PROJECT SYNOPSIS

On

DIGITAL CONTROLLER USING MATLAB

In partial fulfillment of B.Tech.

In

Electronics & Instrumentation Engineering

Submitted to:Submitted By:

Deptt. of ElectronicsPankhuri Shukla(0704632031)

And InstrumentationPooja Sachan(0704632033)

Saumya Tripathi(0704632050)

Saurabh kumar(0704632051)

GAUTAM BUDHH TECHNICAL UNIVERSITY, U.P.

INTRODUCTION

DIGITAL CONTROLLERS :

Advantages in digital electronics have given smaller, faster and cheaper digital integrated circuits i.e., ICs. There have been numerous applications of digital circuits in process control. Subsequently evolution of digital computers have taken place which are with higher speed, higher reliability, smaller size and reduced cost. Naturally, digital computers are extensively used in process control. The techniques have been developed where the computer performs adjustments of loop set-points and provides record of process parameters. Although loops are still analog, but the set points which determine overall process performance are set by a computer on the basis of equations solved by the computer using measured values of process parameters as inputs.

Digital computers are used to perform continuous controller functions and is known as direct digital control (DDC) of a process.

In DDC only analog elements left in the process-control loop are the measurement functions and final control element. The DDC applications were used with mainframe computers which controlled many loops. The development in electronics has moved the DDC applications to minicomputers and microprocessor-based computers. The stage has come where a microprocessor-based computer embedded in the sensor itself controls a single loop. Such smart sensors are interfaced to supervisory computer control and final control elements using serial buses or local area networks(LANs) .

A digital controller is usually cascaded with the plant in the feedback system.The rest of the system is either digital or analog.

Typically, a digital controller requires:

  • A/D CONVERSION to convert analog input to machine readable (digital) format.
  • D/A CONVERSION to convert digital output to a form that can be input to plant(analog).
  • A PROGRAM that relates outputs to the inputs.

OBJECTIVE

Our objective is the utilization of computer- controlled instrumentation to provide ease in designing control systems via MATLAB which may be developed for implementation in real life situations.

The developed controller can be used in most varied situations like industrial control, robotics, cruise controland various other purposes. This controller will offer an error free, cost effective way of controlling the process variables and comparing set points. Controller could be used for long distance transmission of data or long term storage.This technique would be able to detect and monitor a number of parameters that can prove to be too costly otherwise.Chemical/petrochemical; electronics; finishing; food processing; packaging; pharmaceuticals; plastics/rubber; pulp/paper; textiles etc require control at various stages and this controller will help improve performance of the plants in these fields.

MATLAB employing a coding lends reality as to how control laws and estimation algorithms are implemented in practice and will let us explore the effects of controller parameters and sampling interval on responses.MATLABcan be used to represent a physical system or a model. By entering a differential equation model into MATLAB we can represent a physical system.With theconvenience offered by MATLAB for Windows ,problemsmore realistic and can concentrate class time onalgorithms for the design process rather than gettingbogged down with detailed classroom calculations. Inaddition, the Symbolic Toolbox of MATLAB allowssome rather tedious, error-prone algebraic manipulationsto be accomplished with zero errors.

PROBLEM DEFINITION

Typically, analog designs provide minimal process and fault information because only the most critical information is monitored.Both the output setpoint control signal and output transducer signal are sent, via wire connections, between the power control panel and the process control system. Through these individual wires, the control room operator sets the desired output and monitors the results , which requires continuous manual monitoring.With analog technology, each additional fault requires control relays, wiring and digital inputs on the process controller. If each piece of information is to be displayed in the control room, the cost of showing each fault can be substantial, especially for multizone systems.

Analog controllers pose certain other disadvantages such as :

  • lock and phase of the TFTs must be synchronized with the analog signal to avoid pixel jitter, which is a relatively complex issue
  • Cables sensitive to external influences
  • High cost of signal conversion inside the display
  • Upgrade to digital interface not possible

Another problem encountered is that large number of set-points and process variables require lengthy, complexand tedious algebraic calculations which may pose a problem of error in results. The hardware requirement for implementing these control systems was enormous. All this leads to increment in cost and complexity of the system.

