Method and system for cell equalization with charging sources and shunt regulators

Abstract

A system and method for charging a rechargeable, or secondary, battery including a series string of cells, includes a topology of charging sources that selectively provides charging current to cells that need to be charged, but avoids overcharging cells that are already charged above a predetermined voltage threshold. Based on individual cell voltage measurements, the charging current is controlled in a manner to direct charging current to the battery cell(s) needing charge until these cells are fully charged, and by-passes battery cells that are fully charged or become fully charged.

1 . A system for charging a secondary battery, comprising: 
 a plurality of battery cells connected in a series string, wherein said series string comprises: 
 a first battery cell at a load end and an nth battery cell at a ground end, and  
 a cell junction located between each respective pair of battery cells;  
   a plurality of charging sources, wherein: 
 a first charging source electrically coupled to said load end,  
 a second charging source electrically coupled to a first cell junction between said first battery cell and a second battery cell located adjacent to said first battery cell, and  
 a charging source electrically coupled to each cell junction occurring every two cells thereafter; and  
   a plurality of shunt regulators, wherein a respective shunt regulator is connected in parallel across each of said second battery cell to said nth battery cell.    
     
     
         2 . The system of  claim 1 , wherein said plurality of shunt regulators comprises: 
 (n−1) shunt regulators.    
     
     
         3 . The system of  claim 1 , wherein said plurality of charging sources comprises: 
 (n+2)/2 charging sources when n is an even number; and    (n+1)/2 charging sources when n is an odd number.    
     
     
         4 . The system of  claim 1 , further comprising: 
 a charging source electrically coupled to each of said plurality of charging sources, wherein said charging source provides charging current to each of said plurality of battery cells.    
     
     
         5 . The system of  claim 1 , further comprising: 
 a plurality of controllers, wherein a controller is coupled to a respective charging source of said plurality of charging sources, and each of said controllers includes circuitry to at least one of switch on and switch off each of said plurality of charging sources.    
     
     
         6 . The system of  claim 5 , wherein said circuitry is configured to allow only one charging source to be switched on at a time.  
     
     
         7 . The system of  claim 1 , further comprising: 
 a shunt controller coupled to each of said plurality of shunt regulators, wherein each shunt controller is configured to switch on and off each of said plurality of shunt regulators.    
     
     
         8 . The system of  claim 7 , wherein said shunt controller is configured to switch on a shunt regulator if a battery cell with which said shunt regulator is coupled across in parallel is fully charged, and switch off said shunt regulator if said battery cell is not fully charged.  
     
     
         9 . The system of  claim 1 , further comprising: 
 a controller coupled to each charging source and each shunt regulator, wherein said controller includes circuitry to switch on and switch off each of said plurality of charging sources, and switch on and switch off each of said plurality of shunt regulators; and    a plurality of cell monitoring circuits, wherein at least one cell monitoring circuit is coupled to each respective battery cell to monitor an amount of charge within each respective cell monitor, and in communication with said controller, wherein said controller is configured to switch on only one charging source at a time, and    determines one or more of said plurality of battery cells needing to be charged,    determines a target battery cell, wherein: 
 said target cell is at least one of said plurality of battery cells needing to be charged, and  
 said target battery cell is located closer to said load end than any other of said plurality of battery cells that may need to be charged, and  
   switches on a target charging source, wherein: 
 said target charging source is located at a cell junction between said target battery cell and said load end, and  
 said target charging source is located at a cell junction farther away from said load end than another charging source located between said target battery cell and said load end, and  
   wherein said controller switches on and switches off each of said plurality of shunt regulators based upon an amount of charge within a battery cell associated with each respective shunt regulator.    
     
     
         10 . A charging system for charging a rechargeable battery comprised of n cells connected in a serial string from a first cell at one end to an nth cell at another end with a respective cell junction being located between each adjacent cell, the system comprising: 
 a plurality of switched charging sources, selectively coupled with a respective one of the cell junctions, wherein a number of the switched charging sources is less than (n); and    a plurality of shunt regulators, wherein a respective shunt regulator is connected in parallel across each of the second cell through the nth cell, such that a number of the shunt regulators is (n−1).    
     
     
         11 . The charging system of  claim 10 , further comprising: 
 a charging source electrically coupled with each of the switched charging sources such that the switched charging sources may be configured to provide charging current to one or more of the n cells.    
     
     
         12 . The charging system of  claim 10 , further comprising: 
 a respective cell monitoring circuit configured to measure a voltage of an associated cell; and    a controller coupled to each of the cell monitoring circuits, the shunt regulators, and the switched charging sources; wherein the shunt regulators and the switched charging sources are operated by the controller to provide charging current to each having a voltage below a predetermined threshold and to avoid providing charging current to each cell having a voltage at or above a predetermined threshold.    
     
