stop closing the modal by clicking backdrop or outside the modal

$modal.open({
   // ... other options
   backdrop  : 'static',
   keyboard  : false
});

While you creating your modal you can specify its behavior:

Though it is late still it might be helpful for somebody else facing the issue:

 const config: ModalOptions = {
                backdrop: 'static',
                keyboard: false,
                animated: true,
                ignoreBackdropClick: true,
                initialState: {
                  data1: 'new-user',
                  username: 'test'
                }
              };
              this.bsModalRef = this.modalService.show(MyComponent, config);

initialState object is used to pass data to modal.

As per the answer of @anshuVersatile, I understand we need to use some modal options.

Then I create a object of NgbModalOptions and pass it as second parameter of my open method and it works.

Code is as follows :

let ngbModalOptions: NgbModalOptions = {
      backdrop : 'static',
      keyboard : false
};
console.log(ngbModalOptions);
const modalRef = this.modalService.open(NgbdModalContent, ngbModalOptions);

Here is the updated plunker.