Patent ID: 8421271

Claim:
An apparatus comprising: an energy storage device configured to supply electrical energy; a first bi-directional DC-to-DC voltage converter coupled to the energy storage device; a first input device configured to receive electrical energy from a first external energy source; a voltage bus coupled to the first bi-directional DC-to-DC voltage converter and to the first input device; a voltage inverter coupled to the voltage bus and configured to convert a voltage on the voltage bus that is supplied by the energy storage device and the first bi-directional DC-to-DC voltage converter into an AC voltage suitable for driving an electromechanical device; and a controller configured to: control the first bi-directional DC-to-DC voltage converter to convert a first charging energy on the voltage bus into a second charging energy suitable for charging the energy storage device during a charging operation; monitor a voltage of the energy storage device during the charging operation; and control the first bi-directional DC-to-DC voltage converter to convert the first charging energy into a third charging energy configured to maintain the voltage of the energy storage device at a pre-determined value.