Charge redistribution method for cell arrays
A topology is described in which each pair of cells in a string shares a single inductor. Switches permit the single inductor to selectively charge one or the other of the cells. In a variant of the topology, the inductor together with additional switches permit selectively charging multiple cells simultaneously (even one or both cells simultaneously in a pair of cells), drawing upon either an external energy source or upon one or multiple other cells in the string. In this way the number of inductors is minimized while providing isolation among the charging circuits.
1. Apparatus comprising:
a plurality of cell assemblies each having a positive and negative current terminal, the assemblies connected in series by their current terminals,
each cell assembly comprising first and second storage cells each having a respective positive and negative terminal, the positive terminal of the first cell defining the positive current terminal, the negative terminal of the second cell defining the negative current terminal, the negative terminal of the first cell connected with the positive terminal of the second cell, thereby defining a node;
each cell assembly further comprising an inductor and first and second switches, the inductor having first and second leads, the second lead of the inductor connected to the node, the first lead of the inductor connected by the first switch to the positive terminal of the first cell and connected by the second switch to the negative terminal of the second cell,
the inductors of the cell assemblies inductively coupled together,
the apparatus further comprising a controller selectively opening and closing the first switches and the second switches of the cell assemblies.
2. The apparatus of claim 1 further comprising:
an energy sharer, the sharer comprising an inductor inductively coupled with the inductors of the cell assemblies, the inductor of the sharer connected by at least one switch to an energy sharing bus,
the controller selectively opening and closing the at least one switch of the sharer.
3. The apparatus of claim 2 wherein the connection of the inductor of the sharer to the energy sharing bus is further characterized as a full-wave bridge comprising four switches,
the controller selectively opening and closing the four switches of the full-wave bridge of the sharer.
4. The apparatus of claim 1 wherein each cell assembly is further characterized in that its inductor further comprises a third lead, the third lead having the same inductive sense relative to the second lead as the inductive sense of the second lead relative to the first lead,
each cell assembly further comprising third and fourth switches, the third lead connected by the third switch to the positive terminal of the first cell and connected by the fourth switch to the negative terminal of the second cell,
the controller selectively opening and closing the third switches and the fourth switches of the cell assemblies.
5. The apparatus of claim 1 wherein the storage cells are electrochemical storage cells.
6. A method of use of the apparatus of claim 4 , the method comprising the steps of:
closing at least one of the first, second, third, and fourth switches for at least a first storage cell in one of the cell assemblies so as to draw charge from the storage cell connected thereto, said cell defining a first source cell;
closing at least one of the first, second, third, and fourth switches for at least a second storage cell in one of the cell assemblies so as to cause charge to flow into the storage cell connected thereto, said cell defining a first destination cell;
whereby charge is transferred from the first source cell to the first destination cell.
7. The method of claim 6 further comprising:
closing at least one of the first, second, third, and fourth switches for at least a third storage cell in one of the cell assemblies so as to draw charge from the storage cell connected thereto, said cell defining a second source cell;
whereby charge is transferred from the first source cell and from the second source cell to the first destination cell.
8. The method of claim 6 further comprising:
closing at least one of the first, second, third, and fourth switches for at least a fourth storage cell in one of the cell assemblies so as to cause charge to flow into the storage cell connected thereto, said cell defining a second destination cell;
whereby charge is transferred from the first source cell to the first destination cell and to the second destination cell.