Abstract
Keywords
Introduction
Low-frequency oscillations are observed when relatively weak tie lines link large power networks. Until the synchronism loss occurs, these oscillations’ size may rise (Kundur, 1994). Flexible AC transmission systems (FACTS) devices have emerged as a viable concept for power system applications over the last decade due to the rapid and constant advancement of power electronics technology (Sahoo et al., 2023). Within the FACTS family, the IPFC is considered one of the most adaptable gadgets (Ahmed et al., 2022). In addition to providing voltage support and reducing system oscillation, this device also regulates the power flow of the line (Prakash et al., 2023). The IPFC uses two or more VSCs that share a DC link. Every VSC can exchange reactive power with its gearbox system and offer a range of compensation for the chosen line in the gearbox system (Singh and Singh, 2022).
The efficacy of FACTS-based damping controllers in enhancing system stability is intimately linked to their performance (Banaei and Kami 2011). Therefore, numerous control techniques have been proposed to optimize the performance of these FACTS-based controllers (Dhurvey and Chandrakar 2016). Countless trials have shown how IPFC affects power system stability using various controllers. The IPFC controllers were designed using fuzzy logic and artificial neural networks (Naga Sai Kalyan and Rao, 2016). The damping control approach, which uses a fuzzy logic controller that is not ideal, causes the unexplainable settling time of the system's reaction, as explained in (Bento, 2020). Additionally, a certain amount of trial and error is necessary when modifying the initial values of this controller (Kazemi and Karimi 2006; Rajbongshi and Saikia, 2019). To lessen interarea oscillations, a PI supplemental damping controller for the IPFC has been suggested; however, the controller settings have not been optimized (Khan et al., 2024; Martins et al., 2017).
The power system utilities choose a typical lead-lag controller structure due to its ease of online tuning, and other adaptive or variable structure solutions do not guarantee stability (Kumar and Rajan, 2024; Sahu et al., 2022). The Phillips–Heffron linear model has been a standard for small signal stability investigations of power systems for many years (Agrawal et al., 2023; Farhang and Mazlumi, 2014), and tuning the controller parameters is a challenging task (Khadanga et al., 2024). Numerous traditional methods, including the gradient approach for optimization, Eigenvalue assignment, mathematical programming, and current control theory, have been documented in the literature (Aref et al., 2023). Regretfully, the traditional methods take a long time since they are iterative, computationally demanding, and have a slow convergence rate (Singh et al., 2023). Another way to address the stability difficulties is to employ nature-inspired algorithms (NIAs) (Ustun, 2023). Effective NIA applications for power system problems include the Grasshopper Optimization Algorithm (Srivastava et al., 2022), Flower Pollination optimization (Hussain et al., 2020), Sine cosine algorithm (Latif et al., 2021), African Vulture Optimization (Nayak et al., 2023), Particle swarm optimization (Abdolrasol et al., 2023), satin bowerbird optimization (Farooq et al., 2022), drone squadron optimization (Mazumdar et al., 2024), artificial bee colony (Singh et al., 2021a), Chaotic Evolutionary programming (Singh et al., 2021b), Shuffled frog-leaping optimization algorithm (Khadanga and Panda, 2022), COVID-19-based optimization Algorithm (Safiullah et al., 2022), and others. Despite their success in power system design, these approaches usually have a disadvantage: they often become trapped in local optima and have a slow rate of convergence.
In the field of optimization, a novel technique called Gorilla Troops Optimizer (GTO) algorithm has recently acquired popularity. Numerous optimization difficulties have been addressed by this approach, which has been widely used (Patil et al., 2022). The GTO algorithm is not without its limits, despite its wide range of applications. The GTO algorithm's vulnerability to local minima is one of its main problems (Mostafa et al., 2023; Natarajan et al., 2022). Therefore, to overcome the constraints above constraints, the GTO algorithm is improved by modifications, leading to the creation of the modified Gorilla Troops Optimizer (mGTO) algorithm. With these modifications, the algorithm should operate more efficiently and be able to overcome issues like local minima, providing a stronger and more reliable optimization tool.
Motivation research gap and paper organization
Research gap
The following are the main conclusions drawn from the literature review indicated above:
The impact of the modified Philips–Heffron technique on an SMIB power system equipped with IPFC has hardly been studied. The lead-lag controller for the IPFC-based SMIB power system is not being executed, as far as the author is aware. The traditional GTO algorithm has many drawbacks that must be modified to achieve a better effect.
Motivation
The analyzed literature concludes that numerous holes still need to be filled for the SMIB power system to operate consistently. Therefore, it is imperative to spearhead a top-to-bottom focus on frequency support for various system components. Motivated by the circumstances, a unique approach is implemented to examine the dynamic performances of an IPFC-based SMIB power system: the lead-lag damping controller. Like how a system tuned using an advanced improvement technique can ensure promising results for controlling complex power systems is planned using a recently mGTO algorithm. The optimal tuning of the lead-lag controller boundaries has been achieved using the proposed mGTO.
Innovations
The key innovations of the paper are summarized as follows:
The Modified Heffron–Phillips modeling of an SMIB power system with IPFC has been developed. The impact of a lead-lag controller in the said system is examined. It has been demonstrated that the suggested lead-lag controller, built with the recently determined modified GTO computation, provides better frequency regulation than several other controllers. By considering a few benchmark functions, the advantages of the proposed method over several alternative approaches are also evaluated in terms of operation time.
Paper organization
This paper is divided into six primary sections for the remaining portion. “Motivation research gap and paper organization” section describes the idea behind the research in terms of the research gap and Motivation, while “System under study” section presents the modeling of the IPFC in an SMIB power system. “Problem formulation” section describes the objective function and the IPFC controller's structure. “Modified artificial GTO algorithm” section provides an overview of the GTO and mGTO optimization techniques. “Simulation results with discussions” section explains the findings, and last section offers “Conclusions.”
System under study
This study considers an SMIB power system equipped with an IPFC, as seen in Figure 1.

