Sungjoon Cho, Ho-Sung Kang, Kyo-Beum Lee, and Ji-Yoon Yoo, "Performance Improvement of a Grid-Connected Inverter under Distorted Grid Voltage Using a Harmonic Extractor," Electronics, vol. 8, no. 1038, pp. 1–21, Sep. 2019. -SCIE > Paper

This paper introduces an improved current control strategy for a grid-connected inverter system operating under distorted grid

voltage conditions. Although existing current controllers for grid-connected inverters have proportional integral gains with suitable

bandwidth, low-order harmonic components can be generated by distorted grid voltages. The proposed improved current controller

is established in a synchronous reference frame that rotates at harmonic frequency. The input signals for the harmonic current

controller should contain only the specific harmonic components requiring suppression. Therefore, the proposed current controller

uses a harmonic extractor to distinguish current signals from fundamental and specific harmonic components. The harmonic extractor

retains only the relevant harmonic components for individual current controllers with high harmonic signal ratios. This paper

introduces two different strategies to extract specific harmonic components for the current controller. The proposed control strategy

does not require any additional hardware filter circuits and can be implemented easily by designing a suitable digital filter. When

using the proposed method, grid current quality is significantly improved compared to conventional methods that do not include

harmonic extractors. The effectiveness of the proposed method is verified through simulations and practical experiments.