考虑锁相环影响的多逆变器并联接入弱电网稳定性分析

Stability analysis of multi-inverter parallel access to weak power grid considering the influence of phase-locked loop

锁相环在经逆变器并联接入电网时,对确保并网电流与电压保持同步有着至关重要的作用。且在弱电网下电力电子设备的自身动态及其与电网的相互作用明显引发复杂的稳定性问题。文中从多逆变器并网的控制系统出发,建立了计及锁相环、电流调节器等控制环节影响的阻抗分析模型,考虑了各个逆变器对其它逆变器及其与交流电网之间的相互影响,提出了多组逆变器并网的阻抗稳定性判据。分析了随着电网强度、锁相环参数及逆变器数目的变化对系统稳定裕量的影响,并根据所得稳定性判据给出了不同电网强度下可以并联的最大逆变器数目,最后在PSCAD上搭建多个逆变器并联接入弱电网的模型,验证了所得结果的正确性。

The phase-locked loop plays a vital role in ensuring that the grid-connected current and voltage are synchronized when the inverter is connected in parallel to the grid.The dynamics of the power electronics and its interaction with the power grid under the weak grid are obviously complicated,which will cause stability issues.Starting from the control system of multi-inverter grid-connection,an impedance analysis model considering the influence of control loops such as phase-locked loop and current regulator is established.Considering the influence of each inverter on the other inverters and other AC power grids,the impedance stability criterion for grid-connected multi-inverters is proposed.The influence of grid strength,phase-locked loop parameters and the number of inverters on the stability margin of the system is analyzed.According to the obtained stability criterion,the maximum number of inverters that can be connected in parallel under different grid strengths is given.Finally,a model of multiple inverters connected in parallel to the weak grid was built on PSCAD to verify the correctness of the results.