• 전기학회논문지P
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• 제59권2호
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• pp.173-178
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• 2010

Frequency is an important operating parameter of a power system. Due to the sudden change in generation and loads or faults in power system, the frequency is supposed to deviate from its nominal value. It is essential that the frequency of a power system be maintained very close to its nominal frequency. And monitoring and an accurate estimation of the power frequency by timing synchronized signal provided by FDR is essential to optimum operation and prevention for wide area blackout. As most conventional frequency estimation schemes are based on DFT filter, it has been pointed out that the gain error by change in magnitude could cause the defects when the power frequency is deviated from nominal value. In this paper, an advanced frequency estimation scheme using gain compensation for fault disturbance recorders (FDR) is presented. The proposed scheme can reduce the gain error caused when the power frequency is deviated from nominal value. Various simulation using both the data from EMTP package and user's defined arbitrary signals are performed to demonstrate the effectiveness of the proposed scheme. The simulation results show that the proposed scheme can provide better accuracy and higher robustness to harmonics and noise under both steady state tests and dynamic conditions.

• 대한전기학회논문지:전력기술부문A
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• 제51권1호
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• pp.29-36
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• 2002

It is required that the current state of system should be Precisely monitored for efficient and safe operation of the subway power system and it is an important Problem to secure the high quality data for state estimation. The current state of subway power system is estimated by using data transmitted to control center from every measuring instrument. The high accuracy and trust can be maintained if the measured data have a high quality. But it is difficult to estimate the accurate state of system because of the noises in transmitted data and the inaccuracy of measuring instruments. So the object is to reduce the difference between the real values and the measured values in order to improve considerably the inaccuracy due to Instrumental errors and transmission noises using the state estimation method. In this paper, we proposes a new state estimation to estimate the accurate state of the subway power system from the measured values of a Sang-In station in Daegu subway and consider the possibility of application to the real subway power system. on the basis of that. The simulation results show to make sure of the possibility to apply to the real system usefully.

• Journal of Communications and Networks
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• 제12권2호
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• pp.140-149
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• 2010

Green communication is a new paradigm of designing the communication system which considers not only the processing performance but also the energy efficiency. Power control management is one of the approaches in green communication to reduce the power consumption in distributed communication system. In this paper, we propose improved power control schemes for mobile satellite systems with ancillary terrestrial components (ATCs). In order to increase system capacity and reduce the transmitting power of the user's equipment, we propose an efficient channel estimation method consisting of a modified open-loop power control (OLPC) and closed-loop power control (CLPC). The OLPC works well if the forward and reverse links are perfectly correlated. The CLPC is sensitive to round-trip delay and, therefore, it is not effective in a mobile satellite system. In order to solve the above problem, we added monitoring equipment to both the OLPC and CLPC to use information about transmitting power that has not yet been received by the receiver over the satellite/ATC channel. Moreover, we adapted an efficient pilot diversity of both OLPC and CLPC in order to get a better signal to interference plus noise ratio estimation of the received signal.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권2호
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• pp.566-578
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• 2018

In this paper, we design a segment training based individual channel estimation (STICE) scheme for the classical two-way relay network (TWRN) with multi-pair sources (MPS) and amplify-and-forward (AF). We adopt the linear minimum mean square error (LMMSE) channel estimator to minimize the mean square error (MSE) without channel estimation error, where the optimal power allocation strategy from the relay for different sources is obtained. Then the MSE gains are given with different source pairs among the proposed power allocation scheme and the existing power allocation schemes. Numerical results show that the proposed method outperforms the existing ones.

• 한국자동차공학회논문집
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• 제4권1호
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• pp.63-74
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• 1996

Automatic transmission for heavy duty vehicles is a part of the power pack which includes steering and braking systems. This transmission in different from the one for passenger car. Therefore, in order to understand the trend of the important design parameters, maneuverability, acceleration performance and maximum speed, we need to analyze the total performance characteristics of the power transmission systems. In this study, modeling of the automatic transmission in heavy duty vehicle is carried out and the performance analysis method is presented. Results can be used for performance estimation data in the analysis for several combination method which determines the optimal parameters on the basis of penalty functions and weightings. And the estimation method of the important performance parameters such as engine inertia or power loss of engine by experiments is presented.

