1. Institute of Energy Technology, Aalborg University, Pontoppidanstraede 101, Aalborg DK-9220, Denmark e-mail:
2. School of Mechanical and Auto Engineering, South China University of Technology, Wushan Road, Tianhe District, Guangzhou 510641, China; Hebei University of Science and Technology, Yuhua East Road, Shijiazhuang 050018, P. R. China
3. R&D Center, Fuxin Electronic Technology Co. Ltd., No. 20 Keyuan Road 3, Gaoli, Ronggui, District Shunde, Fushan, Guangdong 528306, China