dc machine模块的内部结构：
Armature resistance and inductance [Ra (ohms) La (H) ]：电枢电阻和电感
Field resistance and inductance [Rf (ohms) Lf (H) ]：励磁回路电阻和电感
Field-armature mutual inductance Laf (H) :：电枢与电磁回路互感
当出现如下error时：
error:Initialization commands cannot be evaluated.
Caused by:
The diagram must contain a powergui block. The block should be named 'powergui' and should be located at the highest level of your diagram where Simscape Power Systems (Specialized Technology) blocks are found.
powergui模块为研究人员提供的电能图形界面，power是电能，gui是图形界面。
在电力电子，电路，电机等电气工程模块搭建的仿真模型里面，power是电能、电力，gui指的是图形界面，这个模块是专门为电气工程领域研究人员提供的图形界面，可以设置解算器的解算方式，对波形进行FFT分析等，功能很多。
