Abstract
The impact of a VSC-based generation unit on power system electro-mechanical oscillation modes (EOMs) is two-fold, changing power flow conditions and dynamically coupling with power systems. This paper focuses on the latter one. Usually the dynamic couplings between VSC-based generation units and power systems are thought to be weak due to the excellent performance of vector control. However, it is discovered in this paper that the dynamic couplings would be tremendous if the DC-link voltage control mode of the VSC coincided with any of the EOMs. Under the special condition of modal coincidence, damping of the affected EOM would be degraded substantially. Furthermore, it is found that the strength of dynamic couplings at the point of modal coincidence is positively correlated to the penetration level of the VSC-based generation unit. The effect of damping deterioration is worsened with the increasing of penetration level of the VSC-based generation unit when modal coincidence occurs. Both theoretical analysis and case study are presented in the paper to validate these findings.
I. INTRODUCTION
The large-scale exploitation of renewable energy is a promising solution for the sustainability of energy supply. Voltage source converter (VSC) has been accepted as the most attractive method for the grid integration of renewable energy sources. Therefore, it is of great significance to study the impact of VSC-based generation units on power system small-signal stability.
IV. CONCLUSIONS
The paper investigates the impact of dynamic couplings between VSC-based generation units and power systems on power system electro-mechanical oscillation modes (EOMs). It is found that strong dynamic couplings between interfacing VSC and power systems are present when the control mode of VSC associated with the DC-link voltage control coincides with any of the EOMs of power systems. This phenomenon is called modal coincidence in this paper. It is demonstrated in the paper that the effect of strong dynamic couplings is detrimental to the damping of the affected EOM when modal coincidence happens. Furthermore, the strength of modal coincidence is positively correlated to the penetration level of VSC-based generation unit. In another word, the effect of modal coincidence is enhanced with the increasing of penetration level of VSC-based generation unit.
