewable energy sources (RES) has created instability issues, requiring new controllers for modern smart microgrids [1,2,3]. The need for new control strategies is motivated by the increase of distributed small generators that cause millions of new producers potentially involved in the energy market. In order to preserve the electrical grid from faults and emergency situations, it may be necessary to reduce the power demand and to operate some portions of the medium-voltage grid in islanded mode. These new set-ups require new fast controllers, which can take into account voltage and frequency models

Objectives

Results

Conclusion