Integrating Voltage-Source Active Filters Into Grid-Connected Power Converters—Modeling, Control, and Experimental Verification

More demanding harmonic limits of future grid standards are likely to aggravate the disadvantages associated with the use of passive filters in high-power converters. These include substantial additional losses, a large footprint, and a considerable, power factor dependent voltage drop. For this reason, active filters (AFs) are an increasingly attractive alternative for reducing converter-induced harmonics; however, their performance is often subject to a limited frequency range and a frequency-dependent attenuation. To further improve the potential of AFs for use with grid-connected power converters, this article presents a novel control scheme for a parallel voltage-source AF integrated into a high-power main converter. A detailed converter analysis shows that, due to the advantageous converter configuration, the AF requires only fundamental frequency current control to mitigate converter-induced current harmonics. In contrast to conventional AF applications, this avoids tuning to specific frequencies, identification of individual harmonics, and measurement of high-frequency current ripple and high control bandwidth. The control design is carried out with the aim of minimizing the AF current load in steady state and transient operation. As shown by simulation results, the AF thus allows the mitigation of harmonics up to frequencies above the switching frequency of the main converter at only a small share of the total power and with small passive components. Finally, the hybrid converter is compared to LCL-filter based converter systems and the effectiveness of the presented control scheme is verified experimentally using a silicon carbide demonstrator.