This series brings topics answering basic questions around VFDs such as fundamental components of VFDs, drive system components, working principles, dimensioning considerations etc.
What is the difference between soft starter and VFD soft starter? Today we briefly explain a topic that may sometimes confuse: What is the difference between soft starter and VFD soft starter in motor starting applications? Direct on-line motor start Across the line or direct on-line (DOL) motor start is Read more
What is the best investment in 2024? Beginning of a new year is linked with new goals, ambitions and expectations. In the economic field many people probably hope that the inflation finally drops, the major economies do not fall into recession, unemployment rate remains low and the purchasing power increases. Read more
What is the optimal pulse number of a diode rectifier? Among variable frequency drives (VFD), the voltage source inverter with a diode rectifier is the most common all-rounder. However, there are several arrangements of the diode rectifier varying in the number of pulses. Is a 12-pulse rectifier sufficient? Do I Read more
What is the difference between dv/dt filter and sine filter? Almost every voltage source inverter (VSI) has some kind of inverter output filter. Design of the output filter has major impact on the drive characteristic and performance. For this post we have picked two key representatives. They are widely used Read more
How are the motor load points defined? Customer is often interested in defining the performance (e.g. losses and efficiency) of a motor drive for specific operating points. But how are the motor load points defined? Over the years working with variable speed inverter fed motors I come across this topic. Read more
What is the definition of low voltage and medium voltage VFD? We all probably know that variable frequency drives (VFD) can be classified into two groups based on their voltage: low voltage VFD and medium voltage VFD. But what voltage do we talk about? Let’s shortly explain… IEC 61800 distinguishes Read more
What type of asynchronous motor suits the best for VFD duty? Asynchronous motor is sometimes called the work horse of the industry. And this nickname is well earned. It is because millions of such motors are utilized in different applications across the globe. They help the world turning. While most Read more
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
Fuseless is not useless This post addresses the VFD protection concept and particularly the concept eliminating medium voltage fuses – so called fuseless design. We explain the advantages of such approach and why it is definitely not a useless feature. Concept of fuseless design Solid protection concept is key point Read more
Reactors in drive systems: Where do we find them? Reactors are widely used in variable speed drive systems. They appear as sub-components inside the VFD or as external components on the grid side or machine side. In this post we look at various types of reactors, their location, function and Read more