A Fault Protection Method for Avoiding Overvoltage in Symmetrical Monopole HVDC Systems by Half-Bridge MMC
A Fault Protection Method for Avoiding Overvoltage in Symmetrical Monopole HVDC Systems by Half-Bridge MMC
复制标题
半桥MMC避免对称单极高压直流系统过电压的故障保护方法
DOI：
10.1109/access.2021.3134248
复制
发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Nakayama Hiro
中科院分区：
文献类型：
--
作者：
Sano Kenichiro;Nakayama Hiro
在对称单极直流输电系统中，极地故障会引起非故障极过电压。过电压会增加变流器和传输线的绝缘要求。为了抑制过电压，提出了一种对称单极直流输电系统的保护方法。该方法为由半桥子模块组成的模块化多电平变换器（MMC）引入了“下臂短保护”和“上臂短保护”两种新颖的保护模式。此外，在逆变器的直流端插入阻塞二极管。因此，该方法可以清除直流故障电流，避免非故障极的电压升高。5.5 kw HB-MMC高压直流系统的实验结果表明，该保护方法可以抑制电压上升至额定电压的106%，而传统保护方法会造成200%的过电压。该方法对多端直流输电系统同样有效。即使其中一个传输区段发生故障，也不会引起其他非故障区段的过电压。因此，在直流故障期间和之后，非故障段都可以继续传输电力。
It is known that the pole-to-ground fault in the symmetrical monopole HVDC transmission system causes overvoltage in the non-faulted pole. The overvoltage increases the required insulation level of the converters and transmission lines. To suppress the overvoltage, this paper proposes a protection method for symmetrical monopole HVDC systems. The proposed method introduces novel protection modes “lower arm short protection” and “upper arm short protection” to the modular multilevel converter (MMC) being composed of half-bridge (HB) submodules. In addition, blocking diodes are inserted to the DC terminal of the inverter. As a result, the method enables to clear the DC fault currents and to avoid the voltage increase in the non-faulted pole. Experimental results obtained by a 5.5-kW HB-MMC HVDC system demonstrate that the proposed protection method enables to suppress the voltage increase to 106 % of the rated voltage, while the conventional protection method caused overvoltage of 200 %. The proposed method is also effective to the multi-terminal HVDC systems. Even if a fault occurs in one of the transmission sections, the fault does not cause the overvoltage in the other non-faulted section. Therefore, the non-faulted section can continue the power transmission both during and after the DC fault.