A Review of Cell Equalization s for Lithium Ion and.doc

A Review of Cell Equalization Methods for Lithium Ion and 对锂离子电池均衡方法Lithium Polymer Battery Systems 锂聚合物电池系统Stephen W. Moore 斯蒂芬w摩尔Delphi Automotive Systems 德尔福汽车系统Peter J. Schneider Peter j .施耐德Delphi Automotive Systems 德尔福汽车系统Copyright 2001 Society of Automotive Engineers, Inc. 版权2001汽车工程师学会,Inc .)ABSTRACT 文摘Lithium-based battery technology offers performance 锂离子电池技术提供的性能advantages over traditional battery technologies at the 传统的电池技术优势cost of increased monitoring and controls overhead. 成本增加的监控和控制开销。Multiple-cell Lead-Acid battery packs can be equalized by 多个cell铅酸电池可以平衡的a controlled overcharge, eliminating the need to 过度充电控制,消除了需要periodically adjust individual cells to match the rest of the 定期调整其余的单个细胞pack. Lithium-based based batteries cannot be equalized 包。基于锂离子电池不能平衡的by an overcharge, so alternative methods are required. 的超载,因此替代方法是必需的。This paper discusses several cell-balancing 论述了几种平衡methodologies. Active cell balancing methods remove 方法。活动单元格删除平衡方法charge from one or more high cells and deliver the charge 电荷从一个或多个高细胞和交付费用to one or more low cells. Dissipative techniques find the 一个或多个低细胞。耗散技术发现high cells in the pack, and remove excess energy through 高细胞包,删除多余的能量a resistive element until their charges match the low cells. 电阻元件,直到他们的指控与较低的细胞。This paper presents the theory of charge balancing 介绍了电荷平衡理论techniques and the advantages and disadvantages of the 技术的优点和缺点presented methods. 提出了方法。INTRODUCTION 介绍Lithium Ion and Lithium Polymer battery chemistries 锂离子和锂聚合物电池化学反应cannot be overcharged without damaging active materials 不能充电而不会破坏活性材料1-5. The electrolyte breakdown voltage is precariously 1 - 5。电解液分解电压不稳定close to the fully charged terminal voltage, typically in the 接近完全充电终端电压,通常在range of 4.1 to 4.3 volts/cell. Therefore, careful monitoring 4.1到4.3伏特/单元。因此,仔细的监控and controls must be implemented to avoid any single cell 必须实现和控制,以避免任何单个细胞from experiencing an overvoltage due to excessive 从经历一个过电压由于过度charging. 充电。Single lithium-based cells require monitoring so that cell 单锂电池需要监控,这样细胞voltage does not exceed predefined limits of the 电压不超过预定义的限制的chemistry. Series connected lithium cells pose a more 化学。系列锂电池连接构成complex problem: each cell in the string must be 复杂的问题:字符串中的每个单元格必须monitored and controlled. Even though the pack voltage 监控和控制。即使电压may appear to be within acceptable limits, one cell of the 可能出现在可接受的范围内,一个细胞的series string may be experiencing damaging voltage due 系列字符串可以经历破坏性电压to cell-to-cell imbalances. 细胞失衡。Traditionally, cell-to-cell imbalances in lead-acid batteries 传统上,细胞间失衡在铅酸电池have been solved by controlled overcharging 6,7. Leadacid 已经找到了解决办法控制收费过高6、7。铅酸batteries can be brought into overcharge conditions 电池可以带入超载条件without permanent cell damage, as the excess energy is 没有永久的细胞损伤,多余的能量released by gassing. This gassing mechanism is the 释放的气体处理。这是气体处理机制natural method for balancing a series string of lead acid 自然平衡方法铅酸的一系列字符串battery cells. Other chemistries, such as NiMH, exhibit 电池。其他化学反应,如镍氢,展览similar natural cell-to-cell balancing mechanisms 8. 类似的自然细胞间平衡机制8。Because a Lithium battery cannot be overcharged, there 因为锂电池不能充电,在那里is no natural mechanism for cell equalization. Therefore, 没有自然细胞均衡的机制。因此,an alternative method must be employed. This paper 必须使用另一种方法。