A feedback control circuit and method for a control system used to control
an electrical power generating source that comprises a free piston
Stirling engine driving a linear alternator. A switching mode rectifier
connects the alternator winding to an output circuit that includes an
electrical energy storage means and is controlled by a pulse width
modulator that controls the rectifier switching duty cycle and phase. The
control system controls the pulse width modulator. The improvement
computes a voltage across a virtual tuning capacitor and uses the
computed voltage to control the switching mode rectifier so that the
switching mode rectifier is switched in a manner that makes the
alternator circuit operate as if a tuning capacitor were actually present
and so that the control system controls the piston of the Stirling engine
to maintain balance of the mechanical power generated by the Stirling
engine and the electrical power absorbed from the engine by the
alternator.