TEL402 — Software/Computer Applications in Electrical Engineering: Lecture Note

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Course code: TEL 402 Course title: Software/Computer Applications in Electrical Engineering Course credit load: 2 Units Series 1: Control Systems Architecture and Analysis for Power Systems • Part 1.1: Fundamentals of Control Systems for Power Systems o Sub Part 1.1.1: Control System Concepts and Terminology o Sub Part 1.1.2: Open-Loop and Closed-Loop Control o Sub Part 1.1.3: Control Objectives in Power System Automation • Part 1.2: Analysing a Control Problem o Sub Part 1.2.1: Problem Definition and Requirements Analysis o Sub Part 1.2.2: Identifying Inputs, Outputs, and Constraints o Sub Part 1.2.3: Selecting Control Strategies • Part 1.3: System Architecture for Power System Control o Sub Part 1.3.1: Centralised, Decentralised, and Distributed Architectures o Sub Part 1.3.2: Hierarchical Control Architecture Levels o Sub Part 1.3.3: SCADA and Supervisory Control Architecture • Part 1.4: Automation and Control Functions in Power Systems o Sub Part 1.4.1: Protection and Automation Functions o Sub Part 1.4.2: Monitoring and Data Acquisition Functions o Sub Part 1.4.3: Case Study: Substation Automation Architecture Introduction This is the opening Series of TEL 402: Software/Computer Applications in Electrical Engineering. Modern power systems, from a single substation to a national grid, are increasingly monitored, protected, and operated through software-based control systems rather than purely

manual intervention, and before any specific information model, programming technique, or MATLAB tool examined later in this course can be usefully applied, a learner needs a clear grasp of what a control problem actually is, how a control system is structured, and how that structure scales from a single protection relay to an entire power system's supervisory architecture. The aim of this Series is to equip you with control system concepts and terminology, the analysis of a control problem and its requirements, the design of system architecture for power system control, including centralised, decentralised, and hierarchical structures, and the automation and control functions typically implemented within a power system, forming the conceptual foundation for the information modelling, programming, and MATLAB analysis examined in the Series that follow. We shall commence this Series by examining fundamentals of control systems for power systems. Next, we will consider how to analyse a control problem. Following that, we will examine system architecture for power system control. Finally, we will conclude by examining automation and control functions in power systems. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1: explain control system concepts and terminology, • SLO 1.2: distinguish open-loop from closed-loop control, • SLO 1.3: analyse a control problem and its requirements, • SLO 1.4: identify the inputs, outputs, and constraints of a control problem, • SLO 1.5: select an appropriate control strategy for a given problem, • SLO 1.6: describe centralised, decentralised, and distributed control architectures, • SLO 1.7: describe hierarchical control architecture levels and SCADA systems, • SLO 1.8: analyse automation and control functions for a power system application. 1.1 Fundamentals of Control Systems for Power Systems 1.1.1 Control System Concepts and Terminology A control system is an arrangement of physical or software components that manages, commands, directs, or regulates the behaviour of another system or process to achieve a desired

outcome, and in a power system context this might mean regulating a generator's voltage output, adjusting a transformer's tap position, or coordinating a protective relay's response to a fault, each an example of a specific, well-defined control task examined throughout this course. Key terminology used throughout this Series includes the plant or process, the physical system being controlled; the controller, the component making control decisions; the reference (or setpoint), the desired value of a controlled variable; and the disturbance, any external influence that pushes the plant away from its desired behaviour and that the control system must work to counteract. Worked example: In a generator voltage regulation system, the generator itself is the plant, an automatic voltage regulator is the controller, the desired terminal voltage is the reference, and a sudden change in load is a disturbance the controller must compensate for. Application: This basic vocabulary, plant, controller, reference, and disturbance, is used consistently across every control architecture and automation function examined throughout the rest of this course. Fill in the blank: The desired value of a controlled variable is called the ________ (or setpoint). 1.1.2 Open-Loop and Closed-Loop Control An open-loop control system applies a control action based solely on a predetermined input, or programmed sequence, without measuring the actual output or correcting for any deviation from the intended result, making it simple and inexpensive to implement but vulnerable to disturbances and inaccuracy, since the controller has no way of knowing whether the desired outcome was actually achieved. A closed-loop control system, by contrast, continuously measures the actual output using a sensor, compares it against the reference value, and adjusts the control action based on the resulting error, a process called feedback, allowing the system to actively correct for disturbances and modelling inaccuracies in a way an open-loop system simply cannot, which is precisely why almost every practical power system control application, from voltage regulation to frequency control, is implemented as a closed-loop system. Worked example: A simple timer-controlled irrigation system that waters a garden for a fixed duration regardless of soil moisture is open-loop, while a thermostat-controlled heating system that measures room temperature and adjusts heating accordingly is closed-loop. Application: Recognising whether a given power system control application is open-loop or closed-loop is the first analytical step in evaluating that system's likely accuracy and robustness to disturbances. Fill in the blank: A closed-loop control system uses ________ to compare actual output against the reference value.

