Single-Input-Single-Output Systems

TF 502 Single-Input-Single-Output Systems SIST, ShanghaiTech Introduction Open-Loop Control-Response Proportional Control General PID Control Boris Houska 1-1

Contents Introduction Open-Loop Control-Response Proportional Control General PID Control Single-Input-Single-Output Systems 1-2

Objectives In this lecture we will learn about Single-Input-Single-Output (SISO) systems Open-loop step response Proportional control of SISO systems Integral control PID control Warning: this lecture explains basic tricks to tune a controller based on physical intuition without using mathematical analysis yet (we ll discuss mathematical models later on in the lecture) Single-Input-Single-Output Systems 1-3

SISO Systems Recall from Lecture 1: 1. u(t) R denotes (scalar) input at time t 2. y(t) R denotes (scalar) output at time t Single-Input-Single-Output Systems 1-4

Example 1: oven SISO system: 1. u(t) R voltage at the heating coil 2. y(t) R temperature in the oven Single-Input-Single-Output Systems 1-5

Example 2: pendulum SISO system: 1. u(t) R force of the motor 2. y(t) R excitation angle of the pendulum Single-Input-Single-Output Systems 1-6

Contents Introduction Open-Loop Control-Response Proportional Control General PID Control Single-Input-Single-Output Systems 1-7

Open-loop control-response Idea: Test basic system behavior by making open-loop experiments Send signal u(t) to actuator and observe y(t) Single-Input-Single-Output Systems 1-8

Parameterization of control functions General affine parameterizations of the control function can be written in the form M u(t) = a i ϕ i (t). i=1 The functions ϕ 1,... ϕ M : R R are given basis functions The scalars a 1, a 2,..., a M R are the control parameterization coefficients Single-Input-Single-Output Systems 1-9

Parameterization of control functions General affine parameterizations of the control function can be written in the form M u(t) = a i ϕ i (t). i=1 The functions ϕ 1,... ϕ M : R R are given basis functions The scalars a 1, a 2,..., a M R are the control parameterization coefficients Single-Input-Single-Output Systems 1-10

Parameterization of control functions General affine parameterizations of the control function can be written in the form M u(t) = a i ϕ i (t). i=1 The functions ϕ 1,... ϕ M : R R are given basis functions The scalars a 1, a 2,..., a M R are the control parameterization coefficients Single-Input-Single-Output Systems 1-11

Open-loop step response Open-loop experiment: Introduce the basis functions 1 if t < 0 ϕ 1 (t) = 0 otherwise 1 if t 0 and ϕ 2 (t) = 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called step response For a 1 = 0, a 2 = 1: y is called unit step response Single-Input-Single-Output Systems 1-12

Open-loop step response Open-loop experiment: Introduce the basis functions 1 if t < 0 ϕ 1 (t) = 0 otherwise 1 if t 0 and ϕ 2 (t) = 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called step response For a 1 = 0, a 2 = 1: y is called unit step response Single-Input-Single-Output Systems 1-13

Open-loop step response Open-loop experiment: Introduce the basis functions 1 if t < 0 ϕ 1 (t) = 0 otherwise 1 if t 0 and ϕ 2 (t) = 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called step response For a 1 = 0, a 2 = 1: y is called unit step response Single-Input-Single-Output Systems 1-14

Open-loop step response Open-loop experiment: Introduce the basis functions 1 if t < 0 ϕ 1 (t) = 0 otherwise 1 if t 0 and ϕ 2 (t) = 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called step response For a 1 = 0, a 2 = 1: y is called unit step response Single-Input-Single-Output Systems 1-15

Open-loop step response Open-loop experiment: Introduce the basis functions 1 if t < 0 ϕ 1 (t) = 0 otherwise 1 if t 0 and ϕ 2 (t) = 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called step response For a 1 = 0, a 2 = 1: y is called unit step response Single-Input-Single-Output Systems 1-16

