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Loss calculation for induction machine rotor bar with non-sinusoidal current

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Abstract

To evaluate the rotor bar loss of an induction machine with non-sinusoidal currents, a new analysis approach is proposed. The approach calculates the losses of the currents with different frequencies respectively and, then, adds them together. The method uses the circuit analysis theory instead of electromagnetic field theory to count the skin effect on the bar loss. In the method, a rotor bar is divided into many layers with their own parameters derived. Based on the above theory, it is illustrated why the total bar loss due to the non-sinusoidal current equals the sum of the losses produced by the currents with different frequencies. For a given example, the bar loss produced by each rotor current at different frequencies is calculated. The finite element analysis is also performed to total bar loss calculation with non-sinusoidal current. The analysis verifies the superposition relationship between the respective losses and the total one. By applying superposition principle in rotor bar loss calculation, it not only lowers the computation burden, but also quantitatively determines the loss at a specified frequency.
第 2 7期 
年 9  国 电 工 程 学 报 
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  p. 
 n.c . El 
文章号:  中类号 :T  文标识 :A  学科类号  
步 电耗 
振 ,王祥 珩,罗   
清华 大学 电力系统及 发 电备控制 和仿真 国家重 点实验 室,北京市 淀 区  
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RooR BAR W ITH oNUSoIAL CURRENT 
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摘要:为计算 异步电机转子导条流过非正弦 电流 时的损耗 , 
采用 了先分别计算不 同频率电流对应 损耗再进行 叠加的分 
析方法该方法基 于电路原理而非通过 电磁场分析来计及 集 
肤效应对损耗响,对转子导条分层处理并求出相应参 
数的前提下推导说明导条流过非正弦电流时的损耗等于分 
别流过不频率正弦交流电流时的损耗之和。文中给算例 
并计 了不同频率电流在导条 中产的损 时用 
有限元法直接计算流过实际非正弦电流时的转子导条损耗 
计算结果验证了损耗所满足的叠加关系。用叠加方法 
求取损耗不仅减小了计算工作量而且能定量计算某一特定 
频率 电流生损 
词 :异 步 电机; 导条 损耗 ;叠加 原理 ;集 肤效 应 
  引言 
当用频 电源步 电动供 电【 发 电 
通 过桥 与负载相 连  异 步 电机 出现运  
故 障[时 ,电机 定子绕 组中就 会流 过弦 电 
流。对上述系统中的三相异步电机而言,除了非正 
流基波分量在气隙中产生空间基波旋转磁势 
外,还有非正弦电流各次谐波分量在气隙中产生空 
间基波 旋转磁势 ,不 同间谐波 电流产生 的空间基 
波旋转磁势虽然转速不同,但这些空间基波磁势 
不能通过短距绕组和分布绕组得到有效削弱,若谐 
屯 流大到 一定程度 ,由此产 生的空 间基波磁 势及 
其对机运行性能的影响就无法忽略。 
在转速 各异的气隙 空间基波磁 势作用下 ,异步 
电机 转子导 条中会感 应出不 同频率 的电势和 电流 , 
不 同频率 电流成 非正弦 电流 。因为转子 导条 
电流 决定铜 耗的大 小,而转又 与对 
机运行性能影响甚大的转差率密切相关,因此, 
准确计算转子导条损耗在异步电机性能的分析 
着 重要义 。 
转子 导条损 耗计算 的难点在 于集肤 效应 ,如果 
步 电机在一 频率下 正常运行 ,转子 电流率很 
低 ,集肤效 应可不 计及 ;但 是, 当导条 流过 
由于非 正弦 电流是 由不 同频率 的 
弦 电流成 ,集肤对 损耗就必 须 
考虑。实际上,集肤效应使流在转子导条截面 
非均 匀分布 ,即各 处的 电流密不再等 ,从而 
引起加 ,耗增 加程度 与电流频 率大相 
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。若考 虑集肤 效应,计一频 率下转子导 条损 
很麻 烦 ,确 定不 同频 率合成 电流作用 下的 
总损又增了分难度于集 效应 
本身 属于 电磁 场,通过 电磁有 限元  
计算转子导条集肤效应虽可解决上述难题,但用有 
法计算也存在下述两个主要缺陷:①从计算 
便程度来看,若借助于 A计算,导条 
流过非正弦电流时只能当成瞬态场而不能当成谐 
波场进行处这就使加载电变得很麻烦且大大 
延长 了计算 时物 理规角度虑 , 
结果 只表 明导条 总损耗 大小 ,而难 以 
量 分析 非正 弦 电流 中各 谐波 电流 分对 总 
影响程度,更无法从理论确定这种情况下的损 
耗能否满足叠加关系。 
根据 电路理 论分层计 算异步 电机的 
效应是一种沿 的分析方法文献  
详细分析在单一频率下集肤效应对结构复杂 
双笼转子参的影响。本文借鉴这一方法来计算转 
子导 条流正 弦电流 时的损耗 ,旨在说 明转子导 
条流过频率流时产生的损耗满足叠加关系。 
在把非正弦电流分解为不同频率正弦电流之和的 
上,分别计算各次谐波下的转子导条损耗并相 
加得到导条流过非正弦电流时的总损耗,这不仅大 
少 了计,更说 明谐波 电引起 
的损在 总损耗 中所 占比例 。 
2 损耗计算公式推导与叠加关系理论分析 
  转子导 理方 
理论为基础推导出转子导条损耗计算 
公式 ,而非 由电磁场直 接计出转耗 是本所 
用 分析 方法 的 关键 ,根据 推 导 出的损 耗 计公 
式,再从理论上说明导条流过非正弦电流时的总损 
耗与各次谐波电流产生的损耗满足叠加关系。 
异步 电机转 子导条分 块再的处 
是下面推 导过程 中考虑集 肤效应时导 条损计算 公 
前提 。本文 推导相 应计式之 目的在于从 理 
论上损耗叠加 关系为 方便起见 ,不 影响 
结论前提以矩形子导条为例进行 分析用 
矩形导条的另一好处就是某一频率下反集肤效应 
的导条电阻增加系数有相的解析表达式【  ,这样 
能确定该频率导条的准确数 
矩形转子导条示意图。对矩形转子导 
而言无需分而是直接进行,把图 1 
的导条从槽 槽顶沿高度方向上均匀分成等高 
等 宽的形 薄层 ,总 层数 各 层分别 用  
,… , 示 。 当每层 的高度足 够小 时,可 以认 
流密度在此薄层导条中处相等,即不考虑 
导条 本身 的集肤效 应,将薄层导条 的 电阻当成直 
流 电阻 ,阻值常数 。   
  
