314 IETE JOURNAL OF RESEARCH | VOL 54 | ISSUE 4 | JUL-AUG 2008 A 24-Pulse AC–DC Converter Employing a Pulse Doubling Technique for Vector-Controlled Induction Motor Drives Bhim Singh, Vipin Garg and Gurumoorthy Bhuvaneshwari Department of Electrical Engineering, Indian Institute of Technology, Delhi, New Delhi - 110 016, India. AbstrAct This paper deals with various multpulse AC–DC converters for improving the power quality in vector-controlled induc- ton motor drives (VCIMDs) at the point of common coupling. These multpulse AC–DC converters are realized using a reduced ratng autotransformer. Moreover, DC ripple reinjecton is used to double the rectfcaton pulses resultng in an efectve harmonic mitgaton. The proposed AC–DC converter is able to eliminate up to 21st harmonics in the supply current. The efect of load variaton on VCIMD is also studied to demonstrate the efectveness of the proposed AC–DC converter. A set of power quality indices on input AC mains and on the DC bus for a VCIMD fed from diferent AC–DC converters is also given to compare their performance. Keywords: Autotransformer, Multpulse AC–DC converter, DC ripple reinjecton, Pulse doubling, VCIMD. 1. INtroductIoN The advances in power semiconductor devices have led to the increased use of solid-state converters in vari- ous applications such as air conditioning, refrigeration, pumps, etc. employing variable frequency induction mo- tor drives [1]. These variable frequency drives generally use the three-phase squirrel cage induction motor as the prime mover due to its advantages like rugged, reliable, maintenance free, etc. These induction motor drives are mostly operated in a vector control mode [2] due to its capability of giving a performance similar to that of a DC motor. These drives are fed by a six-pulse diode bridge rectifer, which results in injection of harmonics in the supply current, thus deteriorating the power quality at the point of common coupling (PCC), thereby affect- ing the nearby consumers. To have a control on these harmonics, an IEEE Standard 519 [3] has been reissued in 1992, giving the benchmark for limiting current and voltage distortion. Harmonics can be reduced using different active or pas- sive waveshaping techniques. The active waveshaping techniques result in an increased loss, complex control and higher overall cost. The passive waveshaping tech- niques use passive flters consisting of tuned L–C circuits. However, they require careful application and may produce unwanted side effects, particularly in the pres- ence of power factor (PF) correction capacitors. The most rugged, reliable and cost effective solution to mitigate these harmonics is to use multipulse methods [4-12]. In multipulse converters, the autotransformer-based con- fgurations provide the reduction in magnetics rating as the transformer magnetic coupling transfers only a small portion of the total kVA of the induction motor drive. Various 12-pulse-based rectifcation schemes have been reported and used in practice for the purpose of line cur- rent harmonic reduction [7-12]. With the use of a higher number of multiple converters, the power quality indices show an improvement, but at the cost of large magnetics resulting in a higher cost of the drive. To achieve similar performance in terms of harmonic current reduction, DC ripple reinjection has been used [13-15]. This paper presents an autotransformer-based 24-pulse AC–DC converter with reduced rating magnetics. A pulse multiplication technique is used to improve various power quality indices to comply with the IEEE standard 519 [3]. The scheme needs two additional diodes along with a suitably tapped interphase reactor for increasing the number of pulses. This arrangement results in elimination up to the 21 st harmonic in the input line current. Moreover, the effect of load variation on the vector-con- trolled induction motor drive (VCIMD) is also studied. The proposed AC–DC converter is able to achieve near unity PF in a wide operating range of the drive. A set of tabulated results giving the comparison of different power quality parameters such as total harmonic distor- tion (THD) and crest factor (CF) of AC mains current, PF, displacement factor and distortion factor, and THD [Downloaded free from http://www.jr.ietejournals.org on Tuesday, September 08, 2009]