Patent Publication Number: US-2015061597-A1

Title: Battery management system and method

Description:
BACKGROUND OF THE INVENTION 
     Batteries are the most common electrical energy storage devices for electric vehicles, medical instruments, uninterruptible power supply, and other industrial applications. In use, when a potential higher than a basic potential of a battery is needed, it is common to use a plurality of batteries connected in series. However, even though the batteries are produced with the same structure via a typical production method using the same anode, cathode and electrolyte material, a difference in charging or discharging (and self-discharging) characteristics exists between each of the batteries connected in series. Thus, there is a potential difference between the series-connected batteries, which may cause a problem of unbalanced charging. For example, as the potentials of the series-connected batteries are different from each other, some batteries may reach a prescribed voltage when some other batteries do not reach the prescribed voltage, and therefore an overcharge or undercharge problem or even both overcharge and undercharge problems may occur during charging the series-connected battery string. 
     An overcharged battery may have high risk of explosion, if the chemistry of the battery cannot withstand overcharged state, whereas an undercharged battery may reduce the life cycle of the series-connected battery string. Therefore, the unbalanced charging problem for series-connected battery string needs to be addressed. A common method is to use charge equalization devices to achieve charge equalization for the series-connected battery string. 
     However, in order to balance a large number of batteries, the equalization device may be large and costly. Therefore, it is desired to provide a balancing method for a large number of batteries, which is compact and low cost. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with an embodiment disclosed herein, a system includes a plurality of units. Each of the plurality of units has an energy storage element, a branch switch and a branch diode. The system further includes a transformer which has a primary side and a secondary side and functions as an equalizer for at least one of charging and discharging the energy storage elements to achieve equalization. The plurality of units are connected to the primary side through a control switch and isolated from a secondary circuit connected to the secondary side. 
     In accordance with another embodiment disclosed herein, a system includes a transformer comprising a primary side and a secondary side, and a plurality of branch diodes series connected to the primary side through a control switch and isolated from a secondary circuit connected to the secondary side. Each of the plurality of branch diodes is connected in parallel with a branch switch. Once each of the plurality of branch diodes is further connected in parallel with an energy storage element that is series connected to the branch switch, the transformer is capable of at least one of charging and discharging the plurality of energy storage elements connected in parallel with the plurality of branch diodes respectively to achieve charge equalization. 
     In accordance with yet another embodiment disclosed herein, a system includes a plurality of energy storage elements. Each of the plurality of energy storage elements is coupled to a power conversion unit which interfaces directly with an output of the system and manages charging or discharging power of the energy storage element. 
     In accordance with yet another embodiment disclosed herein, a system includes a plurality of power conversion units. Each of the plurality of power conversion units includes integration of a power electronics circuit for regulating bi-directional power flow between an energy storage element and the output of the system and a balancing circuit for managing charging or discharging power of the energy storage element to achieve charge equalization. The plurality of power conversion units connected with each other. Once each of the plurality of power conversion units is coupled to an energy storage element, it is able to interface directly with an output of the system and manages charging or discharging power of the energy storage element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a diagram showing an example of a battery system having a plurality of battery units connected to a primary side of a transformer, according to one embodiment of the present invention; 
         FIG. 2  is a diagram showing an example of a battery system having a plurality of the batteries, each coupled with an integrated power conversion unit and outputting a DC voltage, according to one embodiment of the present invention; 
         FIG. 3  is a diagram showing an example of a battery system having a plurality of the batteries each coupled with an integrated power conversion unit and outputting an AC voltage, according to one embodiment of the present invention; and 
         FIG. 4  is a diagram showing passive components of a battery system integrated with embedded dielectric material. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, the terms “coupled” and “connected” are not intended to distinguish between a direct or indirect coupling/connection between two components. Rather, such components may be directly or indirectly coupled/connected unless otherwise indicated. 