摘要discusses three categories of cell balancing 讨论了三类细胞平衡methodologies: charging methods, active methods, and 方法:充电方法,积极的方法,passive methods. 被动的方法。Cell balancing is necessary for highly transient lithium 细胞平衡高度瞬态锂是必要的battery applications, especially those applications where 电池的应用程序,尤其是应用程序charging occurs frequently, such as regenerative braking 充电频繁发生,比如再生制动in electric vehicle (EV) or hybrid electric vehicle (HEV) 在电动汽车(EV)或混合动力电动汽车(HEV)applications. Regenerative braking can cause problems 应用程序。再生制动会导致一些问题for Lithium Ion batteries because the instantaneous 锂离子电池因为瞬时regenerative braking current inrush can cause battery 再生制动电流流入会导致电池voltage to increase suddenly, possibly over the electrolyte 电压突然增加,可能在电解液breakdown threshold voltage. 故障阈值电压。Deviations in cell behaviors generally occur because of 通常发生由于偏差在细胞的行为two phenomenon: changes in internal impedance or cell 两个现象:内部阻抗或细胞的变化capacity reduction due to aging. In either case, if one cell 由于老化能力降低。在这两种情况下,如果一个细胞in a battery pack experiences deviant cell behavior, that 在电池组经历异常细胞行为,cell becomes a likely candidate to overvoltage during high 细胞成为可能在高过电压power charging events. Cells with reduced capacity or 电力收费事件。细胞减少或能力high internal impedance tend to have large voltage swings 高的内部阻抗电压波动大when charging and discharging. For HEV applications, it 当充电和放电。为混合电动汽车的应用,它is necessary to cell balance lithium chemistry because of 锂电池平衡化学,因为有必要吗this overvoltage potential. 这种过电压的潜力。For EV applications, cell balancing is desirable to obtain 对于电动汽车应用程序,获取细胞平衡是可取的maximum usable capacity from the battery pack. During 最大可用容量的电池组。在charging, an out-of-balance cell may prematurely 充电时,一个不平衡的细胞可能过早approach the end-of-charge voltage (typically 4.1 to 4.3 方法end-of-charge电压(通常是4.1到4.3volts/cell) and trigger the charger to turn off. Cell 伏特/细胞)和细胞触发充电器关掉。balancing is useful to control the higher voltage cells until 平衡控制细胞电压越高,直到非常有用the rest of the cells can catch up. In this way, the 其余的细胞可以迎头赶上。通过这种方式,charger is not turned off until the cells simultaneously 充电器不是同时关闭,直到细胞reach the end-of-charge voltage. 到达end-of-charge电压。END-OF-CHARGE CELL BALANCING METHODS END-OF-CHARGE细胞平衡方法Typically, cell-balancing methods employed during and at 通常,平衡和期间使用的方法end-of-charging are useful only for electric vehicle 只有电动车end-of-charging是有用的purposes. This is because electric vehicle batteries are 目的。这是因为电动车电池generally fully charged between each use cycle. Hybrid 一般每次使用周期之间的完全充电。混合动力electric vehicle batteries may or may not be maintained 电动汽车电池可能是也可能不是fully charged, resulting in unpredictable end-of-charge 完全充电,导致不可预知的end-of-chargeconditions to enact the balancing mechanism. 条件制定平衡机制。Hybrid vehicle batteries also require both high power 混合动力汽车电池还需要高功率charge (regenerative braking) and discharge (launch assist 充电(再生制动)和放电(启动协助or boost) capabilities. For this reason, their batteries are 或促进)功能。出于这个原因,他们的电池usually maintained at a SOC that can discharge the 通常维持在一个SOC能放电required power but still have enough headroom to accept 所需的电力,但仍有足够的空间来接受the necessary regenerative power. To fully charge the 必要的再生能力。完全充电HEV battery for cell balancing would diminish charge 戊肝病毒电池对电池平衡会减少费用acceptance capability (regenerative braking). 接受能力(再生制动)。CHARGE SHUNTING 充电分流The charge-shunting cell balancing method selectively 有选择地细胞平衡方法shunts the charging current around each cell as they 分流术每一个细胞,因为他们周围的充电电流become fully charged (Figure 1). This method is most 成为充满电(图1)。