Control Systems Overview REV II

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1 Control Systems Overview REV II D R. T A R E K A. T U T U N J I M E C H A C T R O N I C S Y S T E M D E S I G N P H I L A D E L P H I A U N I V E R S I T Y

2 Control Systems The control system is at the heart of mechatronic systems and its selection is arguably the most critical decision in the design process. The controller selection involves two interdependent parts: The control method (i.e. software) The physical controller (i.e. hardware)

3 Basic Control Concepts O P E N V S. C L O S E D L O O P C O N T R O L P R O C E S S V S. M O T I O N C O N T R O L T R A N S I E N T A N D S T E A D Y S T A T E S P E C I F I C A T I O N S

4 Open-Loop Control [Ref] Kilian

5 Closed-Loop Control [Ref] Kilian

6 Control Systems Classification Control systems are classified by application. Process control usually refers to an industrial process being electronically controlled for the purpose of maintaining a uniform correct output. Motion control refers to a system wherein things move. A servomechanism is a feedback control system that provides remote control motion of some object, such as a robot arm or a radar antenna.

7 Process Control [Ref] Kilian

8 Process Control Example [Ref] Kilian

9 Motion Control

10 Motion Control Examples CNC Machine Robot Manipulator [Ref] Kilian

11 General Control System

12 First Order Systems

13 First Order Systems

14 Second Order Systems

15 Performance Criteria

16 Transient Response Transient response is the shape of a signal as it moves between two steady-state points. It is quantified in terms of two parameters: The damping ratio, z, pronounced zeta The natural undamped frequency, wn.

17 Pole Locations The poles location is the major factor for a systems transient response

18 Step Response Comparisons

19 Steady-State Error Accuracy (or steady-state tracking error) is the error between input and output signals in the steady state for a system. Three input signals can be used Step Ramp Parabola

20 Steady-State Error

21 Steady-State Error

22 Stability A stable system is one which produces a bounded, or finite, response when subjected to a bounded input Stability conditions A system is stable if the real part of all poles are < 0. A system is marginally stable if real part of all poles are <= 0. A system is unstable if the real part of any pole is positive.

23 Control Methods T A R E K A. T U T U N J I

24 Control Techniques / Strategies Classical Control Advanced Control Intelligent Control Dr. Tarek A. Tutunji

25 Classical Control Classical control design are used for SISO systems. Most popular concepts are: Bode plots Nyquist Stability Root locus. PID is widely used in feedback systems. Dr. Tarek A. Tutunji

26 Classical Control: On-Off Control This is the simplest method of control. The control action has three possible outputs: on; off; no change. This method is usually used for slow-acting operations (such as a refrigeration unit). The advantage is its ease of design and low cost. However, it cannot vary the controlled variable with precision. On-Off Control Example

27 Classical Control: PID Proportional-Integral-Derivative (PID) is the most commonly used controller for SISO systems u(t ) K p e(t ) K I e(t )dt K D de(t dt ) Dr. Tarek A. Tutunji

28 PD Design Example

29 Analog PID Implementation [Ref] Kilian

30 Digital PID Control Analog Digital Tarek A. Tutunji

31 Digital PID Realization Required Operations: Multiplication Addition Delay

32 Discrete PID Implementation

33 Digital Control Block Diagram

34 Classical Control: Root Locus

35 Discrete Systems: Pole Locations

36 Advanced Control Adaptive control methods modify the control law used by a controller to cope with time-varying parameters. For example, as an aircraft flies, its mass will slowly decrease as a result of fuel consumption; we need a control law that adapts itself to such changing conditions. Robust control methods deal with uncertainty. They guarantee that if the changes are within given bounds the control law need not be changed. Optimal control uses math optimization methods to solve a set of differential equations. Two such methods are: Model Predictive Control (MPC) Linear-Quadratic-Gaussian control (LQG).

37 Intelligent Control Intelligent controllers are used for high-level control Intelligent controllers are also used when the system must make decisions (from several alternatives) based on input data from sensors. Intelligent Control is usually used when the mathematical model for the plant is unavailable or highly complex. The most two commonly used intelligent controllers are Artificial Neural Networks Fuzzy Logic Dr. Tarek A. Tutunji

38 Intelligent Control: Fuzzy Fuzzy set theory provides mathematical tools for carrying out approximate reasoning processes when available information is uncertain, incomplete, imprecise, or vague. Fuzzy logic controllers manage complex control problems through heuristics (IF THEN) and mathematical models provided by fuzzy logic, rather than via mathematical models provided by differential equations. This is particularly useful for controlling systems whose mathematical models are nonlinear or for which standard mathematical models are simply not available