 
  , 
— w 
异 步 电机 矩形 转子条 
Fi  Re     nd   
层 中非正弦 电流 表达式 
设 整 条 流 过 非 正 弦 电 流 为 , 根 据 
r级数 把该 电流 表示 为一系 列不 同频 率 
交流 电流和 ,即各 次谐波 电流之 和 
  x
 ̄s  )   
式 中      分别 为 次谐波 电流相 量 的效 值 
度 、初角 。 
对/波 电肤 效应使 其在转 子导 
上分 布不匀 ,条截面 各处 电密度 不 同导致 
每个薄层导条里的电流不相等。在只考虑 次谐波 
电流 时选 各导条 层 电相 量为待 求解 Ⅳ个知 
量,用相量分析法计算各层电流的程如下:①计 
层 的直流 电、 自感和 每两层 
间的@lⅣ个 导条组成 Ⅳ个独回路 
列 出 1个 以形式 表示 的回路 电压 
导 条两 个节 点中有 1个 
再列 出 个 以相量 形式表 示的节 点电流方 程 
④联列上面 Ⅳ个独立方程并求解得到各电流 
量;把各层中的电流相量转化为瞬时值表达 
电阻、电感参数 的具体 计算方法 与方程组 的求 解过 
程可 见文 
据谐波平衡原理,分别针对不同次波用相 
分析法列出 的 Ⅳ 个独立方程并单独进行求 
解 。从分析 计算过 程 中可以看 出,一种频 率电流 的 
分布不对另一种频率电流的分布产生任何影响。 
第 .层 导中各下 电流值 
式 ,相加 即得 该层 中实际 流过 的非弦 电流 
为 
   s      
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第 l  吴振 新等  异步 电机转 应非正弦 电流导条耗   
式 中   、a 分别为∥次谐 波 电相量 的有效 
值 、角度 、初角 。 
各层 中损耗 的叠加 关系 
于薄层导条高度很小,其电阻认为常值, 
即等过直 流电流时对 应的直流 电阻。第 .导条 
的直流 电阻设为 风 ,该层 导条损 率 )为 
 
  J   
式 中  为非 正流基 波的周 期 
代入进行 得 
  l    EE& ・ 
      V 
≠ 
  ,—a   
由于次谐波的频中等 
式右的第 2 于零导条 损耗 
  ( 
 
