I missed this thread the first time around.
As per post #3, the cos Phi setting is the power factor.
From the manual, it looks like the SMTech is a Sensorless Vector drive.
As far as I can tell, there are some differences between “Vector” and “Sensorless Vector” drives, with the main difference being that “Vector” drives use a sensor attached to the motor to provide feedback to the drive to tell it what what the motor is actually doing.
The feedback is necessary in many industrial applications where extremely high levels of precision are needed.
"We" are unlikely to need high levels of precision or the associated advanced motion control features; in applications like grinders, they add nothing at all to the performance.
If you have acquired a Vector drive at the right price, as mentioned in post #4, you can usually turn off the Vector option.
Sensorless Vector drives offer some, but not all, of the advantages of full Vector drives, but do so without the need for the feedback sensor. Instead, they take very fast measurements of the output waveform and try to work out what is happening at the motor based on these measurements and the known characteristics of the motor concerned. Because motors develop “slip” (they slow down slightly under load), and the amount of slip is load (torque) dependent, SV drives cannot achieve the same level of precision as a full Vector drive with its feedback sensor, particularly under conditions of varying load.
Although SV drives cannot handle the highest-precision applications, they can handle all the applications that a non-vector drive can and more.
With Sensorless Vector drives, you can usually turn off the SV option if you don't have the power factor value for the motor you are using and the drive does not have the ability to run a self-tune to determine the values needed. Most of the SV drives I have come across can self-tune.
Basic drives are often referred to V/f or V/Hz drives and ramp up the Voltage and Frequency (which is measured in Hertz) together, usually with a linear relationship. This means that, for example, at one-fifth of the rated speed, the motor will see one-fifth of the rated Voltage and can, if it pulls the rated current, develop one fifth of the rated power.
Usually, once frequencies get below about 10 Hz and the Voltage gets down below about 35V, the motor is so far from its design point that it stops running smoothly and starts to feel "coggy".
The motor Power Factor is the angular difference between peak Voltage and peak Current.
SV drives measure the Voltage and Current, calculate the angle between them and work out the Power Factor continuously. They then make adjustments to the Voltage on-the-fly to keep the Power Factor at the specified value. It is quite difficult to do, but is the sort of thing that modern electronics makes easy so, once designed and programmed, it adds very little to the manufacturing cost of a drive.
This makes a significant difference to the smoothness of the motor at low speeds and therefore the speed range that it will sensibly run. This particular characteristic of Sensorless Vector drives is definitely useful to us when we are considering grinders and similar machines.
The extended speed range allows slower speeds for sharpening, giving less risk of overheating the all-important cutting edge.
Where the motor frame size is fixed by the design of the machine and a 2-pole motor is the only choice for power at the high end of the speed range, an SV drive can make the difference between a 6:1 (10-60 Hz) speed range and better than 20:1 (3-60 Hz or more). The motor frame size restriction seems to be significant where 56-frame motors are used.
In general, since I started using VFDs almost 30 years ago (when all VFDs were V/Hz), the advice of both motor manufacturers and drive manufacturers has been to use 4-pole motors (rated for around 1800 RPM on 60 Hz mains) and run them over a speed range of 10-100 Hz (300-3000 RPM).
I've never found any problem running to 120 Hz, which gives the 3600 RPM of a 2-pole motor running at 60 Hz.
Because modern manufacturing methods are what they are, I can be pretty sure that any industrial motor I come across will have been designed with mechanical components that are not only safe to 3600 RPM, but can be expected to have a “normal” life expectancy in industrial use at that speed: usually somewhere between 50,000 and 100,000 hours of continuous operation.
I'll be long dead before I can put 50,000 hours on a grinder, so I regard that as adequate.
When I did some tests on a few VFDs a few years ago, I could run my lathe down to 3 Hz (and could probably have gone even lower) on an SV drive without seeing any deterioration in surface finish, where non-SV drives were starting to show poor surface finish between 9 Hz and 7 Hz.
The non-SV drives I tried were AutomationDirect GS2, Siemens G110 and, I think, a Mitsubishi FR-Z024. SV drives were Telemecanique Altivar 11, Telemecanique Altivar 31 and Control Techniques Commander SK. All but the Siemens G110 were 2.2 kW/3HP drives. The Siemens G110 was a 3 kW/4HP drive. All were 230V single-phase in, 230V three-phase out.
The lathe was a 1938 9" SouthBend with underneath drive and was fitted with a 1.1 kW/1.5 HP 4-pole TEFC motor.
To be fair, that's twice the factory motor power, so I was nowhere near working the motor to anything like its full capacity. Whilst I have not been able to observe any benefit to having SV at higher speeds (20 Hz and up) in "our" applications, this does not necessarily mean SV is not better in some way; it may just be that I am not good enough to notice, or that I have not worked a machine hard enough to notice.
Personally, I like SV and, as long as the rated power factor of the motor is known, will happily pay a little more for for an SV drive.
In mainstream drives, there is minimal cost difference between V/Hz and SV drives now. When it comes to sealed drives to NEMA 4 or IP66, the production lives of each model seem to be longer and it still seems to be the norm to find V/Hz drives. I am fairly sure the KBAC-series of NEMA 4 drives, popular in North America, and Invertec IP66 drives, popular in Europe, are still V/Hz drives. Between them, these probably account for 90% of the drives on VFD-equipped grinders that I know of.
I would expect the next generation of Invertec IP66 drives to have SV. I'm less sure about the next generation of KBAC drives. The current KBAC drives seem to be configurable with links or switches, rather than a programming menu, and I don't know whether SV would be compatible with this. Given a choice between SV and the no-menu setup, I suspect most users would prefer the no-menu setup.
Bottom line: if your drive has SV capability and you have the information needed to enable it, it is worth using it.
