Impedance modeling and stability analysis of power electronic converter based microgrids

Abstract

To tackle with the deteriorating environment and finite natural resources, electric energy as one of clean energies is highly expected to for the sustainable development. In this situation, the conventional energies such as fuel-based energy is supposed to be replaced with electric energy. As one of the consequences, the transport vehicles are being electrified and more dependent on electrical power. In the progress of the transportation electrification, more power electronic devices are added into the electric vehicles and their accessories such as the charging station network. As the electrical power systems is becoming larger and the system structure is more complex, the system stability needs to be well analyzed during system design and optimization.

The impedance-based stability criteria have been proposed and verified useful for stability analysis at system level. By figuring out the impedance characteristic of subsystems, the system instability can be predicted, and the system can be stabilized by reshaping the impedance of subsystems. However, it requires the high completeness of impedance model so that the stability analysis can be accurate. More than that, at the same time the power electronics is developing very fast since 1950s. A variety of converter topologies were proposed to achieve higher efficiency, more controllability, galvanic isolation, bidirectional power flow and so on. Hence, the impedance model of these attractive topologies should be investigated in details before they are integrated into the system.

This thesis firstly gives a background of the environment pollution and the transportation electrification, in which the research of the impedance model perfection and system stabilization is motivated. Then, the review of electrification progress of aircraft and the advantages of smart transformer for utility grid is reported. Following that the study is conducted. The first and essential step is perfecting the impedance model of the components applied in the future aircraft and smart transformer microgrid. In this thesis, the impedance of dual active bridge converter, permanent magnet synchronous generator/motor and three-phase voltage source converters are investigated and presented. The obtained impedance model is validated by simulation and experiment. With the validated impedance model, the stability analysis of the microgrids containing these converters is carried out at the system level, in addition, it enables the effective improvements of control strategies on system stabilization. The stabilizing effects of improved control strategies on system are successfully observed in simulation and experiment, proving the validity of the impedance model.

Date of Award	Jul 2022
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Giampaolo Buticchi (Supervisor), Chunyang Gu (Supervisor) & Pat Wheeler (Supervisor)