## 6 Conclusions  
A method for damping inter-area oscillations using a dual-channel modulation controller of DFIG is proposed. The DFIG active-reactive power additional damping controller is obtained by using the improved adaptive particle swarm optimization algorithm. The control effect of the proposed damping controller is verified through the transient simulation of the 2-area 4-machine system with wind farm. The number of oscillations in the torque increases when active power modulation is applied and reaching the damping target when reactive power modulation is applied is difficult. The DCPM controller performs well in suppressing low frequency oscillation and minimizes the adverse effects on torsional damping. The design can better balance DFIG's dynamics and damping low frequency oscillation. It avoids the harmful interaction of the shaft torsional oscillation on the power system and is conducive to the stable operation of the system. Lastly, it can provide effective reference and help for the suppression of low frequency oscillation grid-connected wind turbines. The damping control strategy in this paper is only suitable for offline application, our future work will focus on the online regulation. [PERSON] and [PERSON] conceived and designed the study. [PERSON] and [PERSON] performed the experiments. [PERSON] and [PERSON] wrote the paper. [PERSON], [PERSON] and [PERSON] reviewed and edited the manuscript. All authors read and approved the manuscript. This work was funded by National Key Research and Development Programme (2016 YFB0900100), State Grid Corporation of China (SGJLDK00 KJJS1800061), and Jilin Province Outstanding Young Talents Foundation Project of China (20180520067 JH). The authors declare no conflict of interest. * [PERSON] et al. (2002) [PERSON]; [PERSON]; [PERSON] Doubly fed induction generator systems for wind turbines. _IEEE Ind. Appl. Mag._**2002**, \(8\), 26-33. [CrossRef]
* [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON] [PERSON] Active-Reactive Additional Damping Control of a Doubly-Fed Induction Generator Based on Active Disturbance Rejection Control. _Energies_**2018**, _11_, 1314-1331. * [PERSON] et al. (2012) [PERSON]; [PERSON]; [PERSON] Power oscillation damping supported by wind power: A review. _Renew. Sustain. Energy Rev._**2012**, _16_, 4994-5006. [CrossRef]
* [PERSON] et al. (2006) [PERSON]; [PERSON]; [PERSON] A power system stabilizer for DFIG-based wind generation. _IEEE Trans. Power Syst._**2006**, _21_, 763-772. [CrossRef]
* [PERSON] et al. (2009) [PERSON]; [PERSON]; [PERSON] Control of DFIG-Based Wind Generation to Improve Interarea Oscillation Damping. _IEEE Trans. Energy Convers._**2009**, _24_, 415-422. [CrossRef]
* [PERSON] et al. (2016) [PERSON]; [PERSON]; [PERSON] A Novel DFIG Damping Control for Power System with High Wind Power Penetration. _Energies_**2016**, \(9\), 521. [CrossRef]
* [PERSON] et al. (2011) [PERSON]; [PERSON]; [PERSON] On Active/Reactive Power Modulation of DFIG-Based Wind Generation for Interarea Oscillation Damping. _IEEE Trans. Energy Convers._**2011**, _26_, 513-521. * [PERSON] et al. (2009) [PERSON]; [PERSON]; [PERSON] Contribution of Doubly Fed Wind Generators to Oscillation Damping. _IEEE Trans. Energy Convers._**2009**, _24_, 783-791. [CrossRef]
* [PERSON] et al. (2016) [PERSON]; [PERSON]; [PERSON] A Sliding Mode Based Damping Control of DFIG for Interarea Power Oscillations. _IEEE Trans. Sustain. Energy_**2016**, \(8\), 258-267. [CrossRef]
* [PERSON] (1994) [PERSON] _Power System Stability and Control_, 1 st ed. ; McGraw-Hill: New York, NY, USA, 1994; pp. 1128-1160. * [PERSON] and [PERSON] (2014) [PERSON]; [PERSON] Toward Wide-Area Oscillation Control Through Doubly-Fed Induction Generator Wind Farms. _IEEE Trans. Power Syst._**2014**, _29_, 2985-2992. [CrossRef]
* [PERSON] et al. (2013) [PERSON]; [PERSON]; [PERSON], [PERSON] Modelling of the DFIG Based Wind Farms for Small Signal Stability Analysis of Weak Power Grids. In Proceedings of the Renewable Power Generation Conference IET, Beijing, China, 9-11 September 2013. * [PERSON] et al.