Neuro-fuzzy logic-based power system stabilizers for angle stability enhancement in multi-machine power systems

Improvements in angle stability are commonly a significant emphasis in power system stability management. Although low frequency oscillations (LFOs) may not appear to be too alarming at first appearance, but failure to mitigate the oscillatory signals might cause the system to lose synchronization. To avoid power system disruption, adequate damping force is required for these oscillations. A power system stabilizer (PSS) well-known option for mitigating the effects of these oscillations have good performance for damping local oscillatory modes in general but they cannot sufficiently damp inter-area modes. Also, tuning PSSs control parameters is a difficult task which possess heavy optimization process and sometimes the PSSs design solution does not always provide a satisfactory solution. As a result, traditional PSSs performance fails to provide superior damping under other operating circumstances. Many adaptive control approaches have been proposed to solve this problem, but they are both difficult and expensive. FACTS (Flexible AC Transmission Systems) devices are efficient at suppressing oscillations and increasing power transmission rates. When a power oscillation damping (POD) controller is coupled to the control loop of the FACTS devices, recent research reveal that the FACTS-POD unit can function to introduce additional damping to the inter-area modes sufficiently. POD was connected to an Interline Power Flow Controller (IPFC) in this studies with the purpose of adding further damping to the inter-area oscillation modes found in power systems and simulation results shows a more viable option than PSSs. However, studies have shown that when controller parameters are set incorrectly, different types of controllers may weaken system damping or even worsen system oscillation, thus, the PSS-IPFC-POD controller needs to be designed correctly. Because of this, IPFC-POD coordinated PSSs optimization burden increases the systems computational and simulation cost. To address these shortcomings a Neuro-Fuzzy Controller (NFC) was proposed as a damping controller that is capable of adequately dampening both local and inter-area modes and is independent of coordination of PSSs to avoid optimization burden. The dynamic model of WSCC three-machine system and ten-machine test systems under multiple operating conditions and on SMIB test system was developed with the presence of NFC in SIMULINK. By linearization of the system model around the point of work, the eigenvalues of the system were obtained. Quantitative analysis results from the SMIB test system simulation shows that the proposed NFC model has the requirement to increase the rotor speed and rotor angle stability based on the time to settle by 64% and 28% respectively when compared to the FFA-PSS. In the same way, the proposed NFC SMIB model was observed to maximize the minimum damping ratio by 75% when compare to the PSSs-IPFC-POD model. Under the WSCC system simulation, the proposed NFC model recorded a 32% rotor speed and 66% rotor angle respective angle stability improvement in G2 based on the time to settle when compared to the FFA-PSS model. In the case of comparing the angle stability of the proposed NFC WSCC model to that of the PSS-IPFC-POD WSCC model, the proposed NFC model conceivably maximize the minimum damping ratio for the weakest modes by 38% when compare to the PSSs-IPFC-POD model. After carrying out the time-domain simulation on the New England IEEE test system, the proposed NFC model produced a 13% rotor speed and 43% rotor angle respective angle stability enhancement in G5 based on the time to settle when compared to the FFA-PSS model. Our work has led us to conclude that the simulation results with the proposed NFC model shows a great improvement in angular stability displaying a noticeable increase in the damping of the system oscillations. We have also found a way to achieve an efficient NFC damping controller performance that is capable of dampening both local and interarea modes which avoid optimization burden experienced by the simulation on the PSSs and PSSs-IPFC-POD respectively. To sum up our work, considerable improvement have been made by the NFC controller to withstand long-term oscillations without the use of a supplementary controller which reduces the computational and simulation cost.

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