We have come up with following solutions which are discussed in the next section.

SCOPE OF SOLUTION

Due to above discussed problems we choose to develop a digital controller using MATLAB. This offers following features:

  • Reduced Cost
  • Less hardware required
  • Outputs with nearly zero-error
  • Easy manipulation

Certain advantages of digital controller are :

  1. No signal losses due to D/A and A/D conversion.
  2. Digital components are less susceptible to ageing and environmental variation.
  3. Less sensitive to noise and disturbance.
  4. More compact and light-weight, so single chip processors can be made very versatile and powerful for control applications.
  5. Flexibility in programming the processors.
  6. More reliable
  7. Improved sensitivity to parameter variations.

By using MATLAB software for implementing the digital controller we have certain benefits as allowing us to work in Matrices easily. It lets us do some complicated calculations quickly, without having to write a whole program or spreadsheet. Tons of add-ons and workbenches are available to do a variety of tasks.

PRINCIPLE & BLOCK DIAGRAM

The most widely used controller in plant control systems is the PID controller. Here, we are going to implement digital PID controller using MATLAB.

PID CONTROLLER

In addition to a P-type action, integral and differentiation action on error signal is also used to improve steady state and transient performance of the system. Such a controller using all three actions is called as P-I-D controller or a three term controller. The P-I-D controller calculation (algorithm) involves three separate parameters, these values can be interpreted in terms of time : P depends on the present error, I on the accumulation of past errors, and D on prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element. The practical system in which the transduced signals and set-point values are electrical voltages, an electronic 3-term controller is simpler to incorporate in a control system.

Block diagram of a PID controller

In the absence of knowledge of underlying process , a PID controller is the best controller. By tuning the three constants in the PID controller algorithm, the controller can provide the control action designed for specific process requirements. The response of the controller can be described in terms of responsiveness of the controller to an error, the degree to which the controller overshoots the set-point and the degree of system oscillations. A PID controller is a lag-lead controller and helps in removal of both steady state and transient error. Some applications may require using only one or two modes to provide the appropriate system control. This is achieved by setting the gain of undesired control outputs to zero. A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers are fairly common, since derivative action is sensitive to measurement noise, whereas the absence of an integral value may prevent the system from reaching its target value due to the control action.

BLOCK DIAGRAM OF DIGITAL CONTROLLER

FUTURE SCOPE

This project has wide and varied applications, some of these are

ADAPTIVE CRUISE CONTROL

This new technology will work on forward-lookingradar, installed behind the grill of a vehicle, to detect the speed and distance of the vehicle ahead of it. Adaptive cruise control is similar to conventional cruise control in that it maintains the vehicle's pre-set speed. However, unlike conventional cruise control, this new system can automatically adjust speed in order to maintain a proper distance between vehicles in the same lane. This is achieved through aradar headway sensor,digital signal processorandlongitudinal controller. If the lead vehicle slows down, or if another object is detected, the system sends a signal to the engine or braking system to decelerate. Then, when the road is clear, the system will re-accelerate the vehicle back to the set speed.

IN ROBOTICS

Using PID control can make robot design more stable, robust, and has the potential to improve response characteristics. In robotics commonly seen PID implementation is for motion control, either for drivetrain motors or for other servo actuators.

INDUSTRIAL CONTROL

Theimplementation of the PID is based on digital design, these digital PIDs include many algorithms such as anti-wind-up, auto-tuning, adaptive, and fuzzy fine tuning to improve their performances, but the basic actions remain the same.Many of the new capabilities of digital PID controllers have been introduced by the research community. The industrial control users apply these innovations easily, even enthusiastically. PID control has become one of the most important ways for the scientific specialist in control and the users of industrial control to work together.

BIBLIOGRAPHY

  1. Principles of Control Systems by Bakshi & Goyal
  2. Digital Control System Engineering by M.Gopal