The paper presents a SPWM frequency variable and velocity variable system with SCR as main switching devices. The proposed scheme has been verified through experiment.

介绍一种以SCR作主开关器件的SPWM控制方式的变频调速系统，并通过实验对提出的方案进行了验证。

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The lessons of this experiment have been learned through an existence that has been much more demanding than was ever imagined at the outset.

这个试验的课程是要在（比一开始想像的更加苛刻的）存在中学习。

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This has occurred through the experiment and the different paths it took.

这是通过实验所产生的，可以有不同的道路来选择。

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