Design considerations for six pulse and twelve pulse dioderectifier systems operating under voltage unbalance and pre-existingvoltage distortion with some corrective measures

摘要

In this paper design considerations for six pulse and twelve pulsediode rectifier systems operating under utility voltage unbalance andpre-existing harmonic voltage distortion is discussed. For a six pulsediode rectifier system it is shown that voltage unbalance andpre-existing voltage distortion in the utility generatesuncharacteristic harmonics in the line currents. The amplitude of theseuncharacteristic harmonics are shown to be amplified if the dioderectifier is operating in discontinuous conduction mode. For a twelvepulse diode rectifier system connected in parallel to feed a common DClink via interphase reactor it is shown that a small amount of impedancemismatch, utility voltage unbalance or pre-existing voltage distortiondrastically affects the current sharing capability of the rectifierbridges. This in turn generates additional uncharacteristic andcharacteristic harmonics thereby increasing the THD. In order tomitigate these effects and ensure proper operation of diode rectifiers,specially designed line reactors termed as harmonic blocking reactors(HBRs) are introduced The analysis and design procedure for the HBRs arediscussed. Simulation results illustrate improved performance.Experimental results from a laboratory prototype system show closeagreement with theory