弱电网条件下基于阻抗的稳定性判据重塑

Reconstruction of Impedance-Based Stability Criteria in Weak Grid

弱电网条件下电网阻抗所具有的不确定性以及宽范围变化特性会严重影响逆变器并网系统的控制性能,甚至可能导致系统不稳定。当前利用电网阻抗与逆变器等效输出阻抗的比值来判定系统是否稳定的阻抗分析法,虽然在一定条件下可以判定逆变器并网系统的稳定性,但存在表征系统稳定性裕度不准确,以及当逆变器控制参数发生变化时可能导致的传统基于阻抗的稳定性判据不再适用的问题。针对上述传统阻抗分析法存在的不足,对传统基于阻抗的稳定性判据进行了重塑,重塑后基于阻抗的稳定性判据不仅能够精确表征系统的稳定性裕度,而且对变参数控制并网逆变器也具有普适性,保持了阻抗分析法的优良特性。最后,在弱电网条件下,以三相LCL型滤波的并网逆变器模型为基础,通过仿真分析验证了文中理论分析的正确性与重塑方案的可行性。

Uncertainties and wide range variation characteristics of grid impedance in a weak grid can seriously affect control performance of grid-connected inverter system, and even cause the system unstable. At present, impedance-based analysis using inverter output impedance and grid impedance is adopted to study the inverter-grid system stability. However, using this method to represent system phase margin（PM） is inaccurate. What＇s worse, stability criteria based on traditional impedance may be inapplicable when the inverter control parameters are changed. In order to overcome above shortcomings of traditional impedance analysis method, its stability criterion is reconstructed. The impedance-based stability criterion after reconstructing can not only accurately represent system stability margin, but also apply to variable-parameter-controlled grid-connected inverter system. Finally, by establishing grid-connected inverter model with LCL filter under weak grid condition, correctness of theoretical analysis and validity of the reconstructing method are verified with simulations.