Control method for achieving power transfer between stacked rechargeable battery cells and power transfer circuit thereof

Abstract

A control method for achieving power transfer between stacked rechargeable battery cells and a power transfer circuit are disclosed. The power transfer circuit includes an inductor, a first switch, a second switch and a controller. A loop of the rechargeable battery cell having higher power and the inductor is conducted so that the inductor stores power until the current flowing through the inductor meets the cutoff amount. Then, a loop of the rechargeable battery cell having lower power and the inductor is conducted so that the inductor releases the power saved in the inductor to the rechargeable battery cell having lower power until current flowing through the inductor changes direction. Therefore, balance between the rechargeable battery cells can be achieved.

What is claimed is: 
     
         1 . A control method for achieving power transfer between stacked rechargeable battery cells, comprising steps of:
 providing an inductor, respectively linked to two stacked rechargeable battery cells in parallel but not electrically conducted where the two stacked rechargeable battery cells are connected in series, wherein an anode of one rechargeable battery cell is electrically connected to a cathode of the other rechargeable battery cell directly or indirectly so that a loop is formed;   setting a cutoff amount for current flowing through the inductor;   deciding which one of the two rechargeable battery cells has higher power;   conducting a loop of the rechargeable battery cell having higher power and the inductor so that the inductor stores power until the current flowing through the inductor meets the cutoff amount; and   conducting a loop of the rechargeable battery cell having lower power and the inductor so that the inductor releases the power saved in the inductor to the rechargeable battery cell having lower power until current flowing through the inductor changes direction.   
     
     
         2 . The control method according to  claim 1 , wherein the rechargeable battery cell having higher state of charge has higher power. 
     
     
         3 . A power transfer circuit for achieving power transfer between stacked rechargeable battery cells, comprising:
 an inductor respectively linked to two stacked rechargeable battery cells in parallel but not electrically conducted where the two stacked rechargeable battery cells are connected in series, for storing power and releasing stored power, wherein an anode of one rechargeable battery cell is electrically connected to a cathode of the other rechargeable battery cell directly or indirectly so that a loop is formed;   a first switch, connected to the inductor and one of the two rechargeable battery cells, for conducting a loop linking of the inductor and the rechargeable battery cell connected thereto after receiving a conducting signal;   a second switch, connected to the inductor and the other of the two rechargeable battery cells, for conducting a loop linking of the inductor and the rechargeable battery cell connected thereto after receiving a conducting signal; and   a controller, comprising:
 a first comparator, connected to a first end and a second end of the first switch, for detecting voltage difference across the first switch; 
 a second comparator, connected to a third end and a fourth end of the second switch, for detecting voltage difference across the second switch; 
 a first signal source for sending the conducting signal to the first switch; 
 a second signal source for sending the conducting signal to the second switch. 
   
     
     
         4 . The power transfer circuit according to  claim 3 , wherein a cutoff amount for current flowing through the inductor is preset, when the rechargeable battery cell connected to the first switch has higher power, the first signal source sends the conducting signal to the first switch so that the first switch turns on and the inductor stores power until the current flowing through the inductor meets the cutoff amount, and then the second comparator detects voltage difference between two ends of the second switch and sends the conducting signal to the second switch so that the second switch turns on and the inductor releases stored power to the rechargeable battery cell having lower power until direction of the current flowing through the inductor changes. 
     
     
         5 . The power transfer circuit according to  claim 3 , wherein a cutoff amount for current flowing through the inductor is preset, when the rechargeable battery cell connected to the second switch has higher power, the second signal source sends the conducting signal to the second switch so that the second switch turns on and the inductor stores power until the current flowing through the inductor meets the cutoff amount, and then the first comparator detects voltage difference between two ends of the first switch and sends the conducting signal to the first switch so that the first switch turns on and the inductor releases stored power to the rechargeable battery cell having lower power until direction of the current flowing through the inductor changes. 
     
     
         6 . The power transfer circuit according to  claim 3 , wherein the first switch is an N-channel Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) or a P-channel MOSFET. 
     
     
         7 . The power transfer circuit according to  claim 3 , wherein the second switch an N-channel MOSFET or a P-channel MOSFET. 
     
     
         8 . The power transfer circuit according to  claim 4  or  5 , wherein the rechargeable battery cell having higher state of charge has higher power. 
     
     
         9 . The power transfer circuit according to  claim 4  or  5 , wherein when the current flowing through the inductor changes direction, voltage difference between two ends of the switch connected to the rechargeable battery having lower power is 0. 
     
     
         10 . The power transfer circuit according to  claim 3 , wherein when a difference between values of state of charge of the two rechargeable battery cells is smaller than a minimum difference, the first switch and the second switch both turns off.