I have created a Bot Application using Microsoft Bot Framework and want to achieve the following:
I think that you are missing the bind of your PowerShell
instance to the runspace.
ps.Runspace = runspace;
Take a look to this for more details.
Alternatively, you can create a Pipeline (as explained here) using the runspace and invoke the commands.
Pipeline pipeline = runspace.CreatePipeline("<COMMAND TO EXECUTE REMOTELY>");
var results = pipeline.Invoke();