什么是电池管理系统?

什么是电池管理系统?

这份白皮书是基于我们最近发布的AVID学习播客上的一集,我们回答了一些听众关滚球体育app最新版于电池管理系统(BMS)的更深入的讨论,解释他们在做什么以及为什么需要他们的要求。

电池组

电动和混合动力汽车的关键组成部分是电池组。更高的功率密度和更低的成本的锂电池系统已经改变了我们在车上存储和使用电力的方式。特斯拉的电池组回到早期的电动汽车,使用的是重铅酸电池,但除了一些特殊的小型应用,如叉车和牛奶车,它们没有足够的单位质量存储容量有效。在这之后,我们有了更先进的储能系统,比如镍镉电池和镍氢电池。也有尝试使用熔融钠盐电池,但有很多问题,因为电解质需要保持在非常高的温度,以保持其导电性。随着商业化锂离子电池化学物质的发明,这一步骤发生了变化,这些化学物质显著提高了储能密度和功率因数,使它们非常适合移动应用。我们已经在之前的白皮书和播客中讨论过锂电池,所以请查看这些以获得更多信息。锂电池有一些重大的挑战,需要一个复杂的电子控制系统,即电池管理系统或BMS。
其中一个AVI滚球体育app最新版D科技的电池管理系统
其中一个AVI滚球体育app最新版D科技的电池管理系统

电池管理系统

锂电池相对难以管理,因为它们具有非常非线性充电/放电曲线。通过铅酸电池,非常容易识别出用简单地测量其电压,并且有一种非常直接的方式来解决这些信息的充电状态。然而,利用锂离子电池,相对于电压的电荷状态非常平坦,通过两端具有尖锐的拐点的约60%的电荷/放电曲线非常平坦。这意味着很难判断电池或包装的充电状态。通过锂离子电池电池,通过过度造成永久性损坏并减少细胞也相对容易,因此可以更重要的是,确保电池没有损坏更为重要。还有安全考虑因素,因为损坏的细胞可以过热并进入热失控状态。因此,BMS起着非常重要的作用。它确保我们可以准确地报告电池组的充电状态,并监控单元格,以确保没有可能导致问题的问题,以确保包装可以首先安全地关闭。BMS通常由几个单独的电路板组成。首先,有模块控制单元或MCU,这些有时被称为从属BMS模块。 These units will monitor the voltage of each cell, or a small group of cells in the battery very accurately. The MCU will also typically include some temperature measurements of the inside of the battery pack and possibly the cells themselves. The MCU will communicate up to a master BMS module. The master BMS will aggregate data from all of the slave MCUs and it will also measure bulk current flow in and out of the battery pack. From this, it can work out what the battery state of charge is. And report this so that it can be communicated to the driver. Battery state of charge would also impact things such as how much regenerative braking you can use particularly if the vehicle is not equipped with a braking resistor system. If the pack is already near to the maximum safe level the BMS will prevent the vehicle from dumping more power into the pack under regen braking. This is the reason why there is normally a little bit of useful pack overhead in order to try and keep a consistent braking feel for the driver this feature can usually be turned off with an accompanying warning about braking feel. The capacity of the pack is then limited by the ability to charge each cell up to its maximum safe voltage and discharge it down to its minimum safe voltage. Due to tolerance build up in the manufacturing processes of the cells they have small variations in how quickly they will charge and discharge. In order to make sure that the whole pack is not constrained to the capacity of the cell that gets “full or empty” the quickest, the BMS also serves to balance the cells. It does this by using balancing resistors that switch on and off to discharge off small amounts of power from individual cells or small groups of cells and make sure that the overall pack capacity can be maximised and not constrained to the capacity of the weakest cell. This is also the reason why very fast charging never goes to 100% of the pack capacity because the balancing resistors need some time to do their job when getting very close to the upper limits of the pack. Researchers have been looking into ways to move away from the balancing resistor as these have an impact on the charging efficiency of the pack, whilst in theory, this is possible the practical implementation is currently complex and costly. Also as production methods are improving for lithium cells the need for balancing is reducing to the point where its impact on overall system efficiency is limited. In some smaller battery packs with a low number of cells, the MCU and master may be consolidated into a single device. This would be a typical configuration for a low capacity 48V battery pack for automotive use and also for small batteries for applications such as robotics and other industrial equipment. The BMS needs to be able to communicate with the other powertrain subsystems in order to communicate charge level and send any inhibit messages if there is a problem with the battery pack and will typically broadcast the status of the pack via the CANbus, which is a serial communication protocol widely used in industry. Depending on the vehicle architecture the Master BMS module may directly control things like main DC link pre-charge and power contactors directly or via the vehicle CANbus and a separate vehicle body control unit. The BMS will also interface with both onboard AC/DC chargers and off-board direct DC fast chargers to tell the charger what mode to be charging the battery in. Because of its safety-critical nature both in maintaining the battery in a safe condition and also maintaining vehicle motion i.e. you do not want the BMS instructing the main DC link capacitors to open thinking there is an issue unless it is really a very important issue when the vehicle or machine is in operation. In summary, it can be seen that the battery management system (BMS) is a critical part of the EV powertrain. The BMS is needed to measure the state of charge and condition of the Lithium battery due to their charge/discharge characteristics and safety considerations. It performs several key functions to ensure that the pack capacity can be maximised such as cell balancing and the control of chargers. The BMS will need to be tailored to each different battery pack and powertrain configuration. If you need help with a battery system or BMS development, please do not hesitate to contact AVID Technology directly.滚球体育app最新版AVID Learning Electric Vehicle Technology播客封面艺术

额外的信息

想要了解更多电动汽车技术,请下载并收听流行的“AVID Learning: EV technology”播客。滚球体育app最新版iTunes 钉箱机 Spotify Youtube

关于作者

瑞安·莫恩

瑞安·莫恩

AVID Technology Group Ltd.董事总滚球体育app最新版经理。滚球体育app最新版AVID总部位于英格兰东北部,是重型高性能汽车电气化动力系统设计和制造的领导者。