There was no even “Concept” launched in the field of industrial electrical or industrial electronics engineering automation services 45 years to have the selectable reduced speed of the induction motors without losing it’s horsepower value, in the engaged/coupled with the load status … as presently there is availability on a mass scale of VFD ” جهاز تحكم سرعة الدينمو اى سى ” units with the different “Makers” names in the world market along-with in KSA, Saudi Arabia, Kingdom of Saudi Arabia, Riyadh, Gulf Countries, Gulf Area and Gulf Region .. particular in Middle East Region like the Firm ” SGRIEE ” … Saudi Gulf Raya Industrial Electronics Enterprise and Rayat AL-Inshaat Contracting & Industrial Electronics Maintenance Co. Ltd. …
there are so many other firms that are presenting the services … as … Sellers, Suppliers , Agency Holders, Stockiest , Distributors, Agents , Repairing Services Providers, Maintenance Services Providers, Technical Consultation & Operational Programming Services Providers, Replacement Remedy Services Providers, and Installation / Mounting / Fitting + VFD Parts, Semiconductor Components, Mosfets and
Rectifier Bridge Modules, Display, and VFD control Pcb Boards Supply / Sales / Repairing Services Providers.
Moreover, the Variable Frequency Drives, VFD , or Ac Drives ” تحكم سرعة المحرحك اى سى ”
or Frequency Inverters are known to use for Ac Electric Motors or Ac Induction Motor’s Speed Controllers Units / Devices or “Ac Volt Motor Speed Controlling Unit” with the electronically built-in facility of reverse rotation (counter clock-wise) of motor along with rapidly / instantly braking system at exact switching “Off” stopping time. Anyway VFDs ” الآلات تحكم سرعة للمحركات كهربائية اى سى ” are very effective controllers to vary the speed of the induction motors depending upon the desired operational requirements, but varying the “frequency” output from the “frequency inverter” to supply the motor, since frequency (Hz) is directly related
to the speed of the motor given by:
… Ns=120 x f/p
Working of VFD
The working of VFD actually depends upon a two staged operation.
First the given supply (3 phase 50hz / 60 Hz.) is converted into DC with the help of 6 (rectifier) diodes bridge assembly. These diodes allow current to flow in only one direction and thus the negative cycle of AC is removed, hence by filtering the output via appropriate capacitors, perfect DC output is obtained.
Once DC is obtained we need it convert back into AC, but with our required frequency (adjustable) so that we
can vary the speed of motor in the final consequence.
This DC is further channeled into 6 IGBTs or MOSFETs to perform the switching accordingly .Such that only 2 MOSFETs operates at a time, and making the sequences of the output we have three different square waves displaced by 120 degree. Thus the output is 3 phase once again, and the frequency of the output is determined by the switching sequence of the 6 MOSFETs. This switching can be controlled via some micro-controller or on larger scale it can be executed via Programmable logic controller.At the present time… there are VFD units in those ICBT (integrated gate-commulated bipolar transistor) are used also…and in reduction of ” 1 ” Hz. the speed will go to downward stream with the ratio of 30 rpm per c/s. For example if 60 Hz. 1800 RPM (4 poles wound) induction motor runs on 60 Hz. line voltages with increasing the Hz. from the Variable Frequency Drive then same motor will run on 1500 Rpm…VFD are very use-full device to use in hi volt transmission lines.. if any country imports the electric power in bulk form other country and that power exporting country has 50 Hz. power line then importer country can use the same imported transmitted electric power can be converted into 60 Hz. to connect with the national grid electric power line …
These square wave forms when added together can make sinusoidal output as well quasi square wave form depending upon the requirement. Usually in the industrial application we are more concerned with the sinusoidal wave form of the output.
Applications
One of the most significant changes that has taken place recently is that with the widespread acceptance of the units and the recognition of the energy and maintenance benefits, manufacturers are including VFD / Variable Frequency Inverter / Frequency Inverter / Ac Drive controls as part of their system in a number of applications.
For example, manufacturers of centrifugal chillers offer VFD controls as an option on a number of their units. Similarly, manufacturers of domestic water booster pump systems also offer the controls as part of their system, providing users with better control strategies while reducing energy and maintenance costs.
Other application may include
- VFDees are also used in modern lifts, escalators and compressors / pumping systems
- These are being also used in energy efficient refrigerators, Air-Conditioning units and Outside-air
Economizers. VFDs can provide precise speed or torque control in some commercial applications.