1. School of Electrical and Electronic EngineeringNorth China Electric Power University Beijing 102206 China
2. Digital Grid Research InstituteChina Southern Power Grid Guangzhou 510000 China
3. Department of Electrical EngineeringInstitute of Southern Punjab Multan 60000 Pakistan
4. Shanghai Key Laboratory of Smart Grid Demand ResponseShanghai Electrical Apparatus Research Institute Co. Ltd. Shanghai 200063 China