BPF-based Grid Voltage Feedforward Control of Grid-connected Converters for Improving Robust Stability

Abstract

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter's robust stability against grid impedance variations. The selection method of the BPF's bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system's robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

Admittance Remodeling Strategy of Grid-Connected Inverter Based on Improving GVF

“…GVF control can suppress the background harmonics of the grid voltage and improve the quality of the grid current, and, thus, it has been widely used in grid-connected inverters [16][17][18]. However, grid voltage feedforward can reduce the adaptability of gridconnected inverter systems to a weak grid [19,20]. The literature [21][22][23] has pointed out that the feedforward branch can reduce the stability margin of the grid-connected inverter under weak grid conditions, and may lead to harmonic instability in the grid-connected current.…”