利用改进变分模态分解突变能量的直流配电网保护方法

A DC Distribution Network Protection Method Based on Improved VMD and Abrupt Energy

为了有效识别环状直流配电网中的故障,提高直流配电网保护的可靠性、选择性、速动性和灵敏性,保证系统的稳定运行,提出一种利用改进变分模态分解(VMD)突变能量的线路纵联保护方法。因为VMD算法需要先设置模态数,且模态数与分解效果息息相关,所以首先利用麻雀搜索算法(SSA)找到VMD算法合适的模态数,使得在此参数下的分解效果最优。然后根据线路首末两端突变能量的差异,构造保护方案。将故障时采集的电压、电流故障分量进行SSA-VMD分解,得到若干模态分量并计算其突变能量。根据区内、区外的突变能量大小差异构造区内、外故障判据,由故障时正负极的突变能量比值差异构造故障极判据。在PSCAD/EMTDC中搭建环状直流配电网模型,利用MATLAB进行保护方法验证,结果表明:在不同故障类型下,所提方法均可在3 ms内快速可靠动作;可以识别区内外故障并实现故障选极,保护线路全长;可耐受过渡电阻20Ω,耐受过渡电阻能力强;在40 dB噪声情况下,依旧可以识别故障,有一定的抗干扰能力。

In this paper,a line longitudinal protection method based on improved variational mode decomposition(VMD)and abrupt energy is proposed to effectively identify faults in ring-shaped DC distribution network,improve the protection reliability,selectivity,speed and sensitivity,and ensure the stable operation of the system.To use the VMD algorithm,the number of modes that matters to the decomposition effect needs to be set first.Hence the Sparrow search algorithm(SSA)is used to find a better number of modes for the VMD algorithm so as to ensure optimal decomposition effect under this parameter.Then a protection scheme is devised according to the difference of abrupt energy at the head and tail of the line.The voltage and current fault components collected are decomposed by SSA-VMD to obtain several modal components and calculate their abrupt energy.The internal and external fault criteria are developed according to the difference of abrupt energy in the areas separated by the direct current reactor.The fault pole criteria are developed according to the difference of the abrupt energy ratio between positive and negative poles at the time of failure.A circular DC distribution network model is built in PSCAD/EMTDC,and the protection method is validated by MATLAB.The results show that the proposed method works quickly(within 3 ms)and reliably for different types of faults.It can identify both internal and external faults,realize fault pole selection and protect the full length of the line.It can also well withstand transition resistance(up to 20Ω).Under a noise level of 40 dB,it can still identify faults and resist jamming to a certain extent.