这种方法efficiently employed on systems with known charge rates. 运用效率系统与已知的充电率。The shunt resistor R is sized to shunt exactly the 分流电阻R是并联的大小charging current I when the fully charged cell voltage V is 充电电流我当充满电的电池电压Vreached. If the charging current decreases, resistor R will 达成。如果充电电流减小,电阻Rdischarge the shunted cell. To avoid extremely large 放电的电池。为了避免非常大power dissipations due to R, this method is best used 由于R权力所消耗,使用这种方法是最好的with stepped-current chargers with a small end-of-charge 与一个小end-of-charge stepped-current充电器current. 电流。B1 B2 Bn B2 B1到BnControl 控制R1 R1S1 S1Rn R2 Rn R2S2 Sn S2 SnI 我I1 I2 I1 I2In 在Figure 1. Charge Shunting 图1所示。负责分流Disadvantages of the charge shunting method are the 缺点的分流的方法requirement for large power dissipating resistors, high 要求大功率消散电阻、高current switches, and thermal management requirements. 电流开关和热管理的需求。This method is best suited for systems that are charged 这种方法是最适合的系统often with small charge currents. 经常用小电流充电。ACTIVE CELL BALANCING METHODS 活动单元格平衡方法Active cell balancing methods employ an active chargeshuttling 雇佣一个活跃的chargeshuttling活跃细胞平衡方法element or voltage or current converters to move 元素或电压或电流转换器energy from one cell to another. These devices can be 能量从一个细胞到另一个地方。这些设备可以either analog or digitally controlled. The two major 模拟或数字控制。两个主要classifications of active cell balancing methods are charge 分类的活跃细胞平衡方法shuttling and energy converting. 往复运动和能量转换。CHARGE SHUTTLING 负责穿梭Charge shuttling cell balancing mechanisms consist of a 由一个负责穿梭于细胞平衡机制device that removes charge from a selected cell, stores 装置,消除了电荷从一个选定的细胞,商店that charge, and then delivers it to another cell. There are 电荷,然后交付它到另一个细胞。有several embodiments of charge shuttling schemes, the 收取穿梭计划的一些体现most notable being a flying capacitor (Figure 2). 最引人注目的是一个“飞行电容器”(图2)。B1 B2 B3 Bn B2 B3 B1到BnControl 控制C CS1 S2 S3 S4 S1 S2 S3 S4I 我Figure 2. Flying Capacitor Charge Shuttling Method 图2。电容器充电穿梭飞行的方法The control electronics close the proper switches to 控制电子接近正确的开关charge capacitor C across cell B1. Once the capacitor is 充电电容C细胞B1。一旦电容器charged, the switches are opened. The switches are then 指控,开关被打开。然后将开关closed to connect capacitor C across cell B2. The 关闭连接电容器C细胞B2。的capacitor then delivers charge to B2 based on the 电容器然后B2基于交付费用differential of voltage between B1 and B2 (Eq.1). 之间的电压差B1和B2(Eq.1)。The capacitor is then connected in the same manner 然后连接电容器以同样的方式across B3, B4,Bn, B1, The highest charged cells will B4,B3各地,Bn,B1、最高的细胞charge C and the lowest charged cells will take charge C和收费最低的带电细胞将负责from C. In this way, the charge of the most charged cells 从c。以这种方式,收费最带电的细胞are distributed to the least charged cells. The only 最小的带电细胞分布。唯一的electronic controls needed for this method is a fixed 这种方法是固定所需电子控制switching sequence to open and close the proper 开关打开和关闭适当的序列switches. 开关。A variation on the flying capacitor method is intelligently 变化的飞行电容器的方法是明智的select which cells to balance. In this way, the capacitor 选择细胞的平衡。通过这种方式,电容器can be charged from the highest cell and selectively 可以从细胞和选择性最高discharged to the lowest cell. This method can 最低的电池放电。该方法可以dramatically reduce the time to charge balance the cells, 大大减少充电的时间平衡细胞,especially if the highest and lowest charged cells are on 特别是在最高和最低收取细胞the opposite ends of the pack. Additional controls are 的两端。额外的控制necessary to detect and select the target cells. 必要的检测和选择目标细胞。