Abstract:
In a two-way direct balance circuit for series cells, a control unit activates a pulse generator to transmit high frequency switch control signals, and a flyback converter is utilized to perform electromagnetic transition between the cells that rapidly conveys power from the cells with high RSOC to the flyback converter and to the cells with low RSOC. The direct energy transfer between cells provides fast and highly efficient performance.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a battery balance circuit, and more particularly, to a battery balance circuit implemented in a battery with a number of cells connected in series and capable of balancing the power between different cells. 
         [0003]    2. Description of the Prior Art 
         [0004]    Most electronic devices use rechargeable battery as a power source for its advantageous convenience and capacity, in which batteries using lithium polymer as core substance are regarded as the most mature products with high capacity density specification. A rechargeable battery is primarily charged by a power supply unit or via an AC adapter from an electronic system where the rechargeable battery is installed. 
         [0005]    The rechargeable battery is usually made of cells, each with specific capacity and connected the each other in series. During the charging or discharging process of the cells, imbalance between cells often takes place due to the state of each cell, which would shorten the life and decrease the usable capacity of the cells. Conventionally, some measures have been taken to balance the cells in an attempt to extend the life and maintain the usable capacity of the cells: 
         [0006]    Series balance circuit in parallel with resistance. In a number of cells connected in series with one another, each cell is connected with a resistance in parallel and during the charging process, cell with higher voltage is made to consume its own power through the connected resistance. It is apparently a simple and low-cost, but far less efficient balance solution. 
         [0007]    B. Series balance circuit with switching inductance. A number of inductances are disposed in a rechargeable battery, each connected in parallel with one of the cells. During the charging process, cell with higher voltage is forced to store the power in the inductance by turning on a switch coupled therebetween and the inductance goes on to release the power to a next cell. Given the limitation that electrons in the circuit may only be conveyed to a neighboring cell, more cells in a battery the poorer efficiency the balance solution gets. 
         [0008]    C. Series balance circuit with switching capacitance. A number of capacitances is disposed in a rechargeable battery, each connected in parallel with its neighboring cells via two-way switches. The cells are made to balance through fast turning on and off of the switches. Sharing the same disadvantage as the previous solution, since electrons in the circuit may only be conveyed to a neighboring cell, if the power of a first cell is to be conveyed to a very last cell, through a number of middle cells, the power should have gone through repetitive storing and releasing in every intermediate capacitance. Such long path for conveying the power substantially effect the efficiency of the balance solution. 
         [0009]    These solutions for balancing cells in a rechargeable battery all have efficiency issue while great unnecessary power loss is inevitable. 
       SUMMARY OF THE INVENTION 
       [0010]    To cope with the problem, embodiments of the invention provide a two-way direct balance circuit for series cells that utilizes a flyback converter and takes advantage of electromagnetic transition to convey power between cells, which extensively reduces the power loss during the balance procedure. 
         [0011]    An embodiment of the invention provides a two-way direct balance circuit for series cells. The two-way direct balance circuit includes a flyback converter, a first cell, a second cell, a control unit, and a pulse generator. The first cell is coupled to the flyback converter with coil and a first switch is coupled between the first cell and the flyback converter. The second cell is connected in series connection to the first cell and is coupled to the flyback converter with coil and a second switch is coupled between the second cell and the flyback converter. The control unit is coupled to the first switch and the second switch. The pulse generator is coupled to the control unit, the first switch, and the second switch and is utilized for generating a first pulse signal and a second pulse signal complementary to each other. The first pulse signal determines the turn-on frequency of the first switch and the second pulse signal determines the turn-on frequency of the second switch. When the relative state of capacity (RSOC) of the first cell is greater than the RSOC of the second cell, the control unit is utilized to activate the pulse generator such that the first pulse signal turns on the first switch and the flyback converter is utilized to convert electrical energy of the first cell into magnetic energy, and the second pulse signal turns on the second switch and the flyback converter is utilized to convert magnetic energy into electrical energy as a power supply for the second cell. 
