This series brings topics answering basic questions around VFDs such as fundamental components of VFDs, drive system components, working principles, dimensioning considerations etc.
Comparison of air core and iron core choke There are various reasons for installation a choke¹ within a variable frequency drive system – see [1] for an overview. The next question is about the design of such choke. This post provides a brief comparison of air core and iron core Read more…
When to go for an active front end drive? Abstract Grid side of the VFD can be either Diode Front End (DFE) or Active Front End (AFE). The later one is more expensive but brings several additional options such as regenerative operation of power factor control. This blog post is Read more…
VFD layout options Introduction Default VFD layout is normally a straight lineup. The individual cabinets are installed side by side on a common base frame. However, specific site restrictions may require adaptations of the mechanical layout in order to fit into the available room. Thus, alternative layout options may better Read more…
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…
Fault current considerations for integrated transformer of CHB drive Introduction Cascaded H-bridge (CHB) variable frequency drives (VFD) have the input transformer as an integral part of the VFD. This transformer has high number of secondary windings (equal to the number of VFD power cells). Such multi-winding transformer represents a challenge Read more…
DTC in a nutshell Direct torque control, DTC, is a motor control method famous for its superior dynamic properties. Less known is the fact that DTC optimally utilizes the switching frequency to achieve the target: regulation of torque and flux within specified hysteresis band. Thus, DTC contributes to a high Read more…
What is the difference between cold and hot commissioning? Recently we got a question in our chat group about cold commissioning. That inspired us to write this short post on the difference between cold and hot commissioning. We will focus on a commissioning of a medium voltage variable speed drive 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…
Drive systems according to their working principle Electric drives have many excellent properties that make them a preferred choice [1]. However, there are other types of drives based on other physical principles that also have their own strengths. In this blog post we compare hydraulic, pneumatic, thermodynamic and electric drives. 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…