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Embedded Control Systems: Design and Implementation Essentials

Learn the fundamentals of embedded control systems, from sensors to actuators, controllers to design metrics, and common control algorithms. Explore design strategies for optimal performance and stability under varying operating conditions.

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Embedded Control Systems: Design and Implementation Essentials

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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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