Cruise Control 3RETURN OF THE SPEED CONTROL
J E F F F E R G U S O N , T O M L E I C K
Overview• Background
• Proposed Controller
• Expected Results
• Questions
Background• Closed-loop speed control
• Maintain constant speed under varying loads
• Cruise control system in vehicles
• Improve on results from Labs 4 and 5
Open Loop Behavior • Lab 4 experiments provided data for determining:• Minimum speed control voltage input
• Speed to input voltage ratio
• Effects on speed by application of brake load as shown on the following slide
0 25 50 75 100 125 150 175 200 2250
20
40
60
80
100
120
140
160
Speed vs Load Torque
Input Voltage = 1.0 VInput Voltage = 0.5 V
Load Torque (Nm)
Spee
d (r
ad/s
)
Closed Loop Behavior • Lab 5 experiments provided data for determining:• Simple proportional gain closed loop speed control system characteristics
• Tachometer scale factor (KT)
• Effect of pre-amp gain on error voltage as Brake position increased
0 1 2 3 4 5 6 7 8 9 100
200
400
600
800
1000
1200
Motor Speed vs. Brake Setting
Pre-amp Gain of 1Pre-amp Gain of 5
Brake Position
Mto
tr S
peed
(rpm
)
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
Error Voltage vs. Brake Setting
Pre-amp Gain of 1Pre-amp Gain of 5
Brake Position
Erro
r Vol
tage
(V)
Proposed Controller• Use PID Controller module
• Maintain speed (voltage at tach) for brake position 10 to within 5% of speed at brake position 0
• More concerned with steady-state error than quickness of the response
• Little-to-no percent overshoot
SIMULINK BLOCK DIAGRAMS
Choosing Controller Parameters• In ideal models, any incorporation of an integrator resulted
in zero steady-state error
• Large integrators are difficult to realize
• 0.1 < KI < 0.5
• KD = 0
• Solve for KP using the PID tuning window to match desired response
PID Block Tuning Window from Simulink
Choosing Controller Parameters• KP = 0.1
• KI = 0.4
• KD = 0
Zero Brake Response
PID Block Tuning Window from Simulink
Full Brake Response
Conclusion• System is modelled after automotive speed control system• Not a “fast” system to avoid abrupt accelerator changes
• Little/no overshoot to avoid seasick passengers
• Little steady state error for accurate system
• Expected challenge in adjusting the controller to obtain predicted response
• KI being bigger than KP and KD might cause problems
• Possible saturation from current limitations
Questions