LCL型并网逆变器组合滤波前馈控制策略研究

COMBINED FILTERING FEEDFORWARD CONTROL STRATEGY FOR LCL-TYPE GRID-CONNECTED INVERTERS

不同于强电网,弱电网下的电网电压有复杂的背景谐波和时变性的线路阻抗,传统的PCC电压前馈由于引入电网的网侧电流从而会降低系统的稳定性。针对上述情景,提出组合滤波前馈的控制策略,通过引入陷波器组抑制特定次数的背景谐波,同时适当提高低通滤波器的截止频率,保障系统的稳定性以及动态响应。网侧电流反馈的单环控制是组合滤波前馈控制策略中的关键技术,通过采用LCL滤波器滤除高频开关谐波,数字化的设计组合滤波器的相关参数,从而提高系统的稳定性。根据所提策略研制LCL型并网逆变器的实验样机,通过该样机实验验证,传统的PCC电压前馈方法在弱电网的环境下已完全失效,而所提出的组合滤波前馈控制策略仍能保持系统的正常工作,验证了该策略的有效性。

Different from the strong grid,the grid voltage under the weak grid has complex background harmonics and time-varying line impedance. The traditional PCC(point of common coupling)voltage feedforward will introduce additional grid side current,resulting in the reduction of system stability. In view of this situation,a combined filter feedforward method is proposed. Notch filter banks with specific harmonic times are introduced to suppress background harmonics. At the same time,the cut-off frequency of the low-pass filters is increased properly to improve system stability and dynamic response. For the above scenario,a combined filter feedforward control strategy is proposed to suppress background harmonics with specific times by introducing notch filter banks. The feedforward control strategy of combined filter is a single loop control based on network side current feedback. LCL filter is used to filt high-frequency switching harmonics,and the relevant parameters of combined filter are digitally designed,so as to improve the stability of the system.Based on this strategy,an experimental prototype of LCL grid connected inverter is developed. The prototype verification shows that under the weak current network environment,the traditional PCC voltage feedforward is failed,and the control strategy proposed in this paper can ensure the stable operation of the system. The effectiveness of the proposed strategy is verified.