Short circuit current contribution of a VFD Electric motors and generators contribute to the total fault level at the connection point. Their short circuit current is typically in the range 4…6-times the nominal current of the machine. How is the situation with a variable frequency drive? The answer is rather Read more…
Active filter or AFE drive – What is a better option? When taking care of grid harmonics there are several technical solutions to choose from. You might stand in front of a dilemma: active filter or AFE drive? What is a better choice? Nowadays there are multiple approaches how to Read more…
Abbreviations and Definitions This post summarizes and explains some of the most commonly used abbreviations and definitons from the field of variable frequency drives (VFD), drive systems and associated areas, such as power electronics, harmonics and power quality, monitoring, testing… AFE Active Front End Grid side converter (in drives often Read more…
Active harmonic mitigation with AFE drives In this article we will once again touch the topic of grid side harmonics, particularly focusing on active harmonic mitigation with AFE drives. Abbreviations used: AFE = Active Front End APF = Active Power Filter ASD = Adjustable Speed Drive (synonym to VFD) DFE Read more…
Inverter current higher than input current (New Year’s Eve issue) Can inverter current to the motor be higher than the rectifier input current?That is a question that puzzles some people. Let’s have a closer look in our year-end post inverter current higher than input current. The recent advancements in 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…
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…
Input power factor and reactive power consumption The focus in all energy efficiency initiatives is to minimize the losses, improve the system efficiency and reduce overall power consumption. With “power” people usually refer to active power and this is basically correct. Main purpose of VFD is to reduce active power. Read more…
What efficiency can you expect from your drive system? In general, the efficiency of a drive system utilizing VFD is high. The differences come from the VFD topology, dimensioning and technical solution. As discussed in our previous post, the user shall always compare total efficiency of a complete drive system. Read more…
How to choose a medium voltage VFD:Line side connection and power quality Nowadays modern VFDs offer large variety of line side configurations. Which one to select? That is the topic of today. There are two basic groups of VFDs based on their line side connection: Diode Front End (DFE) Active Read more…