         [0012]    Another embodiment of the invention provides a two-way direct balance circuit for series cells. The two-way direct balance circuit provides a flyback converter, a first cell set, a second cell set, a control unit, and a pulse generator. The first cell set includes a plurality of first cells in series connection. Each of the first cells is coupled to the flyback converter with coil, and between each first cell and the flyback converter is coupled a first switch. The second cell set is connected in series connection to the first cell set. The second cell set includes a plurality of second cells in series connection. Each of the second cells is coupled to the flyback converter with coil, and between each second cell and the flyback converter is coupled a second switch. The control unit is coupled to the first switch of each first cell and the second switch of each second cell. The pulse generator is coupled to the control unit, the plurality of first switches, and the plurality of second switches and is utilized for generating a first pulse signal and a second pulse signal complementary to each other. The first pulse signal determines the turn-on frequency of the plurality of first switches and the second pulse signal determines the turn-on frequency of the plurality of second switches. When the relative state of capacity (RSOC) of one or more first cells of the first cell set is greater than the RSOC of one or more second cells of the second cell set, the control unit is utilized to activate the pulse generator such that the first pulse signal turns on the first switch of said one or more first cells and the flyback converter is utilized to convert electrical energy of said one or more first cells into magnetic energy, and the second pulse signal turns on the second switch of said one or more second cells and the flyback converter is utilized to convert magnetic energy into electrical energy as a power supply for said one or more second cells. 
         [0013]    In the two-way direct balance circuit provided in the embodiment by the invention, the plurality of first switches and the plurality of second switches are high level turn-on switches. The two-way direct balance circuit further includes a charge pump coupled to the control unit and coupled between the pulse generator and the plurality of first switches and the plurality of second switches. The charge pump provides supplementary voltage for turning on the plurality of first switches and the plurality of second switches. 
         [0014]    The two-way direct balance circuit provided in the embodiment by the invention further includes a plurality of first check circuits and a plurality of second check circuits. The plurality of first check circuits is coupled between the plurality of first cells respectively and the flyback converter. The plurality of second check circuits is coupled between the plurality of second cells respectively and the flyback converter. Each of the plurality of first check circuits includes a third switch and a diode in parallel connection, and each of the plurality of second check circuits includes a fourth switch and a diode in parallel connection. The control unit is coupled to the plurality of third switches and the plurality of fourth switches. 
         [0015]    In the two-way direct balance circuit provided in the embodiment by the invention, the control unit is further utilized for monitoring the RSOC of the plurality of first cells of the first cell set and the plurality of second cells of the second cells, and is utilized for controlling the pulse generator to stop generating the first pulse signal and the second pulse signal when the RSOC of said one or more first cells and said one or more second cells is balanced. 
         [0016]    In the two-way direct balance circuit provided in the embodiment by the invention, the first pulse signal and the second pulse signal generated by the pulse generator are high frequency pulse signals with frequency at 100 KHz. 
         [0017]    The two-way direct balance circuit for series cells provided by the invention utilizes a control unit to activate a pulse generator to transmit high frequency switch control signals, and utilizes a flyback converter to perform electromagnetic transition between the cells that rapidly conveys power from the cells with high RSOC to the flyback converter and to the cells with low RSOC. The direct energy transfer between cells, either one to one, one to many, many to one, or many to many, provides fast and highly efficient performance. 
         [0018]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is an illustration of a two-way direct balance circuit for series cells according to an embodiment of the invention. 
           [0020]      FIG. 2A ,  2 B are illustrations showing energy conversion between two cells through the flyback converter. 
           [0021]      FIG. 3A ,  3 B are illustrations of cells and flyback converter according to an embodiment of the invention. 
           [0022]      FIG. 4A ,  4 B are illustrations showing switch and current relation charts corresponding the embodiment in  FIG. 3A ,  3 B respectively. 
           [0023]      FIG. 5A ,  5 B, and  5 C are illustrations of the two-way direct balance circuit of the invention implemented with check circuits. 
           [0024]      FIG. 6A ,  6 B, and  6 C are illustrations showing a number of balance solutions using the two-way direct balance circuit for series cells according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. In the following discussion and in the claims, the terms “include” and “comprise” are used in an open-ended fashion. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Thus, if a first device is coupled to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0026]    Please refer to  FIG. 1 .  FIG. 1  is an illustration of a two-way direct balance circuit for series cells according to an embodiment of the invention. The two-way direct balance circuit  1  may be implemented in a plurality of cells in series connection and can balance the cells by use of a flyback converter. The two-way direct balance circuit  1  includes a flyback converter  10 , a battery module  20 , a control unit  50 , a pulse generator  60 , and a charge pump  70 . The battery module  20  includes a plurality of cells, which can be divided into a first cell set  30  and a second cell set  40  in series connection with the first cell set  30 . The first cell set  30  includes a plurality of first cells  31  in series connection and the second cell set  40  includes a plurality of second cells  41  in series connection. Each first cell  31  and each second cell  41  are coupled to the flyback converter  10  with coil. Between each first cell  31  and the flyback converter  10 , and between each second cell  41  and the flyback converter  10 , switches S 0 , S 1 , . . . , S n-1 , S n  as shown in  FIG. 1  are added to control the energy flow between each cell and the flyback converter  10 . 
