Control Systems Fundamentals

Control Systems

• A system that uses a measurement of the output and compares it to the desired output is a closed-loop system.
• Tuning parameters or components is required to achieve the desired transient response.
• A measurement of the system's output used for feedback to control the system is called a feedback signal.
• Trade-offs are made between conflicting criteria during system design.
• A difference between the complex physical system and the design model is the design gap.
• A system where the control action is dependent on the output is a control system.
• A shorthand, graphical representation of a physical system illustrating functional relationships between components is a block diagram.
• The ratio of physical output to physical input in an industrial process is productivity.
• Risk refers to uncertainties in unintended consequences of a design.
• A measure of how quickly a first-order system responds to input is the time constant.
• The input to a system is sometimes called the reference.
• To reduce steady-state error, analysis and corrective actions are employed.
• The simplest form of a block diagram is a single block.
• Automatic control of an industrial process is called automation.
• A system where the control action is independent of the output is an open-loop system.
• System components are the elements of a system.
• An output transducer measures the output and converts it into a usable form for the controller.
• A system with multiple input or output variables is a multivariable system.
• A steady-state response is the output that remains after the transients have decayed.
• Stability is needed for a system to function effectively.
• Analysis of a system determines performance.
• Design for a system involves achieving desired performance.
• Natural response describes how a system dissipates or acquires energy.
• Forced response depends on the input to a system.
• Control Systems are required for power amplification, remote control, convenience of input, and disturbance compensation.
• Open-loop systems are simple and economical, but usually inaccurate and unreliable. They don't use feedback from the output.
• Closed-loop systems are more accurate and reliable, but more complex and expensive. They use feedback from the output.

System Configuration

• Open-loop systems have control actions independent of the output.
• Closed-loop systems have control actions dependent on the output.
• Control systems have input transducers, controllers, processes, and output transducers.

Analysis and Design

• Analysis determines a system's performance.
• Design establishes a system's performance.
• A control system is dynamic, responding to input with transient and steady-state responses.
• Objectives for systems analysis and design include producing the desired transient response, minimizing steady-state error, and assuring stability. These objectives often need compromises.
• The transient response occurs before the steady state is reached.
• Steady-state response is the output that remains after transients have decayed.

Stability

• System stability is critical.
• The total response is a combination of natural and forced responses.
• Natural response describes how the internal energy of the system dissipates or is acquired.
• Forced response depends exclusively on the input.
• Systems must exhibit natural response that approaches zero if the forced response is maintained.
• Control system design requires the considerations of factors that affect hardware selection, costing, and achieving robust design. Robust designs don't rely on specific parameter values.

Feedback Control Systems

• Feedback control systems compare actual output and reference, computing an error signal, to adjust the controlled output to match the reference.
• Feedback can be either positive or negative.

Laplace Transform

• Laplace transform converts differential equations into algebraic equations, simplifying solution.
• The Laplace transform of a sum is the sum of the transforms.
• The Laplace transform of a product is NOT the product of the transforms.
• Common transform pairs are used to recognize and solve inverse transform problems.

Block Diagram Simplification

• Blocks in series are multiplied to achieve an equivalent transfer function.
• Parallel blocks are added to get the equivalent.
• Feedback loops are manipulated to achieve a simplified equivalent transfer function.

P, PI, PD, PID Controllers

• A proportional controller adjusts the control action in proportion to the error signal.
• An integral controller integrates past errors to reduce steady state error.
• A derivative controller considers the rate of change of the error to improve stability and response speed.
• A PID controller combines P, I, and D controllers to offer robust performance and stability.

Control of 1st and 2nd Order Systems

• Transfer functions and steady-state error are key considerations as these are affected by gain adjustments.