2 22 22 21 2 1 21 12 21 1arg B B Ch e ? CV ? CV 参数B Ch e ?简历吗?简历This method requires a large number of switches (n+5) 这种方法需要大量的开关(n + 5)rated at the peak charging current for C. For a ideal 额定充电电流峰值的c .理想system (no ESR in the capacitor or switching losses) with 系统(没有ESR电容器或切换损失)a very large cell imbalance (Bn = 3.0V, Bm = 4.0V), a flying 一个非常大的细胞失衡(Bn = 3.0 v,博雅= 4.0 v),飞行capacitor could balance these cells at an initial rate of 电容器可以平衡这些细胞的初始速度1Ahr per hour per 1000uF of capacitance switching at ahr每小时1000佛罗里达大学的电容开关1kHz with an average switch current of 1A. Figuring in the 1 khz平均开关电流1 a。计算的capacitor ESR and switching losses dramatically 电容器ESR和切换损失increases the systems time constant for charging and 增加了系统的时间常数和收费discharging, effectively reducing actual balancing current 卸货,有效地减少实际平衡电流by at least an order of magnitude and increasing the peak 至少一个数量级,提高峰值switch current. The larger the capacitor used, the longer 开关电流。使用电容越大,时间越长it will take to transfer a usable charge and the clock rate 需要将一个可用的电荷和时钟频率will have to be decreased and the peak switch current will 将会降低,峰值开关电流将吗increase. A large (100Ahr) battery pack would require a 增加。一个大电池需要气道高反应(100)charge shuttling device with a very large capacitor with 负责穿梭装置与一个非常大的电容器extremely large switch currents. A significant amount of 非常大的开关电流。大量的energy is dissipated as resistive heating in the switches 能量耗散的电阻加热开关and capacitor. A large portion of balancing is simply 和电容器。只是大部分平衡achieved by dissipating the charge from the higher 通过消散的费用更高charged cells up as heat. 充电电池热。Another charge shuttling method shares a flying 另一个负责穿梭方法股票“飞行capacitor for every two battery cells (Figure 3). The 电容器的每两个电池(图3)。capacitor constantly switches between the two cells, 电容器两个单元之间不断切换,thereby swapping charge from the higher charged cell to 从而交换电荷的带电细胞高the lower charged cell. Each capacitor only needs simple 较低的充电电池。每个电容器只需要简单controls to activate the switches. 控制激活开关。B2 B1 B2 B1C CControl 控制I 我Figure 3. Charge Shuttling Between Two Cells 图3。往返于两个单元Several charge shuttling blocks can be cascaded for 几个负责穿梭块可以级联higher voltage packs (Figure 4). Because cells B2.Bn-1 高电压包(图4)。因为细胞B2.Bn-1share flying capacitors with their two neighboring cells, 与他们分享飞行电容器两个相邻细胞,charge can travel from one end of the cell string to the 电荷从一个细胞字符串的结束other. This method would take a large amount of time to 另一个。这种方法需要大量的时间transport charge from high cells to low cells if they are on 运输费用从高到低细胞上the opposite ends of the pack because the charge would 包,因为电荷的两端have to travel through every cell with time and efficiency 必须穿过每一个细胞都随着时间的推移和效率penalties. This method has a packaging advantage: for 处罚。这种方法有一个包装的优势:every two cells, the control circuitry, power supply and 每两个单元,控制电路,电源和capacitor can be packaged in a single unit powered from 电容器可以打包在一个单元供电the cells they are balancing. Units can be added as cell 细胞的平衡。单位可以添加细胞count is increased. 数增加。B2 B1 B2 B1B3 B3C1 C1C2 C2C3 C3C4 C4Control Control 控制控制Control Control 控制控制I1 I3 I1 I3I2 I4 I2预告B4 B4Figure 4. Charge Shuttling with Several Cells 图4。负责穿梭与几个细胞Charge shuttling techniques are of limited usefulness for 负责穿梭技术是有限的HEV applications. Lithium chemistries offer a relatively 混合电动汽车的应用。锂化学反应提供了一个相对flat open cell terminal voltage across a broad range of 平打开电池终端电压范围广泛的SOC from 40%-80% (Figure 5). A cell at a high SOC SOC从40%到-80%(图5),细胞在高SOCdoes not have a significantly large ? V from a low SOC 没有一个很大?