1.1.3 Control Objectives in Power System Automation Power system automation pursues several distinct control objectives simultaneously, including stability, keeping the system operating within safe voltage, frequency, and loading limits; reliability, minimising the frequency and duration of supply interruptions; and efficiency, minimising losses and operating cost while still meeting the first two objectives. These objectives frequently compete with one another, requiring a control system architect to make deliberate trade-offs rather than optimising any single objective in isolation, since, for example, the fastest possible protective response to a fault, favouring reliability and stability, may not be the most economically efficient operating strategy under normal, non-fault conditions, a tension examined further when specific control strategies are selected later in this Series. Worked example: A utility must balance a generator's fast frequency response capability, improving grid stability, against the additional fuel cost and mechanical wear that fast, frequent output adjustments impose, illustrating a typical trade-off between competing control objectives. Application: Recognising and explicitly weighing these competing control objectives is essential before any specific control strategy or system architecture, examined later in this Series, can be sensibly selected for a given power system application. Fill in the blank: Power system control objectives include stability, reliability, and ________. Figure 1.1: Open-loop and closed-loop control system block diagrams.

Pilot questions 1.1 1. Define a control system. (Linked to SLO 1.1) 2. Name the four key terms: plant, controller, reference, and disturbance. (Linked to SLO 1.1) 3. Distinguish open-loop from closed-loop control. (Linked to SLO 1.2) 4. Define feedback. (Linked to SLO 1.2) 5. Name three control objectives in power system automation. (Linked to SLO 1.1) 1.2 Analysing a Control Problem 1.2.1 Problem Definition and Requirements Analysis Before any control system can be designed, the underlying control problem must be clearly defined, stating explicitly what variable or variables must be controlled, what constitutes acceptable performance, and under what range of operating conditions the system must function correctly, since a vague or incomplete problem statement almost inevitably leads to a control system that fails to meet the actual operational need it was intended to address. Requirements analysis translates this problem definition into specific, measurable performance criteria, such as maximum allowable voltage deviation, maximum acceptable response time following a disturbance, and required accuracy, criteria that later serve as the objective standard against which a completed control system's actual performance is tested and verified before it is deployed into operational service. Worked example: A requirement stating simply 'the voltage should be controlled' is too vague to design against, whereas a properly specified requirement stating 'terminal voltage must remain within ±2% of nominal for load changes up to 20% within 5 seconds' gives a control engineer a precise target to design and test against. Application: Writing precise, measurable requirements at the outset of a project is what allows a completed control system to later be objectively verified as meeting, or failing to meet, its intended purpose. Fill in the blank: Requirements analysis translates a problem definition into specific, ________ performance criteria. 1.2.2 Identifying Inputs, Outputs, and Constraints Every control problem must be characterised in terms of its inputs, the quantities that can be manipulated or that influence the system, such as a generator's field current, a transformer's tap

setting, or a measured disturbance such as load demand, and its outputs, the quantities of actual interest that the control system is ultimately trying to regulate, such as terminal voltage, system frequency, or power flow. Equally important are

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