Abstract
Wind farms connected with series compensated transmission network suffer from the risk of sub-synchronous oscillation (SSO). Moreover, the strong active and reactive power control ability of doubly fed induction generator (DFIG) exerts non-negligible influence on SSO. In this study, the impacts of adjustable parameters on SSO are studied based on eigenvalue analysis. The results indicate that increasing inductive reactive power produced by DFIG can provide positive damping to the system; furthermore, the universality of this rule is verified in the whole operating region of DFIG. According to the rule, a reactive power control strategy of DFIG is proposed for SSO suppression. The reactive power is suggested to increase gradually once the SSO is detected and stop until SSO is suppressed or the reactive power limit is reached. The proposed control method is a low-cost method, which only need to adjust the reactive power reference value of DFIG to damp SSO. Finally, the time-domain simulation results illustrate the validity and adaptability of the proposed SSO reactive power control strategy.
1 Introduction
With the increase of construction of large wind power plant in China, the wind power installed capacity keeps growing. The capacitive series compensation of long transmission lines is an effective method to increase the transmission capacity of wind power system. However, one of the hindering factors for the extensive use of series capacitive compensation is the potential risk of subsynchronous oscillation (SSO) [1, 2]. In recent years, SSO occurred in many countries when wind power is transmitted from doubly fed induction generator (DFIG) based wind farm through series compensated lines. These accidents led to large-scale disconnection of wind turbines from power grid and the damage of crowbar circuit [3–5]. These accidents have attracted the attentions of a large number of scholars.
5 Conclusion
In this paper, the influence of adjustable parameters on SSO is analysed based on eigenvalue analysis. The results show that increasing inductive reactive power produced by DFIG can provide positive damping for the system, which is very helpful for SSO suppression. Furthermore, the universality of this rule is verified in the whole operation region of DFIG. Based on the rule, a reactive power control strategy of DFIG-based wind farm for SSO mitigation is proposed in this paper. Time domain simulation indicates that the control strategy could effectively suppress SSO. It is a low-cost control strategy, which provides a new way to mitigate SSO in actual operation of wind power system.