         [0027]    The control unit  50 , the pulse generator  60 , and the charge pump  70  are coupled with one another. The control unit  50  is utilized for detecting and monitoring the relative state of capacity (RSOC) of each cell of the battery module  20 , and based on which, the control unit  50  determines which cells should be put to the balance procedure. Control lines CB 0 , CB 1 , . . . , CB n-1 , CB n  in the control unit  50  correspond to the switches S 0 , S 1 , . . . , S n-1 , S n . For the embodiment in  FIG. 1 , the control lines CB 0 , CB 1 , . . . , CB n-1 , CB n  are respectively coupled to the switches S 0 , S 1 , . . . , S n-1 , S n  through the charge pump  70 . Since the switches S 0 , S 1 , . . . , S n-1 , S n  are high level turn-on switches, the charge pump  70  provide a supplementary voltage for turning on each of the switches S 0 , S 1 , . . . , S n-1 , S n . In other embodiments, the charge pump  70  is optional and may be not used in the circuit such that the control unit  50  is directly coupled to and controls the switches S 0 , S 1 , . . . , S n-1 , S n . Additionally, the pulse generator  60  generates a first pulse signal OSC 1  and a second pulse signal OSC 2  complementary to each other and is coupled to control the turn-on duty and frequency of switches S 0 , S 1 , . . . , S n-1 , S n . 
         [0028]    Please refer to  FIG. 2A ,  2 B.  FIG. 2A ,  2 B are illustrations showing energy conversion between two cells through the flyback converter. A switch S 1  is coupled between the first cell  31  and the flyback converter  10  and a switch S 2  is coupled between the second cell  41  and the flyback converter  10 . When the control unit  50  has detected a larger RSOC of the first cell  31  of the first cell set  30  while the second cell  41  of the second cell set  40  has smaller RSOC, there can be a need for balancing the power between the first cell  31  and the second cell  41 . Hence, in  FIG. 2A , the control unit  50  turns on the switch S 1  such that current flows from the first cell  31  to the flyback converter  10 . Coiled on the flyback converter  10 , the current (electrical energy) from the first cell  31  and passing through the flyback converter  10  is converted into magnetic energy. Next, in  FIG. 2B , the control unit  50  turns off the switch S 1  and turns on switch S 2  so that the magnetic energy on the flyback converter  10  will be converted into electrical energy (current) and conveyed to the second cell  41 , which means to charge the second cell  41 . It should be noted that in the embodiment, the flyback converter  10  makes it possible that electrical energy is conveyed between cells via energy conversion, instead of via voltage difference between the cells. 
         [0029]    Please refer to  FIG. 3A ,  3 B,  4 A,  4 B.  FIG. 3A ,  3 B are illustrations of another embodiment of the cells and the flyback converter according to the invention and  FIG. 4A ,  4 B are switch and current relation charts corresponding the embodiment in  FIG. 3A ,  3 B respectively. As described, the first pulse signal OSC 1  and the second pulse signal OSC 2  generated by the pulse generator  60  are complementary to each other, and the pulse generator  60  is coupled to the switches S 0 , S 1 , . . . , S n-1 , S n  and controls the turn-on duty and frequency of switches S 0 , S 1 , . . . , S n-1 , S n . For example, the first pulse signal OSC 1  may be transmitted to control the turn-on duty and frequency of switches between a plurality of first cells  31 ,  32  of the first cell set  30  and the flyback converter  10 , while the complementary second pulse signal OSC 2  may be transmitted to control the turn-on duty and frequency of switches between a plurality of second cells  41 ,  42  of the second cell set  40  and the flyback converter  10 . 
         [0030]    Referring to  FIG. 3A ,  4 A, four switches S 1 , S 1a , S 2 , S 2a  are disposed as illustrated between the first cell  32  of the first cell set  30  and the flyback converter  10 . During time interval t 0 ˜t 1 , the first pulse signal OSC 1  is high and the switches S 1 , S 1a , S 2 , S 2a  are turned on with duty of 26.6%, but not limited to. At this stage, electrical energy (current) from the first cell  32  flows toward the flyback converter  10  and is converted into magnetic energy. Meanwhile,  FIG. 4B  shows that during the same time interval t 0 ˜t 1 , the second pulse signal OSC 2  is low and the switches S 3 , S 3a , S 4 , S 4a  are turned off, which means there is no energy flow between the second cell  42  and the flyback converter  10 . 
