Ember set Component property in controller

I have a Component, whose property I want to set in a Controller. I seem to be having problems using the computed alias to set it. Please see code below.

My Component is as follows:

 TM.MyModalComponent = Ember.Component.extend({
    totalWidth: '200px',  
    widthStyle: function() { 
        console.log(this.get('totalWidth'));
        return 'width:'+this.get('totalWidth');    
    }.property('totalWidth'),  
 });

I am trying to set the property totalWidth in a parent controller as follows:

modalWidth:Ember.computed.alias("myModalComponent.totalWidth"),
this.set("modalWidth",'100px'); 

It returns a undefined value when I try to console log it and errors with

Property set failed: object in path "myModalComponent" could not be found or was destroyed.

Any help will be much appreciated.

Thanks, Lakshmi