VFD Power Modeling

[wzrdstrm]

Team,
I'm trying to develop a mathematical relatiionship for the HP(or KW)for a Motor controled by a VFD. The motor is a 1150 HP 600VAC, 40 HZ 6 pole motor. I have a theoretical model showing a linear relationship from 0hz to 40hz. HP is constant to a point after that, I know. I'll have different motors later. The idea is to control the amount of KW used for power management (below rated HZ). Basically, I will be given a KW limit and will have to determine the speed necessary to reduce the motors KW to at, or just below this limit. Using the theoretical model, I can use the equation for a line, but was looking for a mathematical formula, such that I can just switch motors and get the data for the new motor (i.e. switching from 1150hp to 1500hp).

 

[Compositepro]

The horsepower is determined by the load, not the motor.

 

[DRWeig]

wzrdstrm,

Compositepro is right. For example, if your load is a pump in a variable-flow system, horsepower at a given speed will depend on the position of the control valves (i.e., how much flow is being demanded).

Rather than trying to model the drive/motor/pump system, which can be extremely complex and subject to lots of measurement error, why not just put a PID controller or PLC in with a watt transducer as input? That could be arranged to control the VFD to maintain whatever upper limit you have set at the time.

All this assumes you have a load that can be safely starved of power, of course... Fans, pumps, etc..., in HVAC systems that aren't critical might be adaptable -- what's your motor doing, anyway? If it were a sewage pump, it could get really messy...

Good on ya,

Goober Dave

 

[fernandoelec]

Recheck if your VFD has the PID function or if you can control it by a torque adjusment fucntion inside. Other option is that you can use the the analog output signal configured as a Power or energy signals and with a small PID controller feedbak the analog VFD's speed input

Fernandoelec