An Improved Current Controller with a Ramp-Based Adaptive Factor for Three-Phase LCL-Type Grid-Connected Inverter

Due to non-linear effect or distorted grid voltage of three-phase LCL-type grid-connected inverter for PV application, the injected-grid current has large low-order harmonic components. Thus, a typical current controller based on Proportional Integral and Resonant (PIR) type is utilized to overcome the low-order harmonics issue in synchronous reference frame. However, the conventional PIR current controller may bring dynamic performance because of slow response resonant part. To address this problem, an improved PIR current controller with a ramp-based adaptive factor is proposed. Moreover, the parameters design process is also given. To evaluate the proposed controller in detail, the Bode diagrams of the inverter's open loop transfer function under different factors are also presented. It can explain the faster dynamic essence of the proposed controller than that of the conventional controller. Finally, simulation and experimental results are given to verify the effectiveness and feasibility of the proposed controller.