Current source and voltage source inverter Current source and voltage source inverter are the two basic types of indirect frequency converters. Therefore, it might be very interesting to describe and compare both types. This article can also be seen as an amendment to the LCI vs VSI series [1] that Read more
LCI versus VSI:60 MW case study Introduction In this post we share some results of a case study comparing load-commutated inverter (LCI) and voltage source inverter (VSI) for a 60 MW variable speed drive system. Due to confidentiality some quantities are only presented as relative values in percentage instead of Read more
Dream VFD You may think that the title of this article – dream VFD – does not sound very serious. However, let us elaborate on the topic a bit. It actually is a serious question: How does your dream VFD look like? What are the features of your dream VFD? Read more
Harmonic filters The continuation of our “Network harmonics” series [1] presents an article about AC harmonic filters. We explain the purpose of harmonic filter. Different types of harmonic filters are shown. Several design considerations are discussed. Main items are illustrated with figures and pictures. Grid side filters are covered in Read more
Network harmonics: Mitigation methods Today’s post focuses on harmonic mitigation methods. Let us review the most common, well proven methods of minimization of harmonic distortion on the grid side. Previous articles presented a general view on harmonics, their origin and effects [1]. The grid side harmonic spectrum of VFDs had Read more
VFD harmonic spectrum Introduction After the theoretical introduction [1] we jump to variable frequency drives as sources of harmonics. This post is about VFD harmonic spectrum. As already mentioned, VFDs belong to non-linear devices with non-sinusoidal currents and/or voltages that they draw from the grid or inject into the grid. Read more
High altitude Majority of variable frequency drive (VFD) systems is installed at altitudes below 1’000 meters above sea level (masl). In such cases no additional considerations due to installation height apply. However, there are sites located at high altitudes. How does it impact the VFD and other drive components? What Read more
E-mobility Our blog is generally focusing on medium voltage drive systems. However, we can’t ignore the trend and the huge potential of electromobility (e-mobility). Since the technology is based on electric motors, variable frequency drives and other power electronics we would like to contribute on this topic as well. Moreover, Read more
Protection of VFD transformers In the introduction to this series we have explained the differences between a distribution/power transformer and a VFD transformer [1]. Due to different design, construction and operation of VFD transformers the protection requirements shall be adapted as well. While many end users, system integrators, EPCs and Read more
Motor start with VFD Our experience shows that the VFD motor start is sometimes not fully understood. This post shall explain how motor start with VFD works, what are the main benefits and how does it compare to a direct on-line start. Abbreviations AFE = Active Front End DFE = Read more