混合型风电场经MMC-HVDC送出系统的振荡模式分析

Analysis of oscillation modes of a hybrid-based wind farm transmitted through MMC-HVDC

大规模海上风电场一般采用基于模块化多电平换流器(ModularMultilevelConverter, MMC)的高压直流输电送出,然而风电场与MMC联接后可能因部分控制参数不合理而导致失稳。针对此问题,首先建立了混合型风电场经MMC-HVDC送出系统的小信号模型,混合型风场同时包含双馈与直驱两种机型。采用特征根法研究系统的振荡模式,研究表明风电场锁相环与MMC电压控制环产生交互影响并形成弱阻尼振荡模式,MMC电压外环控制比例系数对该振荡模式影响很大,比例系数越大系统越稳定,当比例系数过小时会导致系统出现低频振荡。系统的小信号模型与理论分析结果均通过PSCAD/EMTDC仿真进行了验证。该研究成果可为实际工程中风电场经MMC-HVDC送出系统的控制参数合理选择提供参考。

Large-scale offshore wind farms usually use HVDC transmission based on the Modular Multilevel Converter(MMC). However, the system is likely to cause instability because of some irrational control parameters while the wind farm is connected to the MMC. To solve this problem, a small-signal model of a hybrid-based wind farm which contains a Doubly-Fed Induction Generator(DFIG) and Permanent Magnet Synchronization Generator(PMSG) direct-drive wind turbines interconnected with MMC is developed. Then the eigenvalue method is selected to study the oscillation mode of the system. The study shows that there is an interaction between the phase-locked loops of wind farms and the voltage control loop of the MMC, and it also forms a weakly damped oscillation mode. The proportional coefficient of the MMC voltage outer loop control has a great influence on the dominant oscillation mode. The larger the proportional coefficient is, the more stable the system is. When the proportional coefficient is too small, it will lead to low-frequency oscillation of the system. All the results are verified by simulation in PSCAD/EMTDC. The research results will provide a reference for the reasonable selection of control parameters in the engineering of wind farm transmitted power through MMC-HVDC.