In order to improve the quality of the grid with large-scale power electronic equipment

grid-forming converters have been rapidly developed

and the ability to actively improve the power quality of the grid should be a critical characteristic. However

it is difficult to solve the harmonic suppression problem in a distorted grid through modifications of traditional grid-following control methods due to the underdeveloped grid-forming control technology. To improve the waveform quality of the grid

this paper proposes the harmonic current active mitigation method based on a grid-forming converter for a distorted grid. First

the harmonic characteristics of the grid-forming converter under a distorted grid are analyzed

and the harmonic impedance equivalent model is established. Then

a compensation control method for voltage distortion of the grid side is proposed. The phase of the compensated voltage source in a distorted grid is determined by vector optimization without any additional sampling

and the harmonics generated by the converter in the distorted grid can be decreased. Furthermore

a coordinated control combining voltage distortion compensation and impedance reshaping is developed to suppress the harmonic contents injected into the grid by other harmonic sources

such as system loads. Finally

the effectiveness of the proposed method and its superiority over traditional methods are validated through hardware experiments of a 10 kW three-phase inverter which is driven by a digital signal processing (DSP) digital controller.