     
         13 . The charging system of  claim 12 , wherein the controller operates only one of the switched charging sources in the first state at any given time.  
     
     
         14 . A method for equalizing voltage of a secondary battery being charged, the battery comprised of n cells connected in a serial string from a first cell at a load end to an nth cell at a ground end with a respective cell junction being located between each adjacent cell, the method comprising the steps of: 
 coupling the plurality of switched charging sources to the serial string, wherein a first switched charging source is electrically coupled to the one end of the serial string, and second switched charging source is electrically coupled at the cell junction between the first cell and an adjacent second cell; and a respective switched charging source is electrically coupled at the cell junctions occurring every two cells thereafter;    coupling a plurality of shunt regulators to the serial string, wherein a respective shunt regulator is connected in parallel across each of the second cells through the nth cell; and    operating the switched charging sources and the shunt regulators to selectively provide charging current to one or more of the n cells.    
     
     
         15 . The method of  claim 14 , wherein said step of connecting a plurality of shunt regulators to the serial string comprises the step of: 
 connecting (n−1) shunt regulators to the serial string.    
     
     
         16 . The method of  claim 14 , wherein said step of connecting the plurality of switched charging sources to the serial string comprises the step of: 
 connecting ((n−2)/2) switched charging sources to the serial string when n is an even number.    
     
     
         17 . The method of  claim 14 , wherein said step of connecting the plurality of switched charging sources to the serial string comprises the step of: 
 connecting ((n+1)/2) switched charging sources to the serial string when n is an odd number.    
     
     
         18 . The method of  claim 14 , further comprising the steps of: 
 operating each of the switched charging sources in one of a first state and a second state, wherein when a switched charging source is in the first state, the source provides a charging current to the respective cell junction where that switched charging source is electrically coupled; and when the switched charging source is in the second state, the source does not provide a charging current to the respective cell junction where that switched charging source is electrically coupled; and    operating each of the shunt regulators in a first state to bypass charging current around the respective cell across which it is connected and operate as a high-impedance electrical path in a second state.    
     
     
         19 . The method of  claim 14 , further comprising the step of: 
 operating the shunt regulators and the switched charging sources to provide charging current to each cell having a voltage below a predetermined threshold and to avoid providing charging current to each cell having a voltage at or above a predetermined threshold.    
     
     
         20 . The method of  claim 19 , further comprising the steps of: 
 monitoring a respective voltage level of each of the n cells; and    determining which of the n cells is at or above a predetermined voltage threshold.    
     
     
         21 . A method for equalizing voltage of a secondary battery comprising the steps of: 
 a) monitoring an amount of charge contained within a plurality of battery cells utilizing at least one cell monitor to determine if at least one battery needs charging;    b) transmitting a signal to begin charging operations from said at least one cell monitor, to a controller, when at least one of said plurality of battery cells needs charging;    c) determining, by said controller, which charging source, of a plurality of charging sources, to utilize to charge said at least one of said plurality of battery cells needing charging; and    d) switching on, by said controller, an appropriate charging source of said plurality of charging sources to charge said at least one of said plurality of battery cells needing charging, wherein said appropriate charging source is determined by its location with respect to at least one battery cell needing charge.    
     
     
         22 . The method of  claim 21 , further comprising the step of: 
 e) switching on at least one shunt regulator coupled in parallel to at least one of said plurality of battery cells, wherein said at least one shunt regulator is a shunt regulator coupled in parallel across a battery cell including a charge amount greater than a threshold amount.    
     
     
         23 . The method of  claim 22 , wherein said step of switching on at least one shunt regulator occurs prior to said step of switching on an appropriate charging source.  
     
     
         24 . The method of  claim 21 , further comprising the steps of: 
 f) continuing to monitor, by said cell monitor, said plurality of battery cells until at least one battery cell receiving charging current is charged to a threshold amount of charge; and    g) switching on, by said controller, a shunt regulator coupled in parallel to said battery cell receiving charging current when said battery cell receiving charging current contains said threshold amount of charge.    
     
     
         25 . The method of  claim 24 , further comprising: 
 h) repeating steps f) and g) until each of said plurality of battery cells contains said threshold amount of charge.    
     
     
         26 . The method of  claim 25 , further comprising the steps of: 
 i) switching off, by said controller, said charging source when each of said plurality of battery cells contains said threshold amount of charge; and    j) switching off, by said controller, any shunt regulator switched on by said controller.    
     
     
         27 . The method of  claim 21 , wherein step c) comprises the steps of: 
 determining a target battery cell by said controller, wherein:    said target cell is at least one of said plurality of battery cells and a battery cell needing charge, and    said target battery cell is located closer to said load end than any other of said plurality of battery cells needing charge, and switching on a target charging source, wherein:    said target charging source is located at a cell junction between said target battery cell and said load end, and    said target charging source is located at a cell junction farther away from said load end than another charging source located between said target battery cell and said load end.