1. Division of Decision and Control Systems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology , Stockholm SE-100 44 , Sweden
2. Department of Mathematical Sciences “G.L. Lagrange”, Politecnico di Torino , Turin 10129 , Italy
3. Division of Automatic Control, Department of Electrical Engineering, Linköping University , Linköping SE-58183 , Sweden