• Journal of electromagnetic engineering and science
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• 제4권1호
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• pp.23-29
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• 2004

In this paper we analyze convergence constraints and time constant of IT-LMS algorithm and derive a method of making it's time constant independent of signal power by using input variance estimation. The method for estimating the input variance is to use a single-pole low-pass filter(LPF) with common smoothing parameter value, θ. The estimator is with narrow bandwidth for large θ but with wide bandwidth for small θ. This small θ gives long term average estimation(low frequency) of the fluctuating input variance well as short term variations (high frequency) of the input power. In our simulations of multipath communication channel equalization environments, the method with large θ has shown not as much improved convergence speed as the speed of the original IT-LMS algorithm. The proposed method with small θ=0.01 reach its minimum MSE in 100 samples whereas the IT-LMS converges in 200 samples. This shows the proposed, tap-power normalized IT-LMS algorithm can be applied more effectively to digital wireless communication systems.

• 전기학회논문지P
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• 제50권3호
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• pp.101-108
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• 2001

Frequency is an important operating parameter of a power system. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this constraints, it requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the Power system energy balance. This paper describes a digital signal processing technique for measuring the operating frequency of a power system. The fundamental frequency component of 3-phase signal is first extracted by using an algorithm based on FIR filter. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154KV double T/L system by using EMTP software. Some test results are presented in the paper.

• KIEE International Transactions on Power Engineering
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• 제2A권3호
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• pp.109-113
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• 2002

This paper addresses the issue of parameter error identification and estimation in electric power systems. Parameter error identification and estimation is carried out as a part of the state estimation. A two stage estimation procedure is used to detect and identify parameter errors. Suspected parameters are identified by the WLAV state estimator in the first stage. A new WLAV state estimator adding suspected system parameters in the state vector is used to estimate the exact values of parameters. Supporting examples are given by using the IEEE 14 bus system.

• 한국위성정보통신학회논문지
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• 제11권1호
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• pp.46-50
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• 2016

The adaptive power control of Code Division Multiple Access (CDMA) systems for communications between User Equipments (UEs) with a link-budget based Signal-to-Interference Ratio (SIR) estimate which has distance information is applied to three inner loop power control algorithms. The speed estimation performances of these algorithms with their consecutive Transmit-Power-Control (TPC) ratios are compared to each other, and it is concluded that the speed can be estimated using the TPC ratio information of Consecutive TPC Ratio Step-size Closed Loop Power Control (CS-CLPC) and Fixed Step-size Power Control (FSPC).

• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.560-574
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• 2016

This paper presents a novel method for power system harmonic estimation based on the Park transform. The proposed method firstly extends the signal to a group of three-phase signals in a-b-c coordinate. Then, a linear fitting based method is adopted to estimate the fundamental frequency. Afterwards, the Park transform is utilized to convert the three-phase signals from a-b-c coordinate to d-q-0 coordinate. Finally, the amplitude and phase of a harmonic component of interest can be calculated using the d-axis and q-axis components obtained. Simulation studies have been conducted using matrix laboratory (MATLAB) and power system computer aided design/electromagnetic transients including direct current (PSCAD/EMTDC). Simulation studies in MATLAB have considered three scenarios, i.e., no-frequency-deviation scenario, frequency-deviation scenario and the scenario in the presence of inter-harminics. The results have demonstrated that the proposed method achieves very high accuracy in frequency, phase and amplitude estimation under noisy conditions, and suffers little influence of the inter-harmonics. Moreover, comparison studies have proved that the proposed method is superior to FFT and Interpolated FFT with the Hanning Window (IpFFTHW). Finally, a popular case in PSCAD/EMTDC has been employed to further verify the effectiveness of the proposed method.