Why do I see "The RPC server is unavailable" when calling Hysys solver from MATLAB?

Hi! I am trying to automate my hysys model on MATLAB, and successfully linked via actxserver. Added my code below. Currently, I keep getting the error that

Warning: Error during simulation run: Invalid input for argument 2 (rhs2):

Value must be numeric or logical

I tried to see what the problem was and used the code:

>> properties(MySimCase.Solver)

but I received back the error below:

Error: The RPC server is unavailable.

When I code properties(MySimCase), it is able to list for me all the properties, only for solver it isnt.

Please help!

Below is the full code:

>> % Connect to HYSYS Application
try
    MyObject = actxserver('Hysys.Application');
catch ME
    error('Error connecting to HYSYS: %s', ME.message);
end

FileNamePath = 'Test'; % Adjust the filename as needed
try
    MySimCase = MyObject.SimulationCases.Open([cd, strcat('\', FileNamePath, '.hsc')]);
catch ME
    error('Error opening simulation case: %s', ME.message);
end
MySimCase.Visible = true;

% Verify the list of unit operations
try
    unitOperations = MySimCase.Flowsheet.Operations;
    numUnitOperations = unitOperations.Count;
    unitOperationNames = cell(numUnitOperations, 1);
    for idx = 1:numUnitOperations
        unitOperationNames{idx} = unitOperations.Item(idx - 1).Name; % Adjusting index for MATLAB (1-based)
    end
    disp('Available unit operations in the flowsheet:');
    disp(unitOperationNames);
catch ME
    error('Error accessing unit operations: %s', ME.message);
end

% Access the LIC control under unit operations
try
    LICSP = unitOperations.Item('LIC');
catch ME
    error('Error accessing LIC control: %s', ME.message);
end

if isempty(LICSP)
    error('The ''LIC'' control was not found in the flowsheet.');
end

% Display the properties of LICSP for debugging
disp('Properties of LICSP:');
disp(get(LICSP));

% Set the range for the filling level in LIC (SP)
startLevel = 0.5;
endLevel = 0.9;
stepSize = 0.1;

% Initialize variables for storing the results
seagoingBOG = [];
cjkBOG = [];
portBOG = [];
boilerBOG = [];

% Loop through the filling levels
fillingLevel = startLevel:stepSize:endLevel;
for i = 1:numel(fillingLevel)
    % Set the filling level value
    try
        LICSP.SPValue = fillingLevel(i); % Set the setpoint value
    catch ME
        warning('Error setting LIC control set point: %s', ME.message);
        continue;
    end
    
    % Run the simulation case
    try
        MySimCase.Solver.Integrator.RunUntil(MySimCase.Solver.Integrator.CurrentTime)
    catch ME
        warning('Error during simulation run: %s', ME.message);
        continue;
    end
    
    % Obtain Seagoing BOG
    try
        bog2Stream = MySimCase.Flowsheet.MaterialStreams.Item('BOG2');
        seagoingBOG(i) = bog2Stream.MolarFlow.GetValue('kgmole/h') * 8760; % Assuming 8760 hours in a year
    catch ME
        warning('Error accessing BOG2 stream for Seagoing BOG: %s', ME.message);
        seagoingBOG(i) = NaN;
    end
    
    % Obtain CJK BOG
    try
        bog2Stream = MySimCase.Flowsheet.MaterialStreams.Item('BOG2');
        cjkBOG(i) = bog2Stream.MolarFlow.GetValue('kgmole/h') * 8760 * 0.5; % Example: Assuming CJK BOG is 50% of BOG2
    catch ME
        warning('Error accessing BOG2 stream for CJK BOG: %s', ME.message);
        cjkBOG(i) = NaN;
    end
    
    % Obtain Port BOG
    try
        bog3Stream = MySimCase.Flowsheet.MaterialStreams.Item('BOG3');
        portBOG(i) = bog3Stream.MolarFlow.GetValue('kgmole/h') * 8760; % Assuming 8760 hours in a year
    catch ME
        warning('Error accessing BOG3 stream for Port BOG: %s', ME.message);
        portBOG(i) = NaN;
    end
    
    % Obtain Boiler BOG
    try
        bog2Stream = MySimCase.Flowsheet.MaterialStreams.Item('BOG2');
        bog3Stream = MySimCase.Flowsheet.MaterialStreams.Item('BOG3');
        boilerBOG(i) = (bog2Stream.MolarFlow.GetValue('kgmole/h') + bog3Stream.MolarFlow.GetValue('kgmole/h')) * 8760 - cjkBOG(i);
    catch ME
        warning('Error accessing BOG streams for Boiler BOG: %s', ME.message);
        boilerBOG(i) = NaN;
    end
end

% Close the HYSYS application
MyObject.Quit();

Answer 1

[Shubham]

Hi Jun,

The "RPC server is unavailable" error in MATLAB when calling HYSYS via "actxserver" arises from improper COM server closure, timing issues, or system service/firewall problems. This error can occur if a previous COM instance is still running or in the process of shutting down while a new one is being initiated.

To resolve this issue, you can follow these steps:

1. Properly close the COM server at the end of your MATLAB

MyObject.Quit();  % Close the HYSYS application
delete(MyObject);  % Delete the COM object

2. Add a small delay after closing the server to ensure it has enough time to terminate:

pause(5);  % Pause for 5 seconds

Refer to the following documentation link for more information on "pause" function:

https://mathworks.com/help/releases/R2024a/matlab/ref/pause.html

Hope this helps

[Walter Roberson]

Please link to the documentation for codepause ?

[Shubham]

Thanks for catching that @Walter Roberson. I was indeed referring to the "pause" function. Appreciate your attention to detail.