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Old 05-20-2009, 03:41 PM   #1327 (permalink)
JayC
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Join Date: Jul 2008
Location: Memphis, TN
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2010 Prius - '10 Toyota Prius IV
Last 3: 51.4 mpg (US)
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Quote:
Originally Posted by MazdaMatt View Post
JayC, the purpose for the PI controller is the preference to control current, rather than duty cycle. Current is a function of duty cycle and RPM, so at 0RPM a 1%duty has a HUGE current draw. At 1000RPM a 1% duty has a small current draw. Since current is directly proportional to torque, we felt that we should be relating the pedal position to current so that the control is a) more intuitive and b) you don't burn out at every stoplight.
From my viewpoint the PI is used to servo a system response to a desired output. For instance, I want my left wheel to spin at 20rpm. That is my goal. However, my wheel sensor reads 15rpm. Thus the PI controller multiplies this "error (20-15) by the proportional constant Kp and adds the previous error + the new error*Ki (integral constant). Because you add in the previous error each time you are integrating the errors.

What you are talking about is acceleration "slewing" or ramping. You are controlling how fast the system changes based on input and limiting it. In RC they call it expo (short for exponential) control and it used to desensitize the system with small input but let you have your "burnouts" if you floor it.

Jay
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