Showing 6 results for Markov Model
H. Miar-Naimi, P. Davari,
Volume 4, Issue 1 (1-2008)
Abstract
In this paper, a new Hidden Markov Model (HMM)-based face recognition
system is proposed. As a novel point despite of five-state HMM used in pervious
researches, we used 7-state HMM to cover more details. Indeed we add two new face
regions, eyebrows and chin, to the model. As another novel point, we used a small number
of quantized Singular Values Decomposition (SVD) coefficients as features describing
blocks of face images. This makes the system very fast. The system has been evaluated on
the Olivetti Research Laboratory (ORL) face database. In order to additional reduction in
computational complexity and memory consumption the images are resized to 64×64 jpeg
format. Before anything, an order-statistic filter is used as a preprocessing operation. Then
a top-down sequence of overlapping sub-image blocks is considered. Using quantized SVD
coefficients of these blocks, each face is considered as a numerical sequence that can be
easily modeled by HMM. The system has been examined on 400 face images of the Olivetti
Research Laboratory (ORL) face database. The experiments showed a recognition rate of
99%, using half of the images for training. The system has been evaluated on 64×64 jpeg
resized YALE database too. This database contains 165 face images with 231×195 pgm
format. Using five training image, we obtained 97.78% recognition rate where for six
training images the recognition rate was 100%, a record in the literature. The proposed
method is compared with the best researches in the literature. The results show that the
proposed method is the fastest one, having approximately 100% recognition rate.
M. Sefidgaran, M. Mirzaie, A. Ebrahimzadeh,
Volume 6, Issue 2 (6-2010)
Abstract
Reliability of a power system is considerably influenced by its equipments.
Power transformers are one of the most critical and expensive equipments of a power
system and their proper functions are vital for the substations and utilities. Therefore,
reliability model of power transformer is very important in the risk assessment of the
engineering systems. This model shows the characteristics and functions of a transformer in
the power system. In this paper the reliability model of the power transformer with ONAN
cooling is obtained. The transformer is classified into two subsystems. Reliability model of
each subsystem is achieved. Markov process representation and the frequency/ duration
approach are employed to obtain a complete reliability model of the subsystems. By
combining these models reliability model of power transformer is obtained. The reliability
model associated with the transformer is then proposed combining the models of
subsystems. The proposed model contains five states. To make the model more applicable,
the 5-state model is alleviated to a 3-state one. Numerical analysis and sensitivity analysis
relevant to the proposed reliability model are performed for evaluating the numerical values
of the model parameters and the impact of different components on the reliability of the
model.
Y Damchi, J Sadeh,
Volume 9, Issue 4 (12-2013)
Abstract
Appropriate operation of protection system is one of the effective factors to have a desirable reliability in power systems, which vitally needs routine test of protection system. Precise determination of optimum routine test time interval (ORTTI) plays a vital role in predicting the maintenance costs of protection system. In the most previous studies, ORTTI has been determined while remote back-up protection system was considered fully reliable. This assumption is not exactly correct since remote back-up protection system may operate incorrectly or fail to operate, the same as the primary protection system. Therefore, in order to determine the ORTTI, an extended Markov model is proposed in this paper considering failure probability for remote back-up protection system. In the proposed Markov model of the protection systems, monitoring facility is taken into account. Moreover, it is assumed that the primary and back-up protection systems are maintained simultaneously. Results show that the effect of remote back-up protection system failures on the reliability indices and optimum routine test intervals of protection system is considerable.
M. Khalilzadeh, A. Fereidunian,
Volume 12, Issue 4 (12-2016)
Abstract
In this paper, a stochastic approach is proposed for reliability assessment of bidirectional DC-DC converters, including the fault-tolerant ones. This type of converters can be used in a smart DC grid, feeding DC loads such as home appliances and plug-in hybrid electric vehicles (PHEVs). The reliability of bidirectional DC-DC converters is of such an importance, due to the key role of the expected increasingly utilization of DC grids in modern Smart Grid. Markov processes are suggested for reliability modeling and consequently calculating the expected effective lifetime of bidirectional converters. A three-leg bidirectional interleaved converter using data of Toyota Prius 2012 hybrid electric vehicle is used as a case study. Besides, the influence of environment and ambient temperature on converter lifetime is studied. The impact of modeling the reliability of the converter and adding reliability constraints on the technical design procedure of the converter is also investigated. In order to investigate the effect of leg increase on the lifetime of the converter, single leg to five-leg interleave DC-DC converters are studied considering economical aspect and the results are extrapolated for six and seven-leg converters. The proposed method could be generalized so that the number of legs and input and output capacitors could be an arbitrary number.
A. Karimabadi, M. E. Hajiabadi, E. Kamyab, A. A. Shojaei,
Volume 16, Issue 2 (6-2020)
Abstract
The Circuit Breaker (CB) is one of the most important equipment in power systems. CB must operate reliably to protect power systems as well as to perform tasks such as load disconnection, normal interruption, and fault current interruption. Therefore, the reliable operation of CB can affect the security and stability of power network. In this paper, effects of Condition Monitoring (CM) of CB on the maintenance process and related costs are analyzed. For this, A mathematical formulation to categorize and model equipment failures based on their severity is developed. By CM, some of the high severity failures, named major failures, can be early detected and be corrected as a minor failure. This formulation quantifies the effect of CM on the outage rate and Predictive Maintenance (PDM) rate of equipment. Also, by combining the predictive maintenance to preventive maintenance, the Integrated Preventive and Predictive Maintenance Markov model is presented to analyze the effect of CM on the maintenance process. Finally, the optimal inspection rates of CBs based on the minimum maintenance cost in the traditional and the proposed Markov model are determined. To verify the effectiveness and applicability of the method, the proposed approach is applied to the CBs of KREC in Iran.
A. Mirsamadi, Y. Damchi, M. Assili,
Volume 17, Issue 1 (3-2021)
Abstract
Power systems should have acceptable reliability in order to operate properly. Highly available and dependable protective relays help to obtain the desirable reliability. The relays should be periodically evaluated during specific intervals to achieve the mentioned characteristics. The Routine Test Interval (RTI) should be optimized in order to economically maximize the reliability of the protection system. The failure rate of the relays plays a vital role in determination of the Optimum Routine Test Interval (ORTI). Human error is one of the effective factors in the failure rate of the relays. Therefore, in this paper, a Markov model is proposed to investigate the impact of human error on the failure rate and the ORTI of the protection system. The model is applied for the protection system of power transformer. The obtained results indicated that human error has a significant impact on the increase of protection system failure, the decrease of the desired reliability indices, and the reduction of ORTI of the protection system.
