介绍了反电动势过零位置检测的原理及实现方法，并采用了数字式转速、电流双闭环控制。

One kind of sensorless control system for brushless DC motor based on DSP was introduced and the principle of back-EMF zero-crossing detection and realization method was discussed in detail.

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冻结。使当前选择的物体的变换变成物体的零位置。你可以从子菜单中选择冻结移动，旋转，缩放或者所有。

Freeze. Makes the current transformations on the selected objects be the objects' zero position. You can select Translate, Rotate, Scale, or All from the submenu.

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And when we're talking about the amplitude of the wave, we're talking about the deviation from that average level. So, if we define the average level as zero, you can have either a positive amplitude or a negative amplitude.

当我们讨论一个波的振幅时,我们说的是偏离平均位置的量,如果我们把平均位置,定义为零的话，那幅值不是,正的就是负的，有时候人们在。

麻省理工公开课 - 化学原理课程节选