高比例风电及其弱电网条件下双馈风电机组故障穿越研究

In recent years, the high proportion of dispersed wind power has been integrated into weak grid. As a result, the doubly fed induction generator (DFIG)-based wind turbines are required to possess a more advanced fault ride-through capabilities during grid fault, which needs not only maintain uninterrupted operation, but also actively support the voltage and frequency of grid during transient process. However, traditional DFIG lacks the requisite fault transient support capabilities due to the low short-circuit ratio and lack of damping in weak grid. The main contents of this research include: Firstly, build the state space model of reflecting DFIG’s multi-stage transient characteristics during fault ride through in weak grid, quantify the capabilities of fault transient support for DFIG on account of multiple constraints, and study the method of assessing transient controllable domain and stable region under different fault conditions. Secondly, this research proposes a hybrid co-optimization control strategy based on impedance-adaptive design for rotor side and grid side converters to improve robustness and dynamic response characteristics of DFIG during fault ride through, which aims at solving the problem of coupling and oscillation in active and reactive power of DFIG under symmetrical faults of weak grid. And a nonlinear control strategy based on the state observer of virtual power angle is used to improve transient angle stability. Lastly, a coordinated control method based on the hierarchical model predictive control and multi-objective optimization is implemented for addressing the coupling among terminal voltage, frequency, positive sequence and negative sequence components of active and reactive power of DFIG under asymmetrical faults. This research will investigate a new approach for the fault ride-through method of DFIG under the circumstances where the high proportion of dispersed wind power is integrated into weak grid.

随着高比例风电分散接入弱电网，故障穿越要求双馈风电机组（DFIG）实现不脱网运行，更需要具有电压和频率暂态主动支撑能力。但弱电网低短路比和弱阻尼会影响机组故障期间暂态稳定和动态响应，限制其暂态支撑能力。本项目拟开展的主要研究包括：构建反映DFIG在弱电网故障穿越多阶段下暂态特性的状态空间模型，量化机组基于多约束条件的暂态支撑能力，探索不同故障下机组暂态可控稳定区域的评估方法；针对弱电网对称故障下DFIG功率输出耦合和振荡，提出基于阻抗自适应的转子侧和网侧变流器协同优化的混合控制型策略，以提高机组故障穿越及暂态支撑的动态响应特性和鲁棒性，通过基于虚拟功角状态观测器的非线性控制提高弱电网故障下的机组暂态功角稳定性；针对弱电网不对称故障下DFIG正负序功率输出与暂态支撑耦合，提出基于分层模型预测多目标优化的正负序功率协调控制。本项目研究将探索高比例风电接入弱电网的DFIG故障穿越新思路、新方法。

随着高比例风电分散接入弱电网，故障穿越要求双馈风电机组（DFIG）实现不脱网运行，更需要具有电压和频率暂态主动支撑能力。但弱电网低短路比和弱阻尼会影响机组故障期间暂态稳定和动态响应，限制其暂态支撑能力。本项目开展的主要研究包括：电压控制型双馈风电机组暂态模型建立和稳定性分析；建立包含定子侧和网侧的输出阻抗模型。运用D分割法，在多重稳定条件的约束下，得到控制器参数稳定范围和控制器参数变化对系统稳定性的影响，针对故障瞬间电压跌落的电磁暂态过程产生的电流冲击问题，提出了定子暂态磁链补偿方案和基于改进自抗扰的转子过电流抑制策略，抑制了双馈发电机故障时的冲击，针对故障恢复时有功功率和频率脉动问题，提出基于功率比例前馈控制策略和超前滞后校正控制策略，有效抑制了故障恢复后的频率脉动，提高机组暂态响应能力，增强了弱电网下双馈发电机组低电压故障穿越的能力。通过仿真与实验研究，验证了上述控制策略的有效性，本项目研究为高比例风电接入弱电网的DFIG故障穿越提供新思路、新方法。