The new document should contain comment and PI nodes and the only element child from xforms: instance.

新的文档应当包含注释和pi节点，以及来自x forms： instance的惟一子元素。

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The double close loops of speed and current control is introduced in the system and the PI control is implemented in the current and speed loop, the position of rotor pole is detected by hall element.

系统采用电流、速度双闭环控制，电流、速度的调节采用PI调节，转子磁极位置通过霍尔元件检测。

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