     Embodiments of the invention provide low volume electronic systems. In accordance with some embodiments, a plurality of energy storage elements such as batteries may be connected to a multi-input flyback transformer, such that the transformer which functions as an equalizer for at least one of charging and discharging the energy storage elements to achieve equalization. In accordance with some embodiments, a plurality of energy storage elements such as batteries may be each coupled with a power conversion unit, which is capable of both regulating bi-directional power flow between the energy storage element and the output of the whole system and managing charging or discharging power of the energy storage element to achieve charge equalization. Cost effective and high performance charge equalization solutions are provided for multiple energy storage elements in the embodiments as discussed above. As the solutions are particularly applicable in battery systems, which have, for example, series-connected batteries, the following description is directed to battery systems, but can be used in other systems including energy storage elements other than batteries. 
     In some embodiments, referring to  FIG. 1 , a battery system  100  comprises a plurality of battery units (U 1 , U 2 , . . . , U N ). Each of the battery units has a battery (B 1 , B 2 , . . . , or B N ), a branch switch (S 1 , S 2 , . . . , or S N ), and a branch diode (D 1 , D 2 , . . . , or D N ), which are connected in series. The battery system  100  further comprises a transformer  102  which functions as an equalizer for at least one of charging and discharging the batteries to achieve charge equalization. The transformer  102  has a primary side (N P ) and a secondary side (N S ). The battery units U 1 , U 2 , . . . , and U N  are connected to the primary side N P  of the transformer  102  through a control switch (S N+1 ) and isolated from a secondary circuit  104  connected to the secondary side N S  of the transformer  102 . 
     The battery units U 1 , U 2 , . . . , and U N  may be series connected to the primary side N P  of the transformer  102  through the control switch S N+1 . As illustrated, for each battery unit, the battery and branch switch are connected in series with each other, and the series-connected battery and branch are connected in parallel with the corresponding branch diode. The branch diodes D 1 , D 2 , . . . , and D N  of the plurality of battery units are series connected to the primary side N P  of the transformer  102  through the control switch S N+1 . The branch switches interact with the control switch to have one of the battery units charged/discharged by the transformer  102  at a time. 
     The transformer may be a flyback transformer. In some embodiments, the transformer  102  is a multi-input flyback transformer. There are multiple inputs for the transformer  102  such that the plurality of battery units can be connected to the primary side N P  of the transformer  102 . The secondary side N S  of the transformer  102  is a single winding output which can be connected to a secondary circuit  104 . In some embodiments, the secondary circuit  104  is a battery module. In a specific embodiment, as illustrated, the secondary circuit  104  comprises a diode D R1 , a capacitor C F , and a resistor R L . The capacitor C F , and resistor R L  are parallel connected and then connected to the secondary side N S  of the transformer  102 . 
     Either of the branch switch and the control switch, or both of them may be an NPN-type transistor. 
     In implementations, the batteries and the other parts of the system  100  can be produced or provided separately. For example, in some implementations, a system without batteries, but which can be coupled into the batteries to achieve the function as described above may be provided. The system may include some or all parts of the battery system  100  except the batteries. For example, the system may include a transformer having a primary side and a secondary side, and a plurality of branch diodes series connected to the primary side through a control switch and isolated from a secondary circuit connected to the secondary side. Each of the plurality of branch diodes is connected in parallel with a branch switch. Once each of the plurality of branch diodes is further connected in parallel with an energy storage element, such as a battery, that is series connected to the branch switch, the transformer is capable of at least one of charging and discharging the plurality of energy storage elements connected in parallel with the plurality of branch diodes respectively to achieve charge equalization. 
     In some other embodiments, a battery system having a plurality of batteries, each coupled with a power conversion unit, which interfaces directly with the output of the battery system and manages charging or discharging the power of the battery is provided. 
     Referring to  FIG. 2 , an exemplary battery system  200  comprising three batteries (B 1 , B 2  and B 3 ) having a direct current (DC) output. In the system  200 , each of the batteries is coupled with a power conversion unit  210 . The power conversion unit  210  is an integration of a power electronic circuit for regulating bi-directional power flow between the battery and the output of the battery system and a battery balancing circuit for managing charging or discharging the power of the battery to achieve charge equalization, and can interface directly with the output of the battery system and manage charging or discharging power of the battery. As such, the power conversion unit  210  has an integrated function of both an energy management system (EMS) and a battery management system (BMS). As used herein, “EMS” refers to a system of computer-aided tools used to monitor, control, and optimize the performance of the power generation and/or transmission system, and “BMS” refers to an electronic system that manages a rechargeable battery (cell or battery pack), such as by monitoring its state, calculating secondary data, reporting the data, controlling its environment, and/or balancing it. 
