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