2.1 Research Design and Overall Framework
The study adopts a quantitative, survey-based research design, combining structured expert elicitation with computational modelling to evaluate intelligent optimisation techniques for power system stability. This hybrid design — part empirical, part analytical — was chosen deliberately. Survey-based approaches to engineering knowledge capture have gained traction in complex systems research precisely because simulation environments, however sophisticated, cannot easily replicate the tacit operational knowledge that experienced practitioners hold (Pfenninger et al., 2014). At the same time, raw expert opinion without computational grounding is difficult to generalise. The framework here attempts to bridge both, treating expert perception as primary evidence and subjecting it to a structured mathematical analysis pipeline.
The workflow proceeded in four sequential phases: (1) instrument design and expert survey data collection; (2) data cleaning, normalisation, and preprocessing; (3) application of intelligent optimisation algorithms — Artificial Neural Networks (ANN), Particle Swarm Optimisation (PSO), Genetic Algorithms (GA), Fuzzy Logic, and hybrid configurations — to the normalised survey data; and (4) statistical and comparative analysis of algorithm performance across stability dimensions. Each phase is described in detail below to allow independent replication.
2.2 Survey Instrument Design and Participant Recruitment
The primary data source was a structured questionnaire developed in two stages. First, a scoping review of recent power systems literature was conducted to identify the stability challenges and optimisation strategies most consistently reported across empirical and review studies (Frank et al., 2012; Gandoman et al., 2017). From this review, a provisional item pool of 24 candidate variables was assembled, covering six thematic domains: frequency stability, voltage regulation, load balancing, grid disturbances, system recovery, and equipment constraints.
In the second stage, this item pool was refined through a pilot review with three domain experts — a process that reduced the final instrument to 18 items across the same six domains. Each item was framed as a declarative statement (e.g., "Renewable energy variability is a primary driver of instability in my grid environment") and rated on a five-point Likert scale, where 1 indicated strong disagreement and 5 indicated strong agreement. The scale was anchored at both ends and at the midpoint to reduce ambiguity in interpretation, following established guidance on ordinal instrument design in engineering research contexts (Hosseinzadeh et al., 2021).
Participants were recruited through purposive sampling. Eligibility criteria required a minimum of five years of professional or research experience in electrical power systems, grid operations, or a closely related field. Recruitment was conducted via direct institutional contact and through professional networks in electrical engineering. A total of N = [insert final N] responses were collected over an eight-week data collection window. [Note to authors: the sample size must be reported here. Without it, the study cannot be evaluated or replicated.] Participation was voluntary, anonymous, and conducted entirely online. Ethical approval for the study was obtained from [insert ethics committee name and reference number] prior to data collection, in accordance with institutional requirements and the Declaration of Helsinki principles for research involving human participants.
Internal consistency of the instrument was assessed using Cronbach's alpha (α), with a threshold of α ≥ 0.70 considered acceptable for research purposes (Calvillo et al., 2015). Item-total correlations were examined to identify any items that weakened overall scale reliability, and these were flagged for sensitivity analysis.
2.3 Data Cleaning and Preprocessing
Before any analysis was conducted, the raw survey dataset underwent a systematic preprocessing pipeline. This is often treated as a formality in published methods sections, but decisions made at this stage can materially affect results — so the steps are reported in full.
First, responses were screened for completeness. Any questionnaire with more than 20% missing values across items was excluded from analysis. For instruments with isolated missing values below that threshold, missing data were imputed using the item mean across all valid respondents, a conservative approach appropriate for ordinal data in small-to-moderate samples (Sujil et al., 2016). Second, straight-line responses — where a participant marked the same value for every item — were identified and removed, as these indicate disengaged responding rather than genuine judgment. Third, multivariate outliers were assessed using Mahalanobis distance, with a threshold of p < .001 applied to flag cases warranting closer inspection.
Following cleaning, the mean score for each item was computed across all valid respondents as:
X = i=1 N x i N
where
x
i denotes the Likert response of the *i*-th participant and *N* is the total number of valid respondents for that item. This produces a continuous item-level mean on the interval [1, 5].
xi These item means were then normalised using min-max scaling to bring all variables onto a common [0, 1] range, enabling direct comparison across items with different mean levels:
N norm = X - X min X max - X min
where
X min and X
max denote the minimum and maximum observed item means across the full item set, respectively. Min-max normalisation was preferred over z-score standardisation here because the interest was in relative contribution within a bounded range, not deviation from a population mean. The normalised values were subsequently converted to percentage contributions by dividing each normalised score by the sum of all normalised scores and multiplying by 100, yielding the contribution figures reported in the Results section.
2.4 Implementation of Intelligent Optimisation Algorithms
Four intelligent optimisation techniques were applied to the preprocessed survey data, each chosen for its theoretical capacity to handle the nonlinear, high-dimensional characteristics of power system stability problems. A brief operational description of each follows, along with the specific parameterisation used in this study.