         [0031]    Next, in  FIG. 3B ,  4 B, during time interval t 1 ˜t 3 , the first pulse signal OSC 1  is low and the switches S 1 , S 1a , S 2 , S 2a  are now turned off. No energy flows between the first cell  32  and the flyback converter  10 . Meanwhile,  FIG. 4B  shows that during the same time interval t 1 ˜t 3 , the second pulse signal OSC 2  is high and the switches S 3 , S 3a , S 4  are turned on, while the switch S 4a  remains turned off for some reason described later. At this stage, magnetic energy of the flyback converter  10  is converted into electrical energy (current) and flows to the second cell  42 . The first pulse signal OSC 1  and the second pulse signal OSC 2  generated by the pulse generator  60  as high frequency pulse signals with frequency at, say, 100 KHz constantly turn on and off the switches S 1 , S 1a , S 2 , S 2a  and the switches S 3 , S 3a , S 4 , S 4a  and this provides a mechanism of converting the electrical energy of the first cell  32  into magnetic energy via the flyback converter  10  and the magnetic energy being converted into electrical energy conveyed to the second cell  42  to balance the cells. 
         [0032]    Please refer to  FIG. 5A ,  5 B, and  5 C, which are illustrations of the two-way direct balance circuit of the invention implemented with check circuits. Referring to  FIG. 5A , a check circuit is composed by transistor and switch. For example, a switch S 1a  and a transistor  81  in parallel connection and coupled between the first cell  32  and the flyback converter  10  form a check circuit, and a switch S 2a  and a transistor  82  in parallel connection and coupled between the first cell  32  and the flyback converter  10  also form a check circuit. a switch S 3a  and a transistor  83  in parallel connection and coupled between the second cell  42  and the flyback converter  10  form a check circuit, and a switch S 4a  and a transistor  84  in parallel connection and coupled between the second cell  42  and the flyback converter  10  also form a check circuit. Each of the switches S 1 , S 1a , S 2 , S 2a  and switches S 3 , S 3a , S 4 , S 4a  are coupled and controlled to turn on or off by the control unit  50 , or through the charge pump  70 . 
         [0033]      FIG. 5A  shows a state the same as the state in  FIG. 3A , i.e., the switches S 1 , S 1a , S 2 , S 2a  are turned on and electrical energy (current) from the first cell  32  flows toward the flyback converter  10  and is converted into magnetic energy during time interval t 0 ˜t 1 .  FIG. 5B  shows a state the same as the state in  FIG. 3B , i.e., the switches S 3 , S 3a , S 4  are turned on, while the switch S 4a  remains turned off, and magnetic energy of the flyback converter  10  is converted into electrical energy (current) and flows to the second cell  42  during time interval t 1 ˜t 3 . 
         [0034]    Please also refer to  FIG. 4B . Since the switches S 3 , S 3a , S 4  are turned on with duty of 26.6%, the flyback converter  10  will complete converting the magnetic energy into electrical energy (current) conveyed to the second cell  42  at time t 2 . Hence, as shown in  FIG. 5B ,  5 C, the switch S 4a  remaining turned off during time interval t 1 ˜t 3  prevents possible current discharge from the second cell  42  to the flyback converter  10 . 
         [0035]    Please refer to  FIG. 6A ,  6 B, and  6 C. As described, the control unit  50  determines which switches should be turned on and off alternately according to the RSOC of the cells so that cells corresponding to the switches being turned on and off alternately may be balanced. Furthermore, the structure in the embodiments also provide a variety of balance solutions. For example, in  FIG. 6A , a first cell (cell  6 ) of the first cell set  30  and a second cell (cell  14 ) of the second cell set  40  can be balanced. In  FIG. 6B , a first cell (cell  6 ) of the first cell set  30  and a number of second cells (cells  12 - 14 ) of the second cell set  40  can be balanced. In  FIG. 6C , a number of first cells (cells  5 - 7 ) of the first cell set  30  and a number of second cells (cells  12 - 14 ) of the second cell set  40  can be balanced. It should be noted that the balance can be made bi-directional between cells of the first cell set and cells of the second cell set, which means one or more first cells can not only provide energy for one or more second cells but also receive energy from the second cells. 
         [0036]    By monitoring the RSOC of a plurality of first cells  31 ,  32  of the first cell set  30  and a plurality of second cells  41 ,  42  of the second cell set  40 , the control unit  50  is able to selectively determine which cells in both cell sets to convey energy therebetween, through a high frequency pulse signal generated by the pulse generator  60  and through electromagnetic transition provided by the flyback converter  10 . During the energy exchange, the control unit  50  is able to determine if the balance process is done according to the RSOC of the cells. The pulse generator  60  will be controlled to stop generating the first pulse signal OSC 1  and the second pulse signal OSC 2  by the control unit  50  when the RSOC of the first cells  31 ,  32  and the second cells  41 ,  42  meets a balanced state. 
         [0037]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.