Example 1 Single-Input-Single-Output Systems 1-17

Example 1 Single-Input-Single-Output Systems 1-18

Example 2 Single-Input-Single-Output Systems 1-19

Example 2 Single-Input-Single-Output Systems 1-20

Open-loop frequency response Open-loop experiment: Choose a test frequency ω > 0. Introduce the basis functions 1 if t < 0 ϕ 1 (t) = and ϕ sin(ωt) if t 0 2(t) = 0 otherwise 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called frequency response Single-Input-Single-Output Systems 1-21

Open-loop frequency response Open-loop experiment: Choose a test frequency ω > 0. Introduce the basis functions 1 if t < 0 ϕ 1 (t) = and ϕ sin(ωt) if t 0 2(t) = 0 otherwise 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called frequency response Single-Input-Single-Output Systems 1-22

Open-loop frequency response Open-loop experiment: Choose a test frequency ω > 0. Introduce the basis functions 1 if t < 0 ϕ 1 (t) = and ϕ sin(ωt) if t 0 2(t) = 0 otherwise 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called frequency response Single-Input-Single-Output Systems 1-23

Open-loop frequency response Open-loop experiment: Choose a test frequency ω > 0. Introduce the basis functions 1 if t < 0 ϕ 1 (t) = and ϕ sin(ωt) if t 0 2(t) = 0 otherwise 0 otherwise Choose control step parameters a 1, a 2 R Send the control input u(t) = a 1 ϕ 1 (t) + a 2 ϕ 2 (t) to actuator Associated output signal y is called frequency response Single-Input-Single-Output Systems 1-24

Example 1 Single-Input-Single-Output Systems 1-25

Example 1 no steady state, but periodic limit cycle Single-Input-Single-Output Systems 1-26

Example 2 (resonance effect) Single-Input-Single-Output Systems 1-27

Example 2 (resonance effect) Single-Input-Single-Output Systems 1-28

Bounded-Input-Bounded-Output Systems A system is called a bounded-input-bounded-output (BIBO) system if there exists for every contant C 1 < a constant C 2 < such that u L C 1 y L C 2 In words: if the input is bounded, then the output is bounded Warning: the amplification factor y L u L might be large Single-Input-Single-Output Systems 1-29

Bounded-Input-Bounded-Output Systems A system is called a bounded-input-bounded-output (BIBO) system if there exists for every contant C 1 < a constant C 2 < such that u L C 1 y L C 2 In words: if the input is bounded, then the output is bounded Warning: the amplification factor y L u L might be large Single-Input-Single-Output Systems 1-30

Bounded-Input-Bounded-Output Systems A system is called a bounded-input-bounded-output (BIBO) system if there exists for every contant C 1 < a constant C 2 < such that u L C 1 y L C 2 In words: if the input is bounded, then the output is bounded Warning: the amplification factor y L u L might be large Single-Input-Single-Output Systems 1-31

Resonance catastrophe Small inputs can lead to large outputs... Single-Input-Single-Output Systems 1-32

System Response Norms The largest possible ratio between input and output norm, sup u y u is called system response norm (largest possible amplification factor). Common choices for are L 2 or L -norms Single-Input-Single-Output Systems 1-33

System Response Norms The largest possible ratio between input and output norm, sup u y u is called system response norm (largest possible amplification factor). Common choices for are L 2 or L -norms Single-Input-Single-Output Systems 1-34

Contents Introduction Open-Loop Control-Response Proportional Control General PID Control Single-Input-Single-Output Systems 1-35

Set points Goal: Design the closed-loop system such that y(t ) y ref after a short transient phase T > 0 Notation: The point y ref R is called set point The function e(t) = y(t) y ref is called the tracking error Single-Input-Single-Output Systems 1-36

Set points Goal: Design the closed-loop system such that y(t ) y ref after a short transient phase T > 0 Notation: The point y ref R is called set point The function e(t) = y(t) y ref is called the tracking error Single-Input-Single-Output Systems 1-37

