近年来，以风光为代表的新能源快速发展，电力系统呈现高比例可再生能源和高比例电力电子装备的“双高”发展趋势。随着新能源渗透率增大，涌现出宽频带电磁振荡等新型稳定性问题，并伴随“耦合”与“非线性”两大突出振荡特征，给建模和稳定分析带来了新的挑战。新能源电力电子装备的低惯性、弱抗扰性和控制多时间尺度耦合特性，是导致“双高”电力系统的动态行为和稳定特性深刻变化的根源：在小干扰下，新能源设备呈现单频率扰动输入、多频率扰动输出的宽频带频率耦合效应，使激励-响应维度倍增，判稳复杂度加剧；在大干扰下，新能源设备过载能力低，控制限幅等环节易动作，并伴有等幅振荡或极限环等非线性振荡行为，难以通过小信号线性化的模型开展分析。本文针对频率耦合振荡、等幅振荡、暂态同步角振荡这三类振荡中的典型非线性问题，从系统建模、特性分析、协调控制三方面入手开展工作，具体成果如下：针对频率耦合振荡问题，提出了新能源变流器的宽频带交直流多端口导纳模型及单输入-单输出型振荡稳定性判据。宽频模型易于重构，可有效鉴别交流-交流端口和交流-直流端口间的频率耦合效应诱发的失稳模式，实现振荡源的快速准确定位；振荡判据基于电路端口消去原理，实现了高维系统向低维系统的线性映射，在保证精度的前提下大幅改善了高维系统的判稳效率。针对等幅振荡问题，充分考虑不同频段振荡特性的差异。在中高频段，计及主导振荡分量和内环非线性，提出了变流器的大信号导纳模型及等幅振荡的频域RLC电路判据，定量分析了振荡由线性向非线性阶段过渡时振荡频率和阻尼随振幅的非线性变化规律。在次/超同步频段，计及频率耦合振荡分量和外环非线性，构建了高维系统的多输入-多输出闭环传递函数模型及等幅振荡的幅相轨迹判据，提出了振荡幅频参数解析计算的图解法，并在新疆哈密风电场算例中得到验证。针对暂态同步角振荡问题，揭示了锁相环非线性和控制限幅非线性间的暂态相互作用对同步稳定性的影响，提出了刻画系统同步动态的广义范德波尔振子模型，基于摄动平均法获得了振子方程的近似振荡解及系统的大干扰稳定边界，评估了振荡的失稳形态（单调发散、周期发散、等幅振荡）与控制参数间的非线性变化规律，给出了大干扰下发生等幅振荡的临界条件和同步稳定的镇定控制策略。

In recent years, with the rapid deployment of renewables such as wind and solar photovoltaic, power systems worldwide have been developing towards a "double high" trend, i.e., high penetration of renewable energy power generation and high penetration of power electronic equipment. The increasing proportion of such renewables brings challenges to the safe and stable operation of power systems, including the wideband frequency electromagnetic oscillation with two prominent characteristics of “coupling” and “nonlinearity”. The dynamic and stability issues in “double high” power systems arise due to the low inertia, weak immunity, and multi-time scale coupling characteristics of power electronic converters. During small-signal disturbances, the wideband frequency coupling effects with a single-input-multiple-output frequency response characteristic emerge among ac and dc ports of converts, complicating the modeling and stability analysis; while during large-signal disturbances, protection devices like control limiters are prone to activate due to the low overload capacity of power electronic devices, pushing the system towards nonlinear operations with even sustained oscillations or nonlinear limit cycles. To solve these issues, this paper proposes new methodologies and theories regarding time- and frequency-domain modeling of high-dimensional systems, characteristic analyses of nonlinear coupled oscillations, and coordinated suppression strategies of oscillations. The main contributions are as follows. For the analysis of frequency-coupled oscillations, the ac/dc multi-port admittance model and single-input-single-output (SISO) oscillatory stability criterion are proposed. The multi-port admittance model can be reconstructed and expanded efficiently. It is feasible to distinguish whether an unstable mode is caused by frequency-coupling effects between ac-ac ports or between ac-dc ports, enabling the fast and accurate identification of the oscillating source. The SISO stability criterion is established based on the principle of circuit port elimination. It accurately maps the high-dimensional linear system to a low-dimensional linear system, which greatly improves the stability assessment efficiency without compromising the analysis accuracy. For the first time, the consistency between the ac and dc admittance-based stability analysis results is mathematically demonstrated based on the proposed model and criterion.For the analysis of sustained oscillations, the differences in oscillations’ characteristics between low- and high-frequency bands are taken into full consideration during modeling and stability analysis. In the middle and high frequencies, the large-signal admittance model and RLC circuit criterion are proposed with the dominant oscillating component and inner-loop control nonlinearities considered. The proposed model and criterion are used to quantitatively investigate the dynamical variation trends of the oscillation frequency, amplitude, and damping. In sub- and super-synchronous frequencies, a closed-loop multi-input-multi-output (MIMO) transfer function model of large-scale wind power systems is established with frequency-coupling effects and outer-loop control nonlinearities considered. The frequency-domain amplitude-phase trajectory criterion is proposed to compute the amplitude and frequency of sustained oscillations graphically. The proposed model and criterion are validated using field-measured data from the Hami wind farm in Xinjiang Province, China. For the analysis of transient synchronization angle oscillations, the impacts on system synchronization stability from nonlinearities in the phase-locked loop, hard limiters, and circular limiters are investigated. A generalized Van Del Pol oscillator model is proposed for the modeling and quantitative analysis of synchronization stability. Based on the average method from the nonlinear oscillation theory, the periodic solution of the generalized oscillator model is computed, which facilitates the obtainment of analytic large-signal stability boundaries of the system. With the help of such analytic results, the impacts of operation conditions, control schemes, and limiters’ parameters on the instability form of oscillation (monotone divergence, periodic divergence, sustained oscillation) are revealed. The critical occurrence condition of the sustained oscillation under large disturbances is obtained, accompanied by supplementary control strategies for the enhancement of synchronous stability.