Abstract
Many studies have been made in the field of load frequency control (LFC) through the last few decades because of its importance to healthy power system. It is important to maintain frequency deviation at zero level after a load perturbation. In decentralized control, the multi-area power system is decomposed into many single input single output (SISO) subsystems and a local controller is designed for each subsystem. The controlled subsystems may have slow poles; these undesired poles may drive the aggregated overall system into the instability region. Thus, it is required to relocate these poles to much more stable places to avoid their effect upon the overall system stability. This study aims to design a new load frequency controller based on the powerful optimal linear quadratic regulator (LQR) technique. This technique can be applied over subsystem level to shift each subsystem undesired poles one by one into a prespecified stable location which in turn shift the overall system slow poles and reduce the effect of the interaction between the interconnected subsystems among each other. This procedure must be applied many times as the number of undesired poles (pairs) until all the desired poles are achieved. The main objective is considered to get a robust design when the system is affected by a physical disturbance and ±40% model uncertainties. LQR can be applied again over the aggregated system to enhance the stability degree. Simulation results are used to evaluate the effectiveness of the proposed method and compared to other research results.
Highlights
load frequency control (LFC) is one of the most important problems in electric power system design/operation and is becoming much more significant nowadays especially with the increasing dimensions and complexity of the interconnected power systems
This study aims to design a new load frequency controller based on the powerful optimal linear quadratic regulator (LQR) technique
These values make the 4-area open loop power system stable, but the open loop system performance is affected by changes in the equivalent inertia constants Mi and synchronizing coefficients Tij (Table 2) more than changes of other parameters; these parameter values may lead the system into the instability region
Summary
LFC is one of the most important problems in electric power system design/operation and is becoming much more significant nowadays especially with the increasing dimensions and complexity of the interconnected power systems. In [7] the author has designed local independent H∞ controllers to decentralized two-area power system He has used a condition based on the structured singular values (SSVs). In [8] local independent LFCs have been designed for interconnected two-area power systems to realize satisfactory performances based on the SSV μ. (i) Maintaining system stability and performance for the overall power system and each control area throughout ±40% uncertainty of Mi and Tij (ii) Minimizing the effectiveness of step load disturbance on output signals to zero (iii) Recognizing a minimum overshoot and undershoot values (iv) Minimizing settling time on the frequency deviation signal and obtaining zero-steady state error for individual control area
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