📄 电机用滤波器的一些特殊问题.htm
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</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> 对从事电机驱动项目的工程师来说，电磁兼容性要求是十分重要的。大多数新型交流电机需要高效的换向器，这就要求功率半导体具有高的转换速率和极快的上升时间。傅立叶变换表明其谐波占有的带宽可达数十兆赫。若需要满足</span><span
lang=EN-US style='font-size:9.0pt'>EMC</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>指令，则需要在共模和差模都具有连续且较宽阻带的低通滤波器。为了满足</span><span
lang=EN-US style='font-size:9.0pt'>EMC</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>要求，建议设计者可首先处理好电机</span><span lang=EN-US
style='font-size:9.0pt'>/</span><span style='font-size:9.0pt;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>换向器组件，然后针对存在的</span><span
lang=EN-US style='font-size:9.0pt'>EMC</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>问题挑选一标准滤波器来改进</span><span lang=EN-US style='font-size:
9.0pt'>EMC</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>。在许多场合，由于没有对内部电路参数予以充分的考虑，结果找不到一个适宜的解决方法。</span><span
lang=EN-US style='font-size:9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> 根据我们多年在实验室里反复测试获得的经验，我们认为“凑巧的话“，精心筛选出的滤波器能够恰好解决现场问题。恰好解决的意思是产品能够满足指定标准的最低要求。然而，考虑不周的设计，例如对地电容过大，会引起巨大的浪涌电流，造成过载保护动作。正确的解决方案对整个工程的长期效应、可靠性及使用寿命来说都是至关重要的。我们的结论是，要使产品具有较高的质量，使用高质量的特制器件是一个更经济的途径。</span><span
lang=EN-US style='font-size:9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> 特制的优点显而易见，这由图</span><span
lang=EN-US style='font-size:9.0pt'>1</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>、图</span><span lang=EN-US style='font-size:9.0pt'>2</span><span
style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>、图</span><span lang=EN-US
style='font-size:9.0pt'>3</span><span style='font-size:9.0pt;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>可看出，这是我们</span><span
lang=EN-US style='font-size:9.0pt'>EMC</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>测试室内</span><span lang=EN-US style='font-size:9.0pt'>R&S
EP6</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>自动测试系统的记录结果，这是单相电机的例子。</span><span
lang=EN-US style='font-size:9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> ．图</span><span
lang=EN-US style='font-size:9.0pt'>1</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>是系统没有滤波时的性能；</span><span lang=EN-US style='font-size:
9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> ．图</span><span
lang=EN-US style='font-size:9.0pt'>2</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>是安装了从滤波器样本中选择的标准滤波器后的性能；</span><span lang=EN-US
style='font-size:9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> ．图</span><span
lang=EN-US style='font-size:9.0pt'>3</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>是安装了专门设计的滤波器后的性能。</span><span lang=EN-US
style='font-size:9.0pt'><br>
</span><span style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'> 安装滤波器后获得的改进效果由图</span><span
lang=EN-US style='font-size:9.0pt'>1</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>与图</span><span lang=EN-US style='font-size:9.0pt'>2</span><span
style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>的比较中可以看出。从图</span><span
lang=EN-US style='font-size:9.0pt'>4</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>所示的预期的滤波器特性曲线后，会发现一个粗心的工程师易犯的严重错误。图</span><span
lang=EN-US style='font-size:9.0pt'>4</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>所示的滤波器特性是在理想电阻性负载条件下测试得到的，而实际情况并非如此。作为例子，我们研究</span><span
lang=EN-US style='font-size:9.0pt'>2MHz</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>处预期的滤波器特性及实际结果，则可清楚地看到：预期大约为</span><span lang=EN-US
style='font-size:9.0pt'>60dB</span><span style='font-size:9.0pt;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>衰减的曲线实际上只改善了</span><span
lang=EN-US style='font-size:9.0pt'>38dB</span><span style='font-size:9.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>，在</span><span lang=EN-US style='font-size:9.0pt'>10MHz</span><span
style='font-size:9.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>只改善了不到</span><span lang=EN-US
style='font-size:9.0pt'>20dB</span><span style='font-size:9.0pt;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>。</span><span
style='font-size:9.0pt'> <span lang=EN-US><o:p></o:p></span></span></p>
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图1 无滤波电机<o:p></o:p></span></p>
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图2 使用现成滤波器的电机<o:p></o:p></span></p>
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图3 使用特制滤波器的电机<o:p></o:p></span></p>
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图4 标准滤波器的响应曲线<o:p></o:p></span></p>
<p> 图<span lang=EN-US>1、图2、图3是电源线上产生的传导干扰电压与EN55011：1991 B级标准中规定的平均值与准峰值极限值的比较结果。<br>
传统滤波理论是在负载已知且恒定的前提下发展的，在这里，允许有很小的寄生参数作用。用这个理论计算一个低通滤波器中的器件参数是一个极其简单的事，这个低通滤波器在通带内是无损的，但阻带上的衰减是从源看进去的阻抗的函数。理想情况也许如此。可是，在各种负载及速度条件下，换向器供电条件是十分复杂的，对设计人员而言是十分不确定的。在这种条件下，设计经验与工程经验的结合和对整个系统的电子与机械构造的详尽认识比传统理论要可靠得多。<br>
图5和图6是专为某个电机驱动项目设计的单相和三相滤波器的电路结构，注意共模线圈的使用。在三相滤波器中，电容星形接地和中线的连接方法可以是体积最小。电机滤波器的负载电流为从几安至280安。<o:p></o:p></span></p>
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图5 专用电机单相滤波器电路结构<o:p></o:p></span></p>
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图6 专用电机三相滤波器电路结构 <o:p></o:p></span></p>
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