多端柔性直流接入对交流系统功角稳定性的影响

Angular Stability of Power Systems Integrated With VSC-MTDC Grid

针对多端柔性直流电网（multi terminal direct current network based on voltage source converter,VSC-MTDC）接入对交流电力系统小干扰功角稳定性影响的问题。通过建立交直流混联系统的线性化互联模型,采用分解的思想得到了VSC-MTDC接入主要在2个方面影响交流系统小干扰功角稳定性：一是改变了交流系统的潮流,二是与交流系统的动态交互作用。采用阻尼转矩分析的结果表明：交直流系统之间动态交互的影响一般很小,直流系统接入主要是改变了交流系统的潮流,可等效为恒功率源进行研究。针对＂潮流＂部分的影响,进一步分解为直流电网的注入功率和接入地点2个部分,提出并研究了以下2个猜测：1）输入功率变化等效于发电机出力改变,二者对交流系统小干扰功角稳定性的影响是一致的;2）直流电网接入地点在平衡机附近时对交流系统小干扰功角稳定性造成的影响是较小的。以新英格兰系统为例,通过计算和仿真演示验证了上述猜测,并可借此避免多端柔性直流电网接入对交流电力系统小干扰功角稳定性的不利影响。

This paper investigates small-signal angular stability of AC power system affected by an integrated multi-terminal DC （MTDC） network. An interconnected linearized model of AC/MTDC system is established. The model clearly shows that MTDC affects small-signal angular stability of AC system by introducing changes in dynamic interactions and load flow. Dynamic interactions are usually small according to damping torque analysis. Impact of load flow change brought by MTDC is the primary factor. Considering power flow change related to DC power injection and its location in AC system, this paper proposes following two ideas： 1. The DC power change is balanced by balance machine in AC system, so impact of DC power injection on AC system is equal to the impact of balance machine; 2. The impact of DC power injection on AC system may be smaller when location of DC system is near the balance machine with smaller power flow change. Above ideas, avoiding adverse effect on angular stability of AC system, are demonstrated and verified with calculation and simulation with New England System as an example.