Stability analysis of virtual synchronous machine control strategy in power system

Zhao, Min (2021). Stability analysis of virtual synchronous machine control strategy in power system. University of Birmingham. Ph.D.

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Abstract

With massive integration of power electronic interfaced renewables including wind and solar power, one of the big challenges is the continuous reduction in power system inertia. In order to deal with this issue, virtual synchronous machine (VSM) control is proposed. Associated with such a solution, it is of great interest to know the impacts of VSM on power system stability, in particular, power system oscillations. Hence, the focus of this doctoral research work is to investigate the effects of VSM control on power system oscillations including sub-synchronous oscillations (SSO), low-frequency oscillation (LFO) and forced power oscillation.
The sub-synchronous oscillation (SSO) of wind farm with series compensated network has attracted increasing attention from researchers. Considering the potential risk of phase-locked loop (PLL) on system sub-synchronous stability, VSM control is implemented which can synchronise power converters to AC grid without PLL-related issues. The permanent magnetic synchronous generator (PMSG)-based wind farm with series-compensated network controlled by vector current control (VCC) and VSM are studied in the first section. The small signal stability and time-domain simulations are compared to show the superiority of VSM on system stability in the sub-synchronous frequency range.
Then a coordinated supplementary damping control (SDC) design for multiple VSMs is proposed to enhance system damping performance. As VSM control emulates the dynamic behaviour of traditional synchronous generator (SG), it may introduce LFO similar to the interaction between multiple SGs. The supplementary channel is added to the reactive power loop of VSM to avoid undesired mechanical vibration when prime mover power comes from a wind turbine. The design process is based on Prony method which is utilised to obtain system modes information. The decentralised sequential design, which can reduce the dependency on communication and the adverse interactions between auxiliary controllers, is implemented to make multiple VSMs to work cooperatively.
Finally, the probability of electro-mechanical interactions between VSMs and other devices especially SGs in power system is higher because of the mentioned reason before. Besides, the renewable energy will suffer some sustained disturbances and thus is prone to exciting forced oscillation due to the resonance between natural LFO mode and external disturbances. Therefore, the impacts of VSM control on forced oscillation is investigated in the last section. The analytical results of infinite bus system with VSM and multi-machines system with VSM are explicitly conducted.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):