Why can SVG reduce THD, while capacitors increase THD?

SVG achieves harmonic suppression through a closed-loop control system of "detection-calculation-compensation." It incorporates a high-precision current sensor and a high-speed signal processor (DSP), based on a Fast Fourier Transform algorithm, to extract the amplitude and phase of grid harmonics in real time. Based on the detection results, it generates a compensation current command with the same amplitude but opposite phase as the harmonics. Finally, the compensation current is injected into the grid through an IGBT power module, canceling the original harmonic current vector and ultimately reducing THD.

 Capacitors lack harmonic handling capabilities. When their capacitive reactance is coupled with inductive components in the grid, they easily induce harmonic amplification. The inductive reactance Xl of transformers, motors, and other inductive components in the grid, together with capacitor Xc, forms an LC circuit. When the harmonic frequency approaches the inherent resonant frequency of the LC circuit, series and parallel resonances occur, causing a sharp amplification of harmonic current and voltage amplitudes, ultimately increasing THD.