This series brings topics answering basic questions around VFDs such as fundamental components of VFDs, drive system components, working principles, dimensioning considerations etc.
Transformerless drives – Truth and myths Most medium voltage VFDs are supplied from the grid through an input isolation transformer. This transformer provides several key functions, such as voltage adaptation, galvanic isolation, limitation of fault current, often also harmonic reduction by phase shifting etc (for more details see [1]). However, Read more
Asynchronous and synchronous motor drives in comparison Medium voltage variable frequency drive (MV VFD) systems mostly utilize two types of electric motors: asynchronous and synchronous machine. This article compares some of the characteristics of both technologies. Aspects such as power and speed range, efficiency, system dimensioning, control and instrumentation and Read more
How well do you know variable frequency drives and drive systems? Take a short quiz to test your knowledge about variable frequency drives (VFD) and VFD based drive systems. 1. Nominal current of asynchronous motor with pf = 0.88 is 500 A (FLC). How much is the current at 50% Read more
Operation of medium voltage drives: A service cost of ownership This post provides important considerations about the lifecycle cost of a medium voltage variable frequency drive (MV VFD) from the service perspective. The “end of life” and “life extension” options are described. It is a relevant topic for every owner Read more
Speed and position encoders in variable speed drive systems Abstract Modern variable frequency drives often operate in speed-encoderless mode. It means that there is no physical sensor to measure the rotational speed of the motor. Although the encoderless operation is generally preferred, some applications require speed or position encoder. This Read more
What has a transformer and a gear in common? Transformer and gearbox are two quite different devices. Nevertheless, they have something in common. The analogy described in this article may help to understand how a drive system is dimensioned and configured, what limitations the designer faces and finally how do Read more
What is the relationship between VFD input and output current? Introduction Variable frequency drive (VFD) is often seen as a black box. This black box converts fix voltage and frequency supplied from the grid into variable voltage and variable frequency delivered to the motor. But what is the relationship between Read more
Different types of drive redundancy and their use cases Redundancy in medium voltage (MV) drives is a critical design consideration aimed at enhancing the reliability and availability of motor-driven systems. Drives with some types of redundancy are used in applications where high availability is requested. The reasons for this lay Read more
VFD Soft Starters – Methods of Synchronous Transfer Abstract Purpose of a VFD soft starter is to start and accelerate the motor up to the nominal speed. The final step is to synchronize the machine with the grid and transfer it to a grid operation. Two basic methods of synchronous Read more
Most common medium voltage VFD topologies in comparison Abstract Medium voltage drives consist of several topologies. While some of them are seldom found in industrial applications, others are very popular and create integral part of the portfolio of most global VFD manufacturers. In this article we look at the most Read more