Valeri Mladenov

Prof. Dr. Valeri Mladenov

Fundamentals of Electrical Engineering, Technical University of Sofia, Sofia, Sofia-Grad, Bulgaria
orcid

Research Focus & Metrics

Academic Career Length

39Years (1988-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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15 November 2023 in Electronics
Verified
Journal Article
Open access
PDF file
CPChristos Pavlatos
Christos Pavlatos
EMEvangelos I. Makris
Evangelos I. Makris
Georgios FotisGeorgios Fotis
Georgios Fotis
Vasiliki VitaVasiliki Vita
Vasiliki Vita
Valeri MladenovValeri Mladenov
Valeri Mladenov
Precise anticipation of electrical demand holds crucial importance for the optimal operation of power systems and the effective management of energy markets within the domain of energy planning. This study builds on previous research focused on the application of artificial neural networks to achieve accurate electrical load forecasting. In this paper, an improved methodology is introduced, centering around bidirectional Long Short-Term Memory (LSTM) neural networks (NN). The primary aim of the proposed bidirectional LSTM network is to enhance predictive performance by capturing intricate temporal patterns and interdependencies within time series data. While conventional feed-forward neural networks are suitable for standalone data points, energy consumption data are characterized by sequential dependencies, necessitating the incorporation of memory-based concepts. The bidirectional LSTM model is designed to furnish the prediction framework with the capacity to assimilate and leverage information from both preceding and forthcoming time steps. This augmentation significantly bolsters predictive capabilities by encapsulating the contextual understanding of the data. Extensive testing of the bidirectional LSTM network is performed using multiple datasets, and the results demonstrate significant improvements in accuracy and predictive capabilities compared to the previous simpleRNN-based framework. The bidirectional LSTM successfully captures underlying patterns and dependencies in electrical load data, achieving superior performance as gauged by metrics such as root mean square error (RMSE) and mean absolute error (MAE). The proposed framework outperforms previous models, achieving a remarkable RMSE, attesting to its remarkable capacity to forecast impending load with precision. This extended study contributes to the field of electrical load prediction by leveraging bidirectional LSTM neural networks to enhance forecasting accuracy. Specifically, the BiLSTM’s MAE of 0.122 demonstrates remarkable accuracy, outperforming the RNN (0.163), LSTM (0.228), and GRU (0.165) by approximately 25%, 46%, and 26%, in the best variation of all networks, at the 24-h time step, while the BiLSTM’s RMSE of 0.022 is notably lower than that of the RNN (0.033), LSTM (0.055), and GRU (0.033), respectively. The findings highlight the significance of incorporating bidirectional memory and advanced neural network architectures for precise energy consumption prediction. The proposed bidirectional LSTM framework has the potential to facilitate more efficient energy planning and market management, supporting decision-making processes in power systems.

12 March 2023 in Electronics
Verified
Journal Article
Open access
PDF file
Vasiliki VitaVasiliki Vita
Vasiliki Vita
Georgios FotisGeorgios Fotis
Georgios Fotis
Vesselin ChobanovVesselin Chobanov
Vesselin Chobanov
CPChristos Pavlatos
Christos Pavlatos
Valeri MladenovValeri Mladenov
Valeri Mladenov
Power transformers’ reliability is of the highest importance for distribution networks. A possible failure of them can interrupt the supply to consumers, which will cause inconvenience to them and loss of revenue for electricity companies. Additionally, depending on the type of damage, the recovery time can vary and intensify the problems of consumers. This paper estimates the maintenance required for distribution transformers using Artificial Intelligence (AI). This way the condition of the equipment that is currently in use is evaluated and the time that maintenance should be performed is known. Because actions are only carried out when necessary, this strategy promises cost reductions over routine or time-based preventative maintenance. The suggested methodology uses a classification predictive model to identify with high accuracy the number of transformers that are vulnerable to failure. This was confirmed by training, testing, and validating it with actual data in Colombia’s Cauca Department. It is clear from this experimental method that Machine Learning (ML) methods for early detection of technical issues can help distribution system operators increase the number of selected transformers for predictive maintenance. Additionally, these methods can also be beneficial for customers’ satisfaction with the performance of distribution transformers, which would enhance the highly reliable performance of such transformers. According to the prediction for 2021, 852 transformers will malfunction, 820 of which will be in rural Cauca, which is consistent with previous failure statistics. The 10 kVA transformers will be the most vulnerable, followed by the 5 kVA and 15 kVA transformers.

