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Most of variable speed drives are applying on high temperature fans, kiln head coal mill fans, kiln head surplus fans, raw mill circulating fans and so on. Two production lines with daily productivity 5000T in the Cement factory. By variable speed drive, the two production lines achieve ideal energy-saving effect. Nowadays variable speed drive technology is more mature and failure rate is lower. It is an ideal equipment for energy-saving reconstruction in cement industry.
Variable frequency technology is a new drive technology which adopts advanced electronic technique, computer control technique and communication technique. It goes ahead of any other speed adjusting methods. Variable speed drive is bound to be widely used in more and more plants in future.
A lot will depend on the final application. In the murky, oily world of motor and drives there is no need to have high frequency switching. Due to this there is not the need to use fast devices such as MOSFETs.
From an amplifier design standpoint, the Safe Torque Off (STO) is redundant with the enable input to the amplifier. I'm not sure what "problem" this STO requirement is trying to solve that the enable/disable doesn't solve, unless there's some variable speed drives out there that don't implement the enable/disable correctly and tend to take off when not commanded.
The VSD main advantage is saving electricity, saving rate depends on the application and running time. The other advantage is protecting the electric motor, you can see if a high power machine start, other machines will be effected like low voltage. After you use VSD to control the motor, the power grid line is more stable and no instantaneous current shock to the electric motor.
Contact the local variable frequency drive distributors and see if there are any classes on VFDs you can attend. These are periodically given by there various manufacturers to promote the use of their brand. If you have a particular application the distributor may show you how to do it with their brand of drive. You can also go on various manufacturer web sites and go through the technical support library.
Instead of using brushes, I have been using either a sine wave filter or a dv/dt filter at the output of the variable speed drive. A sine wave filter eliminated all the high frequency from the VFD output and I have very good luck with that implementation -- have not seen bearing burn out. When using dv/dt filter, I like to keep the dv/dt below 200 volt / micro-second. The dv/dt filter design must have the common mode capability.
If you are trying to switch faster than 1 microsecond your physical layout is essential. You should have a ultrafast freewheel diode as close to the IGBT as you can get it. Even if you think your load is resistive your wires , traces etc are not. THEN, your gate drive has to be very stiff. You have to hold it off when it switches off and the gate tries to follow the collector due to miller capacitance.
Comparision about AC 4 quadrant drives and hydraulic couplers application for downhill conveyors.
1. Energy saving
4Q drives boast perfect energy saving goal, can reach high power factor up to1, with energy feedback functions, regeneration energy can be returned to main supply, low heat loss of 1%.
Hydraulic couplers feature low energy saving effect, will waste 75% of energy at low speed.
I think the reason why industry hasn't really latched onto it is because (unless you are using an IPM with a single large saliency) it really requires good knowledge of the particular motor saliencies, so it's not much use for general-purpose variable frequency drives (IPMs are not popular in general-purpose applications). However, for specific-purpose drives, it's very useful.
But, compare with imported variable frequency drives, China domestic VFD's technologies need to take some time to catch up. Although in recent years the use of localization VFD brands have some advantages, but in overall, the strength of China variable frequency drive's industries is still relatively weak. Despite technology, manufacturing, industrial design, or in financial, China domestic VFD brands still have a certain gap with foreign brands.
Therefore, such operation methods not only meet the heating requirements, improve operational efficiency, but also save lots of electricity energies. However, in those operation methods, it requires the variable frequency drive has speed tracking feature, particularly from the commercial power supply switches to variable frequency operation. Thus, the motor has a smooth switching when power supply cut off, from idle to restart, thereby enhance the system reliability and stability in continuous operation.
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service VSD blog: A deep observation of automation control industry, especially in AC motor variable speed drive for industrial motor controls.

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