适用于不对称情况的线换相换流器动态相量模型

Dynamic Phasor Model of Line Commutated Converter Under Unbalanced Conditions

为满足大规模交直流输电系统快速精确仿真的需求,采用动态相量法对不对称情况下的线换相换流器进行建模。首先分析不对称情况下换流器的实际触发及换相原理,提出计及换流器交流侧3次谐波、直流侧2次谐波时的触发角和换相角计算方法,改进传统的换流器开关函数,在此基础上,通过忽略不必要次项建立适用于不对称运行情况的计及低次非特征谐波的换流器动态相量模型,以简化模型的计算过程。将其应用于Cigre-Benchmark标准直流系统,与PSCAD仿真结果对比,结果表明模型准确有效。基于改进开关函数模型,进一步判断换相失败与否,结果表明计及交流侧3次谐波以及直流侧2次谐波能更准确有效地判断换相失败。

To meet the need of rapid accurate simulation of the large-scale AC/DC hybrid power system, dynamic phasor method is applied to a model of line commutated converter under unbalanced conditions. Firstly, the principle of switching instants and commutation under unbalanced conditions is analyzed. A calculation method for triggering angle and commutation angle considering the third harmonic at AC as well as the second harmonic at DC is established. The traditional switching function model is improved for unbalanced conditions. Also, calculation process is simplified by ignoring non essential harmonics, and an advanced dynamic phasor model for the line commutated converter, which is suitable for normal operating and unbalanced conditions, is proposed. Based on the Cigre-Benchmark DC system, the model has been compared with the simulation results from PSCAD, and the result shows the effectiveness of the model. Based on the improved switching function model, the failure of the commutation is further determined. The result shows that the failure of the commutation can be determined efficiently by considering the second harmonic at DC and the third harmonic at AC.