Advanced hierarchical control structure for virtual oscillator-based distributed generation in multi-bus microgrids under different grid dynamics and disturbances

Tran, Trung Thai; Monti, Antonello (Thesis advisor); Raisz, David Mark (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2020, 2021)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center ; ACS, Automation of complex power systems 89
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

The power electronic-based converters, which are used as an interface between distributed generations and with the main utility grid, play a crucial role in increasing the integration of renewable energy resources into existing power systems. Thanks to advanced control technologies, power converters can provide various functionalities and a whole range of auxiliary services such as voltage, frequency regulation, power-sharing capability, power quality control, and synchronization. This dissertation's main objective is to propose an innovative control approach for power converters that make them able to overcome the most challenging technical problems associated with multi-bus microgrid operation and control, namely, voltage quality, power-sharing improvement, synchronization, and power flow control. Unlike most of the work in literature, this dissertation adopts the Virtual Oscillator Control for the primary control layer. Additional controllers are designed to utilize a unified hierarchical control structure that guarantees microgrid stability, reliability, and high quality of power generation under different operating conditions, grid disturbances, and uncertainties. Firstly, a completely decentralized control method that adopts a novel sliding modecontrol is developed to compensate for voltage distortion at the point of common coupling, which is not directly connected to the converter terminals. The proposed control method uses a high-pass filter technique to reduce the order of the final control law. This dissertation's second contribution in primary level control is the design of a new control method that consists of low order sliding mode control and modified virtual oscillator control to improve a power-sharing task of power converters in Photovoltaic-dominated (PV) microgrids. The proposed control method allows the PV system to seamlessly switch between different operation modes, namely Maximum Power Point Track (MPPT) and power-sharing modes, without the need of controller reconfiguration. The overall system stability is maintained even under various irradiation levels and load conditions. At the secondary control layer, this dissertation firstly implements a distributed control strategy based on average consensus protocol to eliminate power-sharing inaccuracy among distributed generations caused by the mismatches between the equivalent impedances seen from the outputs of distributed generations, as well as the complexity of the network topology. The proposed consensus-based distributed control algorithm uses only limited information between a distributed generation and its neighbors. As a result, the communication structure is simplified. Besides, the adverse impact of communication time-delays is analyzed based on eigenvalue based stability analysis. This analysis is used to define the time-delay margin that maintains the system stability and to design a compensator to increase the time delay margin. The second contribution of this research on the secondary control layer is an autonomous synchronization control strategy to achieve a smooth transition between operation modes of a multi-bus microgrid. The control signal is sent from the synchronization controller to one or several leading distributed generations. Then, all the remaining distributed generations cooperate in a distributed manner by using a consensus-based distributed protocol to force the voltage at the microgrid side to synchronize with the main utility grid. This dissertation's last contribution is to introduce a new degree of freedom K into the conventional control structure of Virtual Oscillator Control to improve its power dispatching capability in grid-connected mode. The analytical expression is derived to explain the relation between K factor and the converter power, voltage outputs. Two control approaches are introduced based on the theoretical analysis results to control converter power outputs to follow the desired setpoints from the upper control level. The first step of demonstrating the practical possibility of the proposed control methods is introduced in this dissertation by implementing control Hardware-in-the loop (CHiL) simulation in the Opal-RT platform.

Institutions

• E.ON Energy Research Center [080052]
• Institute for Automation of Complex Power Systems [616310]