Experimental modeling and adaptive power control of a 750MW once-through boiler

H. Unbehauen and I. Kocaarslan

Ruhr-University Bochum, Department of Electrical Engineering,

P.O. Box 102 148. D-4630 Bochum 1, Germany

 

Abstract. This paper presents the reduced mathematical model for the power generation of a steam power plant. Plant measurements have been made for four different operating points. The dynamic model for these operating conditions of the multivariable plant has been developed by application of parameter estimation methods. Based on these multivariable models, three different types of adaptive control schemes as well as a conventional PID-control structure have been tested by extended simulation studies. Due to the very promising results, preparations for the practical application results in the plant are now under work.

 

Keywords. Power plant, once-through boiler, identification, modeling, multivariable model reference adaptive control, decentralized adaptive control.

 

9. Condense the information of the texts and write down the summaries to them in English:

I. Industrial robot

from Wikipedia, the free encyclopedia

An industrial robot is defined as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. The field of robotics may be more practically defined as the study, design and use of robot systems for manufacturing (a top-level definition relying on the prior definition of robot).

Typical applications of robots include welding, painting, assembly, pick and place (such as packaging, palletizing and SMT), product inspection, and testing; all accomplished with high endurance, speed, and precision.

II. Robot types, features

The most commonly used robot configurations are articulated robots, SCARA robots and Cartesian coordinate robots, (aka gantry robots or x-y-z robots). In the context of general robotics, most types of robots would fall into the category of robotic arms (inherent in the use of the word manipulator in the above-mentioned ISO standard). Robots exhibit varying degrees of autonomy:

- Some robots are programmed to faithfully carry out specific actions over and over again (repetitive actions) without variation and with a high degree of accuracy. These actions are determined by programmed routines that specify the direction, acceleration, velocity, deceleration, and distance of a series of coordinated motions.

- Other robots are much more flexible as to the orientation of the object on which they are operating or even the task that has to be performed on the object itself, which the robot may even need to identify. For example, for more precise guidance, robots often contain machine vision sub-systems acting as their "eyes", linked to powerful computers or controllers. Artificial intelligence, or what passes for it, is becoming an increasingly important factor in the modern industrial robot.

III. Defining parameters

- Number of axes – two axes are required to reach any point in a plane; three axes are required to reach any point in space. To fully control the orientation of the end of the arm (i.e. the wrist) three more axes (yaw, pitch, and roll) are required. Some designs (e.g. the SCARA robot) trade limitations in motion possibilities for cost, speed, and accuracy.

- Degrees of freedom which is usually the same as the number of axes.

- Working envelope – the region of space a robot can reach.

- Kinematics – the actual arrangement of rigid members and joints in the robot, which determines the robot's possible motions. Classes of robot kinematics include articulated, Cartesian, parallel and SCARA.

- Carrying capacity or payload – how much weight a robot can lift.

- Speed – how fast the robot can position the end of its arm. This may be defined in terms of the angular or linear speed of each axis or as a compound speed i.e. the speed of the end of the arm when all axes are moving.

- Acceleration - how quickly an axis can accelerate. Since this is a limiting factor a robot may not be able to reach its specified maximum speed for movements over a short distance or a complex path requiring frequent changes of direction.

- Accuracy – how closely a robot can reach a commanded position. When the absolute position of the robot is measured and compared to the commanded position the error is a measure of accuracy. Accuracy can be improved with external sensing for example a vision system or Infra-Red (see robot calibration). Accuracy can vary with speed and position within the working envelope and with payload (see compliance).

- Repeatability - how well the robot will return to a programmed position. This is not the same as accuracy. It may be that when told to go to a certain X-Y-Z position that it gets only to within 1 mm of that position. This would be its accuracy which may be improved by calibration. But if that position is taught into controller memory and each time it is sent there it returns to within 0.1mm of the taught position then the repeatability will be within 0.1mm.

