In our practice, we find frequency converters with small dc-link in an increasing ammount. Unfortunately the distortions in the grids, created by such devices, are often much higher than expected.

Source of the problem is the reduced or even eliminated dc-link capacitor. In this case, the whole switching ripple of the vsd output must be compensated by the feeding grid. High voltage distortions, as shown in the diagram, can happen. Especially in cases without chokes and a high ammount of such drives.

Fast aging and defects of other devices in the same grid can be expected.