Magnitude-Reshaping Strategy for Harmonic Suppression of VSG-Based Inverter Under Weak Grid

Abstract

Driven by inertial demand from the grid, the virtual synchronous generators (VSGs) are widely utilized in distributed generation systems. However, harmonic sources in the distributed generation systems with high grid impedance will cause grid voltage distortion. Distorted voltage greatly affects the power quality of VSG. Moreover, it is difficult to suppress different types of harmonics (such as sub-synchronous harmonics and non-integer high-frequency harmonics) by one conventional solution in VSG-based grid-connected system. To solve the problem, this paper proposes a magnitude-reshaping strategy to increase the output impedance in all harmonic-frequency-bands, thereby suppressing the harmonics. The magnitude-reshaping strategy consists of a notch filter and harmonic regulator. The notch filter extracts harmonic components of grid current, whereas the harmonic regulator increases the equivalent harmonic impedance. The equivalent harmonic circuit of reshaped VSG-based system is equivalent to open circuit. Therefore, the power quality of grid-connected current can be guaranteed. To analyze the performance of the magnitude-reshaping method, frequency-coupling impedance model of VSG is established. Furthermore, Comparing with the conventional harmonic suppression methods, the frequency response characteristics of the equivalent harmonic impedance are analyzed. Finally, the effectiveness of proposed control strategy is validated by experiment results.

Keywords

• Virtual synchronous generator
• weak grid
• magnitude-reshaping
• harmonic suppression
• frequency-coupling impedance model