39 Fuzzy Control

40 Fuzzy Control

41 Intelligent Control: ANN Artificial Neural networks (ANN) are nonlinear mathematical models that are used to mimic the biological neurons in the brain. ANN are used as black box models to map unknown functions ANN can be used for: Identification and Control Dr. Tarek A. Tutunji

42 ANN: Single Neuron x 1 x 2 w 0 w 1 w M f(net) y x M M y f x m w m m 1

43 Neural Nets Plant Output Plant Input TDL TDL Weights Weights + Log Weights + Function Log Function Net Output First Layer Second Layer

44 ANN: Identification and Control Control Identification

45 ANN: Identification and Control

46 Intelligent Controllers Applications

47 Intelligent Controller Application Low Level PID Control for velocity control High Level Intelligent Control: Fuzzy for Decision making Neural nets for Image Analysis

48 Hardware Controllers D R. T A R E K T U T U N J I

49 Analog vs. Digital Control Systems Analog Digital Time variable Continuous Discrete Time equations Differential equations Difference equations Frequency transforms Laplace Z-Transform Stability Poles on LHS Poles inside unit circle Controller Hardware: Op-Amps Software: None Hardware: Microcontroller Software: Program Dr. Tarek A. Tutunji

50 Criteria for Choosing Controller Price Size and Weight Number of Digital Inputs and Outputs Number of Analog Inputs and Outputs Speed Required Interrupt Required hardware Communication Interface Reliability Memory Programming Capability Software Support Dr. Tarek A. Tutunji

51 Hardware Controllers Microcontroller PLCs DSPs FPGA PC with DAQ Dr. Tarek A. Tutunji

52 Microcontrollers Microcontroller is a special type of small computer that can perform a specific job

53 Microcontrollers The microcontroller is a computer-on-chip. It is an integrated circuit that contains microprocessor, memory, I/O ports and sometimes A/D converters. It can be programmed using several languages (such as Assembly or C/C++). It can be used in manufacturing lines, but requires additional hardware. Microcontrollers are mainly used in engineering products such as washing machines and air-conditioners. Dr. Tarek A. Tutunji

54 Microcontrollers Companies

55 Microcontroller Market Share

56 Arduino Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. The hardware consists of a simple open source hardware board designed around an 8-bit Atmel AVR microcontroller, though a new model has been designed around a 32-bit Atmel ARM

57 The ARM architecture describes a family of RISC-based computer processors designed and licensed by British company ARM Holdings. As an IP core business, ARM Holdings itself does not manufacture its own electronic chips, but licenses its designs to other semiconductor manufactu rers ARM

58 PLCs A Programmable Logic Controller (or PLC) is a specialized digital controller that can control machines and processes. it monitors inputs, makes decisions, and controls outputs in order to automate machines and processes

59 Programmable Logic Controller PLC s are a user-friendly, microprocessor-based, specialized computer that is used for process control. It contains input/output (I/O) modules for appropriate sensors/actuator interfaces. It is mainly used in automated manufacturing lines. The PLC is usually used for simple logic operations. It is considered reliable and easy to program (using ladder diagrams, instructions, or function blocks). Dr. Tarek A. Tutunji

60 PLC Manufacturers

61 PLC vs. Microcontroller Usually PLCs are used in an industrial environment, where as the microcontrollers are smaller and well suited for embedded situations. PLCs are programmed with ready made blocks or programming elements, whereas in Microcontrollers a programming language must be used to write a programming code

62 PLC Advantages They are highly reliable, fast and flexible. They can handle severe conditions such as dust, humidity etc. They can communicate with other controllers. They are easy to program and troubleshoot. They include display units.

63 Digital Signal Processors Digital Signal Processing (DSP) is the arithmetic processing of discretetime signals. A/D is needed for analog signals Digital signal processors (DSP) are specialized microprocessors with advanced architectures (such as multiple buses, parallel processing, hardware multipliers and fast sampling rate) that are designed to reduce the number of instructions and operations necessary for efficient processing. DSP chips enable developers to implement complex algorithms and perform computationally efficient and fast algorithms. DSP are preferred over microcontrollers when the need for complex and iterative control algorithms is required. Dr. Tarek A. Tutunji

64 DSP Operations: Convolution x(n) h(n) y(n) y(n) x(n)* h(n) x(k)h(n k) k - Convolution requires: Reflection Shift Multiplication Addition

65 DSP Architecture Features Parallel Processing (Modified Harvard) Deep Instructions Pipeline Very Fast A/D Hardware Multiplier Barrel Shifter RISC Dr. Tarek A. Tutunji

66 Modified Harvard Architecture A Harvard architecture employs separate program and data buses to access separate data and program memories. A modified Harvard architecture. DSP use multiple data buses (and multiple associated address buses) so that the processing of two signals can be done in parallel. The address buses are also separate. This multiple bus arrangement increases speed since instructions and data can move in parallel, and execute simultaneously rather than sequentially.

