Problem with the Transformer model in matlab simulink

When I run the simulation without the transformer block, everything works fine. However, when I add the transformer to the network, the waves become rectangular, and I receive the following error message:

"Warning: Could not evaluate MaskDisplay commands of block IEEE34bus_v2019b_Discrete_ZIPload/Three-Phase Transformer (Two Windings)1': Unable to resolve the name ST.satx."

The model involves connecting the transformer to a three-phase load with a constant current of 150 kW and 75 kVAR. How can I resolve this issue?

[Umar]

Hi @Asi angel,

You mentioned, “When I run the simulation without the transformer block, everything works fine. However, when I add the transformer to the network, the waves become rectangular, and I receive the following error message: "Warning: Could not evaluate MaskDisplay commands of block IEEE34bus_v2019b_Discrete_ZIPload/Three-Phase Transformer (Two Windings)1': Unable to resolve the name ST.satx."The model involves connecting the transformer to a three-phase load with a constant current of 150 kW and 75 kVAR. How can I resolve this issue?”

Please see my response to your comments below.

The issue seems to arise from the transformer block's inability to resolve certain parameters or variables, specifically the variable ST.satx which indicates that the variable is either undefined in the workspace or not properly initialized. The rectangular waveforms suggest that the transformer is not functioning correctly, likely due to the improper handling of the input signals or parameters.

To resolve this issue, follow these steps:

Step#1 ,Check Variable Definition:

Make sure that the variable ST.satx is defined in the MATLAB workspace. You can do this by executing the following command in the MATLAB Command Window:



   evalin('base', 'ST.satx');

For more information on “evalin” function, please refer to

https://www.mathworks.com/help/matlab/ref/evalin.html


If it returns an error, you need to define it appropriately.

Step#2,Initialize the Variable:

If ST.satx is not defined, you can initialize it in your MATLAB script or directly in the workspace. For example:



ST.satx = <appropriate_value>; % Replace <appropriate_value> with   the  correct value for your model


Step#3, Review Transformer Parameters:

Double-check the parameters of the transformer block to ensure they are set correctly. Pay special attention to the winding ratios and any other settings that might affect its operation.

Step#4, Simulate Again:

After making the necessary adjustments, run the simulation again to verify that the issue has been resolved.

I would also suggest running your Simulink model in new version because sometimes the old version have some bugs which gets fixed in newer version.

Hope this helps.

[Asi angel]

I tried the above but unfortunately nothing work , when I changed the placement of the transformer and transmission line, the problem was resolved.

[Asi angel]

@Umar

[Umar]

Hi @Asi angel,

First, let me address your first query, “I tried the above but unfortunately nothing work”

I did mention in my comments about “Review Transformer Parameters”

Addressing your query, “when I changed the placement of the transformer and transmission line, the problem was resolved.”

However, after looking at the block diagram with symbols such as pi transmission, Yg to Delta configured transformer and load transformer with delta shape shared by you, please see my response below.

Detailed explanation of theory

First, let me briefly explain the basics of transformer below.

Transformer Basics

Yg Transformer: This configuration provides a neutral point which is useful for grounding and helps manage unbalanced loads. It also allows for easier conversion between line-to-line and line-to-neutral voltages.

Delta Transformer: This configuration typically offers higher efficiency and better handling of transient conditions but does not have a neutral point.

Rectangular Waveforms

So, these rectangular waveforms in your output makes sense which typically arises from non-linear loads or improper transformer configurations that introduce harmonics into the system. Also, you should notice abrupt transitions in voltage levels which indicates saturation effects or misalignment in phase relationships between the transformers.

Transmission Line Model

Now, let me briefly explain theory behind the pi-shaped transmission line model which assumes that capacitance is distributed along its length, which can affect voltage profiles and phase angles. Please bear in mind if not correctly configured in relation to the transformers, this could lead to instability in voltage levels at the output.

Impact of Placement Changes

So, when you mentioned in your comment that changing the placement of the transformer relative to the transmission line resolved the problem, you likely altered how impedance is reflected back through the network. This adjustment can influence phase angles and help mitigate resonance conditions that may have been causing harmonic distortion. So, in my opinion it is possible that your initial configuration created conditions where reactive power was not adequately managed, resulting in waveform clipping or distortion.

So, it is very important that your three-phase load is balanced; unbalanced loads can exacerbate issues related to harmonics and waveform shape.

Hope this helps.

[Asi angel]

@Umar

What do you think is the best solution for this issue?

moreover, when I tried adding the power flow buses to the distribution network, I encountered the following error: 'Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.218374e-17.'"

[Umar]

Hi @Asi angel,

You asked, “What do you think is the best solution for this issue? moreover, when I tried adding the power flow buses to the distribution network, I encountered the following error: 'Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.218374e-17.'"

Please see my response to your comments below.

My analysis for the errors you encountered in your Simulink model are listed below.

Please bear in mind that a matrix is singular when it does not have an inverse, which typically occurs when its determinant is zero. In practical terms, this means that the equations represented by the matrix are linearly dependent,some equations do not provide new information. So, in my opinion the causes of the error are due to

Poor Scaling: This can happen when there are large disparities in the magnitudes of the elements in the matrix. For example, if some values are very large while others are very small, numerical methods may struggle to find accurate solutions.

Modeling Issues: If the distribution network is incorrectly modeled (e.g., missing connections or incorrect parameters), it could lead to a situation where the system is not fully defined, contributing to singularity.

Insufficient Data: If there are not enough buses or branches defined in your network model, it might not be possible to solve for all variables.

So, based on the above mentioned causes of error, I will propose the following solutions to help you resolve your problem.

Check Model Configuration: Make sure that all buses and branches in your distribution network are correctly defined and connected. Also, review the parameters of each component (e.g., resistances, reactances) to ensure they are realistic and correctly specified.

Scaling Adjustments: Normalize values within your model if there is a wide range of magnitudes. For example, consider using per-unit (pu) systems for more consistent scaling across components.

Matrix Conditioning: Use techniques such as regularization to improve matrix conditioning. This involves adding a small value to the diagonal elements of your matrix to prevent singularity. You can also apply numerical techniques such as pivoting or iterative solvers that are more robust against poorly conditioned matrices.

Simulink Diagnostics: Utilize built-in diagnostics within Simulink to identify potential issues with your model configuration. Tools like Model Advisor can help spot common pitfalls. Please click the link below for more information regarding “Model Advisor”.

https://www.mathworks.com/help/simulink/ug/select-and-run-model-advisor-checks.html

Examine simulation settings and solver options; sometimes adjusting these can alleviate numerical problems. Also, before scaling up your model, test it with a simplified version that has fewer components but maintains similar characteristics. This can help isolate the source of errors.

Hope this helps.

[Shivam Gothi]

Hello @Asi angel,

can you please shared the simulink model file along with the parameters necessary to initialise in base workspace so that I can reproduce the error from my end and suggest some solution?

I also faced similiar issue, but I managed to get some workaround by correcting power system network.