This series about various aspects of variable frequency drive (VFD) dimensioning
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…
Power, speed and torque The purpose of variable speed drive systems is basically the ability to provide required torque at corresponding speed. In simple words: to turn the shaft. Of course, the quantities of power, speed and torque are coupled together. This article is a bit more theoretical review. However, Read more…
Multidrives and their benefits Multidrive concept is a VFD solution where multiple motors are supplied and controlled from one VFD having several inverters connected to a common dc link. This concept has several advantages and is especially popular in certain applications, for instance rolling mill drives or specific test stands. Read more…
Load types and characteristics Type of load is relevant for VFD hardware dimensioning and selection of most suitable VFD topology [1]. Sometimes the load type determines what kind of rectifier (front end) is required. Also, load type may affect some options and features that the VFD shall have. Therefore, it Read more…