Stability Enhancement of Grid-Connected Inverters Using Weighted Average Current Control Method

Among different factors that threaten the stability of LCL-filtered inverters in grid-tied mode, the variation of grid impedance and computational delay in digital systems are the most important ones. Often, a control system based on either the inverter- or grid-side current and a combination of impedance estimation and delay compensation methods are used to deal with these challenges. Such control systems are quite effective, however, they often involve a quite high implementation complexity. Especially, computational and PWM delay causes a critical frequency, which may deteriorate the stability conditions in grids with varying grid impedance. To deal with this challenge, a robust approach based on a weighted average current control method is proposed in this paper. The suggested control system employs the point of common coupling (PCC) voltage as a control variable, which increases the system stability in weak grids. Thus, the control system does not need any delay compensation or grid impedance estimation methods, which in turn, simplifies the control system. The effectiveness of the proposed method is examined using the experimental results in different case studies.