{HEAD ~ The magnitude} of a power component common to all the power sources or frequency, if the power sources are AC generators driven by constant speed drives, is compared to {TAIL ~ a reference} to provide an error signal 
is compared to
{ HEAD ~ The magnitude } of a power component common to all the power sources or frequency , if the power sources are AC generators driven by constant speed drives , is compared to { TAIL ~ a reference } to provide an error signal
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH