distributed generation; linear generator; microgeneration; piston generator; power quality; wave energy converter Distributed power generation; Finite element method; Free piston engines; Hydroelectric generators; Permanent magnets; Pistons; Power converters; Power quality; Quality control; Wave energy conversion; Distributed generation system; Laboratory experiments; Linear generators; Microgeneration; Permanent-magnet linear generators; Power electronic converters; Power quality assessment; Wave energy converters; Electric generators