Decentralised control and stability analysis of a multi-generator based electrical power system for more electric aircraft

The more electric aircraft initative results in significant challenges in the design of aircraft electrical power systems. Different power system architectures are currently being studied by the engineering community. In this thesis, a promising single DC bus-based, multiple-source multiple-load power system is investigated in terms of power management and stability. Due to its inherent modularity and ease of implementation, droop control, as a decentralised control method, has been widely used to cope with power sharing among parallel sources in the studied architecture. The thesis proposes a comparative study of different droop control approaches by focusing on steady-state power sharing performance and stability. • Different droop control methods may lead to different stability margins. Until now, the effect of different droop control schemes on system stability has not been fully investigated. The thesis presents the control scheme for current-mode and voltage-mode systems, derives the corresponding output impedance of the source subsystem and analyses the stability of the power system. Based on the developed mathematical model, comprehensive modal analysis of the power system is performed. • A generalised analytical impedance analysis is extended to a multi-source multi-load power system. To facilitate the analysis, the thesis proposes the concept of “global droop gain” as an important factor to determine the V-I bus characteristic and the stability behaviour of a parallel sources based DC system. • Considering the tradeoff between voltage regulation and power sharing accuracy in droop control, this thesis proposes an improved voltage regulation method in multi-source based DC electrical power system. Due to the absence of additional controllers or communication lines, the proposed approach can be relatively easily implemented in a small scale DC electrical power system. The proposed approach effectively improves the load sharing accuracy under high droop gain circumstances with consideration of cable impedance. Optimal droop gain settings are investigated and the selection of individual droop gains has been described in order to reduce the distribution losses. Finally, the above-mentioned analytical results are confirmed by time-domain simulations and experimental results