多回MMC-HVDC馈入极弱交流系统的控制策略

Control Strategy of Multiple MMC-HVDC Feed into Extremely Weak AC System

随着模块化多电平换流器型直流输电(MMC-HVDC)工程数量的增多及容量的增大,未来区域电网必将形成多回MMC-HVDC馈入弱交流系统的场景。本文深入研究了这类场景下的控制策略。为了使MMC换流站具有同步发电机一样的特性,提出了一种模拟同步发电机的控制方法。该控制方法包含3个控制环,分别为有功功率-频率环、无功功率-电压环和电流内环。其中,利用有功功率-频率环来模拟同步发电机的摇摆过程,利用无功功率-电压环来模拟同步发电机的励磁系统,并采用电流内环来限制故障电流和提高MMC响应速度。针对多MMC-HVDC馈入系统,提出了动态功率分配控制。该控制不仅能够在换流站间精确分配功率,而且可以起到二次调频的作用。在PSCAD/EM TDC软件中搭建了改进的3机9节点模型,验证了本文所提控制策略的有效性。

With the increase of the number and capacity of MMC-HVDC projects,the multiple MMC-HVDC feeding into weak AC system will be a very common scene in the future reginal power grid. This paper studies the control strategy for such scenes. In order to make the MMC station have the same characteristics as the synchronous generator,the synchronous generator emulation control（ SGEC） is proposed. The control method consists of three loops,namely active power and frequency loop（ PF loop）,reactive power and voltage loop（ QU loop）,and inner current loop. The PF loop is used to simulate the swing process of the synchronous generator（ SG）. The QU loop is used to simulate the exciter system of the SG. The inner current loop serves to limit fault currents and increase MMC response speed. For the multi-infeed MMC-HVDC system,a novel control of dynamic power allocation is proposed. This control scheme can not only allocate the power among MMC stations precisely,but also achieve the secondary frequency regulation. Finally,the effectiveness of the proposed control strategy is verified through the PSCAD/EMTDC simulation of improved 3 machine 9 node system.