The ETC case study in VTB

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The ETC case study in VTB
Ansgar Fehnker
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The ETC in VTB

• The ETC system
• The ETC controller
• The ETC implementation model
• The system requirements
• The model requirements
• Simulation based VV

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The ETC hardware

• Components
• D.C. motor
• Return spring
• Throttle body Plate
• Potentiometer (TPS)
• (Can be viewed as second order non-linear system)

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The ETC controller

• ETC controls the throttle angle, given desired
  angle, mode, set points,
• Application layer divided in manager, monitor and
  servo control (throttle plate feedback control)
• Controller has four normal control modes, among
  them human control and cruise control mode.
• Two failure modes
• Sliding mode controller in human control mode
• Control law for other modes undefined
• 5th order linear filter for drivers input
  (desired angle)

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The ETC implementation model

• Discrete sliding mode controller
• Discretized filter
• Explicit task scheduler
• PWM interface between DC-motor and ETC
• Sampled sensor input
• Two sets of requirements
• that ensure the performance of the
  implementation model
• that show that the implementation model is close
  to the idealized, simplified model

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Performance requirements

• Rise time requirement
• Settle time requirement
• Percent overshoot requirement
• Tracking Requirements
• Steady state tracking error
• Input resolution
• (Battery Voltage)

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Model requirements

• Single mode model vs Full model
• Discrete time model vs continuous time model
• PWM vs Gain
• Sampled input requirements

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VTB view
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Simulation based VV
Rise time requirement Given step input two
thresholds maximal rise time gt Test succeeds
if the output hits 2nd threshold less than the
maximal rise time after hitting the 1st
threshold
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Simulation based VV
Rise time requirement for the ETC Step input from
0 to 90 degrees 10 and 90 thresholds 100
ms gt Test succeeds if throttle angle reaches
90 within 100ms after reaching 10
input
90
10
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Simulation based VV
Settle time requirement for the ETC Step input
from 0 to 90 degrees 90 and 95 thresholds
40 ms gt Test succeeds if throttle angle
reaches 95 within 40ms after reaching 90
input
95
90
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Simulation based VV
Input/Output range test Given input and output
range number of iterations number of
switches gt Test fails if it finds within the
given number of iterations a random input,
within the input interval and given number of
switches, that leads to a violation of the
output range
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Simulation based VV
Overshoot requirement For any input in
0.2,89.8 degrees output should be in 0,90
degrees
overshoot
input
output
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Simulation based VV
Tracking test Keep the input constant after some
period of randomized input. gt Test succeeds if
the error between the final output value and the
desired final value smaller than given bound
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Simulation based VV
Steady State Tracking Error Keep the input a
0 after some period of randomized input. gt
Test succeeds if the error throttle Angle is
smaller than 1.8 degrees.
input
output
tracking error
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Simulation based VV
Angle Resolution Error Keep the input a 0.5 after
some period of randomized input. gt Test
succeeds if the error throttle angle is 0.5
0.02
resolution error
output
input
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VTB view
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Simulation based VV

• Model consistency
• Compare OEP blocks with simplified version
• Determine behavior of OEP in the loop for
  randomized input
• Offer the same input to simplified block
• Define a measure for the error
• Test fails if the error beyond a certain threshold

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Simulation based VV
OEP controller vs single mode controller Compare
output of OEP blocks with output of the
simplified version for randomized input Test
fails is the integrated error gt 0.1 Similar
tests for other model requirements
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VTB view
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Conclusions

• The VTB helped to
• decompose the system requirements
• validate the rise time and settle time
  requirement
• find violations of the overshoot, and tracking
  requirements
• show that the implementation model is close to
  the ideal continuous time model