Accuracy and repeatability are different measures. Repeatability is usually the most important criterion for a robot. ISO 9283 sets out a method whereby both accuracy and repeatability can be measured. Typically a robot is sent to a taught position a number of times and the error is measured at each return to the position after visiting 4 other positions. Repeatability is then quantified using the standard deviation of those samples in all three dimensions. A typical robot can, of course make a positional error exceeding that and that could be a problem for the process. Moreover the repeatability is different in different parts of the working envelope and also changes with speed and payload. ISO 9283 specifies that accuracy and repeatability should be measured at maximum speed and at maximum payload. But this results in pessimistic values whereas the robot could be much more accurate and repeatable at light loads and speeds. Repeatability in an industrial process is also subject to the accuracy of the end effector, for example a gripper, and even to the design of the 'fingers' that match the gripper to the object being grasped. For example if a robot picks a screw by its head the screw could be at a random angle. A subsequent attempt to insert the screw into a hole could easily fail. These and similar scenarios can be improved with 'lead-ins' e.g. by making the entrance to the hole tapered.

- Motion control – for some applications, such as simple pick-and-place assembly, the robot need merely return repeatably to a limited number of pre-taught positions. For more sophisticated applications, such as welding and finishing (spray painting), motion must be continuously controlled to follow a path in space, with controlled orientation and velocity.

- Power source – some robots use electric motors, others use hydraulic actuators. The former are faster, the latter are stronger and advantageous in applications such as spray painting, where a spark could set off an explosion; however, low internal air-pressurization of the arm can prevent ingress of flammable vapors as well as other contaminants.

- Drive – some robots connect electric motors to the joints via gears; others connect the motor to the joint directly (direct drive). Using gears results in measurable 'backlash' which is free movement in an axis. Smaller robot arms frequently employ high speed, low torque DC motors, which generally require high gearing ratios; this has the disadvantage of backlash. In such cases the harmonic drive is often used.

- Compliance - this is a measure of the amount in angle or distance that a robot axis will move when a force is applied to it. Because of compliance when a robot goes to a position carrying its maximum payload it will be at a position slightly lower than when it is carrying no payload. Compliance can also be responsible for overshoot when carrying high payloads in which case acceleration would need to be reduced.

 

IV. End –of-arm Tooling

The most essential robot peripheral is the end effector, or end-of-arm-tooling (EOT). Common examples of end effectors include welding devices (such as MIG-welding guns, spot-welders, etc.), spray guns and also grinding and deburring devices (such as pneumatic disk or belt grinders, burrs, etc.), and grippers (devices that can grasp an object, usually electromechanical or pneumatic). Another common means of picking up an object is by vacuum. End effectors are frequently highly complex, made to match the handled product and often capable of picking up an array of products at one time. They may utilize various sensors to aid the robot system in locating, handling, and positioning products.

 

V. Controlling Movement

For a given robot the only parameters necessary to completely locate the end effector (gripper, welding torch, etc.) of the robot are the angles of each of the joints or displacements of the linear axes (or combinations of the two for robot formats such as SCARA). However there are many different ways to define the points. The most common and most convenient way of defining a point is to specify a Cartesian coordinate for it, i.e. the position of the 'end effector' in mm in the X, Y and Z directions relative to the robot's origin. In addition, depending on the types of joints a particular robot may have, the orientation of the end effector in yaw, pitch, and roll and the location of the tool point relative to the robot's faceplate must also be specified. For a jointed arm these coordinates must be converted to joint angles by the robot controller and such conversions are known as Cartesian Transformations which may need to be performed iteratively or recursively for a multiple axis robot. The mathematics of the relationship between joint angles and actual spatial coordinates is called kinematics. (See robot control).

Positioning by Cartesian coordinates may be done by entering the coordinates into the system or by using a teach pendant which moves the robot in X-Y-Z directions. It is much easier for a human operator to visualize motions up/down, left/right, etc. than to move each joint one at a time. When the desired position is reached it is then defined in some way particular to the robot software in use.

 

VI. Robotics

Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots. Robotics is related to the sciences of electronics, engineering, mechanics, mechatronics, and software.

