Vector drives vs PWM vs CSI vs VSI?
I'm guessing that most of the drives I'm looking at are PWM, but not sure how to tell since not many say what they are?
What is the best drive to use for simple single to three phase convertion, 10hp or less, small shop or hobby use?
Pulse width modulation is a great control methode for DC drives
Variable Frequency drives are useful to control the speed of an AC induction motor. Low end FVD's can change single phase input into poly phase output, as the input is rectified internally before being chopped to provide the frequency modulation and sent out in a Volts vs Hertz Relationship.
Vector drives actually sense the drive motor condition and can output variable voltage at any given frequency. This function is useful for power control.
If you are satisfied with fixed frequency conversion only, The V/Hz VFD will answer youyr requirements.
Search this form and you will uncover more information than anyone really cares for. ;-)
Reason I'm asking is I noticed on the manufacturers web site they are more expensive than regular ac drives. On the other hand I seem to be able to find them for cheaper brand new than regular VFD's on selling sites like ebay?
Makes me wonder if there is any advantage for me one way or the other. ie. If the same HP rated vector drive is same price or cheaper than the PWM, should I buy it?
For eg. Any reason I shouldn't concider this Hitachi unit?
Seems reasonable concidering I would be going straight from 230v single phase to 230v three phase. Would be running a 3 PHASE 10HP baldor mtr at full load amps = 26 ish.
Is Hitachi amoung the higher end of reputable VFD's? Like AC Tech, Allen Bradley ect?
Last edited by amoniave; 02-06-2012 at 04:42 PM.
amoniave you should be clear what terms you r using.... u r mixing terms that make them meaningless..... here is a primer:
PWM=Pulse Width Modulation. ALL -- get it -- ALL as you put it, vector drives, vfds, csi, vsi things are PWM today. So this is not a meaningful term to use for picking one thing over another.
vector drive: this is vs. non vector drive, or v/hz drive. vecotr drive can hold your commanded speed +/- a couple rpm; non vector will hold motor to 0-50rpm. No other difference to speak of in general terms. this probably means nothing to u the way u will use this drive so the extra $ 200 for vector version may be a waste of money to you,
csi: u can tell us where u heard this term and what it exactly staNDS for for exact wording, but I assume this means CURRENT (sense?) I(current) controller. this is nothing more than industry buz word to identify a vector drive - see above.
VSI: u can tell us where u heard this term and what it exactly staNDS for for exact wording, but I assume this means VOLTAGE (sense?) I(current) controller. I assume this is nothing more than industry buz word to identify a non-vector or vhz drive - see above.
I see nothing less good about a Hitachi than an AB or other brand you mentioned. they are all very similar.
I would caution buying from that ebay seller: anyone who lies about a drive rating should be watched closely; the 110 model is a 15hp model, not 20hp. it IS capable of 20hp in variable torque mode which is NOT sufficient for a 20hp motor running as a spindle at lower than base speed; that is why it is rated 15hp for constant torque applications like you would use.
that said, this price is about $ 200 less than we would sell it for, so it is a good price. but we would call it what it is: 15hp drive.
THAT said, I would consider YOUR application, and tell you that YOU could use it just fine for YOUR spindle application since it is an oversize for your 10hp motor and there are technical reasons it will work fine for you. But I would NOT falsely advertise it as a "20hp" drive.
Hope this helps!
Mike, thanks for taking the time to post, GREAT info for me and a great help as I am trying to settle on what I should go with.
Originally Posted by mike_kilroy
I was reading an article on VFD's and it seperated them into 4 catagories. PWM, CSI , VSI and the newer vector units. Since I hadn't come across it on here, I was unsure if it was something I was missing or wasn't understanding, so I brought it up for my own clarification.
Here's the link to that page, Understanding variable speed drives(part 1); http://ecmweb.com/mag/electric_under...iable_speed_4/
On the vector drives, I'm not trying to lean toward buying one, I'm just finding that (on ebay anyway) they are cheaper than a regular VFD. This seems contrary to what I've read, but if it's actually a better unit and less $'s I can't see not buying it!
Those Hitachi WJ200 series drives are THE least expensive name brand 230v drives I have found by several hundred $'s. Although, if I take into concideration what you said about it being a 15hp unit, then it's much closer.
