code: public function actionImport()
      {
          $field = [
              'fileImport' => 'File Import',
          ];
          
          $modelImport = DynamicModel::validateData($field, [
              [['fileImport'], 'required'],
              [['fileImport'], 'file', 'extensions'=>'xls,xlsx','maxSize'=>1024*1024],
          ]);
  
          if (Yii::$app->request->post()) {
              $modelImport->fileImport = \yii\web\UploadedFile::getInstance($modelImport, 'fileImport');
              if ($modelImport->fileImport && $modelImport->validate()) {                                
                  $inputFileType = \PHPExcel_IOFactory::identify($modelImport->fileImport->tempName );
                  $objReader = \PHPExcel_IOFactory::createReader($inputFileType);
                  $objPHPExcel = $objReader->load($modelImport->fileImport->tempName);
                  $sheetData = $objPHPExcel->getActiveSheet()->toArray(null,true,true,true);
                  $baseRow = 2;
                  while(!empty($sheetData[$baseRow]['A'])){
                      $model = new Mahasiswa();
                      $model->nama = (string)$sheetData[$baseRow]['B'];
                      $model->nim = (string)$sheetData[$baseRow]['C'];
                      $model->save(); 
                      //die(print_r($model->errors));
                      $baseRow++;
                  }
                  Yii::$app->getSession()->setFlash('success', 'Success');
              }
              else{
                  Yii::$app->getSession()->setFlash('error', 'Error');
              }
          }
          
          return $this->redirect(['index']);
      }
docs: /*
  IMPORT WITH PHPEXCEL