An Improved 3L APF Control Strategy Utilizing the Oscillated DC-Link Voltage Command to Enhance the Harmonic-Compensation Performance

Given interactions exist between dc-link voltage oscillations and ac currents in three-level active power filters (3L APF), the output of the outer voltage loop will inevitably affect the current control loop, impairing the harmonic-compensation performance. In this article, the oscillated dc-link voltage command is utilized to enhance the harmonic-compensation performance. First, the dc-link voltage oscillations caused by ac current harmonics in 3L APF converters are mathematically analyzed and derived. Then, to eliminate the dc bias in the integration for calculating the oscillated dc-link voltage command, the multiple second-order generalized integrator frequency-locked loop is adopted and improved by combining with low-pass filters. And an improved 3L APF control strategy utilizing the oscillated dc-link voltage command is proposed to enhance the harmonic-compensation performance. Finally, the proposed 3L APF control strategy is verified by simulations and experiments, presenting an improved harmonic-compensation performance, and a fast dynamic performance of the dc-link voltage can still be guaranteed.