DESIGN CONSIDERATIONS FOR 12-PULSE DIODE RECTIFIER SYSTEMS OPERATING UNDER VOLTAGE UNBALANCE AND PREEXISTING VOLTAGE DISTORTION WITH SOME CORRECTIVE MEASURES

In this paper design considerations for 12-pulse diode rectifier syste ms operating under utility voltage unbalance and pre-existing harmonic voltage distortion are discussed, For a 12-pulse diode rectifier syst em connected in parallel to feed a common de link via an interphase tr ansformer it is shown that a small amount of impedance mismatch, utili ty voltage unbalance or pre-existing voltage distortion drastically af fects the current sharing capability of the rectifier bridges, This in turn generates additional uncharacteristic and characteristic harmoni cs thereby increasing the THD, In order to mitigate these effects and ensure proper operation of diode rectifiers, specially designed line r eactors termed Harmonic Blocking Reactors (HBR's) are introduced, The analysis and design procedure for HBR's are discussed, Simulation resu lts illustrate improved performance, Experimental results from a labor atory prototype system show close agreement with theory.