问尝试禁用日期选择器中的过去日期时，为什么会出现验证错误？

EN

<div class="input-group">
  <input class="form-control" [minDate]="ngdate" placeholder="yyyy-mm-dd" name="dp" formControlName="startDate" ngbDatepicker #d="ngbDatepicker">
  <div class="input-group-append">
    <button class="btn btn-outline-secondary calendar fa fa-calendar" (click)="d.toggle()" type="button"></button>
  </div>
</div>

ngdate: NgbDateStruct = {
    year: new Date().getFullYear(),
    month: new Date().getMonth() + 1,
    day: new Date().getDate()
};

this.registerForm = this.formBuilder.group({
    startDate: ['']
});