Dream VFD
You may think that the title of this article – dream VFD – does not sound very serious. However, let us elaborate on the topic a bit. It actually is a serious question: How does your dream VFD look like? What are the features of your dream VFD?
Users have various requirements when it comes to variable frequency drives (VFD). The requirements depend on the industry segment, application, customer’s philosophy or even the position within the end user’s company (purchaser usually as different view than the maintenance personnel). As you can probably imagine, it might be hard if not impossible to fulfill all of them at once. That is the reason why major VFD manufacturers have a broader porfolio of VFD products [1]. “One fits all” simply does not exist.
What makes a dream VFD
However, what are the key features that a dream VFD shall have? How would you prioritize your requirements? What features are necessary and which of them are just nice to have?
Safety features
Personal safety is highest priority for most companies. Therefore, safety with regards to VFD operation and maintenance will probably rank high on the list.
See [2] for more details.
Reliability
VFD is expected to have high reliability that then translates into high overall availability of the drive system and process. Reliability is essential for most customers as downtimes mean significant loss of production etc. Especially in applications without redundancy on system level high reliability is very critical.
See [3] for more details.
Efficiency
VFD is often used to reduce electricity consumption and save energy. However, there are still some differences between manufacturers and their products. Small percentage improvement on efficiency means large energy and cost savings over the life cycle of 20-30 years.
See [4] for more details.
Lifetime
Users typically expect lifetime of 20 or more years. One thing is how long the product lasts, other thing is how costly it becomes to keep it operational. Ideal VFD design uses high quality components and appropriate design margins to support long lifetime.
Motor friendliness
The inverter shall have motor friendly waveform avoiding high motor dielectric insulation stress, harmonic heating, sparks, bearing currents etc. In ideal case the output voltages and currents would be sinusoidal. That would allow simple interface with any motor.
See [5] for more details.
Dynamic operation
Fast response is not always required. In particular, applications such as pumps, fans or compressors mostly do not require dynamics. On the other hand, rolling mill drives and certain test stands require high dynamic operation and accurate control in dynamic mode.
Robustness
Robustness is linked with protection, reliability and other aspects. Dream VFD is robust to withstand all kind of faults meaning that VFD does not get damaged, but it also does not trip and saves the process. Important is to withstand various grid faults without tripping.
Braking options
Many applications do not require any active braking at all. They simply coast down when the motor stops delivering a driving torque. Other applications require braking due to the process or safety concerns. Dynamic braking can be dissipative, i.e. using chopper and braking resistors, or regenerative.
Footprint
For some customers the overall dimensions of VFD panel(s) are very important. Space costs money, especially when it comes to offshore installations or containerized solutions. Small footprint requires high power density. Some topologies have larger footprint while other have smaller.
Purchase price and life cycle cost
Dream VFD fulfills all above features, but is also affordable. It has adequate purchase price, but also reasonable life cycle cost.
See [6] for more details.
Installation and commissioning
Dream VFD can be easily installed and commissioned. User does not need to read hundreds of pages in user manuals. Control parameters are clearly defined and do not require long trial & error phase.
Maintenance and serviceability
Easy maintenance is desired as well. It helps to minimize the maintenance effort during the life time. Good accessibility of all components inside the VFD allows quick repair/replacement supporting max. uptime. Good product supports serviceability.
See [7] for more details.
Dreams and reality
As you can imagine it is not possible to combine all the goodies into one single product. Therefore, some compromises need to be taken.
For example, minimized footprint might be in conflict with easy maintenance and good accessibility of components. High dynamics might be in conflict with motor friendliness. Precise control might affect commissioning time.
Your dream VFD
What features do you expect the ideal VFD to have? Please write your priorities below (ideally numbering them from most important to less important).
References
[1] Medium voltage AC drive portfolio, https://new.abb.com/drives/medium-voltage-ac-drives
[2] How to choose a medium voltage VFD: Protection concept, https://mb-drive-services.com/choosing-mv-vfd-protection/
[3] VFD reliability series, https://mb-drive-services.com/category/reliability-and-availability/
[4] VFD energy efficiency series, https://mb-drive-services.com/category/energyefficiency/
[5] How to choose a medium voltage VFD: Motor compatibility, https://mb-drive-services.com/choosing-mv-vfd-motor-compatibility/
[6] How to choose a medium voltage VFD: Life cycle cost, https://mb-drive-services.com/selecting-mv-vfd-lcc/
[7] Sustainable drive systems, https://mb-drive-services.com/sustainable-drive-systems/
