Pneumatic drives have been widely used alongside with
electrical machines. They have many distinct advantages
compared to electrical drives, such as simple in structure,
safe in hazard operating conditions and low-cost in
manufacturing. Its major weakness is low energy efficiency
and it is reported that only less than 30% efficiency is
achieved in most cases [1, 2]. With the expansion of the
usage of compressed air and the rapid development of
multi-scale Compressed Air Energy Storage (CAES), the
attention to pneumatic drives increases in recent years, due
to searching for efficient energy conversion devices to
convert compressed air energy to mechanical energy and in
turn electrical energy.