The best priced NEW VFD's 20hp 230v are in the 1100-2400$ range. So even the WJ200-150LF (proper 20hp rated) is still the best buy at the low end of 1100.00$, AND it's a vector!
One question I have, could you explain why the 15hp unit (the 20hp one in the link from ebay) will work in my application and could I also use it for my future 10hp compresser mtr? I do not want to buy it if I really need the larger 20hp 60amp one.
Judging by the constant torque amps and the fact that I'm using it under rated for single phase input, I would have guessed I needed the REAL 20hp model?
Great job Mike, couldn't have done it better myself.
But to fill in:
CSI = Current Source Inverter. It's a long complicated dissertation to explain exactly what that means, but suffice to say that it is only used on very VERY large drives. Completely irrelevent to things having to do with this forum. In a nutshell though, a CSI drive changes the voltage up front in the converter section and then only changes the frequency at the inverter section, but is dependent on the circuit impedence to switch the power devices, so they have to be matched to the motors they control. Nobody would want to do all that on a 5HP machine spindle, but on a 2000HP pump, OK. CSI drives are well know to be bulletproof, hence the desire to use them on very big important motors.
VSI = Voltage Source Inverters. Virtually all of the PWM drives that we buy and use today are VSI drives: voltage is just rectified in the front end, voltage AND frequency are controlled in the inverter section. So the use of the term is only relevent in discussions like this where they are being compared to "other" methods, i.e. CSI (there are actually other types as well, even more rare, like LCI, Line Commutated Inverter). So nobody really uses that term to describe their type of small VFD any longer. It's kind of like saying "My car engine is internal combustion." As opposed to what? There hasn't been an "external combustion" (open fire box) engine used in a vehicle for 100 years.
Re: Vector drives being cheaper than non-vector drives.
It might be true. The reason would be that most mfrs are stopping production of non-vector drives now. Advances in microprocessor power has mad it so that there really is very little difference in the cost to make them, so once a new model comes out, it's typically (sensorless) vector. Newer models of electronic things tend to be less expensive than older models, it's just sort of the law of the land, so it's entirely possible for a new vector drive to be less expensive than an older V/Hz drive, especially if a seller owns it at a higher price. Very few sellers want to lose money.
"CSI = Current Source Inverter. It's a long complicated dissertation to explain exactly what that means, but suffice to say that it is only used on very VERY large drives. Completely irrelevent to things having to do with this forum."
I strongly suspect that today's 10,000 to 50,000 watt AM broadcast transmitters are CSIs.
Basically, there are quite a number of H-bridges which, under both carrier control (540 kHz, ..., 1710 kHz) and modulation control (the audio input), connect quite a number of current sources to the output 50 ohm transmission line.
For convenience and necessity, there are a number of individual dc power supplies which are driven by a 277Y480 supply. The voltages could be as great as a few hundred volts or as small as a few volts, but there might be a dozen or so individual supplies which supply the H-bridges.
The incoming audio is A-to-D converted and this, in combination with the carrier frequency, drives the H-bridges on or off, or connected to the +'ve rail or connected to the -'ve rail.
The outputs of all the H-bridges contribute to the RF ouput.
A low-pass filter and possibly an impedance converter follows all the H-bridges.
The result is 50,000 watts of fully modulated RF for only about 86,000 watts of input power.
"Back in the day", a 50,000 watt transmitter would have consumed 150,000 watts, if not more.
Better things, for better living, through chemistry ... er, through solid state electronics.
The parallel between the thyratron drives of old and the VFDs of today is somewhat similar.
thanks Jraef & Peter for correcting my senior moment on csi/vsi
as stated, vsi controls the output voltage, so it will be a v/hz drive, & csi controls output current, so it probably cannot be a v/hz drive since v/hz by definition means controlling the output VOLTAGE and ignoring the current (except for limits). To control output current and ignore output voltage (it will go where it needs to in order to control the current) pretty much defines it as a vector drive since that is what vector means - controlling the vector current in the motor, not the voltage. Make the vector current right & the proper voltage will follow.
Just for reference, a Hitachi 10hp X200-075 v/hz drive has a list price of $ 850.00: the vector model XJ200-075 is $ 1100.00; I am not sure about other mfgrs, but I suspect they too still have higher prices for vector drives but distributors are driving the price of the vector drives down with their marketing methods..... as of today, ALL Hitachi vector models are higher price than non vector.
