Influence of PWM modulations on the DC-Link capacitor power losses of multiphase VSIs

Abstract

In traction applications, particularly in transport electrification, multiphase drives are increasingly being an interesting alternative over their three-phase counterparts due to a range of advantages outweighing the additional cost, e.g. smoother torque performance, higher current capability, enhanced fault tolerance, higher efficiency and lower DC-Link current ripples. This work focuses on the impact this multiphase drives modulated by continuous and discontinuous PWM techniques have in a such a pricey and bulky component as it is the DC-Link capacitor. Taking into account that the equivalent series resistance of the DC-Link capacitor varies with frequency, the typical approximated calculation of the power losses in this component by means of the RMS value of the current is often inaccurate. Therefore, the spectral analysis of the DC-Link current has been carried out for the five-phase two-level VSI in order to estimate more accurately the power losses in the DC-Link capacitor and see which PWM modulation technique benefits this bulky and expensive component depending on its ESR curve and the selected switching frequency. Index Terms—Multiphase, DC-Link capacitor, DC-Link current spectrum, PWM modulation, ESR, power loss.