Modelling of AC Servomotor

[abdulwali]

Hi,
i want to model an AC Servomotor where i assume that a dynamic load is attached to the shaft of AC Servomotor. the paper that i have attached to this post has ac servomotor model running without load thats why in equation 5 TL(s) (the load torque)=0 . Now i want to include TL(s) in the model which means that a load is connected to the shaft of the motor. in order to include TL(s) into the system i need to know the formulla of the TL(s) becouse i can not simply include TL(s) in the equation else i will not be able to get the final transfer function ( Theta(s)/E(s) ). So i am thinking to put in the components of the TL(s) into the equation such as T=KI or T=J(inertia) * a(accelaration).

So May someone plz help me that what can be the correct equation of TL(s) in this case so i can subtitute in? or/and how can i include the load torque (TL(s)) into the motor model.

 

[samantha_philip]

you need to check it about the proper configuration of AC servomoto, the tls equation formula could be found in some relevant blog or forum to that.

 

[Fish4Fun]

Hi abdulwali, welcome to EP!

It might help to give some context to your inquiry.

The paper you attached appears to me to be a formal scientific research paper essentially pitching "synchronous control" vs "sensor control" in cases where a driver is specifically designed for a particular motor in a particular application (ICM method). The unstated implication being that for some applications the added complexity of sensor (or even "sensorless", ie Back EMF) designs could be eliminated for a particular driver / motor pair.

In an abstract way the proposed ICM approach resembles bipolar stepper motor operation while traditional servo operation relies on "feedback" (typically from encoders or scales) and uses PID control to keep the error nominal.

The internal model control (IMC) philosophy relies on
the Internal Model Principle, which states that control can
be achieved only if the control system encapsulates, either
implicitly or explicitly, some representation of the process
to be controlled. In particular, if the control scheme has
been developed based on an exact model of the process,
then perfect control is theoretically possible.

To be honest I only skimmed the article, so I may have missed a salient point or two ... regardless, unless you are attempting to formally model a specific motor (ie rotor/stator construction, winding characteristics etc, etc) and then design a driver specifically for that motor as an engineering requirement of due-diligence in a high-budget project, you would likely be better off defining your application and requesting some input about typical solutions to similar applications.

A common example might be moving a stage with a lead screw .... given the mass of the stage + work, Force, acceleration and velocity requirements combined with "static load requirements", lead screw pitch, gearing, accuracy requirements, etc, etc it is actually a fairly trivial matter to "guesstimate" a suitable motor/driver based on existing production solutions .... For a more precise modeling a few AC servo manufactures offer online calculators for their products that use all of the above data (plus a few other design criteria) to help you select the best option from their line of products ...

At the end of the day, motors typically come in a limited number of output powers, and most solutions simply "round up" ... if the math says you need a 2760W motor, the closest match might be a 3000W Motor/Driver. If the math says you need a 3050W motor it is quite possible the "next step up" might be a 5000W motor ...

If the design is to be mass produced, there might be cost savings to design a 2800W motor/driver specifically for the product.... but such cases are few and far between. (For example: Consumer Cordless tools.) In most cases your selection will be limited by economics to readily available production motors/drivers.

Good Luck!

Fish