That said, I have not seen schematic of equiv vector & non vector side by side, but I believe both are built almost identically with same parts just different cases to distinguish them for marketing reasons. The difference is in the processor programming - I believe the vector is more expensive today simply as a marketing feature, and to help recoup the r&d costs to have developed the program for the processor.... so as time goes on, it may well be that all drives will have both types built in & mfgrs may just decide to reduce their costs more by building only 1 model instead of 2.
The reason you can use that Hitachi 15hp CT model for your 10hp motor is it is ALSO rated 20hp VT (variable torque). The derate for 1ph input as has been stated many times in the past, is 10hp of 1ph current is almost 2x 3ph current, so you need a drive with INPUT circuitry (rectifiers) rated for this higher current. The rest of the drive is ok since it is at least the size you need anyway (10+hp). But the Hitachi model you looked at is marketed for 15/20hp ct/vt - result you can see is the input circuitry is designed for a 20hp current! So you only have to upsize to the VT rated model. Think of it for a moment: that 15hp ct drive you mentioned is also rated 20hp VT.... means it will run a 20hp motor at rated speed at 20hp forever - hence, it IS rated for 20HP - at base speed - just not rated for this same current at low speeds. But if rated for full 20hp at base speed, that means it can handle continuous 20hp currents all the time. More marketing. Perhaps there is some additional watts losses at LOWER output speeds that limits its current capability but I can't see them - in this case, I again consider this a marketing scheme. Anyway, as a Hitachi distributor, I did check with their application engineers and they had to agree that one can use the VT rating on THEIR drives for 1ph input doubling rule....
since the limitation on 1ph into 3ph motor is input circuitry, there is no reason you would want to buy a bigger drive for compressor duty motor; your 10hp compressor motor will be fine on the 15 or 20hp oversized drive.
Again, Great info guys! Don't have a clue what I'd be doing if I hadn't joined this forum!
I fully understood 3 phase VFD's to the point of the only weakness for single phase input WAS the input itself (rated for 3 phase amp load) so much so that I took 2-3 times explaining it to my brother the other night till he got it.
What confused me was the 15hp rating for constant torque/ 20hp variable torque and 47.0 CT/ 56.0 VT amps. For some reason I was thinking this vector drive would be running the 10hp mtr in costant torque and the mtr would only be limited to 47.0 amps?
Now 2 x 26 amps through the single phase is 52 (I know it's not a true 2x) so I figured it was close, just wasn't sure it was right.
So CT is only for low rpm programing? Any benefit on my applications?
Bear in mind that HP is torque times speed so to keep full HP at 1/2 speed you must double torque. Some tools demand less HP at lower speeds others don't change much.
Kind words there Mike, but I think I'll need to take in a little more before I step to far into a conversation on here.
You have ALL helped me immensely, and being the kind of person who doesn't like moving forward without feeling as confident as possible that every option has been carefully concidered (this can frustrate some people) I can truly say that I'm running out of questions! lol
I will start by finishing my threads showing some detail on exactly what I went with and how it all worked out. Maybe after going through it all I could answer some of the super simple questions out there
So back to the Hitachi vector drive. I'm guessing it will have option for VT or CT? And that I will only be able to use the VT? (if that made sense)
I guess what I'm trying to say is, even though it's a vector drive, I will be using like a normal VFD. (non vector, VT) Correct?
Before going too far you should also know that many people are running motors that are bigger than the drive, eg a 5hp motor on a 3hpdrive. This is doable mainly because industrial machines are often fitted with larger motors than required for the work. Consumer goods are constrained by 15 amp circuits and lowest price possible.
no no no! u r simply oversizing in order to not overload the current rating of the input rectifiers. thats it. period. the rest of the drive can do whatever it is rated to do. period.
Originally Posted by amoniave
so, yes, there is a parameter in the wj200 to pick vt or ct mode - YOU JUST USE THE BETTER CT MODE AND BE DONE WITH IT! and yes, you can use it as a full sensorless vector drive on ur 10hp motor if u want.
i apologize for being too confusing.
47amp is simply rating for a 15hp motor - nothing to do with ct or vt.