IPFC-based SMIB power system.
Linearized equations
The nonlinear equations can be linearized around an operational condition to provide these system linear equations which can be expressed as (Prakash et al., 2023):

IPFC-based modified Heffron–Phillips model.
Problem formulation
Controller structure
This study uses the widely known lead-lag structure as the IPFC-based extradamping controller, as shown in Figure 3 (Khan et al., 2024). The said structure comprises three blocks as phase correction block with T1, and T2 as time constants; gain block (Ks); and the signal washout block (Ahmed et al., 2022). The gain block comes first, giving the controller the proper gain. Next is the phase compensation block. This block compensates for the phase lag between the input and output signals from the controller, helping to provide the required phase lead. The final component is a high-pass filter called a signal washout block. This screen allows the signals that are connected to the input oscillations signal to flow through it without any changes. The change in the control vector is the output, while the speed deviation is the input signal. The literature study suggests that the washout time constant for the controller can be varied between 1 and 20, and for the proposed research, it is taken as 10. Once the controller gets KT, it is necessary to determine the controller constants T1 and T2.

Damping controller structure.
Objective function
The objective function J in the current study is an ITAE error of the speed deviations, which is represented as Rai and Das (2022):
The objective function can be expressed as a design problem and is assessed in a bounded region as Khadanga et al. (2024):
Minimize J
Subject to
Modified artificial GTO algorithm
Artificial GTO algorithm
The group behaviors seen in gorillas serve as an inspiration for the GTO algorithm. This clever program uses signals from the relationships and behaviors of gorilla battalions to create an optimization strategy that is effective and flexible. The main benefit of the GTO algorithm is its ease of use in engineering applications. The gorilla tracking approach (GTO) is divided into three main segments: exploitation, exploration, and initialization. These segments are based on different gorilla behaviors. These activities include exploring new areas, returning to well-known areas, approaching other gorillas, respecting the Silverback's choices, and competing with them for the attention of adult female gorillas. The exploration phase starts when the initialization phase is over. Moving to new habitats, returning to known locations, and approaching other gorillas are its three primary behaviors. Similarly, two basic gorilla behaviors are included in the exploitation phase of GTO: hunting silverbacks and fighting for older females. The following is a description of the three stages of GTO (Singh et al., 2021a):
Initialization phase
The
Exploration phase
At each step, all
Exploitation phase
The silverback displays specific behaviors when it trails when the GTO algorithm executes the phase using one of two tactics for adult females. If so, the silverback gorilla's choice is respected. The following mathematical assertion demonstrates the behavior (Safiullah et al., 2022):
Equations (15a), (15b), and (15c) illustrate the fierce rivalry amongst juvenile gorillas in their pursuit of older females.
Modified artificial GTO algorithm
In the original GTO method, the variables M and N depend on the variable D, which is computed as the algorithm runs. Equation (9), which is used in the optimization process, is probably used to find the value of C depending on attributes. An optimization algorithm that has a high degree of exploration capability is less likely to become stuck in local minima. Excessive exploration capability can be detrimental, but it can also help prevent local minima and expand the search space by introducing extra randomness.
Excessive exploitation leads to less unpredictability since the algorithm focuses too much on refining and utilizing preexisting solutions. As a result, there is a possibility that the algorithm will fail to identify the global minimum and become stuck in local minima. Consequently, striking a balance between the exploitation and exploration phases is essential to the algorithm's efficacy. D can be updated using Equation (9) as:

