Comparative Evaluation of DC-link Capacitor RMS Current Stress for Conventional and Reduced Common Mode Voltage SVPWM based Inverters

This work investigates the comparative assessment of DC-link current ripples in perspective of reduced common mode voltage (RCMV) PWM schemes. The anticipated simultaneous reduction of ripple current on DC-link capacitor and common mode voltage compared to traditional PWM approach is seen to exist in certain regions of operation. This may result in reduced thermal stress and consequently in enhanced reliability and operational lifetime. Another increasingly important consideration is for DC microgrids where the inverters are connected directly to the dc-bus and ripple reduction and RCMV for one or more of these inverters is critical for reliable operation. This work utilizes the piece-wise sinusoidal form of DC-link current computing a closed form RMS current expression that is further analyzed for varying load and mod-indices. The RMS DC-link current of conventional space vector PWM has also been analyzed as base case. It would be seen that these modified PWMs mostly put higher ripple stresses on capacitor. However, there are specific regions where one PWM scheme can be employed for reducing DC-link stress.