Prevention of Traction Drives Stator Insulation Faults Based on Overvoltage Reduction Utilizing Active Edge Shaping

Modern inverter-fed traction drives frequently operate near and even above their rated values leading to high strains on the machine and especially on its winding insulation system. With new emerging semiconductor technologies higher inverter switching frequencies will be possible and high inverter dv/dt rates appear, resulting in transient overvoltages at the machine stressing the insulation system. A strategy to avoid/minimize such overvoltages is proposed by active edge shaping of the inverter. The semiconductor switches (IGBTs) are driven by a feedforward gate current profile which is adaptively modified cycle-by-cycle such that finally a Gaussian-shaped reference switching profile of the inverter's output voltage is achieved. First, experimental results of this concept tested at a 1.4MW induction machine for railway application are presented. Additionally, a brief overview of the characteristics and parameters influencing the overvoltage oscillation at the stator winding of inverter-fed machines will be given.