增强并网逆变器对电网阻抗鲁棒稳定性的改进前馈控制方法

随着分布式电源并网功率的逐渐增加及接入点的广泛分布,电网越来越表现出弱电网特性,即电网阻抗相对较大,此时在并网逆变器中广泛应用的电网电压前馈控制会严重影响到系统的稳定性。以L型滤波并网逆变器为研究对象,采用框图等效变换的方法分析弱电网情况下前馈控制对并网逆变器特性的影响机理,以及电网等值电感和阻感比对系统稳定性的影响规律,并在电压前馈通道中引入一种带通滤波环节,提高弱电网下并网逆变器的鲁棒稳定性。分析表明,附加带通滤波环节的电压前馈控制可使得逆变器在短路比较小的弱电网中仍能够稳定工作。最后,搭建一台66k V·A并网逆变器实验样机,实验结果验证了理论分析的正确性和所提改进策略的有效性。

An Improved Grid Voltage Feedforward Strategy for Grid-Connected Inverter to Achieve High Robust Stability Against Grid-Impedance Variation

In the wake of the gradual increase in penetration of distributed power generation systems and the wide distribution of access points, the grid can't be treated as the ideal sinusoidal voltage source any more. Instead, it contains a large set of grid impedance values, featuring as a weak grid. In this case, the grid-voltage feedforward widely used in grid-connected inverter control will challenge the system stability. Taken the L-filtered grid-connected inverter as an object, the influence mechanism of the feedforward control on the inverter's characteristics in weak grid is clarified by the equivalent transformations of the control block diagram. Moreover, the effects of the inductance and the resistance-to-inductance ratio of grid impedance on the stability of grid-connected inverter are investigated. Furthermore, a band pass filter (BPF) is incorporated into the feedforward path, to improve the robust stability of the grid-connected inverter in weak grid. As a result, the grid voltage feedforward control with the BPF can ensure that the grid-connected inverter works stably in the weak grid with small short current ratio (SCR) range of the grid impedance. Finally, the experiments on a 66kW inverter prototype have verified the theoretical analyses and the effectiveness of the proposed improved method.