提高LCL型并网逆变器对电网阻抗鲁棒性的阻抗调节方法

A Grid Impedance Shaping Method to Improve Robustness of LCL-type Grid-connected Inverter Against Grid Impedance Variation

电容电流反馈有源阻尼是解决LCL型并网逆变器谐振影响的有效途径。然而,当逆变器采用数字控制时,数字控制引入的控制延时会影响电容电流反馈的阻尼效果,导致并网逆变器对电网阻抗的鲁棒性变差。该文提出一种在公共耦合点并联RC支路的电网阻抗调节方法,使调整后的电网阻抗与并网逆变器的输出阻抗始终满足基于阻抗的稳定性判据。所提出的电网阻抗调节方法能够确保并网逆变器适应电网阻抗宽范围变化,且具有实现简单、可靠性高、成本低、引入的损耗小等优点。最后,在一台6 k W的实验样机上做了实验验证,实验结果验证了理论分析的正确性。

Capacitor-current-feedback active damping is an effective way to damp the resonance of LCL-type grid-connected inverter. However, when the inverter adopts digital control, the damping effect would be weakened by the control delay caused by digital control, thus the robustness of inverter against grid impedance variation becomes worse. A grid impedance shaping method is proposed in this paper which is achieved by adding a resistor and capacitor in parallel with the grid impedance at the point of common coupling, to ensure that the shaped grid impedance and output impedance of inverter always satisfy the impedance-based stability criterion. With the proposed method, the grid-connected inverter can be adapted to the wide variation of grid impedance. And the method has the advantages of simple realization, high reliability, low cost and small power losses. Finally, the theoretical analysis is validated by experimental results from a 6 k W LCL-type single-phase grid-connected inverter.