Limit Cycle Estimation and Suppression in Automatic Load Frequency Control of Single and Two-Area Power Systems Using Advanced Control Strategies

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Chinese explanation / 中文解读

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Original abstract

To maintain system stability, especially in interconnected grids, a dedicated control strategy is required. This leads to the concept of Load Frequency Control (LFC). There is an ample choice of controllers used in LFC. While PI/PID controllers are popularly used, modern systems increasingly rely on proficient approaches like LQR and Fuzzy Logic Controllers (FLC) for improved control and optimization. We have considered four models of LFC in order to conduct a comparative study based on the primary objective of minimizing the deviation of frequency from its nominal value. Four models are selected. First, a single-area load frequency control system is analyzed through a comparative evaluation of PI, optimal, and fuzzy logic controllers. The second model is selected as an automatic LFC of two area systems using the LQR method, where the controller selects the most advanced optimal solution, which uses the Riccati Equation. The third model is selected, which is expected to render full satisfaction/fulfilment of the basic concept of LFC with the full utilization of battery energy storage system (BESS), wind turbine (WT), photovoltaic (PV), high voltage direct current (HVDC), and synchronous generator (SG). This promise guarantees frequency stability and maintains balanced tie-line power, and proposes a new coordinated frequency control approach for the LFC two area system to enhance frequency stability and address the concerns of low-inertia systems. In the selected models, the primary components are speed governors, turbines, and synchronous generators. The governors have inherent backlash nonlinearity, which is responsible for exhibiting self-sustained oscillations and is otherwise known as Limit Cycles (LC) that needs to be completely mitigated/suppressed for proper functioning of LFC. This has been given necessary weightage, and signal stabilization by Gaussian/ deterministic signal have been adopted after estimation of LC in different models. In order to maintain frequency stability, the challenges of low inertia have been resolved with an LFC hybrid model integrating SG, WT, PV, BESS, and HVDC is proposed in the present work. This promises a guarantee for frequency stability and maintain balanced tie-line power and proposes a new coordinated frequency control strategy for the LFC in two-area systems to maintain the frequency stability and addresses of low inertia. Our basic objective is to reach the goal of achieving the minimum deviation of frequency in the minimum time with the use of a single controller in the four models selected for their specific performance characteristics, used in a specific environment. We proposed four steps procedure which includes a preliminary test appropriately obtained step response conducted on selected models with governors removing their backlash nonlinearity; secondly the estimation of LC in all models with governors in presence of their backlash nonlinearity, third step elimination of LC by signal stabilization with high frequency deterministic signals/Gaussian (random) signals on the models finally application of digital deadbeat controllers on all models. Besides a simple model included as a sample model which has undergone four steps procedures like other models to achieve guaranteed frequency stability in terms of frequency deviation (Δf=0, in time t=0). The system is modeled and analyzed through simulations carried out in the Simulink environment of MATLAB, yielding the anticipated performance outcomes.

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