Feedback laws Strategy: If we observe y(t), we set u(t) = µ(y(t)) The function µ : R R is called feedback law Secret assumption : Evaluation of µ is fast compared to the system dynamics Single-Input-Single-Output Systems 1-38

Feedback laws Strategy: If we observe y(t), we set u(t) = µ(y(t)) The function µ : R R is called feedback law Secret assumption : Evaluation of µ is fast compared to the system dynamics Single-Input-Single-Output Systems 1-39

Affine feedback (P-control) Proportional control is based on affine feedback laws, µ(y(t)) = u ref + K(y(t) y ref ) = u ref + K e(t) Constant u ref R is a control offset The constant K R is called the proportional gain Single-Input-Single-Output Systems 1-40

Affine feedback (P-control) Proportional control is based on affine feedback laws, µ(y(t)) = u ref + K(y(t) y ref ) = u ref + K e(t) Constant u ref R is a control offset The constant K R is called the proportional gain Single-Input-Single-Output Systems 1-41

Affine feedback (P-control) Proportional control is based on affine feedback laws, µ(y(t)) = u ref + K(y(t) y ref ) = u ref + K e(t) Constant u ref R is a control offset The constant K R is called the proportional gain Single-Input-Single-Output Systems 1-42

P-control tuning: Step 1 If the system is stable: Play around with the open loop system. Adjust u(t) = u ref such that open-loop system satisfies y(t ) y ref after (a possibly long) time T. Single-Input-Single-Output Systems 1-43

P-control tuning: Step 1 If the system is stable: Play around with the open loop system. Adjust u(t) = u ref such that open-loop system satisfies y(t ) y ref after (a possibly long) time T. Single-Input-Single-Output Systems 1-44

Tuning Step 1 Single-Input-Single-Output Systems 1-45

Tuning Step 1 Single-Input-Single-Output Systems 1-46

Tuning Step 1 Single-Input-Single-Output Systems 1-47

P-control tuning: Step 2 Increase / decrease the control gain K and test the closed-loop behavior of the system Fine-tuning of u ref and K if needed. Single-Input-Single-Output Systems 1-48

P-control tuning: Step 2 Increase / decrease the control gain K and test the closed-loop behavior of the system Fine-tuning of u ref and K if needed. Single-Input-Single-Output Systems 1-49

Tuning Step 2 Single-Input-Single-Output Systems 1-50

Tuning Step 2 K = 0.25 [ ] V C Single-Input-Single-Output Systems 1-51

Tuning Step 2 K = 0.50 [ ] V C Single-Input-Single-Output Systems 1-52

Tuning Step 2 K = 2.00 [ ] V C Single-Input-Single-Output Systems 1-53

Tuning Step 2 K = 1.00 [ ] V C Single-Input-Single-Output Systems 1-54

P-control tuning If the system is unstable at the set-point: open-loop experiments are not possible / difficult pre-stabilize the system with a suitable K Tune u ref (and K) to reduce output error Single-Input-Single-Output Systems 1-55

P-control tuning If the system is unstable at the set-point: open-loop experiments are not possible / difficult pre-stabilize the system with a suitable K Tune u ref (and K) to reduce output error Single-Input-Single-Output Systems 1-56

P-control tuning If the system is unstable at the set-point: open-loop experiments are not possible / difficult pre-stabilize the system with a suitable K Tune u ref (and K) to reduce output error Single-Input-Single-Output Systems 1-57

Inverted pendulum: P-control u ref = 0 K = 0.5 [ ] N rad Single-Input-Single-Output Systems 1-58

Inverted pendulum: P-control u ref = 0 K = 1.0 [ ] N rad Single-Input-Single-Output Systems 1-59

Inverted pendulum: P-control u ref = 0 K = 2.0 [ ] N rad Single-Input-Single-Output Systems 1-60

Inverted pendulum: P-control u ref = 0 K = 4.0 [ ] N rad Single-Input-Single-Output Systems 1-61

