Control Schemes for Reducing the Second Harmonic Current in Two-Stage Single-Phase Converter: An Overview from DC-Bus Port-Impedance Characterization

摘要

The instantaneous input and output power of the single-phase converter are imbalanced, resulting in second harmonic current (SHC). This paper provides an insight for reducing the SHC in two-stage single-phase converter from the perspective of the dc-bus port-impedance characterization. It is found that the dc-dc converters in the two-stage single-phase converter can be categorized into two types. One is operating as a bus-voltage-controlled converter (BVCC) whose dc-bus port-impedance is approximately inverse-proportional to the voltage loop gain. The other is operating as a bus-current-controlled converter (BCCC) whose dc-bus port-impedance is a negative resistor. Based on the dc-bus port-impedance characterization, critical points for SHC reduction are summarized, indicating that, for reducing SHC in BVCC, proper control scheme needs be incorporated for increasing the dc-bus port-impedance at twice the input frequency (2fin) or output frequency (2fo); concurrently, the dc bus voltage ripple should be limited for reducing the SHC in the dc source or load; by contrast, for reducing SHC in BCCC, the dc bus voltage ripple should be reduced; simultaneously, the loop gain at 2fiin or 2fo should be high enough for eliminating the SHC in the dc source or load. Thereafter, proper SHC reduction approaches are recommended for different types of two-stage single-phase converters, and pros and cons of different SHC reduction schemes are carefully reviewed. Finally, potential challenges and issues related to this research topic are discussed.