A compound semiconductor substrate 10 according to the present invention is comprised of a Group III nitride and has a surface layer 12 containing a chloride of not less than 200\xd71010 atomscm2 and not more than 12000\xd71010 atomscm2 in terms of Cl and an oxide of not less than 3. The converter serves for the production of converter output voltages from a direct current source, which form a three-phase system which, inside the machine, produce a rotating field suitable for the generator function for the formation of rotating fields suitable for the generator function. In this manner, various pieces of information may be sent over the secondary logic channel.