Invited lecture: Input dc voltage and output ac current ripples in voltage source inverters



Nowadays, voltage source inverters (VSIs) are the most popular switching converters due to their capability to interface dc and ac power systems. Applications are ranging from few kilowatts up to several megawatts, with many possible configurations regarding the phase number (i.e, single-phase, three-phase, and multiphase) and the number of output voltage levels (two-level and many multilevel topologies). Specifically, a VSI can be found in all the grid-connected energy-concerning systems, since the energy storage and most of the renewable generation systems are based on dc technologies (batteries, supercapacitors, fuel cells, photovoltaics, etc). Even in case of ac generation systems, an intermediate dc-link to connect the ac grid is usually adopted (i.e. back-to-back configurations for wind and hydroelectric generation, flywheels, etc). A VSI can be also found in all the motor-drive applications, for the known advantages of ac motors over dc motors, with an increasing interest towards multiphase machines for the sake of the drive reliability and the post-fault operation capabilities.

As all the switching converters, VSIs suffer the concern of voltage and current harmonics, both at the dc (input) and the ac (output) sides. The mitigation of the switching harmonics is performed by ac-link series inductors, leading to a residual ac current ripple, and dc-link parallel capacitors, leading to a residual dc voltage ripple. The design of these reactive components is a key aspect for the performance of the whole dc/ac conversion system, and the analytical determination/prediction of current and voltage input/output ripples becomes a crucial element.

This lecture summarize one of the possible approaches for voltage and current ripples estimation, basing on instantaneous peak-to-peak ripple analysis applied to the output ac current(s) and the input dc voltage, considering the main inverter topologies. Basing on the peak-to-peak ripple profiles over the fundamental period, the maximum, the average, and the RMS of the switching ripple amplitudes can be easily carried out. In this way, the design of reactive components can be finalized and ripple minimization strategies can be defined. The analytical developments are supported by simulation results and experimental tests carried out on laboratory prototypes, considering the different inverter configurations.

  Date and Time




  • Faculty of electrical engineering
  • Trzaska 25
  • Ljubljana, Slovenia
  • Slovenia 1000
  • Room Number: P11
  • Co-sponsored by UL FE


Gabriele Grandi

Address:Dept. of Electrical, Electronic, and Information Engineering, Alma Mater Studiorum – University of Bologna, Bologna, Italy