式(表 示第 导条 总损等 于其 中次谐 波 
电流 单独生 的损耗之 和 ,即该损耗 满足 
加关系。 
4 导条损耗 的叠关系 
各层损耗相加就是整个导条的总损 
∑∑   ( 
l / 
换上 式 中号 的次序 ,得 
∑∑   ( 
  j 
  表  
=I 
所产损耗 
说 明导 条正 弦 电流 时的 总损耗 等 
于各 次谐波 电流单独 作用产 生的损 耗之和 ,也就 是 
总损 耗满足 叠加关系 。 
5 导条总 实用计算式 
然总损耗满足叠加关系,计算总损耗就归结 
为计算各次谐波单独产生的损耗。对某次谐波而 
言 ,集 肤效导致 的损增加 相 当于在 电流有效值 
变 的情况 下 电阻值加 ,值 增加后 的 电阻称 为 
交流电阻。导条的交流电值不仅与导条结构尺寸 
电阻率有关,还与流过导条的交流流频率有 
关,显然,不同次谐波对应的交流电值不相等。 
为定量表示电阻值增加的程度,定义 谐波对应 
阻增 数为 
=    
式 中 直 流 电阻  为∥下 
条 的交流 电阻 。 
若 已知波 下电阻增加系数 , 
损耗的实公式 
  ( 
 
  电阻加 系数的 求取法 
机转子矩形导条的电阻增加系数可用解析 
公式 求取 ,但 对于其 它形状 的转导条 ,相 应 
的解 析计算 公式,只 能用解法 。有 限元法 和分 
法 均属数 值解法 ,与前 述过程 一致 ,本 文求 
取 电阻增 加系数用 分层计 算法 。 
文献【详细阐用分层法计算某一频率 
电阻加 系数 的过程 ,简而 言,就是 首先计 算 
集 肤效应 时的导耗 ,即等于 电流有 效值 
的平与 导条流 电阻 的乘积 ;然后虑 集肤 
,在分 层的基础上 ,由 2简述 的方法 求出各 
流值并据此计算出各层损耗,各层损耗相加后 
损耗 ;用 考虑效 应导条 损 
耗 除考 虑肤 效应 时 的导耗 就得 到该 频 
率下的电增加系数。 
表 I了图 I 导条  
频 率 阻 增 加 系 计 算 值 ,矩 形 导 的 高 
m,   m,导条 电阻率 =  Q 
导条率 m。在用数值法导 
条均匀分 为 4层 ,每层 的高度为 0。矩形条 
电阻增加系数的解析计算 公式取 自文献 [ 
  =h 
=   糌    
表 I 应不同频率下的电阻增加系数 
  Rnc  
wi o dfes  
表 I解析法求得的结果认为是准确值当每 
层高为 0m 时分层数值的结果相对 
误差 绝对值 )均 在 0%以数值法计 算的结果相 
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当准确也验证所用分析方正确 
3 损耗叠加关系的数值验证 
  谐 波损之和 与直算 的总损对 比验证 
为进 一步说 明其 正确性 ,下面 通过两 种方法 的 
数值 计算结 果加 以验 证。 
值 验 证 时仍 用 上面 算 例 , 导条 中通 以  
  s   s+1  s的 
弦 电流 ,其次 谐波 的频 率分别 为  
。 目前直 接计算 流过非 正时 
转子 导条总 损耗只 有采用 有限法 ,  
中的态 场可这 一问题 。若用 瞬态场 计算 ,电 
加载 时较为麻烦 ,需要在非 正弦 电流 的一个 周 
期 0内取出若时刻并计出相时刻电流 
,然后 把这些 电流值 作为 激励源 加入 ,再用有 限 
元对 整条进 行剖分 ,最终 求出总 损耗 。 
表 2给 出了基 于解析法 和基 于分层计 算数值 法 
求得各次谐波下单位长度的导条损耗以及根据 
加关系直接把各次谐波下损耗相加后的损耗, 
用有限元瞬态场法求出导直接通非正弦电流时 
损耗也列在表中。在用分层法具体计算时导条 
仍均 匀分 层 ,各 频率下 的电阻用表  
中的数据 ;在用有 限元法 具体时 ,截 
域剖 分为边长 为 0m 的 8正方元 , 
剖分 后的单数 为 5 
表 2 用不 同方法计算的转子导 条损耗 
  Ro   ul  fe m e 
由表 可 以看 出把转子 导条 中非正 弦电流 
解 为不 同频谐波 电,分算 出不 同频率 
下导条损耗,再相加所得到的损耗与导条直接 
正弦 电流计算 出的损耗相等 ,这一数值计算 结 
说明了损耗满足叠加关系,从而验证了前面的理 
论推 导分析 的正确 性。矩形 导条损 耗可 由解析法 计 
出准 确结,通过 与准结果 比较 发现,分层 法 
和有 限元法 数值计 算结果 的相对误 差 绝对值 )分 
为 0和 0%。 限元  
在于计算过程中既要对加载的非正弦电流进行 
时间上的离散,又要对整个导条进行空间上的剖分 
散 ,所以 电在 一个周期 内的离散数 、导条截 面 
上 的剖数 均对结 果产影 响;而层 
计算 某一率 下的损时 ,计算差只 来 自分 
条的层数,产生误差的根源较少。 
接 计算不 同电流下 的总损 耗进行对 比验证 
量 形式表 示某波 电流 ,导条中 
生 的耗 只应 该与 电流相 量频 率有 效有 
而与 电流相 量的初角 无关 。因,对于 不同 
的非正 弦电,若它分解 后各次 谐波 电流 的频率 
有效值相等,当损耗满足叠加关系时,些不同 
非正弦电流在导条中产生的损耗就应该相等这 
理论分析应该得出的结论。从计算的出发, 
采 用 有元 法 中的瞬 态直 接求 出这 些不 同非 
正弦电流在导产生的损耗,果这些损耗的 
算值相等则从数值上验证损耗满足叠加关系。 
现给满足相应条件的任意 个非正弦流波形 
) i   n1 ̄+2  O  ̄ 
 Om 
)i  n1  、 
 
