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Embedded Control Systems

Embedded Control Systems. Dr. Bonnie Heck School of ECE Georgia Tech. Introduction. Goal: Meet design specifications on performance even under varying operating conditions Examples: car cruise control, temperature control, flight controls, motor control, robotic manipulator. Disturbance.

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Embedded Control Systems

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  1. Embedded Control Systems Dr. Bonnie Heck School of ECE Georgia Tech

  2. Introduction • Goal: Meet design specifications on performance even under varying operating conditions • Examples: car cruise control, temperature control, flight controls, motor control, robotic manipulator

  3. Disturbance Reference Output System to be controlled + Controller Actuator - Measurement Sensor Feedback Control

  4. Embedded Control Components • Sensors: transducers that convert physical quantities to voltage • Controller: Analog or digital implementation of the control • Digital controller: DSP board, microcontroller, or PC with ADC and DAC • Actuators: physical device that converts controller outputs to system inputs • Drive Electronics: power, power amplifier, analog filters

  5. Performance

  6. DC Value Magnitude Bandwidth 0 Frequency (Hz or rad/sec) Closed Loop Frequency Response

  7. Design Metrics • Speed of Response • Speed at which transient decays (bandwidth) • Accuracy • Smallness of error (DC value) • Relative Stability • Amount of error tolerated in model before system goes unstable

  8. Reference Output System to be controlled + Controller Actuator - Measurement Error, E(z) Command, U(z) Sensor Reference To actuator Control D(z) + DAC - ADC From sensor Design Procedure

  9. Common Controllers • Proportional • Proportional + Derivative (PD) • Proportional + Integral (PI) • Proportional + Integral + Derivative (PID)

  10. DC Value Magnitude Bandwidth 0 Frequency (Hz or rad/sec) Desired Responses Frequency Response Time Response

  11. Design Strategy • Speed of Response • Bandwidth increases as K increases • Accuracy • DC value approaches 1 as K increases • Relative Stability • Often relative stability goes down as K increases

  12. Control Algorithm General Form:

  13. Pseudo-code //Initialize u_1 = 0; u_2 = 0; e_1 = 0; e_2 = 0; while(1){y = readsensor(); e=r-y; u = -a1*u_1-a2*u_2+e+b1*e_1+b2*e_2; output(u); //pass to actuator driver u_2=u_1; u_1 = u; e_2 = e_1; e_1 = e; wait(sample_time); } /* a better way is to use a hardware timer to trigger an event, the event handler runs this code */

  14. Sampling Period • Nyquist: sample at twice the highest frequency • But, the signal being sampled is not bandlimited Rule of thumb: sample at 10 to 20 times the bandwidth of the closed loop system, slower reduces performance and may destabilize the system

  15. Summary • Feedback control adds robustness (good performance even with varying conditions) • Embedded controls implemented with DSP boards, microcontrollers, PCs, FPGA boards • Larger gain, K: faster response, better accuracy, possibly lower stability • Sample at 10-20 times the closed loop bandwidth

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