Topologies and control of single-phase low harmonic rectifiers

High-frequency switching power converters can be constructed to perform ac line voltage rectification with low line current harmonics and a power factor close to one. In a power-factor-corrected (PFC) low-harmonic rectifier designed for universal-input operation, the wide range of ac line voltages imposes substantial voltage and current stresses on passive and active components of the rectifier. Circuit topologies and control techniques aimed at reducing the stresses and improving performance of universal-input PFC rectifiers are addressed in this thesis.; Converters operating in the boundary conduction mode (BCM) offer optimized current stresses and magnetic size, and provide inherent power factor correction without the need for a current regulation loop. BCM converters for dc-dc and ac-dc applications are analyzed and modeled to understand large-signal steady-state features and small-signal dynamic characteristics.; A switchable converter topology can switch between a single-switch buck-boost converter (flyback or SEPIC) and a boost converter, for high-line and low-line input respectively, such that (1) the output voltage can be set to a value higher than the peak low line voltage, (2) worst-case low-line current stresses are significantly reduced by using the boost topology and the reduced output voltage. Switchable topologies operating in the boundary conduction mode offer high performance, simple and low-cost solution for universal input rectifiers. Combined design considerations of BCM switchable topologies in terms of component stresses, switching frequency distribution and output voltage regulation are presented.; In addition to the use of a one-time or slow switch as in the switchable topologies, power converter topologies with two completely controllable switches are also investigated. A two-switch converter can function as a boost or as a buck depending on the input/output operating conditions. Families of two-switch buck-boost converters that can achieve minimum indirect energy delivery are generated through a synthesis method based on ac and do equivalent circuits [1]. One of the new two-switch buck-boost converters (boost-interleaved buck-boost, or BoIBB) is identified with switch stresses significantly smaller than in other two-switch buck-boost and conventional single-switch converters, and with lower copper losses and smaller magnetic size compared to the boost converter. The operating modes and control of the BoIBB converter as a universal-input rectifier are suggested and experimentally verified, demonstrating low input current harmonics and high efficiency over the entire ac line input voltage range.; Digital control techniques are proposed to improve dynamic performance of low-harmonic rectifiers. It is shown how predictive digital current programmed control, which takes into account sampling and processing delays, can achieve fast input current regulation. A prototype boost PFC rectifier operating at the switching frequency of 100 KHz or 200 KHz is constructed using a DSP system to implement the predictive average current control. Very low total harmonic distortion of the input line current is demonstrated even in the case when the rectifier is supplied from a high-frequency (400–800 Hz) line voltage typical for avionics power systems.