Ultra-Fast Dynamic Response and Current Harmonic Reduction in PFC Applications

This article introduces a digital zero crossing voltage control (ZCVC) strategy designed for general power factor correction (PFC) applications. The ZCVC approach performs voltage control calculations and updates the current reference precisely at input voltage zero-crossings. This timing ensures that the control output remains constant for each half-grid cycle, resulting in a pure sinusoidal ac current waveform. This method effectively eliminates second harmonic distortions in the bus voltage without requiring a notch filter (NF), thereby reducing even harmonics from the RMS filter. ZCVC offers a significantly faster dynamic response, achieving stability within 1.5 grid cycles during load changes, input voltage fluctuations, or step changes in output voltage reference. This preserves a power factor close to unity and results in very low total harmonic distortion. Furthermore, the proposed ZCVC considerably reduces the computational burden on the microcontroller by minimizing the execution of the digital voltage loop controller per grid cycle, thereby eliminating the need for NFs. The mathematical average model of the ZCVC is derived for general PFC applications. Various scenarios are simulated to validate the effectiveness of this method compared to prior approaches. The implementation of ZCVC on a 7.2 kW GaN-based interleaved totem pole PFC confirms the claimed improvements, demonstrating four times faster dynamic response and very low harmonic distortion. Additionally, the ZCVC reduces voltage sampling and control computations from a typical range of 200 times per grid cycle to only two times, achieved by eliminating the need for notch and low-pass filters.