Motivation

 

The evolution of microgeneration technologies increase the integration of Distributed Generation in High Voltage (HV) and Medium Voltage (MV) networks and consequently also at the Low Voltage (LV). Therefore, a new paradigm appears in the electric power systems operation - the Microgrid - that is growing quickly.

The MG is a LV network connected to MG small units (fuel cells, microturbines, solar photovoltaic panels, small wind generators, energy storage units, etc.), and it is a system totally controlled by appropriated mechanism.

The highest integration of microgeneration in the present days it is Photovoltaic Panels and in a close future will be the Electrical Vehicles. Which requires at certain moments of MG operation a coordination in order to maintain the operation security of the system.

The storage devices and the flexible loads are also important elements in the Microgrid that need to be coordinated with other network elements.

The MG can operate in two ways, interconnection with the Medium Voltage (MV) grid upstream or autonomously (operating in emergency mode) following disturbances of the upstream network.

 Operating in emergency mode, the characteristics of the MG - high resistance levels in comparison with the reactance - requires the identification of voltage regulation mechanisms through active power control, thus being a possible conflict with the frequency regulation. Additionally the significant number of single-phase loads and Microsources may cause significant voltage unbalances, mainly during islanding operating conditions.

In this context, the study of this thesis aims the development of the necessary control strategies, in the adequate elements of the MG. In order to coordinate the frequency and voltages at system and improve their values, particularly during emergency operation mode.

 

Objectives

 

1. Study the mathematical models of Microsources dynamic response characteristics and respective power electronic interfaces;

2. Exploit MG dynamic simulation platforms in order to address the operation of the system under severe conditions (such as unbalanced operation with high power production and low load);

3. Identification of potential problems resulting from voltage and frequency control functionalities in microgrids islanding operation conditions;

4. Identification of coordination actions to improve microgrid operation during islanding operation regarding the potential interaction between voltage and frequency control functionalities;

5. Validation of the coordination actions through extensive simulation.