Create controller for partial view in ASP.NET MVC

Why not use Html.RenderAction()?

Then you could put the following into any controller (even creating a new controller for it):

[ChildActionOnly]
public ActionResult MyActionThatGeneratesAPartial(string parameter1)
{
    var model = repository.GetThingByParameter(parameter1);
    var partialViewModel = new PartialViewModel(model);
    return PartialView(partialViewModel); 
}

Then you could create a new partial view and have your PartialViewModel be what it inherits from.

For Razor, the code block in the view would look like this:

@{ Html.RenderAction("Index", "Home"); }

For the WebFormsViewEngine, it would look like this:

<% Html.RenderAction("Index", "Home"); %>

It does not need its own controller. You can use

@Html.Partial("../ControllerName/_Testimonials.cshtml")

This allows you to render the partial from any page. Just make sure the relative path is correct.

If it were me, I would simply create a new Controller with a Single Action and then use RenderAction in place of Partial:

// Assuming the controller is named NewController
@{Html.RenderAction("ActionName", 
                     "New", 
                      new { routeValueOne = "SomeValue" });
}