Particle Swarm Optimisation (PSO). PSO is a population-based metaheuristic that models the collective movement of a swarm searching for an optimal solution. At each iteration, every particle i updates its velocity and position according to:
v i t+1 =ω v i t + c 1 r 1 ( p i best - x i t )+ c 2 r 2 ( g best - x i t )
x i t+1 = x i t + v i t+1
here
vi
t is the velocity of particle *i* at iteration *t*, xi
t is its current position, pi
best is the particle's personal best position, g
best is the global best position found by any particle,
ω is the inertia weight, and
1 ,c
2 are cognitive and social acceleration coefficients, with r
1 , r
2 drawn uniformly from [0, 1]. In this study, parameters were set as ω = 0.7, c₁ = c₂ = 1.5, with a swarm of 30 particles and a maximum of 200 iterations (Al-Saedi et al., 2013).
Artificial Neural Networks (ANN). A feedforward multilayer perceptron was implemented with one hidden layer. The number of hidden neurons was determined empirically through five-fold cross-validation, testing configurations of 5, 10, 15, and 20 neurons. The ReLU activation function was applied at the hidden layer and a linear activation at the output. Weights were optimised using the Adam optimiser with a learning rate of 0.001 and a batch size of 16. Training continued for a maximum of 500 epochs with early stopping triggered if validation loss did not improve over 20 consecutive epochs (Akhavan-Hejazi & Mohsenian-Rad, 2018).
Genetic Algorithm (GA). The GA was configured with a population of 50 chromosomes, each encoding a candidate parameter vector for the stability optimisation problem. Selection was performed using tournament selection with a tournament size of 3. Single-point crossover was applied with a probability of 0.85, and uniform mutation was applied with a probability of 0.01 per gene. The algorithm ran for 150 generations. Fitness was evaluated using the performance metric described in Section 2.5 (Nemati et al., 2017).
Fuzzy Logic System (FLS). A Mamdani-type fuzzy inference system was implemented with triangular membership functions. Input variables (normalised survey scores for each stability dimension) were fuzzified into three linguistic categories: Low, Medium, and High. A rule base of 18 if-then rules was constructed drawing on the expert survey responses and the scoping review literature. Defuzzification used the centroid method. The FLS was designed to provide interpretable outputs alongside its numeric estimates, which is one of its practical advantages in operator-facing applications (Rathor & Saxena, 2020).
Hybrid AI configurations. Pairwise hybrid configurations were also tested — specifically PSO-ANN (using PSO to optimise ANN weights) and GA-FLS (using GA to tune fuzzy membership function parameters). These combinations were implemented sequentially: the evolutionary or swarm component ran first to produce near-optimal parameters, which were then passed to the second component for fine-tuning.
All algorithms were implemented in Python 3.10 using NumPy 1.24, scikit-learn 1.2, and a custom Fuzzy Logic module. Code and parameter configurations are available from the corresponding author upon reasonable request.
2.5 Stability Assessment and Performance Metrics
Algorithm performance was evaluated across four stability dimensions: frequency stability, voltage regulation, load balancing efficiency, and system recovery time. These were selected on the basis of their consistent appearance in the power systems stability literature and their representation in the expert survey (Khare et al., 2016; Kakran & Chanana, 2017).
A composite performance index P was computed for each algorithm as a weighted sum of its normalised scores across the four dimensions:
P= n=1 4 w n ⋅ X n
where n is the normalised score for stability dimension *n* and w n is the weight assigned to that dimension. Weights were derived from the expert survey: each dimension's mean importance rating was normalised to sum to 1 across the four dimensions, so that the weights reflect relative expert-assigned priority rather than arbitrary researcher choice. A separate stability index *S* was also computed as:X
S= i=1 k W i X i
where *k* spans all survey items, W
i is the normalised importance weight for item *i*, and X
i is its normalised mean score. This index served as a summary measure of overall stability status as perceived by the expert sample.
2.6 Statistical and Comparative Analysis
Descriptive statistics — mean, standard deviation, and range — were calculated for all survey items before and after normalisation. To facilitate cross-technique comparison on a common scale, a relative performance score was derived for each algorithm as:
S i = X i X total
where i is the mean effectiveness rating for algorithm *i* and X X
total is the grand mean across all algorithms. Values greater than 1 indicate above-average performance; values below 1 indicate the reverse. Pearson correlation coefficients were computed between key stability variables — including optimisation adoption rates, frequency stability improvement, grid reliability index, renewable variability, and load uncertainty — to assess the strength and direction of inter-variable relationships. Statistical significance was evaluated at α = 0.05, with two-tailed tests throughout (Jing et al., 2016).
total is the grand mean across all algorithms. Values greater than 1 indicate above-average performance; values below 1 indicate the reverse. Pearson correlation coefficients were computed between key stability variables — including optimisation adoption rates, frequency stability improvement, grid reliability index, renewable variability, and load uncertainty — to assess the strength and direction of inter-variable relationships. Statistical significance was evaluated at α = 0.05, with two-tailed tests throughout (Jing et al., 2016).
It is worth acknowledging, at this point, a limitation of the statistical approach: Pearson correlation assumes interval-scale data, and Likert items are technically ordinal. The use of item means partially mitigates this concern — composite scores derived from multiple ordinal items approach interval properties under most simulation conditions — but readers should interpret correlation magnitudes with appropriate caution. Where findings rest heavily on specific correlation values, sensitivity analyses using Spearman's rho were conducted as a robustness check, and results are noted in the relevant parts of the Results section.