Inverted pendulum: P-control u ref = 0 K = 8.0 [ ] N rad Single-Input-Single-Output Systems 1-62

Proportional Control Circuit Replace computer by electrical circuit (e.g. for our oven): (here y(t), y ref and K(y(t) y ref ) are voltages) Use summing amplifier (or modify above circuit) to add offset Single-Input-Single-Output Systems 1-63

Proportional Control Circuit Replace computer by electrical circuit (e.g. for our oven): (here y(t), y ref and K(y(t) y ref ) are voltages) Use summing amplifier (or modify above circuit) to add offset Single-Input-Single-Output Systems 1-64

Contents Introduction Open-Loop Control-Response Proportional Control General PID Control Single-Input-Single-Output Systems 1-65

Affine feedback (PI-control) Proportional-Integral (PI) control uses feedback laws of the form t u(t) = u ref + K(y(t) y ref ) + K I (y(τ) y ref ) dτ t = u ref + Ke(t) + K I e(τ) dτ The constant K I R is called the integral gain For discrete-time systems: replace integral by running sum 0 0 t 0 e(τ) dτ where δ is the samping time t/δ 1 k=0 e(kδ) δ, Single-Input-Single-Output Systems 1-66

Affine feedback (PI-control) Proportional-Integral (PI) control uses feedback laws of the form t u(t) = u ref + K(y(t) y ref ) + K I (y(τ) y ref ) dτ t = u ref + Ke(t) + K I e(τ) dτ The constant K I R is called the integral gain For discrete-time systems: replace integral by running sum 0 0 t 0 e(τ) dτ where δ is the samping time t/δ 1 k=0 e(kδ) δ, Single-Input-Single-Output Systems 1-67

Affine feedback (PI-control) Proportional-Integral (PI) control uses feedback laws of the form t u(t) = u ref + K(y(t) y ref ) + K I (y(τ) y ref ) dτ t = u ref + Ke(t) + K I e(τ) dτ The constant K I R is called the integral gain For discrete-time systems: replace integral by running sum 0 0 t 0 e(τ) dτ where δ is the samping time t/δ 1 k=0 e(kδ) δ, Single-Input-Single-Output Systems 1-68

Integral Gain Tuning K = 1.0 [ ] V C K I = 0.0 [ ] V C s Single-Input-Single-Output Systems 1-69

Integral Gain Tuning K = 1.0 [ ] V C K I = 1.0 [ V C s ] Single-Input-Single-Output Systems 1-70

Integral Gain Tuning K = 1.0 [ ] V C K I = 0.5 [ V C s ] Single-Input-Single-Output Systems 1-71

Integral Gain Tuning K = 1.0 [ ] V C K I = 0.1 [ V C s ] Single-Input-Single-Output Systems 1-72

Integral Gain Circuit Operational amplifier integrator: Needs to be refined for non-ideal op-amps. Single-Input-Single-Output Systems 1-73

Integral Gain Circuit Operational amplifier integrator: Needs to be refined for non-ideal op-amps. Single-Input-Single-Output Systems 1-74

Affine feedback (PD-control) Proportional-Differential (PD) control uses feedback laws of the form u(t) = u ref + Ke(t) + K D ė(τ) The function ė(t) denotes the time derivative of the error function e(t) = y(t) y ref. The constant K D R is called the differential gain Assumes that we can measure ẏ(t) directly ( velocity measurement) Single-Input-Single-Output Systems 1-75

Affine feedback (PD-control) Proportional-Differential (PD) control uses feedback laws of the form u(t) = u ref + Ke(t) + K D ė(τ) The function ė(t) denotes the time derivative of the error function e(t) = y(t) y ref. The constant K D R is called the differential gain Assumes that we can measure ẏ(t) directly ( velocity measurement) Single-Input-Single-Output Systems 1-76

