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