Study on Comprehensive Analysis and Compensation for the Line Current Distortion in Single-Phase Three-Level NPC Converters

Providing a sinusoidal line current with few low-order harmonics is important for power converters. First, the influence mechanisms of multifactors for the line current distortion in single-phase three-level neutral point clamped converters are analyzed in theory. Second, the corresponding compensation methods for various factors are discussed, respectively. Particularly, the phenomenon that deadtime effects on harmonics is revealed by the theoretical derivation of Fourier series, and a corresponding quantitative calculation method is proposed and used to solve the compensation component of the deadtime delay. The detailed and strict mathematical deduction provides an alternative theoretical system for the quantitative analysis and compensation of deadtime and forward voltage drops effects. As for the component to compensate the unsteady forward voltage drops, it is online computation with current variations. Then, a comprehensive distortion compensation method by injecting offset voltage in the modulated signal is proposed to improve the line current waveform quality. Finally, simulation results verify the correctness of the quantitative calculation of deadtime effect on harmonics, and experimental tests verify that the proposed method can effectively reduce total harmonic distortion and improve waveform quality of the line current.