Introduction, Stable and Unstable Control Loops

Introduction

2 Introduction

2.1Basic Principles of Model Predictive Control

A general overview of model predictive control is provided by the White Paper “How to improve the Performance of your Plant using the appropriate tools of SIMATIC PCS 7 APC-Portfolio?”

https://pcs.khe.siemens.com/efiles/pcs7/support/marktstudien/WP_PCS7_APC_EN

.pdf

The application note including the basic principles of the MPC can be found here:

http://cache.automation.siemens.com/dnl/zI/zIzMzM1MwAA_37361208_Tools/373 61208_MPC_en.pdf

2.2Stable and Unstable Control Loops

Most of the control loops in process plants show a stable behaviour - after a step- wise change in the manipulated variable the control variable shows a transient be- haviour reaching a new steady state after some time. The controlled process is “stable” with respect to systems dynamics, even without a controller.

Example: The temperature of a reactor is increasing after the heating power is in- creased stepwise. With increasing temperature the heat loss of the reactor to the environment is also increasing, until finally a new equilibrium condition at a higher temperature is reached, where the increased heat loss is equal to the enlarged heating power, and compensates for it.

Thought experiment: Please imagine a reactor with ideal thermal insulation, which means no thermal loss to the environment. Now, if the heating power is increased stepwise starting from the equilibrium condition, the temperature starts to rise. The increase of the temperature is undamped and continuous, as no physical effect in the opposite direction (an increasing heat flow to the environment according to the rising temperature) exists. Therefore, no new equilibrium condition is reached, re- sulting in an unstable control loop with respect to systems dynamics. This behav- iour is called integral action.

There are other forms of instability besides the integrating behaviour, e.g. increas- ing oscillations. Such behaviours can rather be found in mechanical systems (e.g. the famous inverse pendulum). In process plants, such instabilities if appearing at all, are mostly due to inappropriate controller tunings, and only rarely appear in open loop.

MPC Level	7
V 1.0, Beitrags-ID: 42200753

PCS 7 specifications

Siemens PCS 7 is a powerful and comprehensive process control system designed for various industrial automation applications. It is part of the Siemens Totally Integrated Automation (TIA) portfolio, providing seamless integration with various Siemens products and services. The system is known for its flexibility, scalability, and reliability, making it suitable for industries such as energy, water treatment, chemicals, pharmaceuticals, and manufacturing.

One of the main features of Siemens PCS 7 is its modular architecture, which allows users to customize and scale their control solutions according to their specific needs. The system supports a diverse range of hardware and software components, from powerful servers and workstations to field devices and controllers. This modularity ensures that the system can adapt to different operational requirements while remaining cost-effective.

Another key feature is the advanced visualization capabilities offered by PCS 7. Users can create intuitive graphical interfaces that improve process monitoring and control. The system's Process Control and Monitoring (PCM) application enables real-time visualization of processes, enhancing decision-making and responsiveness.

Siemens PCS 7 is built on open and industry-standard communication protocols, such as Profibus and Profinet. This ensures interoperability with a wide array of third-party devices and systems, allowing seamless integration into existing infrastructures. The system supports a variety of communication interfaces, enhancing data exchange and connectivity within the control architecture.

The PCS 7 system also incorporates sophisticated process automation technologies, including batch control, continuous process control, and advanced process control algorithms. These capabilities not only facilitate efficient operation but also optimize production processes through improved resource management and reduced waste.

Security is a critical aspect of Siemens PCS 7, addressing the growing concerns of cybersecurity in industrial environments. The system incorporates robust security measures, including user authentication, data encryption, and regular software updates, ensuring that industrial operations remain protected against potential threats.

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