Power System Operation and Control

In order to keep any power system in steady state the flow of active and reactive power must be checked. The objective of the control strategy is to generate and distribute power in an interconnected system as economically and reliably as possible while maintaining the frequency and voltage within permissible limits.

Changes in real power mainly affect the system frequency. Reactive Power however, is immune to changes in frequency and mainly depends on voltage changes. Thus real and reactive power is controlled separately. The Load Frequency Loop (LFC) controls the real power and frequency and the automatic voltage regulator (AVR) controls the reactive power and voltage magnitude.

Today, in modern energy control centers the methods developed for control of individual generations, and eventually control of large interconnections are of critical importance. Modern Energy Control Centers (ECC) are equipped with on-line computers performing all signal processing through the remote acquisition systems known as supervisory control and data acquisition (SCADA) systems.

The operational objectives of LFC are to maintain reasonably uniform frequency by uniformly distributing loads between generators thus controlling the tie-line interchange. Frequency deviation and tie-line real power are sensed, which is a measure of change in the rotor angle. In an interconnected power system Load Frequency Control and Automatic Voltage Regulator equipment are installed for each generator. Small changes in real power are mainly dependent on changes in rotor angle and thus frequency. The reactive power is mainly dependent on voltage magnitude. Cross coupling between LFC.

The factors influencing power generation at minimal cost are operating efficiencies, fuel cost and transmission losses. Successful achievement of these operational targets entailed the development of Optimal Dispatch Solutions to find the optimal dispatch of generation for an interconnected power system. Optimal Dispatch is sometimes treated within framework of LFC. In direct digital control systems, the digital computer is included in the control loop which scans the unit generation and tie-line flows. These settings are compared with optimal settings derived from the solution of the optimal dispatch program. If the actual settings are off from the optimal values, the computer generates the raise/lower pulses which are sent to the individual units. The allocation program will also take into account the tie-line power contracts between the areas.

With the development of modern control theory, several concepts are included in automatic generation control (AGC) which I will discuss in my coming articles. The fundamental approach is the use of more extended mathematical models. In retrospect, AGC can be used to include the representation of the dynamics of the area, or even of the complete system. There are schemes which employ stochastic control concepts, e.g., minimization of some expected value of an integral quadratic error criterion. Usually, this results in the design of the Kalman filter which is of value for the control of small random disturbances.

With the incorporation of AGC in power systems several problems started to arise which mainly include black outs and tripping of lines in the interconnected power system. AGC has been quite a concern for researchers and Power Engineers due to its significance in the operation of interconnected power system. As power system continues to expand and become more complex in operation, demand for reliable and sustainable AGC solutions would be critical. Researchers are already working on the development of intelligent automatic generation control which incorporates smart algorithms that are more flexible and robust to large frequency and voltage disturbances in power system. These intelligent controllers are designed with the use of very sophisticated and smart algorithms that include Fuzzy Logic and Artificial Neural Networks.

“Power System Operation and Control” is a very theoretical topic, we’d love to debate with you. Let’s talk!

1 Comment

  • A very good article. AGC is my research project for studies. Could you please write an article in detail about AGC & LFC?

    I need to know about them.

    Thanks in advance :)

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