The individual sources are responsive to an error signal representing the difference between {HEAD ~ a component} of power common to {TAIL ~ the sources} or frequency, if the power sources are AC generators, and a reference and to individual signals representing a variable power component 
common to
The individual sources are responsive to an error signal representing the difference between { HEAD ~ a component } of power common to { TAIL ~ the sources } or frequency , if the power sources are AC generators , and a reference and to individual signals representing a variable power component
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH