Can anyone provide a little background or anything to explain this sentence taken from a VFD Cutsheet:
What's the difference between V/HZ, Sensorless Vector, and FLux Vector?
And whats the difference between speed and torque control?? Don't we give all VFD's a speed setpoint?
Finally, exactly what is the difference between a VFD set for "variable torque" and one for constant torque? Another manufacturer provides these options.
Steve
V/HZ, Sensorless Vector, and FLux Vector:
V/Hz = VFD does just that, changes V and Hz to change speed. Has no idea if that accomplished what you wanted, no feedback.
Vector (in general): uses feedback signals to determine what happened in the motor, then adjusts the vector of V/Hz to maximize the output to match your criteria; i.e. speed or torque etc. Vector control is divided by the type of feedback:
Sensorless Vector = the feedback to the drive's mP is taken from the current signal of the power itself as it goes to the motor. the VFD creates and remembers a mathematical model of the motor performance and as it watches that performance, uses the error it sees to tweak the output.
Flux Vector = the feedback is much more accurate because it comes from an encoder attached to the motor shaft. So like a servo, the mP is watching exactly where the rotor shaft is at any given moment so that it can tweak that output pattern to maximize the flux in the motor and provide high (highest) precision in the output performance. With this you can achieve the holy grail of AC motor use: replacing a DC drive and motor so that you can get 100% torque at zero speed, i.e. a hoist motor that needs to make absolute sure the motor is in control of the load before a brake releases it. Also, just like a servo, you can do rudimentary positioning control. Servos are better at it, but try to find a 200HP servo!
And whats the difference between speed and torque control?? Don't we give all VFD's a speed setpoint?
Maybe yes, maybe no. Ever watched a wire winder? You have overall speed control, but the pay-out and take-up reels are rapidly changing speeds relative to each other and if you don't precisely control torque, will stretch the wire. So for winders, you typically use a Torque setpoint. All this means is, the VFD is smart enough to be set to do either. A V/Hz only drive (although now rare) will not be able to do this.
Finally, exactly what is the difference between a VFD set for "variable torque" and one for constant torque? Another manufacturer provides these options.
Any drive is capable if controlling either, this is mainly a marketing issue. A VT load, like most centrifugal pumps for instance, will never need full torque at reduced speed, because the nature of the load changes quadratically with speed. that means that the HP reduces at the cube of the speed reduction; at 50% speed for example, the LOAD will draw .5 x .5 x .5 of the HP it would at full speed, so that's 12.5% HP, which means the VFD output current requirement will vary as well. So because it's accepted that the VFD will probably never get over loaded, they can play a "numbers game" with the ratings. So what would work for a 50HP Constant Torque load, may be OK for a 60HP VT load and therefore will be a little cheaper for that 60HP VT application. That's all it means.