Affine feedback (PD-control) Proportional-Differential (PD) control uses feedback laws of the form u(t) = u ref + Ke(t) + K D ė(τ) The function ė(t) denotes the time derivative of the error function e(t) = y(t) y ref. The constant K D R is called the differential gain Assumes that we can measure ẏ(t) directly ( velocity measurement) Single-Input-Single-Output Systems 1-77

Affine feedback (PD-control) Proportional-Differential (PD) control uses feedback laws of the form u(t) = u ref + Ke(t) + K D ė(τ) The function ė(t) denotes the time derivative of the error function e(t) = y(t) y ref. The constant K D R is called the differential gain Assumes that we can measure ẏ(t) directly ( velocity measurement) Single-Input-Single-Output Systems 1-78

Inverted pendulum: PD-control u ref = 0 K = 2.0 [ ] N rad [ K D = 0.1 N rad/s ] Single-Input-Single-Output Systems 1-79

Inverted pendulum: PD-control u ref = 0 K = 2.0 [ ] N rad [ K D = 0.5 N rad/s ] Single-Input-Single-Output Systems 1-80

Inverted pendulum: PD-control u ref = 0 K = 2.0 [ ] N rad [ K D = 1.0 N rad/s ] Single-Input-Single-Output Systems 1-81

Inverted pendulum: PD-control u ref = 0 K = 2.0 [ ] N rad [ K D = 4.0 N rad/s ] Single-Input-Single-Output Systems 1-82

Affine feedback (PID-control) Proportional-Integral-Differential (PID): t u(t) = u ref + Ke(t) + K I e(τ) dτ + K D ė(τ) 0 Rule-of-the-thumb based PID tuning use K to pre-stabilize system use K I to reduce /eliminate offsets use K D to reduce oscillations/overshoot Warning: there are systems which behave differently; we ll analyze this later in more detail Single-Input-Single-Output Systems 1-83

Affine feedback (PID-control) Proportional-Integral-Differential (PID): t u(t) = u ref + Ke(t) + K I e(τ) dτ + K D ė(τ) 0 Rule-of-the-thumb based PID tuning use K to pre-stabilize system use K I to reduce /eliminate offsets use K D to reduce oscillations/overshoot Warning: there are systems which behave differently; we ll analyze this later in more detail Single-Input-Single-Output Systems 1-84

Affine feedback (PID-control) Proportional-Integral-Differential (PID): t u(t) = u ref + Ke(t) + K I e(τ) dτ + K D ė(τ) 0 Rule-of-the-thumb based PID tuning use K to pre-stabilize system use K I to reduce /eliminate offsets use K D to reduce oscillations/overshoot Warning: there are systems which behave differently; we ll analyze this later in more detail Single-Input-Single-Output Systems 1-85

Affine feedback (PID-control) Proportional-Integral-Differential (PID): t u(t) = u ref + Ke(t) + K I e(τ) dτ + K D ė(τ) 0 Rule-of-the-thumb based PID tuning use K to pre-stabilize system use K I to reduce /eliminate offsets use K D to reduce oscillations/overshoot Warning: there are systems which behave differently; we ll analyze this later in more detail Single-Input-Single-Output Systems 1-86

Affine feedback (PID-control) Proportional-Integral-Differential (PID): t u(t) = u ref + Ke(t) + K I e(τ) dτ + K D ė(τ) 0 Rule-of-the-thumb based PID tuning use K to pre-stabilize system use K I to reduce /eliminate offsets use K D to reduce oscillations/overshoot Warning: there are systems which behave differently; we ll analyze this later in more detail Single-Input-Single-Output Systems 1-87

PID-control circuit (many variants exist) Single-Input-Single-Output Systems 1-88

Summary / Keywords SISO systems (without using models) Control parameterization Open-loop response, step response, frequency response Steady state / periodic limit cycle BIBO systems, system response norm P, PI, PD, PID control + tuning by hand basic electrical circuits for PID control Single-Input-Single-Output Systems 1-89