从一个低SOC Vcell, unless one of those cells are on a voltage knee over 细胞,除非其中一个细胞电压超过膝盖90% SOC or below 20% SOC. HEV batteries operate in SOC SOC 90%或低于90%。戊肝病毒电池操作the mid-SOC range, and this is where the cell-to-cell mid-SOC范围,这是细胞的地方voltage differentials are the smallest, thus limiting the 电压差异最小,从而限制了usefulness of charge shuttling techniques. 有用的穿梭于技术。Voltage vs. State of Charge 电压和电荷状态3.2 3.23.4 3.43.6 3.63.8 3.84 44.2 4.24.4 4.40 20 40 60 80 100 0 20 40 60 80 100State of Charge 电荷状态Voltage 电压Figure 5. Open Cell Voltage of Lithium Polymer Battery 图5。打开电池电压的锂聚合物电池Charge shuttling techniques are useful for EV 穿梭于技术用于电动汽车充电applications. Because an EV can be routinely fully 应用程序。因为电动车可以经常完全charged, the voltage differential between a fully charged 充电,充满电之间的电压差cell and a lesser-charged cell is greater near the ends of 细胞和lesser-charged电池的两端附近的更大the voltage curve (Figure 5). This increases the 电压曲线(图5),这就增加了effectiveness of the technique. 这一技术的有效性。ENERGY CONVERTERS 能量转换器Cell balancing utilizing energy conversion devices employ 细胞平衡利用能量转换设备使用inductors or transformers to move energy from a cell or 电感或变压器将能量从一个细胞group of cells to another cell or group of cells. Two active 组的细胞转移到另一个细胞或一组细胞。两个活动energy converter methods are the switched transformer 能量转换方法转换变压器and the shared transformer. 和共享的变压器。The switched transformer method shares the same 开关变压器的方法相同的股票switching topology as the flying capacitor method (Figure 切换拓扑飞行电容器方法(图6). Current I is taken from the entire pack and is switched 6)。现在我来自整个包和切换into transformer T. The transformer output is rectified 为变压器t .整流变压器输出through diode D and delivered into cell Bn, which is 通过二极管D和交细胞Bndetermined by the setting of switches S. Electronic 由交换机的设置电子control is required to select the target cell and set 控制需要选择目标细胞和设置switches S. 开关。Sn+1 Sn + 1B3 B2 B1 Bn B3 B2 B1 BnControl 控制S1 S2 S3 S4 S1 S2 S3 S4I 我n:1 n:1T TD 维Figure 6. Swiched Transformer 图6。号变压器This method can rapidly balance low cells at the cost of 该方法可以快速平衡低细胞为代价的removing energy from the entire pack. Disadvantages 把能量从整个包。缺点include high complexity, high parts count in terms of 包括高复杂性、高数的部分control, magnetics, and switches, and low efficiency due 控制、磁学和开关,和低效率to switching losses and magnetics losses. 切换损失和磁学损失。A shared transformer has a single magnetic core with 一个共享的变压器有一个磁芯secondary taps for each cell (Figure 7). Current I from the 二级阀门为每个细胞(图7)。目前我的cell stack is switched into the transformer primary and 堆栈是细胞转换到变压器初级和induces currents in each of the secondaries. The 诱发电流的辅助。的secondary with the least reactance (due to a low terminal 二次最少的电抗(由于较低的终端voltage on Bn) will have the most induced current. In this 电压Bn)会有感应电流。在这way, each cell receives charging current inversely 方式,每个单元接收反向充电电流proportional its relative SOC. 其相对SOC成比例。I 我T TB3 B2 B1 Bn B3 B2 B1 BnControl 控制I1 I2 I3 In I1 I2 I3在Figure 7. Shared Transformer 图7。共享的变压器The only active component in the shared transformer is 唯一的活性成分共同的变压器the switching transistor for the transformer primary. No 变压器的开关晶体管初选。没有closed-loop controls are required. The shared transformer 闭环控制是必需的。共享的变压器can rapidly balance a multicell pack with minimal losses. 可以迅速平衡多单元的包以最小的损失。Disadvantages of this cell balancing method includes 这个细胞平衡方法的缺点包括complex magnetics and high parts count due to each 复杂的磁学和高数由于每个部分secondarys rectifier. The balancing ci