Capacitance Requirement Reduction in Single-Phase PFC With Adaptive Injection of Odd Harmonics

This article presents an adaptive harmonic injection approach for single-phase power factor correction (PFC) converters that reduce capacitance requirements and allow the use of smaller and more reliable film capacitors instead of electrolytic capacitors. Many applications require the converter's rated power only during temporary intervals, whereas most of the time, the output power is much lower. In the proposed approach, the converter operates with a unity power factor below a given output power level. When the output power exceeds this value, then odd harmonics are linearly injected into the input current reference, up to the limits presented by IEC 61000-3-2. This approach reduces the voltage ripple across the power ripple buffering capacitor (PRBC), reducing the required capacitance value. The proposed approach is applied to the theta-converter using enhanced automatic power decoupling (EAPD) control. The dynamic model to control PRBC average voltage is presented. A 1-kW prototype is built to validate the approach using a metalized polypropylene film capacitor as the PRBC. At full power, injecting third and fifth harmonics, the PRBC capacitance can be reduced from 22 to 15 mu F or 32%. It represents a further reduction in capacitance requirements for a converter that already requires low capacitance.