The concept and creation of machines that could operate autonomously dates back to classical times, but research into the functionality and potential uses of robots did not grow substantially until the 20th century. Today, robotics is a rapidly growing field, as we continue to research, design, and build new robots that serve various practical purposes, whether domestically, commercially, or militarily.

 

10. Translate the text into English. Condense the information of the text and write down the summary to it in English:

Функции АСУ ТП

Функции АСУ ТП подразделяются на:

1) Информационные, содержанием которых является сбор, обработка и представление информации о состоянии автоматизированного технологического комплекса (АТК) оперативному персоналу или передача этой информации для последующей обработки. Например, централизованный контроль и измерение технологических параметров, косвенное измерение параметров процесса, формирование и выдача данных оперативному персоналу АТК, подготовка и передача информации в смежные системы управления, обобщенная оценка и прогноз состояния АТК и его оборудования.

2) Управляющие, результатом которых являются выработка и реализация управляющих воздействий на ТОУ. Например, регулирование (стабилизация) отдельных технологических переменных, однотактное логическое управление операциями или аппаратами, программное логическое управление группой оборудования, оптимальное управление установившимися или переходными технологическими режимами, адаптивное управление объектом в целом. Отличительная особенность управляющих и информационных функций АСУ ТП – их направленность на конкретного потребителя (ТОУ, оперативный персонал, смежные системы управления).

3) Вспомогательные, функции обеспечивающие решение внутри системных задач. Они имеют потребителя вне системы. Например, контроль за функционированием и состоянием технических средств, контроль за хранением информации и т.п.

 

11. Control questions “What do you know about automatic control systems and cybernetics?”:

1. What is automation?

2. What does automation deal with?

3. What components does an automatic industrial process include?

4. How did ancient automatic toys contribute to the development of automation?

5. What inventors of the past centuries helped in developing automation?

6. Under what conditions can an ACS be formed?

7. How did electronics contribute to the development of automation?

8. What are the advantages of ACSs?

9. In what fields of technology are ACSs used?

10. What control systems can be called automatic?

11. How can ACSs be classified?

12. What five components can every ACS contain?

13. Can you draw the scheme of the basic control system operation?

14. What is the function of a driver?

15. What is the function of the error detector?

16. What do transducers serve for?

17. What do relays serve for?

18. What is the principle of amplifiers operation based on?

19. What was the first automatic regulatory system?

20. What does the “cybernetics” mean?

21. Who is considered to be the founder of cybernetics?

22. What did N. Wienner do for the development of cybernetics?

23. Why can cybernetics be called an interdisciplinary science?

24. What fields does contemporary cybernetics connect?

25. What is the first law of cybernetics?

26. What is the role of the first law of cybernetics in understanding this science?

27. What is cybernetics?

28. What does cybernetics study?

29. What is the subject matter of cybernetics?

30. What can serve examples of cybernetic systems?

31. What does any control process imply?

32. What operations does any control process involve?

33. Can you draw the scheme of the control process?

34. What are the cornerstones of cybernetics?

 

Grammar Reference

Passive Voice

	Present	Past	Future
Simple	am/is/are linked	was/were linked	will be linked
Continuous	am/is/are being linked	was/were being linked	__
Perfect	have/has been linked	had been linked	will have been linked

 

На русский язык глаголы в Passive Voice переводятся:

1) Сочетанием глагола быть (в прошедшем и будущем времени) с краткой формой причастия II смыслового глагола:

The equipment was tested in different conditions. – Это оборудование было проверено в различных условиях.

2) Глаголом с окончанием на – ся, -сь:

The problem is solved easily. – Проблема решается легко.

3) Неопределенно-личным предложением (без подлежащего):

The fax will be sent tomorrow. – Факс отправят завтра.

Если в английском предложении за сказуемым в Passive следует предлог, относящийся к подлежащему, то при переводе предложение начинается с этого предлога:

This system is much spoken about. – Об этой системемного говорят.