Synchronized Hybrid PWM for High Power IM Drives Operated in Vector Control Mode

Railways propulsion system deploys high power induction motor (IM) drives (≥ 750 kW). On account of high voltage and current levels, motor drive suffers from high switching energy losses. Thus switching frequency ( f
sw
) is restricted below 500 Hz for such motor drives to curb the switching energy losses. Constant f
sw
asynchronous sine triangle (AST) pulse width modulation (PWM) results into poor thermal and steady state performances in low and high fundamental frequency (f
1
) zones, respectively, for these motor drives. Traditional synchronous sine triangle (SST) PWM improves the overall thermal performance. However SST PWM leads to high total harmonic distortions in line current (I
THD
) over moderate and high f
1
zone where pulse number ( P, ratio of f
sw
and f
1
) comes below 9 (e.g. P =7, 5). This paper proposes a hybrid PWM which consists of AST and SST PWMs in the low f
1
zone and optimized PWM for moderate and high f
1
zones while restricting the maximum f
sw
below 350 Hz. Proposed hybrid PWM is shown to have superior thermal and steady state performances over complete range of f
1
. This paper also discusses about the implementation of proposed hybrid PWM in vector controlled IM drives. Simulation results presented in the paper pertaining to two level VSI fed 850 kW, 2.2 kV, 65 Hz IM validate the theoretical findings.