56amp is simply rating for a 20hp motor - nothing to do with ct or vt.
said another way, a 15hp motor is typically rated around 47 amps at base speed irregardless of ct or vt mode.
said another way, a 20hp motor is typically rated around 56 amps at base speed irregardless of ct or vt mode.
consider current into a motor producing torque.....
so, in ct mode, 56 amps into a 20hp motor will produce 20hp worth of torque (60#-ft) from any reasonable slow speed upto base speed.
so, in ct mode, 47 amps into a 15hp motor will produce 15hp worth of torque (45#-ft) from any reasonable slow speed upto base speed.
ct mode means you are allowed to put 56 amps into that 20hp motor from slow speed to base speed and hence use the 60#-ft of torque all the way.
ct mode means you are allowed to put 47 amps into that 15hp motor from slow speed to base speed and hence use the 45#-ft of torque all the way.
but in vt mode, you are not ALLOWED to put 56 amps into the 20hp motor all the way down to a low speed. vt torque mode means you cannot pull more than a reduce torque or current below base speed. ie, the drive reduces the v/hz curve below base speed artifically so the motor gets reduced voltage and so it cannot produce rated torque (or pull rated current). this is a way to save money on motor applications that can survive this kind of reduction - like fans. their torque load goes up as the cube of the speed; so as u go down in speed below motor base speed, one can reduce the voltage to the motor and save energy by using this feature called variable torque. you can see it is not for spindle applications!
make any better sense?
I think I'm getting it. So if a VFD can start a compressor in VT mode, what advantage to running it in CT? Also, what mode is easier/harder on the spindle?
OK, I think you are misinterpreting the concept of VT and CT as being a "mode". As mentioned earlier, it is nothing more than a marketing term, let it go.
Variable Torque or Constant Torque refers to the LOAD profile. Constant Torque means that the load requires the same amount of shaft torque regardless of speed, which means there is a linear relationship to speed and power required. So at 1/2 speed, the torque is still the same but because the speed is 50%, the HP required is 50%. That relationship remains linear. All machine tooling spindle and motion applications are Constant torque.
A Variable Torque load is one like a centrifugal pump or fan, because as you change the speed, you change the flow and the power required by the load will vary at the cube of the flow. So at 1/2 flow, your load has not fully "coupled" with the motor so the motor HP required is only .50 x .50 x .50 or 12.5% (1/8th) of the HP required at full flow. Since flow follows speed for the most part, you can relate that to speed.
So what does that mean for the VFD? nothing really, except that the VFD supplier can take ADVANTAGE of the reduced power requirements of a variable torque LOAD to sell you a smaller and thereby cheaper drive. There is no difference in the drive, there is just a difference in the RATING of the drive. So if you have a VT rated 20HP, that just means you are "cheating" the size rating from 15HP top 20HP IF (and ONLY if) you use it on a true Variable Torque load like a centrifugal pump or fan, because the mfr knows that at lower speeds, where it is going to operate most of the time, it will not have to be capable of full power.
So your idea of "starting in VT mode" is preposterous, the VFD cannot dictate what the load is. An air compressor, in most cases*, is a Constant Torque load so if it has a 20HP motor on it, a 20HP VT drive will likely trip off trying to get it to start at all.
Some drive manufacturers attempt to cloud the issue by using terms like "VT Mode" and "CT Mode" when describing setup steps that have to do with the V/Hz pattern, but that's almost deliberate obfuscation. All that means is that IF you have a VT load, using the VT V/Hz pattern can maximize your energy savings by reducing the magnetizing current at the lower speeds when you know you don't need full power anyway. If you do that on a CT load, all it does is further weaken the motor output and hasten the stall.
* There are centrifugal compressors, but they are typically specialized.
Great post Jraef!
OK, I definetly get it now! Sorry it seems to take me so long to grasp this stuff, but you are correct in saying that the industry does NOT help with their "terminology" of these devices.
Several manufacturers sites that I went to, gave the distinct impression that the VFD had two seperate modes and you could actually choose one or the other. ie. switch from VT to CT.
I think this is what was confusing me. Rather than the mtr and load dictating the current needed, it made me think the VFD was MAKING the spindle "bow" to it's will!
Now I did read on one site, where the poster said ALL vfd's are CT capable. I should have paid more attention to that a little more!
So, in a nut shell, the new Vector drives are just capable of meeting the spindle/load "needs" better than the non vector VFDs before them.
Thanks again for all of your patience and input!!!