Synchronous machine saturation instabilities

Simulating the synchronous machine below, i am unable to model saturation without immediately creating a numerical instability. The data has been sourced from factory tests, and manufacturer calculated datasheet values where tests were not possible. Decreasing sample time from 25µs to 0.25µs improves stability, but creates unacceptable simulation times.

Characteristics of the data that i am aware of:

1. OC saturation curve (from test data) does not intersect the declared 1pu operating point for excitation current @ nominal volts. Scaling the saturation data to fit (1,1) has not helped.
2. X''d & X''q are more different (compared to each other) than anticipated
3. Increasing the parasitic load on the machine from 5-15% improves stability, but then offsets the true operating point for the rest of the model.

SM.Rating.S             = 1938e3;
SM.Rating.Vline         = 690;
SM.Rating.F             = 60; 
SM.Rating.Poles         = 4;

SM.Mech.gensetH         = 0.8516;
SM.Imped_Std.Ra         = 0.0054;                                   %Stator resistance @ 75degC [pu]
SM.Imped_Std.Xdst_RI    = 13.7e-2;                                  %X"d unsat pu
SM.Imped_Std.Xdt_RI     = 21.9e-2;                                  %X'd unsat pu
SM.Imped_Std.Xd_RI      = 222e-2;                                   %Xd unsat pu

SM.Imped_Std.Xqst_RI    = 18.4e-2;                                  %X"q unsat pu 
SM.Imped_Std.Xq_RI      = 113e-2;                                   %Xq unsat pu  
SM.Imped_Std.X1         = 6.6e-2;                                   %Stator winding leakage reactance pu

SM.TimeConsts.Tdst_RI   = 0.017;                                    %T"d 
SM.TimeConsts.Tdt_RI    = 0.267;                                    %T'd 
SM.TimeConsts.Tqst_RI   = 0.018;                                    %T"q 

SM.base.Iexc            = 0.85; 
SM.SatData.If_OC_ST     = [0.19 0.35 0.55 0.6 0.67 .72 .8 .89 .92 .98 1.09 1.31 1.61 2.52]/SM.base.Iexc;
SM.SatData.V_OC         = [259 374 553 586 621 659 689 716 724 742 760 793 828 897]/SM.Rating.Vline;

My first post; so please advise if i can compose my questions better! Thanks

Answer 1

[Meme Young]

Hi Dude I am doing sync machine modelling as well. It seems that you are imitating the simulink sync machine model. How do you use these parameters in Simulink?

[Scott Hill]

Hello,

Do you mean, how do you use parmaters from the workspace in Simulink?

The code snippet i made above will load parameters into the workspace. These parameters can then be written into the Simulink model (as words, instead of numbers). This way, you can parameterise the same model with a variety of machines. ie load different parameter sets. The Simulink model then just reads (for example) SM.Rating.S from the workspace.

[Meme Young]

Yes you are right. I mean, these parameters you posted look like standard style, like Xd Xq Xd' Xq' Xd'' Xq'' Td Tq these things. There are also another kind of parameter style called fundemental, like Lmq Lmd Rfd Llfd Rkd Lkd these things. Both styles exist in Simulink sync machine models, but under the mask all the parameters are fundemental when simulation.

But I cant find the way to convert standard parameters to standard ones.The thing that I wanna do is to create a model using controlled sources that can imitate the sync machine model, and there is a existing example in Simulink, so it may be a good idea to just find the way of parameter conversion and copy this example, instead of creating a brand new model using standard parameters. I am just wondering if you know how to convert standard parameters to fundemental ones? I would appreciate if you could help.

[Scott Hill]

Are you trying to describe the difference between:

Synchronous Machine SI Fundamental block

Synchronous Machine pu Fundamental block

Synchronous Machine pu Standard block

See here: https://uk.mathworks.com/help/physmod/sps/powersys/ref/synchronousmachine.html

Otherwise, i'm sorry, but i'm not sure what your question relates to...

Regards

Scott

[Meme Young]

Yes, thank you, I am trying to describe the difference between

Synchronous Machine pu Fundamental block

and

Synchronous Machine pu Standard block.

I am just trying to find a way to create 2 Synchronous machines, one is pu fundemental and the other is pu standard, and they have identical transient and steady-state characteristics. That means I need to find a way to convert parameters between pu standard and pu fundemental, but no documentation of matlab mentioned the exact way. The references of matlab documentation is also very confusing and chaotic, and the parameters and circuits in these references may not be suitable for matlab sync machine models at all. I am wondering if you could figure it out.

Regards

Young

[Adrián Solís Bajo]

The methodology for the exact conversion of synchronous machine parameters from standard form to fundamental form was first described by I. M. Canay. You can find it in his article: DETERMINATION OF SYNCHRONOUS MACHINE MODEL PARAMETERS FROM THE CHARACTERISTIC QUANTITIES APPLICABLE ALSO TO SUB-SUBTRANSIENT DATA. You can also find the conversion process in the user help documentation of several power system simulation programs.