PROJECT TITLE: Designing Advanced Phase-Locked Loops and Synchronization Techniques for Microgrids
PhD period: 2016.01.01 – 2018.03.31. (has been prolonged till 2018.05.31)
Section: Power Electronic Systems
Research Programme: Microgrids
Supervisor: Josep M. Guerrero
Co-Supervisor: Juan Carlos Vasquez
Collaborator: North China Electric Power University.
Funding: DSF Sino-Danish Project “Intelligent DC Microgrid Living Lab”.
In recent years, the concept of distributed generation (DG) system and, as a result, Microgrid, hybrid DC/AC grid, and DC nanogrid have attracted more attention mainly because of growing concerns about the harmful environmental effects of traditional fossil fuel power plants and also ever increasing concerns about energy shortages. A Microgrid, in simple words, can be defined as a cluster of power electronics interfaced DG units and electrical loads within the main grid, which can operate in either grid-connected or islanded mode.
Most often, the voltage source converters (VSCs) are employed as the power electronic interface between the DG units and the grid. A crucial issue in the control of these converters is the proper synchronization with the grid. To deal with this issue, several synchronization techniques have been proposed in recent years. These techniques can be divided into two major categories: 1) open-loop synchronization techniques; and 2) closed-loop synchronization strategies.
The most closed-loop synchronization techniques are based on phase-locked loop (PLL) algorithms. A PLL is a nonlinear feedback control system with three distinct parts: 1) a phase detector; 2) a loop filter; and 3) a voltage controlled oscillator. The main difference among various PLLs typically lies in the different filtering stages that are included either within their control loops or before their inputs to improve their speed/accuracy trade-off.
The open-loop synchronization strategies are often based on the Kalman filter, the weighted least square estimation, and the Fourier transform. The key advantage of these techniques over the closed-loop ones is their inherently stable structure, which makes them a suitable choice for the Microgrid synchronization. They, however, suffer from a serious drawback: their performance tend to worsen in the presence of frequency drifts.
The speed, accuracy, and stability of the synchronization technique have a considerable effect on the stability and performance of the DG units and, therefore, the whole Microgrid. The main aim of this project is to enhance the Microgrid permanence by developing and designing more advanced and efficient open-loop and closed loops synchronization techniques.
Publications in journals and conference papers may be found at VBN.