基于阀侧交流最大电流时序特征的换相失败检测

Commutation Failure Detection Based on Temporal Feature of AC Maximum Current on the Valve-Side

换相失败是高压直流输电系统运行中的常见事件,体现了换流器的脆弱性。由于现有检测换相失败的判别方法容易受故障因素、控制调节等影响,导致检测方法存在灵敏性不足的问题。准确、可靠地检测换相失败对系统的控制与保护极其重要。基于此,本研究从阀导通状态入手,提出一种基于阀侧交流最大电流时序特征的换相失败检测方案。利用端口交流电流的单边极性电流与三相交流电流最大值一半的比值构造交流最大电流特征量。为减少运行工况的影响,以换相两阀电流的交点为分界点,利用交流最大电流特征量幅值的一半构造阀虚拟导通状态;对其在周期时间内进行积分求取累积宽度,判别阀虚拟导通状态是否异常;根据换相过程中前导换虚拟导通状态超长和后导换阀虚拟导通状态缩短的互锁关系判别换相失败。通过对功率扰动和故障暂态以及采样步长的分析,推导判别换相失败的阈值,推荐阈值为1.3 ms。基于PSCAD/EMTDC电磁暂态仿真和录波数据再现的仿真结果,验证了所提换相失败检测方案的有效性。与电流差动判据相比,在不同的故障条件的仿真结果表明,所提换相失败检测方案受交直流系统工况、故障发生时刻、故障严重程度等因素的影响较小,具有较强的鲁棒性。所提方案可定位换相失败的阀,为控制系统的调节提供更多的时间裕度。

Commutation failure(CF)is common for the operation of HVDC transmission system,and it reflects the vulnerability of converter.The existing methods for judging CF are subject to influence of fault factors and control adjustments,resulting in the insufficient sensitivity of the methods.Accurate and reliable detection of CF is extremely important to control and protection.Therefore,the paper proposed a detection scheme for CF based on temporal feature of AC maximum current on the valve-side starting from detecting the valve conduction interval.Firstly,the characteristics of AC maximum current was constructed based on the ratio between the unilaterally polarity current of AC current on the converter terminal and the half of the maximum value of the three-phase AC current.Secondly,to reduce the impact of operating conditions,taking the current intersection of two commutating valves currents as the demarcation point,the virtual conducting state of the valve was constructed by using half of the amplitude of the characteristic quantity of AC maximum current,and the accumulated width was calculated by integrating it in a period to determine whether the virtual conducting state of the valve is abnormal.Then,the interlocking relationship between the lengthened and shortened virtual conduction width was used to determine the commutation failure during the commutation process.According to the analysis of power disturbance,fault transiency and the sampling step,the threshold for commutation failure was derived.The recommended threshold value is 1.3 millisecond.Finally,based on the PSCAD/EMTDC electromagnetic transient simulation and wave recorded data,the results show that the proposed detection method is reliable to detect commutation failure.Compared with the detection method based on differential current,the proposed method for detecting commutation failure is less affected by factors,such as operating conditions of AC and DC system,fault moment,and fault severity under different fault conditions.This proposed method can locate the valve of commutation failure and provides more margin for the adjustment of the control system.