Device for balancing parallel strings

A battery plant system, comprising:

• power conditioning means for converting alternating current electrical power to direct current electrical power during the charging of said battery plant and converting direct current electrical power to alternating current electrical power during the discharging of said battery plant;
• a plurality of battery strings connected electrically in parallel across common bus conductors to said power conditioning means;
• a plurality of battery modules connected electrically in series to form each of said battery strings;
• bypass switching means, in association with each of said battery modules, for redirecting electrical current flow around a failed battery module in response to a failure condition;
• and
• magnetic circuit means in association with each of said battery strings for balancing the electrical current flow through said battery strings in response to at least one failed battery module by equalizing the voltages across said common bus conductors for each of said battery strings.

A method of balancing the electrical current flow through a plurality of battery strings which are connected electrically in parallel and in which each of said battery strings is formed by a plurality of batteries connected electrically in series, comprising the steps of:

• providing a saturable reactor in association with each of said battery strings such that each of said saturable reactors has a main winding connected electrically in series with one of said battery strings;
• sensing the electrical current flow through each of said battery strings;
• and
• controlling the magnetic flux density through a magnetic core of each of said saturable reactors such that the voltages across each of said main windings equalizes the voltages across common bus conductors for each of said battery strings.