电网电压骤升下双馈风力发电机轴系振荡抑制的改进控制策略

Improved Doubly Fed Induction Generator Drive-chain Oscillation Restrain Control Strategy Under Grid Voltage Swell

双馈感应发电机在电网电压骤升时,定子磁链中含有暂态直流分量和骤升的稳态分量。电磁转矩中含有骤升的稳态扰动量、同步频率和二倍频率的暂态扰动量。电磁转矩的扰动量经过两质量块模型传动链放大,导致传动链的扭转载荷加剧和故障过后传动链扭矩的振荡。该文首先通过对电网电压骤升故障时发电机电磁暂态过程的理论计算,分析得出电网电压骤升下电磁转矩的解析表达式。通过对传动链两质量块模型的建模,得出柔性传动链自身阻尼较低和对电磁转矩低频扰动的放大特性。为了加速电压骤升恢复后轴系振荡的衰减,通过叠加与扭矩微分量成正比的补偿转矩来增大传动链阻尼,并且通过扭矩观测器来实现对补偿转矩的提取,最后通过仿真和实验验证了所提控制策略的有效性和可行性。

Grid voltage symmetrical swell will cause transient DC flux components and higher steady-state flux component in the doubly fed induction generator（DFIG） stator windings. Electromagnetic torque will generate elevated step steady-state disturbance, synchronizing frequency and double frequency transient disturbance.The disturbance is amplified in transmission chain based on two-mass model, and it will cause torsion load aggravation and oscillation of shaft torque after the grid fault. This paper obtained analytical expressions of electromagnetic torque by analyzing the dynamic behavior of DFIG during symmetrical voltage swell. By analyzing the two-mass model, it can be concluded that flexible transmission chain has the low damping and amplification characteristic to low frequency electromagnetic torque disturbances. A control strategy was proposed to restrain the oscillation of shaft torque after the grid fault. A compensation torque which is proportional to differential of shaft torque was compensated to electromagnetic torque, and a shaft torque observer was designed to obtain the compensation torque. The correctness and effectiveness of this paper was verified by simulation and experimental results.