基于控保协同的光伏直流升压汇集系统直流故障判别方法

光伏直流升压汇集系统由于内部直流变压器间特殊的串联形式,正常运行时直流变压器汇集端口电压、电流随光伏单元出力变化而波动,当在系统出力较小且直流侧发生较大过渡电阻故障时,故障特性与正常运行出力波动的暂态过程类似,系统故障特征不明显,保护难以实现故障的准确识别。针对上述问题,设计了基于控保协同的无通信直流故障检测方案。在分析直流变压器谐波产生机理的基础上,通过改变其载波频率产生谐波扰动,并根据谐波流通路径差异实现对系统故障工况的可靠检测。PSCAD仿真结果表明,所提方法仅利用换流器本地量测信息即可实现汇集系统直流故障的可靠识别且不受光伏出力影响。

Control and Protection Coordination Based Identification Strategy of DC Fault for Photovoltaic DC Boosting Integration System

Due to the special series connection form of the DC transformers in photovoltaic(PV)DC boosting integration system, the voltage and current of the collecting port of DC transformer will fluctuate with the PV panel outputs in normal operation. When the high-impedance fault occurs and the system output is very low, and fault characteristics are similar to the transient process of normal operating output fluctuations. So the system fault characteristics are unobvious and the protection configured on the DC transformer port is difficult to identify the fault effectively. A DC fault identification strategy based on the coordinated control and protection is designed to solve the above problems. On the basis of analyzing the harmonic generation mechanism of DC transformer, the harmonic disturbance is generated by changing its carrier frequency, and working condition of system fault can be quickly identified according to the difference of the harmonic flow paths. The simulation results of PSCAD show that the proposed method can reliably determine the DC fault of integration system only by using the local measurement information of the inverters, which is not affected by PV outputs.