Patent ID: 7701075

Claim:
A method for operating an electrical power source, the power source having a free-piston Stirling engine including a piston driving a linear alternator connected through a rectifier to a bus to apply a voltage to the bus, the power source also having a battery, the method allowing the electrical power supplied from the power source to a load to, at times, exceed the maximum power that can be delivered from the free-piston Stirling engine driving the linear alternator, the method comprising: (a) modulating the stroke of the engine piston between a maximum and a minimum stroke to maintain the bus voltage at a design nominal bus voltage (V 1 ) and charging the battery if it is not charged, when and so long as the bus voltage does not fall below the design nominal bus voltage (V 1 ); (b) operating the Stirling engine at the maximum piston stroke and charging the battery if it is not charged when the bus voltage is in the range between the design nominal bus voltage (V 1 ) and a design minimum battery charging bus voltage (V 2 ) that is less than the design nominal bus voltage (V 1 ); (c) operating the Stirling engine at the maximum piston stroke and disconnecting the battery so it can not charge when the bus voltage is in the range between the design minimum battery charging bus voltage (V 2 ) and a design minimum bus voltage (V 3 ) that is less than the design minimum battery charging bus voltage (V 2 ); and (d) operating the Stirling engine at the maximum piston stroke and applying power from the battery to the bus for maintaining the bus voltage at the design minimum bus voltage (V 3 ) when the power supplied from the alternator operating at its maximum stroke is less than the power demand of the load.