火辣西米秀 发表于 2024-9-27 08:30

新能源车的高压电池管理系统BMS的管理的几个方面

本帖最后由 火辣西米秀 于 2024-9-27 08:30 编辑

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<p><span style="font-size:16px;">从判断电池故障、荷电状态和容量估算等简单管理阶段,进阶为覆盖电池方方面面状态的全面管理阶段。</span></p>

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<p><span style="font-size:16px;"><strong>BMS功能清单</strong></span></p>
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<p><span style="font-size:16px;">可以将BMS功能简单分为三大部分。</span></p>

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<p><span style="font-size:16px;"><strong>BMS基础功能</strong></span></p>
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<p><span style="font-size:16px;">V/I/T采样,保护功能(过压、过流、过温、绝缘电阻),继电器驱动,状态采样,继电器粘连检测,CAN通信;</span></p>
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<p><span style="font-size:16px;"><strong>BMS核心功</strong></span></p>
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<p><span style="font-size:16px;">电芯均衡、SOP(功率)、SOE(能量)、SOC(荷电状态),SOH(健康程度);</span></p>
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<p><span style="font-size:16px;"><strong>BMS应用相关</strong></span></p>

<p><span style="font-size:16px;">碰撞信号检测、交/直流充电、充电器状态检测、热状态、加热/冷却需求、预充、唤醒/休眠、与VCU通信</span></p>
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<p><span style="font-size:16px;">不过从用户角度来理解,可大致分为两大功能&ldquo;电池体检&rdquo;&amp;&ldquo;安全卫士&rdquo;。</span></p>
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<p><span style="font-size:16px;"><strong>01.</strong>电池体检</span></p>
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<p><span style="font-size:16px;"><strong>从时效性来说,对电池的体检强调的是即时性,BMS必须精准掌握电池状态。</strong></span></p>

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<p><span style="font-size:16px;"><strong>即时&ldquo;体检&rdquo;,指的是电池数据采集和状态评估。</strong></span></p>

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<p><span style="font-size:16px;">数据采集,可简单理解为给电池做例行的&ldquo;体检&rdquo;;在充放电过程中,实时采集电池组中每块电池的端电压、温度、充放电电流及总电压,防止电池发生过充电或过放电现象。</span></p>

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<p><span style="font-size:16px;">这种&ldquo;体检&rdquo;是在线的、持续的、不间断的。过程中当发现数据异常时,可及时查询对应电池状况,并挑选出有问题的电池,从而保持整组电池运行的可靠性和高效性。</span></p>

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<p><span style="font-size:16px;">&ldquo;体检&rdquo;结束之后,会进入分析、诊断、计算的阶段,之后生成&ldquo;体检报告&rdquo;,这个过程可以理解为电池的状态评估。</span></p>

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<p><span style="font-size:16px;"><strong>02.</strong>安全卫士</span></p>
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<p><span style="font-size:16px;"><strong>安全卫士只得是保护电池及人身安全</strong>。</span></p>

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<p><span style="font-size:16px;">电池过充、过放会带来局部过热,影响电池寿命不说,严重时会威胁到电池组的安全,进而引发人身安全隐患。这时,BMS的&ldquo;充放电管理&rdquo;模块就开启了保护职能,一方面与整车、充电机实现通讯,另一方面实时提供电池状态,便于及时发出指令控制,有效防止高充、低放的发生。</span></p>

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<p><span style="font-size:16px;"><strong>在保护电池的模块,均衡也是很重要的一环,是保护并提升电池寿命的必要手段。</strong>另外,电池的保护还包括过压、欠压、过温、过流等的保护。简单来说,当实际参数高于或低于某约定值时,系统将自动做出判断,并采取断开、预充等方式保护电池安全。</span></p>

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<p><span style="font-size:16px;">在人身安全方面,BMS通过高压控制的手段来保护。<strong>电池高压可达300-500V,远超人体安全电压36V,风险隐患极大,必须做好高压控制,最常见的就是继电器、高压互锁、绝缘防护。</strong>周全的高压防护控制,可有效保护司机、乘客和维护人员的人身安全。</span></p>

