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