luokai0 Control Systems Expert
Before Starting
- Continuous or discrete time system?
- SISO or MIMO?
- Classical or modern control approach?
Core Expertise Areas
System Modeling
Transfer function: Laplace domain ratio of output to input for LTI systems. Block diagram: graphical representation of system interconnections. State-space: x-dot = Ax + Bu, y = Cx + Du, more general than transfer function. Linearization: approximate nonlinear system around operating point. System identification: estimate model parameters from input-output data.
Classical Control Design
PID: proportional integral derivative, most widely used industrial controller. Root locus: graphical method to design gain for desired closed-loop poles. Lead compensator: improves phase margin, speeds up transient response. Lag compensator: improves steady-state error, reduces high frequency gain. Ziegler-Nichols: empirical PID tuning from step response or ultimate gain.
Frequency Domain Design
Gain margin: additional gain before instability, read from Bode at phase -180. Phase margin: additional phase lag before instability, read from Bode at 0 dB. Bandwidth: frequency range of effective control, affects disturbance rejection. Sensitivity function: closed-loop sensitivity to disturbances and model errors.
Digital Control
Discretization: convert continuous controller to discrete, Tustin or ZOH method. Sampling rate: choose 10 to 20 times bandwidth for adequate digital control. Quantization: finite word length effects, limit cycles in digital controllers. Computational delay: accounts for processing time, degrades phase margin.
Best Practices
- Always verify stability margins before deploying controller
- Tune conservatively and increase aggressiveness only if needed
- Test controller on simulation model before hardware
- Document tuning rationale for future maintenance
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Insufficient phase margin | Add lead compensation to improve phase margin |
| Integral windup | Implement anti-windup for all integrating controllers |
| Sampling too slow | Sample at minimum 10 times controller bandwidth |
| Ignoring actuator saturation | Include saturation in analysis and add anti-windup |
Related Skills
- circuit-analysis-expert
- signal-processing-expert
- control-theory-expert