     The power conversion unit  210  for each battery may comprise a switch module  211  connected in parallel with the battery and a transformer  212  for isolating the battery and switch module from a secondary circuit  213  for converting an alternate current (AC) voltage to a DC voltage. In some embodiments, the switch module  211  comprises at least four switch devices, each having a transistor (T 1 , T 2 , T 3 , or T 4 ) and a diode (D 1 , D 2 , D 3 , or D 4 ) parallel connected to the transistor. The transistors T 1 , T 2 , T 3 , and T 4  may be selected from the group consisting of metal-oxide-semiconductor field effect transistors, insulated gate bipolar transistors, and bipolar-junction transistors. As illustrated, the battery B 1 , B 2  or B 3  and its corresponding switch module  211  are connected to a primary side of a full bridge transformer  212 , which has a secondary circuit  213  coupled to a secondary side thereof. The output of the full bridge transformer  212  can be connected in series to provide a higher DC output voltage, for example, 300-400V for electric vehicle, and 700-800V for medical instruments, such as CT, MRI and X-ray applications. In the specific embodiment as illustrated, the secondary circuit  213  comprises four diodes D 5 , D 6 , D 7  and D 8 , a capacitor C O , and a resistor R O . The four diodes D 5 , D 6 , D 7  and D 8  constitute a diode bridge, which is connected with the capacitor C O  and resistor R O  in parallel. 
     The transformer  212  not only takes the BMS balancing function for battery charge and discharge equalization, but also takes the responsibility as an EMS power regulator. The BMS balancing and EMS power regulator functions are realized by either phase shift control or frequency control, or combined phase shift control and frequency control strategy of the full bridge transformer  212 . 
     Referring to  FIG. 3 , an exemplary battery system  300  comprising three batteries (B 1 , B 2  and B 3 ) having an AC output. In the system  300 , each of the batteries is coupled with a power conversion unit  310 , which has an integrated BMS and EMS function, and can interface directly with the output of the battery system and manage charging or discharging power of the battery. In the specific embodiment, as illustrated, the power conversion unit  310  for each battery comprises a switch module  311 . Similar to that in the system  200 , as described above, the switch module  311  comprises at least four switch devices, each having a transistor (T 1 , T 2 , T 3 , or T 4 ) and a diode (D 1 , D 2 , D 3 , or D 4 ) parallel connected to the transistor. As illustrated, each of batteries is coupled in parallel with a switch module  311 , and the switch modules of the batteries are connected in series by connecting their midpoints of legs, to provide an AC voltage higher than what a single battery can provide. 
     Similarly, in some implementations, the batteries and the other parts of the system  200  or  300  can be produced or provided separately. For example, a system without batteries, but which can be coupled into the batteries to achieve the function as described above may be provided. The system may include some or all parts of the battery system  200  or  300  except the batteries. 
     In the battery system, as described above, the battery may be a single battery cell or a collection of two or more parallel connected battery cells (battery pack). The diode may be a single diode or a collection of two or more parallel connected diodes (diode pack). 
     In some embodiments, active electronic components of the battery system, including but not limited to, power semiconductor devices, gate driver integrated circuit, sensor, and control electronics, are integrated in a single active application-specific integrated circuit, for example, by a silicon or gallium nitride on silicon packaging technology. In some embodiments, passive components of the battery system, including but not limited to, two or more discrete inductive components sharing the same magnetic core, and capacitive components, are integrated with an electromagnetic technology, for example, by using embedded dielectric material. The passive components may be integrated by winding the inductive components and capacitor in series or in parallel connection. For example, as illustrated in  FIG. 4 , in a system  400 , the passive components including inductors  401  and capacitors  402  are integrated with embedded dielectric material such that they can share a same ferrite core  403 . 
     It is to be understood that not all objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.