 
)i  n1  ) 
 
2sm 一 
有 限元瞬场直 接计算 了 不 同非正 弦 
电流 所对应 转子 的导条 损结果 见表  
表 3 不同 电流波 耗 
  Rorbr ls frd  wa 
电b  损耗/ 
2.274 
 
2.279 
由表 虽然 非 正弦 电形不 同 
在 转子条 中产 生的损等 ,由此证 了损 
耗 的叠关 系。上面 3个损略有 差别 的原 
由离散精 度所致 。 
3 由叠系求取 
叠加关系求取导条总损耗有下优点:①可 
以确 定 某谐 波 电流 引起 的损 耗在 总 损耗 中所 占 
的份额 ,可 以采用 削弱某 些次谐 波电流 来减小 
导条损耗的方法;②计算任意形状导在单一频率 
波 电流下 的损耗 可 以用 分层法 ,与用有 限 
的损相 比,前者不 仅 
程简单、计算速度较快,且在一情况下计算的 
准确性更高。 
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第 l  吴振 新等  异步 电机转子 非正时的导条耗   
顺便提及计算单一频率下的转子导条损耗也 
用 有 限元法 ,借 助 的谐波 场分 
析 。谐波场 只涉及 一种频率 的 电相量 ,在 进行 电 
载 时输入 电流值 、频率和 初相角 即可 ,不 
用 瞬态流加 载那样 麻烦 ,因此 , 
用有限元谐波场计算各次谐波下损耗再叠加的方  【 
虽 不如便 ,但 比直接用 有限元 瞬态场 计 
耗 的方简单 。 
4 结   
在 电力 电子装与异 步电机 组成的 系统为 
准确计算考虑集肤效应时非正弦电流在异步电机 
子 导条生 的损耗 ,本文理论 分析计 
算两方面进行较为详细的研究。在对导条分层处 
的前提下 ,础 ,从论 上推 
导说明了损耗所满足的叠加关系,给出了计算损耗 
实用 公式简述 了电阻增加 系数 的过程 。论 
通过矩形导条这一实例,用解析法和分层数值 
法分别求出各次谐波损耗并相加得到总损耗, 
同时 通有 限瞬 态 场接计 算 了非弦 电流 产 
耗 ,两种情 况下总耗 相等 ,从数值 上验 
叠加 关系 。另 外,通过直 接计满足 
定条 件的不 同非正弦 电流产 生的损耗 ,得了损 
相 等这一 符合分 析的结果 ,进一步 从数值 计 
算 的角验 证了理分 析结果 。 
根据损耗关系计算考虑集肤效应时非正 
流产生的导条损耗是具有一定新意的实用方 
法。该方法使用方便,而且能定量确定某一频率电 
产 生损耗 在总损耗 中的 比例,可做有针 对性地 
取通过减小哪些次谐波电流来有效降低导条损 
耗 的措施 。 
在数值计算方分层计算方法能够处理某些 
用传统解析方法无法解决的问题,计算准确性高。 
与有限元分析方法相比,分层计算方法编程简单、 
计算时间短。因此,分层法可推荐为算转子导条 
耗 时优用 的数方 法 。 
致 谢 
费仁言博士在文修改 
过程 中所提 供的 帮助 ! 
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】陈世 坤.电机 设计【北京:机 械工业 出版社  
收稿 日期:2 
者简  
吴新振 (,博 士研究 ,青岛 大学电气 工程 系教 授, 
电机 系统分 析与控 制等方面 的研究工作 ; 
王祥 , 男,教授 ,博 士生导 师,从 事电机 系统分与 
、电机 故障与保护 、电气传动 自化等方 面的研究工作 : 
, 男,硕 士研究 生,从事 电机 电磁场 分析算方 
面 的研究工 作。 
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