67 Modified Harvard Architecture DAGEN A Memory A Memory B DAGEN B ALU Multiplier Shifter Accumulators DAGEN C Memory C Shifter

68 Instruction Pipelining Up to six levels of pipelining are implemented. DSP can execute instructions in parallel Overall execution times are accelerated so that high

69 Hardware Multiplier A 16- by 16-bit hardware multiplier multiplies and stores results in a 40-bit accumulator (8 guard bits) in a single instruction cycle. Thus, multiply and accumulate operations can be performed in a single clock cycle in a DSP; conventional processors may require tens of cycles for this operation.

70 Shifters and RISC Hardware shifters allow scaling, prevent overflows, and maintain required precision. An on-chip hardware stack reduces interrupt response time and minimizes stack pointer manipulations. DSP use reduced instruction sets tailored to digital signal processing operations. For example, the MACD command implements four operations in one instruction: multiplies two values moves data adds the product to a previous result transfers the result to an adjacent register.

71 Digital Signal Controllers Manufacturers Texas Instruments. TMS320C2000 DSP Platform Microchip. dspic30f3010 Motorola

72 Custom made DSP Engines

Field Programmable Gate Arrays The field-programmable gate array (FPGA) is a semiconductor device that can be programmed after manufacturing.

73 Field Programmable Gate Arrays The field-programmable gate array (FPGA) is a semiconductor device that can be programmed after manufacturing. Instead of being restricted to any predetermined hardware function, an FPGA allows you to program product features and functions, adapt to new standards, and reconfigure hardware for specific applications even after the product has been installed in the field hence the name "field-programmable". FPGAs can be used to implement any logical function that an application-specific integrated circuit (ASIC) could perform. One advantage is its ability to update the functionality after shipping.

74 FPGAs vs. Microcontrollers FPGAs can perform concurrent operations while the microcontrollers operations are sequential. This makes FPGAs better suited for real-time applications such as executing DSP algorithms. FPGA are flexible, you can add subtract the functionality as required. This can not be done in microcontroller. FPGAs are hard-wired and the random attack of alpha rays can not destroy/corrupt the memory areas hence collapse the device functionality. FPGA based development is longer while microcontrollers change too often and there is lots re-work required to do in order to keep pace with changing technology. This is necessary to save the design from being obsolete. Dr. Tarek A. Tutunji

75 FPGAs vs. Microcontrollers The development time for microcontroller is shorter and that of FPGA The microcontroller peripherals are readily available and tested by the vendor. As for the FPGA, open source soft-peripherals are available, but still need to be embedded and tested. Microcontroller are power efficient. Microcontroller are low-cost, much lower than FPGAs. This is specially true for small applications and large quantities. Microcontrollers are available in easy to solder SOIC and QFP package while FPGAs offer limited sources. Dr. Tarek A. Tutunji

76 Personal Computers Personal computers are used when extensive signal processing and in-depth analysis is required. This will require Data Acquisition Cards (DAQs) to interface the I/O power and signals between the PC and the environment. Advantages include superior graphical and software flexibility. However, the cost is high and, therefore, they are not suitable for a large number of products Another disadvantage is the speed Dr. Tarek A. Tutunji

77 PCs and DAQs

78 Summary The selection of the controller is arguably the most important issue of the mecahtronics system This choice can be divided into two parts: 1. Software/Firmware algorithm On-Off, PID, Adaptive, Robust, Optimal, and Intelligent 2. Hardware system Microcontroller, PLC, DSP, FPGA, and PC-DAQ Dr. Tarek A. Tutunji

ANNA UNIVERSITY :: CHENNAI MODEL QUESTION PAPER(V-SEMESTER) B.E. ELECTRONICS AND COMMUNICATION ENGINEERING EC334 - CONTROL SYSTEMS

ANNA UNIVERSITY :: CHENNAI MODEL QUESTION PAPER(V-SEMESTER) B.E. ELECTRONICS AND COMMUNICATION ENGINEERING EC334 - CONTROL SYSTEMS ANNA UNIVERSITY :: CHENNAI - 600 025 MODEL QUESTION PAPER(V-SEMESTER) B.E. ELECTRONICS AND COMMUNICATION ENGINEERING EC334 - CONTROL SYSTEMS Time: 3hrs Max Marks: 100 Answer all Questions PART - A (10