孤岛新能源场站接入柔性直流高频振荡机理及抑制策略

Mechanism and Suppression Strategy of High-frequency Oscillation Caused by Integration of Islanded Renewable Energy Station into MMC-HVDC System

大规模新能源孤岛经柔性直流送出系统的高频振荡问题在近期工程中日渐突出。文中建立了考虑一次主电路设备内部动态过程、控制链路延时、序分量分离环节、内外环控制环节的不同频率耦合特性的柔性直流换流器阻抗数学模型,并对数学模型进行简化,确定孤岛新能源场站接入柔性直流换流器的高频振荡机理为控制链路延时与内环电流反馈、电压前馈环节共同形成了柔性直流系统高频负阻尼,进一步得到了影响柔性直流换流器高频阻抗特性的关键因素。针对关键影响因素设计了孤岛新能源场站接入柔性直流系统的高频振荡抑制方案。相应解决方案在PSCAD模型中得到验证,同时解决了中国张北、如东新能源经柔性直流送出工程现场的高频振荡问题。

The high-frequency oscillation of large-scale renewable energy islanded transmission system through the modular multilevel converter based high voltage direct current(MMC-HVDC) system is increasingly prominent in recent projects. In this paper, a mathematical impedance model of MMC with different frequency-coupling characteristics is developed with consideration of the inner dynamic process of the primary main circuit equipment, control link delay, sequence component separation link, inner and outer loop control links. The mathematical model is simplified to determine the high-frequency oscillation mechanism caused by the integration of islanded renewable energy station into the MMC-HVDC system, which is that the control link delay, inner loop current feedback and voltage feedforward link format the high-frequency negative damping of the MMC-HVDC system. The key factors affecting the high-frequency impedance characteristics of the MMC are obtained. Based on the key factors, the suppression schemes of high-frequency oscillation caused by the integration of islanded renewable energy station into MMC-HVDC system are also suggested. The corresponding solutions have been verified in the PSCAD model and the high-frequency oscillation problem in the engineering sites of Zhangbei and Rudong renewable energy transmission projects of China through the MMC-HVDC system has been solved.