Control scheme for power modulation of a free piston Stirling engine

DETAILED DESCRIPTION The present invention provides a new control system which essentially maintains a constant displacer-to-piston stroke ratio and their relative phase angle, and therefore maintains a high cycle efficiency, over a wide range of operating conditions.
This control scheme is especially advantageous for use in controlling the operation of a solar powered free piston Stirling engine-linear alternator generator generator system feeding power to a utility power line.
In particular, the present invention provides a controlling scheme for a permanent linear alternator wherein an autotransformer is connected in series with tuning capacitance between a linear alternator and a grid.
Thus, the autotransformer control scheme provides an automatic means to modulate the engine power and heat input rate in a natural manner maintaining a high efficiency over a wide operating range.
It also provides a simple start-up and shut down procedure by changing the alternator terminal voltage in a continuous and smooth manner from zero to full load voltage, thus limiting the start-up and shut down transients to very low levels.
If the alternator is of the type having a field winding rather than being of the permanent magnet type, then instead of or in addition to the autotransformer, a current control means may be employed to control the energization of the field winding of the alternator to provide for maintaining the desired high engine cycle efficiency over the Stirling engine operating range.
The present invention further includes a radiator fan on-off control to provide a simple and cost effective means of allowing the power module satisfactory operation at much lower than nominal ambient temperatures.