BATTERY PACK WITH TRIPLE-ACTIVE BRIDGE DC-DC CONVERTER

1 . A battery pack comprising:

a triple-active bridge DC-DC converter having a transformer, first and second bridges on a first side of the transformer, and a full-bridge on a second side of the transformer, wherein at least one of the two bridges is a fractional bridge;

a first battery electrically connected in parallel with each of the first and second bridges on the first side of the transformer; and

a second battery electrically connected with the full-bridge on the second side of the transformer.

2 . The battery pack of claim 1 , wherein each bridge on the primary side of the triple-active bridge includes a capacitor and an inductor in series with a transformer inductive winding.

3 . An energy storage system comprising a plurality of battery packs of claim 2 arranged in series.

4 . The battery pack of claim 1 , wherein the magnetic flux at a magnetic core of the transformer is asymmetric.

5 . The battery pack of claim 4 , wherein two-thirds of the total magnetic flux on the first side of the bridge is induced by the first bridge on the first side of the transformer and one-third is induced by the second bridge on the first side of the transformer.

6 . A process for operating the triple-active bridge DC-DC converter of claim 2 as a double-active bridge DC-DC converter, comprising maintaining switching elements in the full bridge in selected static states such that the full bridge effectively functions as a half-bridge.

7 . The battery pack of claim 1 , wherein the first bridge on the first side of the transformer is a full-bridge and the second bridge on the first side of the transformer is a half-bridge.

8 . The battery pack of claim 1 , wherein the first bridge on the first side of the transformer is a full-bridge and the second bridge on the first side of the transformer is a quarter-bridge.

9 . The battery pack of claim 1 , wherein the first bridge on the first side of the transformer is a half-bridge and the second bridge on the first side of the transformer is a quarter-bridge.

10 . A battery pack comprising:

a triple-active bridge DC-DC converter having a transformer, the transformer including a magnetic core, a first winding on a first side of the transformer having a predetermined number of turns, wound around one leg of the core and a second winding on the first side of the transformer having the same number of turns wound around a second leg of the core, a first bridge for inverting a DC input to produce an AC output electrically connected with the first winding, a second bridge for inverting the DC input to produce an AC output electrically connected with the second winding, and a third winding on a second side of the transformer electrically connected to an input side of a third bridge for rectifying an AC current to provide a DC output; and

a battery having an output electrically connected to an input of each of the first and second bridges on the first side of the transformer.

11 . The battery pack of claim 10 , wherein each bridge on the primary side of the triple-active bridge includes a capacitor and an inductor in series with a transformer inductive winding.

12 . An energy storage system comprising a plurality of battery packs of claim 10 arranged in series.

13 . The battery pack of claim 10 , wherein the first bridge on the first side of the transformer is a full-bridge and the second bridge on the first side of the transformer is a half-bridge.

14 . The battery pack of claim 10 , wherein the first bridge on the first side of the transformer is a full-bridge and the second bridge on the first side of the transformer is a quarter-bridge.

15 . The battery pack of claim 10 , wherein the first bridge on the first side of the transformer is a half-bridge and the second bridge on the first side of the transformer is a quarter-bridge.