1 January 2006
Verified
Conference Paper
Closed access
GTGeorgi Tsvetanov Tsenov
Georgi Tsvetanov Tsenov
AZA.H. Zeghbib
A.H. Zeghbib
FPF. Palis
F. Palis
NSN. Shoylev
N. Shoylev
Valeri MladenovValeri Mladenov
Valeri Mladenov
Myoelectric signals (MES) are the electrical manifestation of muscular contractions and they can be used to create myoelectric prosthesis which is able to function with the amputee's muscle movements. This signal recorded at the surface of the skin of the forearm has been exploited to provide recognition of the movement of the hand and finger movements of healthy subject. The objective of the paper is to describe the identification procedure, based on EMG patterns of forearm activity using various neural networks methods and to make a comparison between different intelligent computational methods of identification, which are used in this work. Then an online algorithm for movement identification and classification that utilises the trained neural networks is presented

2 July 2021 in Electronics
Verified
Journal Article
Open access
PDF file
Valeri MladenovValeri Mladenov
Valeri Mladenov
In this paper, a unified and open linear technology simulation program with integrated circuit emphasis (LTSPICE) memristor library is proposed. It is suitable for the analysis, design, and comparison of the basic memristors and memristor-based circuits. The library could be freely used and expanded with new LTSPICE memristor models. The main existing standard memristor models and several enhanced and modified models based on transition metal oxides such as titanium dioxide, hafnium dioxide, and tantalum oxide are included in the library. LTSPICE is one of the best software for analysis and design of electronic schemes. It is an easy to use, widespread, and free product with very good convergence. Memristors have been under intensive analysis in recent years due to their nano-dimensions, low power consumption, high switching speed, and good compatibility with traditional complementary metal oxide semiconductor (CMOS) technology. In this work, their behavior and potential applications in artificial neural networks, reconfigurable schemes, and memory crossbars are investigated using the considered memristor models in the proposed LTSPICE library. Furthermore, a detailed comparison of the presented LTSPICE memristor model library is conducted and related to specific criteria, such as switching speed, operating frequencies, nonlinear ionic drift representation, boundary effects, switching modes, and others.

19 January 2023 in Sustainability
Verified
Journal Article
Open access
PDF file
Vasiliki VitaVasiliki Vita
Vasiliki Vita
Georgios FotisGeorgios Fotis
Georgios Fotis
CPChristos Pavlatos
Christos Pavlatos
Valeri MladenovValeri Mladenov
Valeri Mladenov
The danger of a total blackout in a wide area or, even worse, in a country is always present. The restoration methods after a blackout mainly focus on the strategy that the dispatchers in the control centers of the Transmission System Operator will follow than the abilities that the distribution’s microgrids have. This study suggests a restoration technique to improve distribution system resilience following a blackout, using distributed generation for the restoration of important loads. The goal of the restoration problem is to maximize the number of critical loads that are restored following the catastrophic incident. Under the restrictions of the DGs and the network, the DGs with good black start capability are restored first. Load weight and node importance degree are suggested during the recovery path selection procedure, while taking node topological importance and load importance into account. A mixed-integer linear program (MILP) is used to simulate the issue, and the modified IEEE 39-bus test system is used to verify the efficacy of the suggested restoration approach.

26 May 2023 in Technologies
Verified
Journal Article
Open access
PDF file
CPChristos Pavlatos
Christos Pavlatos
EMEvangelos I. Makris
Evangelos I. Makris
Georgios FotisGeorgios Fotis
Georgios Fotis
Vasiliki VitaVasiliki Vita
Vasiliki Vita
Valeri MladenovValeri Mladenov
Valeri Mladenov
In the energy-planning sector, the precise prediction of electrical load is a critical matter for the functional operation of power systems and the efficient management of markets. Numerous forecasting platforms have been proposed in the literature to tackle this issue. This paper introduces an effective framework, coded in Python, that can forecast future electrical load based on hourly or daily load inputs. The framework utilizes a recurrent neural network model, consisting of two simpleRNN layers and a dense layer, and adopts the Adam optimizer and tanh loss function during the training process. Depending on the size of the input dataset, the proposed system can handle both short-term and medium-term load-forecasting categories. The network was extensively tested using multiple datasets, and the results were found to be highly promising. All variations of the network were able to capture the underlying patterns and achieved a small test error in terms of root mean square error and mean absolute error. Notably, the proposed framework outperformed more complex neural networks, with a root mean square error of 0.033, indicating a high degree of accuracy in predicting future load, due to its ability to capture data patterns and trends.