Flowchart for the proposed modified Gorilla Troops Optimizer (mGTO) algorithm.
Simulation results with discussions
Modified GTO algorithm's performance evaluation
Using a few benchmark test functions, the suggested mGTO approach's performance was first examined. The basic algorithm parameters are displayed in Table 1. The study's population size is set at 30. All algorithms’ dimensions are set to 30 (
Algorithm parameters.
The statistical analysis of the recorded results is summarized in Table 2. From the recorded values attained, the mean, best, and worst were computed, tabulated, and compared. The mean of each of the 30 recorded and simulated fitness values is calculated and tabulated. The statistical results for a few unimodal (f1–f7) and multimodal (f8–f10) functions are also shown in Table 2 (Khadanga et al., 2023). Table 2 presents the results from SCA-AOA (Khadanga et al., 2023), ASO (Singh et al., 2021a), MGWO-CS (Khadanga et al., 2022), and GTO (Patil et al., 2022) to support the claim that the method is superior. The proposed improved method outperforms rival algorithms for nearly all test functions.
Benchmark function testing.
The convergence characteristics for both the suggested mGTO algorithm for the

Convergence profile for modified Gorilla Troops Optimizer (mGTO) algorithm.
The computation times for the mGTO and GTO approaches for 30 iterations of each benchmark function are also included in Table 3. It demonstrates that for all functions (
Computational time comparison.
Implementation of the proposed modified GTO algorithm
By using GTO and mGTO to minimize the fitness given in Equation (6), the suggested IPFC-based additional damping controller parameters are optimized. An increase in mechanical power input of 10% is considered while calculating the goal function. The fitness function is recorded after 20 iterations of the optimization process (Feleke et al., 2023). Table 4 presents the top 50 runs, indicating that the suggested method yields superior outcomes concerning the objective function. Now, taking these conclusions into account, the following research has been done:
Value of different controller parameters.
Δ1 damping controller
Using an IPFC damping controller based on δ1, the system's performance is showcased under the considered contingency. The system response depicted in Figure 6 indicates that the system performs marginally better when using the suggested mGTO optimized δ1-based IPFC damping controller.

Response of δ1 controller.
m1 damping controller
At

Response of m1 controller.
Δ2 damping controller
The system response for the same change in mechanical input contingency with an IPFC damping controller based on δ2 is shown in Figure 8, from which the suggested method outperforms the alternative damping controller.

Response of δ2 IPFC controller.
m2 damping controller
With an m2-based IPFC damping controller, the system's performance is confirmed under the same condition, and Figure 9 illustrates the system's response. The suggested mGTO-optimized damping controller outperforms the GTO-designed controller in terms of system performance.

Response of m2 IPFC controller.
Comparison of all IPFC damping controllers
Another disturbance is considered to evaluate the robustness of the suggested method and compare the performance of all IPFC-based damping controllers. Figures 10 and 11 display the system's dynamic response with each of the four alternate damping controllers. At

Response of all controllers with change in reference voltage using GTO parameter.

Response of all controllers with change in reference voltage using modified Gorilla Troops Optimizer (mGTO) parameter.
Conclusions
This study significantly enhances the original GTO algorithm by incorporating scaling variables, thereby giving rise to the mGTO algorithm. The efficacy of this proposed algorithm is meticulously evaluated by subjecting it to a battery of standard benchmark functions. Furthermore, both the modified and original GTO algorithm strategies are harnessed for the design of a FACTS-based controller. The design problem of an IPFC-based controller is meticulously examined to assess performance. Parameters of the controller are fine-tuned utilizing both GTO and mGTO optimization techniques. It is strikingly evident that when the proposed modified GTO algorithm is applied, there is a notable reduction in the objective function (J) for the IPFC-based damping controller. Moreover, simulation results unequivocally establish that the mGTO-based IPFC controllers yield superior results to other standard controllers, solidifying its position as a pioneering advancement in controller design methodologies.
The main flaw in the suggested approach is that it derives a Small-Signal model of an SMIB system by ignoring the following:
The resistances of every system component, including the generator, transmission lines, transformer, and series converter transformer. The transients associated with the transformers, synchronous generator stator, fixed series capacitor, and transmission lines. Moreover, linear approaches are unable to accurately depict the intricate dynamics of the system, particularly during significant disruptions.
In future research, a large-scale power system can be used to evaluate the effectiveness of the proposed technique. Only IPFC is considered in this work; other FACT devices may be evaluated in the SMIB system in a subsequent iteration. Integration of distributed energy sources like wind power plants, and photovoltaic systems can also be considered for further study. Moreover, the writers aim to integrate sophisticated soft computing methods for intricate optimization issues. Investigating how the mGTO algorithm performs in scenarios involving renewable energy integration or grid stability enhancement could provide valuable insights into its effectiveness in addressing contemporary challenges in power system control. Additionally, exploring the potential for incorporating real-time data and adaptive strategies into the mGTO algorithm could further enhance its applicability in dynamic power system environments, ultimately contributing to more robust and efficient control solutions.
Footnotes
Author contribution
All authors contributed equally to this work. RKK, DD, SP, SRM, MKK, TSU, and AK—Conceptualization, Investigation, Writing—original draft, Writing—review & editing.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
