This series about various aspects of variable frequency drive (VFD) dimensioning
What is the time constant of a dc link? Introduction Most commercially used variable frequency drives (VFD) belong to the category of indirect frequency converters. The AC power of a fix frequency (usually 50 or 60 Hz) is first rectified and then the DC signal is inverted into AC power Read more
How does skin effect impact the drive system? This short article provides a brief description of the skin effect and its impact on a drive system. As it will be explained, the skin effect influences the system in both negative and positive way. It always depends on the point of Read more
Can 50 Hz rated equipment operate on 60 Hz grid and vice versa? Globalization affects various areas of our lives. Variable speed drive systems are no exception. It happens that components manufactured in a “50 Hz country” will be used in a “60 Hz country” or the other way round. Read more
Why is it important to keep reasonable switching losses? Switching frequency is a decisive design parameter of a VFD – especially in medium voltage drives where the semiconductor capability may be more restricted. But switching losses have much bigger impact on the system. The end user shall understand it properly Read more
When is transformer tap changer needed? The input isolation transformer in a drive system may be equipped with a tap changer. Such device provides some flexibility but adds cost and potentially also complexity to the transformer design. Thus, the question is whether a tap changer is needed or not. The Read more
Finding an optimum field weakening point Motors supplied from variable frequency drives (VFD) have the freedom to set the field weakening point almost arbitrarily. By doing that you can optimize the drive system. The message of this article is how to find an optimum field weakening point. Let’s start with Read more
Overdimensioning of VSDS – What are the consequences? How to dimension a variable speed drive system (VSDS) properly? Underdimensioning is a No Go but what about overdimensioning? Besides the initial investment cost, how does overdimensioning affect the technical side of the system? This post answers the most relevant questions related Read more
Short circuit currents appearing in variable speed drive systems The knowledge of short circuit current level in variable speed drive systems is crucial for the design of system components as well as for the system protection. Inadequate dimensioning, unsuitable protection concept or wrong parameterization may lead to fatal consequences: Hazard Read more
VFD switching frequency The heart of every variable frequency drive (VFD) is the power semiconductor. By switching on and off in a proper modulation scheme the frequency conversion functionality is achieved. Let’s look at various aspects of VFD switching frequency. Switching frequency of medium voltage VFDs Having medium voltage VFD Read more
Current, voltage and power scaling of VFD Variable frequency drives (VFD) became unthinkable part of industrial motor drives. They cover voltages from some 120 V up to 13.8 kV (special designs go even higher) and power range from fraction of kW until 100 MW and beyond. Enabler of such wide Read more