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OPC connection with siemens TIA portal

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omkar tulankar
omkar tulankar on 29 Oct 2020
Commented: omkar tulankar on 18 Nov 2020
I have developed a model of motor speed control using variable frequency drive and established the server by defining OPC connection. The motor that I am using is asynchronous motor with parameters 5.5kw power and 1500 rpm. When I run the model and log the data through PLC , the value changes from full load condition to the fed value. For example , If I feed the rpm speed as 1000 rpm , the motor speed will first go to the full load condition i.e 1500 rpm and then go to 1000 rpm. What I want to do is the value should move from 0 to 1000 rpm(fed value). I am attaching the code that I am using for it.
function [x] = Read_OPC_Func(y)
% variables
persistent init_Server;
persistent init_Nodes;
persistent uaClient;
persistent Var_Node_In;
persistent Var_Node_Out;
persistent testVal;
% initialize variables
if (isempty(init_Server))
testVal = 0;
init_Server = 0;
init_Nodes = 0;
% OPC UA server (PLC) address and connecting client (Simulink) to the
% server
if init_Server == 0
init_Server = 1;
uaClient = opcua('',4840);
% define variable nodes in the server
if uaClient.isConnected == 1 && init_Nodes == 0
init_Nodes = 1;
% find DB "OpcInterface" of the server
%DB_Node = findNodeByName(uaClient.Namespace, 'OpcInterface', '-once');
% find variables "ref_speed" and "Motor_speed" in the DB "OpcInterface
Var_Node_In = opcuanode(3, '"OpcInterface"."ref_speed"',uaClient);
Var_Node_Out = opcuanode(3, '"OpcInterface"."Motor_speed"',uaClient);
% read and write variables of the server
if uaClient.isConnected == 1 && init_Nodes == 1
% read "ref_speed" value from server and store in "val"
[val, ~, ~] = readValue(uaClient, Var_Node_In);
% assign input y of the function to "Motor_speed" variable
writeValue(uaClient, Var_Node_Out, y);
% assign "val" to variable "testVal"
testVal = val;
% assign "Motor_Speed" ("testVal") value to the output x of the function
x = double(testVal);


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Answers (1)

Joel Van Sickel
Joel Van Sickel on 2 Nov 2020
Hello Omkar,
it is quite possible the problem isn't with this code itself. As this is just a function, the question is where is the motor getting full speed from? Does the actuall controller of the motor start it at full speed, and then the first command from this code actually works and sets it to 1000. Do you have something that is calling this code before your submit the value of 1000? I would look beyond this code for your issue. Is there a default value for your ref speed that is automatically setting it to 1500?
To debug, you could modify this code to create a function that only reads speed and also read reference speed and check to see if these values are what you expect them to be without commanding anything.


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omkar tulankar
omkar tulankar on 17 Nov 2020
Hi Joel ,
Is there any limitations or prerequisite changes required to be done while using simscape electrical blocks for
establishing communication via OPC. Beacause when I try to establish communication for pure physical models , the communocation is working fine , but then I am trying to the same with using simscape electrical blocks , it is creating problem as mentioned before.
I am also attaching the simulation model I am trying to interface with OPC.
Please provide solution to this problem.
Joel Van Sickel
Joel Van Sickel on 17 Nov 2020
Hello omkar,
it possible that your simulation is not converging, and maybe even proving inf/nan values. The discrete time step you have isn't fast enough to simluate a switching frequency of 7500. You would ideally set your time step to be 1/7500/100, which would also make your model significantly slower. I would recommend using the universal bridge set to average mode as an inverter to start with before attempting to capture switching events in this way.
omkar tulankar
omkar tulankar on 18 Nov 2020
Thanks Joel , I tried changing the time step according to the frequency and it is working much better, though the exact values are not achieved , but variations are lowered down. Thanks for your help ansd handling my queries patiently.

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