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<p><span style="font-size:16px;"><strong>电池状态评估</strong></span></p>
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<p><span style="font-size:16px;">下面我们就来对BMS的几个核心功能做下详细说明。</span></p>

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<p><span style="font-size:16px;">如同手机通过检测电池的电压和电流来估算电池荷电状态,为用户显示剩余电量,动力电池的BMS系统也是通过估算电量的SOC,来为整车控制系统提供数据输入,为驾驶员提供电量和续航里程数据作为车辆使用的参考信息。</span></p>

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<p><span style="font-size:16px;"><strong>SOC的全称State of Charge,荷电状态,也称为剩余电量。</strong>满充的电池,其SOC为100%,反之则为0%。</span></p>

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<p><span style="font-size:16px;">用户可通过车上仪表显示,看到这些数据,从而确认电池的工作、功能状态。据此,在保护电池的基础上,将潜力发挥最大化,大大提升驾乘体验。</span></p>

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<p><span style="font-size:16px;"><strong>因此SOC等数据估算的准确与否,就显得特别重要。估算不准带来的后果,有可能是汽车抛锚、与预期的行驶里程数不符等。</strong></span></p>

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<p><span style="font-size:16px;">举个例子,满电情况下续航里程为400公里的车辆在道路行驶。若估算准确,当SOC显示为10%时,还可能行驶的里程是40公里;若估算不准,SOC达到15%,则用户以为的里程为60公里,事实上可能在行驶40公里之后,就已经没电了。很显然,对于用户来说,这样的情况很糟糕。</span></p>

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<p><span style="font-size:16px;"><strong>SOC外,BMS还会估算电池的放电深度(DOD)、健康状态(SOH)、功能状态(SOF)、能量状态(SOE)等:</strong></span></p>

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<p><span style="font-size:16px;"><strong>SOC</strong></span></p>
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<section><span style="font-size:16px;">State of Charge,电池剩余电量百分比;</span></section>
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<p><span style="font-size:16px;"><strong>SOE</strong></span></p>
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<section><span style="font-size:16px;">State of Energy,电池剩余电量,对整车而言意味着剩余里程;</span></section>
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<p><span style="font-size:16px;"><strong>SOH</strong></span></p>
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<section><span style="font-size:16px;">State of Health,电池健康度,电池当前的容量与出厂容量的百分比;</span></section>
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<p><span style="font-size:16px;"><strong>SOF</strong></span></p>
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<section><span style="font-size:16px;">State of Funtion,电池功能状态,是BMS控制策略中的一个参数;</span></section>
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<p><span style="font-size:16px;"><strong>DOD</strong></span></p>
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<section><span style="font-size:16px;">Depth of discharge,放电深度,指从电池取出电量占额定容量的百分比,相同容量的电池,放电深度越大,电池释放能量就越多,电池寿命越短。</span></section>
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<section><span style="font-size:16px;"><strong>功率估算</strong></span></section>
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<p powered-by="xiumi.us"><span style="font-size:16px;"><strong>车辆控制系统根据刚才这些数据,确定系统的动力输出形式,以及输出功率。</strong></span></p>

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<p><span style="font-size:16px;">比如:以混动车举例,何时启动纯电模式,何时启动发动机,何时关闭电机,这些控制逻辑都需要以电池的荷电状态,最大放点电流、最大充电电流、最高充电电压、最低充电电压等数据作为输入,而BMS则是这些关键数据的提供方。</span></p>

<p><span style="font-size:16px;">其实,BMS的剩余容量估算是BMS的核心内容也一直是业界难点。首先它是一个估算值,根据电池组电压,电流,放电倍率,温度等因素经过算法计算得出的值,这就要求整个系统先要采集的足够准,足够快才能保证最后的结果准确。</span></p>

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<p><span style="font-size:16px;">可是这又受制于主控芯片的处理速度,AFE的精度,采集电流的方案选择,温度传感器的精度。</span></p>

