Optimal Interleaved Phase-Disposition PWM for Paralleled Cascaded H-Bridge Inverters

This paper generalizes the analytical expressions of the voltage harmonics induced by paralleled cascaded H-bridge (CHB) inverters operating with interleaved PWM for the two most relevant carrier signals phase-shift angle θ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (π/N and 2π/N). In accordance with the international standards such as API 617, the expressions of the induced torque harmonics have been also derived for torsional analysis purposes. In high-power applications such as oil and gas, optimizing the system performance can lead to substantial economic saving. As a result, a performance comparison is conducted based on the voltage and current THDs as well as the motor torque ripple to identify the optimal θ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> for such systems. The simulations carried out on 10MW induction motor driven by 2-paralleled 7-level CHB inverters validate the accuracy of the proposed expressions. Furthermore, the IPWM with θ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> = 2π/N provides the best power quality performances for such systems due to suppression of the most significant voltage harmonics in the point of common coupling of paralleled inverters.