PWM-Vector Drive

Hello,
I am confused
What type of inverter Vector drive have?
Does it use PWM,VVI( Voltage source Inverter) or CSI (Current source inverter)

I know that vector drive changes the amplitute and angle of the Current to control the toqrque.Does this mean that it requers adjustable current source and adjusts the frequency.

The whole thing is not clear for me.
Do you guys know any refrences that I can refer to ?

Thanks alot

Vector drives are all voltage source drives as far as I know.

Current source AC drives are mostly a thing of the 6-step past now.

Also, vector drives don't actually play with current limits or anything like that, rather, they use either a calculated or lookup table motor model to determine exactly how to seperate the magnetizing flux component from the torque generating flux component.

Dick_DV is the one to answer this question

Vector drives, whether flux vector or sensorless vector, are simply drives that have the processing capability and speed to separate out the two vector components of motor current, magnetizing amps and torque-producing amps. The vast majority of drives these days are PWM inverters but this is a completely unrelated issue to processing motor current vectors.

The advantage of being able to separate magnetizing and torque amps is that, when motor shaft torque is known, shaft slip can also be calculated accurately. Also, motor torque can be regulated directly and much better motor behavior results especially at low speeds and heavy loads.

A flux vector drive is one that requires a motor shaft encoder. It is thru the encoder feedback that exact shaft speed is known and therefore slip and torque is also known.

A sensorless vector drive is one which depends upon high speed processing capability to do the math necessary to separate magnetizing from torque amps. Usually, the drive requires the establishment of a motor model of some sort as part of the drive startup procedure to help speed the processing. There are huge differences in capabilities between different brands of sensorless vector drives, some of them little better than a V/Hz drive and some of them with stunning dynamic and static performance which eliminates the need for an encoder in all but the most demanding applications. As far as I understand these differences, it seems they are primarily due to the quality of the motor model that is set up during startup.

The big plus with sensorless vector drives is cost; not drive cost but motor cost. Flux vector always requires a motor encoder which requires an encoder mounting surface on the motor. NEMA motors don't have that mounting surface so, in addition to buying the encoder, you must now buy a special inverter duty motor too. If motor thermal conditions permit, with sensorless vector you can get away with a NEMA motor for a lot less money.

Hope this helps clear this matter up.

Thanks alot DickDV,
We all are happy to have you here.

Torque-PWM & Vector

Couple more questions

I know that in PWM drive V/HZ ratio stays constant.so motor produces contant torque unless the Torque speed curve is chnaged based on the application.
This is somtimes a hassle,If I have a variable torque application and I don't know about load caractristics.
So my understanding is to go with Vector drive because they can produce higher torque if needed.Is that right?

I have heard that vector drives have same torque caractristics as a DC drive producing cnstant torque below base speed ?is this correct?

Thank you

Most drives whether variable torque rated or constant torque rated will come from the factory with a constant V/Hz curve (except HVAC drives). But all that means is that constant torque is AVAILABLE from the motor as it slows down. If you have a variable torque load, it just doesn't ask for as much torque in the slower speeds. The motor is happy to produce less torque than the maximum possible. I have many fans and pumps running with a constant V/Hz curve in the drive and all is well.

The only real motive for picking a squared function (variable torque) V/Hz curve is to save a little (and I mean little) energy on fans and pumps.

Vector drives do produce slightly more torque per amp generally. The real difference is fast response to speed reference changes and better torque at low speeds. Sensorless vector is about as good as flux vector except in applications where cumulative speed error is not tolerable. These would be web processes with tensioning and similar jobs.

As for comparisons with DC motors, you have to be a little careful. A simple V/Hz drive will produce constant motor torque from base speed down to around 5Hz where the performance starts to deteriorate. So, if your application is only in this speed range, you can come very close to duplicating the DC motor. If your application requires constant torque down to near zero speed, you will need a good vector drive and then you will get DC-like performance. If you need full rated torque right at stall, a flux vector drive (with encoder) will be needed with one exception. ABB's Direct Torque Control drive, the ACS800, will also produce full torque at stall without an encoder. If there are other sensorless systems that will do that, I haven't seen them.

A common myth about DC is their speed regulation capabilities. An armature feedback DC system is typically good for 2-3% from no load to full load. DC systems with analog tachs have been claimed to have near zero speed error but, considering that the tachs are spec'ed to be no better than 1% accurate, the speed regulation can't be any better than that. Systems with encoders are very accurate, in fact, so accurate that % really doesn't mean anything. Probably the best way to express encoder error, whether AC or DC, is one pulse plus or minus one pulse, non-cumulative.