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<p><span style="font-size:16px;">还有从系统整体考量采样频率的大小诸多因素有关。选用高处理速度高精度的芯片势必会增加成本,采样频率越快系统负荷也越大,所以目前技术条件下大家都是参考具体项目来权衡各方面因素。</span></p>

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<p><span style="font-size:16px;"><strong>简单来说,就是根据V/I/T测量值,对内阻,容量进行估算,得出SOC估计值,SOH估计值,综合两者得出SOP可用功率,并最终反应到用户那里,就是剩余可行驶里程数。</strong></span></p>

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<p><span style="font-size:16px;"><strong>估算值精度</strong></span></p>
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<p powered-by="xiumi.us"><span style="font-size:16px;">以上提及的估算值精度,按国标定义,可汇总如表格所示:</span></p>

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<p><span style="font-size:16px;"><strong>电池过充/电池过放</strong></span></p>
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<p powered-by="xiumi.us"><span style="font-size:16px;">在解释BMS对电池充放电进行均衡管理前,需要了解电池过充、过放的概念。</span></p>

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<p><span style="font-size:16px;">电池过充,指的是用超过单体电池上限的充电电压充电,或者在电池已经充满的情况下继续充电。</span></p>

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<p><span style="font-size:16px;">电池过充,不仅会引起电池性能下降,有时还会引起过热甚至是冒烟起火。</span></p>

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<p><span style="font-size:16px;"><strong>电池过放的概念则与过充相反。</strong></span></p>

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<p><span style="font-size:16px;">在电池放电到低于下限电压时,仍然被要求继续放电,称为过放。</span></p>

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<p><span style="font-size:16px;">出现电池过放时,电池内部会发生异于常态的化学反应,导致内部活性物质出现不可逆的变化,使电池容量下降,严重的情况,该单体电池将无法使用。</span></p>

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<p><span style="font-size:16px;"><strong>因此,BMS需要监控各单体电池的电压,控制其充电电流和放电电流,既不能超过上限电压,又不能低于下限电压。</strong></span></p>

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<p><span style="font-size:16px;"><strong>SOC过充/过放上下限</strong></span></p>

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<p><span style="font-size:16px;"><strong>电池均衡方式</strong></span></p>
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<p><span style="font-size:16px;">不同车企对BMS的算法采取不同的设计理念,对于车辆过充和过放的范围也是不一样的,有些车型限定使用容量的60%,通常充电到80%,放电到20%。</span></p>

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<p><span style="font-size:16px;">低电量电池经过长期存放后,会出现自放电现象。限定使用容量的做法,本质上是为了保留部分电量,降低由于电池自放电而引起的过放概率。</span></p>

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<p><span style="font-size:16px;">BMS对电池电压压差进行检测,通过电池均衡,起到维护改善成组电池一致性,提高电池组性能的目的。</span></p>

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<p><span style="font-size:16px;"><strong>电池均衡的方式一般有两种:</strong></span></p>

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<p><span style="font-size:16px;"><strong>01.</strong>被动均衡</span></p>
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<p><span style="font-size:16px;"><strong>指的是先行消耗高能电池的多余能量,一般是通过电阻放电的方式,对高能电池进行放电,通常以热量形式释放电量,为其他低能电池争取更多充电时间。</strong></span></p>

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<p><span style="font-size:16px;">被动均衡的优点是成本低、电路设计简单。缺点是受限于荷电残余量最少的电池,无法增加低能电池的容量,对释放电量而产生的热量而言,是一种浪费。</span></p>

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<p><span style="font-size:16px;"><strong>02.</strong>主动均衡</span></p>
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<p><span style="font-size:16px;"><strong>指的是将高能电池上的电量转移到低能电池上,从而达到电池均衡的目的。</strong></span></p>

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<p><span style="font-size:16px;">由于能量可以被转移,电池均衡的效率比较高,能量损失小,充电时间短。缺点则是结构复杂,成本高,带有主动均衡功能的BMS普遍高于被动均衡功能的BMS。</span></p>
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