两电平电压源型换流器负阻性与容性效应特征指标研究

为评估两电平电压源型换流器(VSC)并网系统的谐振不稳定风险,定义了4个描述两电平VSC负阻性与容性效应的特征指标.首先,基于简化等效电路,通过奈奎斯特稳定判据论证了VSC负电阻引起谐振不稳定的简单机理.然后,通过分析两电平VSC的交流侧扰动响应特性建立其端口阻抗模型.在此基础上,通过简化分析建立VSC端口电阻和端口电抗的宽频近似模型;据此定义了VSC负阻性与容性效应的特征指标,并对其影响因素进行了分析.最后,通过电磁暂态仿真验证了宽频近似模型的准确性和特征指标的有效性.算例分析表明,文中提出的特征指标可以定性评估两电平VSC并网系统的谐振不稳定风险.

Research on Characteristic Indices for Negative Resistive and Capacitive Effect of Two-level Voltage Source Converter

To evaluate the resonance instability risk of the two-level voltage source converter (VSC) grid-connected system, four characteristic indices describing the negative resistive and capacitive effect of the VSC are defined. Firstly, based on the simplified equivalent electrical circuit, the simple mechanism of the resonance instability caused by the negative-resistance of the VSC is illustrated by the Nyquist stability criterion. Then, the AC-side disturbance response characteristics of the two-level VSC are analyzed to build its port impedance model. On this basis, the broad-band approximate model of the port resistance and port reactance of the VSC is established through simplified analysis. Furthermore, the characteristic indices describing the negative resistive and capacitive effect of the VSC are defined and their influencing factors are analyzed. Finally, the accuracy of the broad-band approximate model and the effectiveness of the characteristic indices are verified by electro-magnetic transient simulation. Case studies indicate that the resonance instability risk of the two-level VSC grid-connected system can be evaluated qualitatively through the proposed characteristic indices.