How to creat a power system model using Sumulink

I want to creat a model like figure below,and I have some problems.

1.I try to creat using Simulink like figure below(the blocks except "D" are transfer function),is it correct or not ?

2.We assume "D" is a constant in this system, I use the "Transfer fun" block , is it correct or not?

If I mentions before are wrong, please support me with some new ideas?

Thank you!!

[wu chia-wei]

By the way,if we assume this system is a per unit system with baseline power P_base=2000 MVA. I don't really understand the definition of "per unit". For example:If constant D=1(pu), how can I set in Simulink? set 1 directly or need to change?

[Stefan Raab]

For your constant D you can use a Gain block from library Simulink/Math Operations.

Answer 1

[Sebastian Castro]

That looks fine.

As Stefan commented, you can use a Gain block from Simulink > Math Operations if your transfer function is just a static gain.

To answer your per-unit question, the most robust thing to do is to create MATLAB variables for all your per-unit reference values, such as rated voltage and power. Then, all the quantities that operate on per-unit can be multiplied/divided by that variable accordingly.

The following MathWorks documentation page for SimPowerSystems has a pretty thorough explanation of the per-unit system -- with examples!

http://www.mathworks.com/help/physmod/sps/powersys/ref/per-unit-and-international-systems-of-units.html

- Sebastian

[wu chia-wei]

I have a little problem. If I got the 0.3 per unit as input to this per unit system. Can I take this value as input directly or I should operate to multiple the base value. Thank.

[Sebastian Castro]

It depends on whether your calculations are in per-unit or SI values. As with any engineering problem, you have to make sure your units (or lack thereof) are consistent.

Typically, you would want to do all your calculations in per unit so that changing the base values doesn't affect the controller's performance.

- Sebastian