Abstract
In variable speed drive systems, diode rectifiers or thyristor rectifiers are usually used as the AC/DC front-end. The advantages of the conventional rectifier include low cost, simplicity, and high reliability. However, these rectifiers draw significant harmonic current from the utility grid and lack regeneration capability. Industry standards, such as IEEE-519 and IEC-61000-3-2, are adopted to address these issues. Recently, Insulated Gate Bipolar Transistor based active front-end (AFE) converter systems are widely utilized by industries thanks to the advantages of bi-directional power flow, unity power factor, low harmonic distortion of the line current and small filter size. This dissertation presents a synchronous reference frame based model for AFE converter and discusses in detail how the control design affects the disturbance rejection capability and robustness. While achieving high-power factor operation and regeneration capability, however, AFE converters cost much more than diode rectifier front-ends. Therefore this dissertation proposes an auxiliary converter (AXC) for the diode rectifier front-end system. The AXC and diode rectifier are connected in parallel on the AC side. Both are also connected on the DC side via diodes. The AXC system operates as a shunt active filter to compensate for current harmonics of the diode rectifier, and provides regeneration capability. Thus it can accomplish the functionalities of an AFE converter, but with only 0.3-0.5 pu of converter rating. The simulation results and experimental results are used to validate the performance of the AFE and AXC converter system. Keywords: active filter, active front-end converter, auxiliary converter