直驱风电场与柔直互联系统的传递函数模型及其低频振荡稳定性分析

Transfer Function Model and Low-frequency Stability Analysis for PMSG-based Wind Farm Interconnected With Flexible-HVDC System

风电场经柔直送出是消纳新能源的重要手段,然而风电变流器、柔直换流器以及多控制环节的相互耦合作用使得风电场与柔直互联系统的稳定性问题时有发生。为了解析揭示互联系统中不同子系统以及控制环节之间的交互影响,同时能采用经典频域判据进行稳定性分析,该文针对直驱机组构成的风电场与柔直互联系统建立单输入单输出(single-input single-output,SISO)传递函数模型,基于SISO模型利用奈奎斯特(Nyquist)判据研究风电功率波动变化与柔直换流站定交流电压控制(AC voltage control,AVC)对互联系统稳定性的影响;同时研究风电场锁相环(phase locked loop,PLL)与柔直站AVC控制之间的交互影响关系。研究表明,当风电场输出功率传送至额定功率时,互联系统存在低频振荡失稳风险,通过调节柔直站AVC电压外环控制器参数可抑制互联系统振荡并实现稳定运行;此外通过一定范围内改变风电场PLL控制带宽后发现,随着风电场PLL控制带宽的增加,柔直站AVC控制参数的可行域减小;若要保持互联系统稳定,柔直站AVC电压外环控制器的比例系数不能过小。最后,通过PSCAD/EMTDC环境下电磁暂态仿真验证理论分析结果的正确性。

The grid integration of wind farms by flexible HVDC is an important means to achieve the consumption and transmission of renewable energy.However,the coupling of multi-control loops makes potential instability problems in the system.In order to reveal the interaction between control loops in the system analytically,a single-input and single-output(SISO)transfer function model was developed for permanent magnet synchronization generator(PMSG)-based wind farm interconnected with flexible HVDC system.Based on the SISO model,the influence of wind power fluctuation and AC voltage control(AVC)of flexible HVDC on the stability of interconnected system was studied by using Nyquist criterion and the results show that the interconnected system has the risk of low-frequency oscillation instability while the wind farm output power was transmitted to the rated power.By adjusting the outer loop control parameters of the AVC,the oscillation can be suppressed well.All the results of theoretical analysis are verified by the detailed electromagnetic transient simulation in PSCAD/EMTDC.