中文摘要：

针对接入弱交流电网的电压源换流器（voltage sourced converter,VSC）所采用的无功类控制器的适用性进行分析,并提出了改进的无功功率控制方法。首先针对连接到弱交流电网的VSC整流侧和逆变侧系统,分别建立了两个系统在定有功功率定无功功率控制和定有功功率定交流电压控制下的小信号模型,其次利用参与因子法分析影响主导极点的主要状态变量,基于此提出了一种改进的无功功率控制方法,分别在VSC整流侧和逆变侧系统中进行验证,并分析了参数k的选取。最后,在PSCAD/EMTDC环境下进行仿真实验,验证了建立的小信号模型正确性,同时,考虑VSC系统运行极限分析了不同无功类控制下系统的临界有功功率传输极限值。所得结论为：对于连接到弱交流电网的VSC类换流器,定交流电压控制较定无功功率控制更适用于极低短路比（short-circuit ratio,SCR）的交流系统,在选取合适的参数k的条件下,采用改进的无功功率类控制可以提高有功功率传输极限,更有效地增强系统稳定性。

英文摘要：

Applicability analysis of reactive power controllers used in Voltage Source Converter（VSC） connected to weak AC grid is discussed and an improved reactive power control method is proposed in this paper. Firstly, rectifier/inverter system of VSC in weak AC grid is investigated, and small signal equivalent models of the two systems with constant active/reactive power control and constant active/AC voltage control are established respectively. Secondly, main physical parameters influencing dominant poles are analyzed with participation factor method, and then an improved reactive power control method proposed. The paper verifies the method in rectifier and inverter systems respectively, including analysis of parameter k selection. Finally, simulation models are established in PSCAD/EMTDC environment. Contrast between simulation and theoretical analysis verifies validity of small signal models. Considering operating limit of VSC system, critical active power transfer limits of the systems under different reactive power controls are analyzed. It is concluded that for VSC connected to weak AC grid, constant AC voltage control is more suitable for low SCR condition than reactive power control. With proper parameter k selection, both rectifier and inverter side systems with improved reactive power control are able to enhance critical active power and improve system stability effectively.