• Journal of Korea Multimedia Society
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• v.24 no.9
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• pp.1251-1260
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• 2021

This paper discusses missing data processing using simple moving average (SMA) and kalman filter. Also SMA and kalman predictive value are made a comparative study. Time series analysis is a generally method to deals with time series data in photovoltaic field. Photovoltaic system records data irregularly whenever the power value changes. Irregularly recorded data must be transferred into a consistent format to get accurate results. Missing data results from the process having same intervals. For the reason, it was imputed using SMA and kalman filter. The kalman filter has better performance to observed data than SMA. SMA graph is stepped line graph and kalman filter graph is a smoothing line graph. MAPE of SMA prediction is 0.00737%, MAPE of kalman prediction is 0.00078%. But time complexity of SMA is O(N) and time complexity of kalman filter is O(D²) about D-dimensional object. Accordingly we suggest that you pick the best way considering computational power.

• The KIPS Transactions:PartB
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• v.9B no.4
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• pp.421-428
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• 2002

The local prediction method utilizing embedding vector loses the prediction power when the parameter r estimation is not exact for predicting the chaos time series induced from the high order differential equation. In spite of the fact that there have been a lot of suggestions regarding how to estimate the delay time ($\tau$), no specific method is proposed to apply to any time series. The inclinded linear model, which utilizes inclinded netter, yields satisfying degree of prediction power without estimating exact delay time ($\tau$). The usefulness of this approach has been indicated not only theoretically but also in practical situation when the method w8s applied to economical time series analysis.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.251-255
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• 2003

This paper proposes a novel UPQC(unified power quality conditioner) based on H-bridge modules, isolated through single-phase multi-winding transformers. The dynamic performance of proposed system was analyzed by simulation with EMTDC/PSCAD, assuming that the UPQC is connected with the 22.9kV distribution line. The proposed system can be directly connected to the transmission line without series injection transformers. It has flexibility in expanding the operation voltage by increasing the number of H-bridge modules and can compensate reactive power, harmonics, voltage sag and swell, voltage unbalance. The control strategy for the proposing UPQC was derived using the instantaneous power method. The proposing UPQC has the ultimate capability of improving power quality at the point of installation on power distribution systems and can be utilized for the future distribution system.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.33 no.9
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• pp.347-354
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• 1984

This paper presents a method of improving the power factor and , the waveform of A.C line currents and the output waveforms of AC to DC fully bridge converter systems which is achieved by connecting CON I.II and CON III.IV in series and parallel. The basic principle of the CON I.II.III.IV's operation is simple and feasibility of thease converter is proved by experiments. CON I and CON III are constructed of natural commutation, CON II and CON IV are constructed of forced commutation. The experimental results show that the power factor and waveform of the source currents and the output waveforms are improved by the method of connecting converter in series and parallel and driving it in I, II, III, IV quadrant.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.6
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• pp.1443-1447
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• 2012

In this paper, the characteristic of temperature variation was reviewed according to pattern variation. In order to degrade of diagnosis of power supply by using time series data for temperature measured by infrared camera it was transformed into 2 dimension phase plane using Takens embedding method. As a simulation results we cannot completely confirm the characteristic behaviors of nonlinear dynamics in phase plane. However these results has a certain patterns, it requires verification method through additional research in the future.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.4
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• pp.316-324
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• 2022

This paper uses seasonal auto-regressive integrated moving average (S-ARIMA), which is efficient in seasonality between time-series models, to predict the degradation tendency for lithium-ion batteries and study a method for improving the predictive performance. The proposed method analyzes the degradation tendency and extracted factors through an electrical characteristic experiment of lithium-ion batteries, and verifies whether time-series data are suitable for the S-ARIMA model through several statistical analysis techniques. Finally, prediction of battery aging is performed through S-ARIMA, and performance of the model is verified through error comparison of predictions through mean absolute error.

• Kyungpook Mathematical Journal
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• v.52 no.3
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• pp.347-357
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• 2012

When Newton's method, or Halley's method is used to approximate the pth root of 1-z, a sequence of rational functions is obtained. In this paper, a beautiful formula for these rational functions is proved in the square root case, using an interesting link to Chebyshev's polynomials. It allows the determination of the sign of the coefficients of the power series expansion of these rational functions. This answers positively the square root case of a proposed conjecture by Guo(2010).

• Korean Journal of Artificial Intelligence
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• v.12 no.1
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• pp.17-24
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• 2024

This paper introduces a novel approach to time-series estimation for energy load forecasting within Virtual Power Plant (VPP) systems, leveraging advanced artificial intelligence (AI) algorithms, namely Long Short-Term Memory (LSTM) and Seasonal Autoregressive Integrated Moving Average (SARIMA). Virtual power plants, which integrate diverse microgrids managed by Energy Management Systems (EMS), require precise forecasting techniques to balance energy supply and demand efficiently. The paper introduces a hybrid-method forecasting model combining a parametric-based statistical technique and an AI algorithm. The LSTM algorithm is particularly employed to discern pattern correlations over fixed intervals, crucial for predicting accurate future energy loads. SARIMA is applied to generate time-series forecasts, accounting for non-stationary and seasonal variations. The forecasting model incorporates a broad spectrum of distributed energy resources, including renewable energy sources and conventional power plants. Data spanning a decade, sourced from the Korea Power Exchange (KPX) Electrical Power Statistical Information System (EPSIS), were utilized to validate the model. The proposed hybrid LSTM-SARIMA model with parameter sets (1, 1, 1, 12) and (2, 1, 1, 12) demonstrated a high fidelity to the actual observed data. Thus, it is concluded that the optimized system notably surpasses traditional forecasting methods, indicating that this model offers a viable solution for EMS to enhance short-term load forecasting.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1453-1459
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• 2015

Loss of excitation (LOE) relay is prevalently used to protect synchronous generator. The widely used method for synchronous generator LOE protection is a negative offset mho relay with two zones. The basis of this relay is identical to mho impedance relay. In other words, this relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of series compensation, changes measured voltage and current signals during loss of excitation. This paper reveals that the presence of series compensators such as fixed series capacitors (FSCs) and static synchronous series compensator (SSSC) causes a significant delay on the performance of generator LOE relay. It is also shown that the presence of SSSC causes the LOE relay to be under-reached. Different operating modes of the power system, the SSSC and also different percentages of series capacitive compensations have been considered in the modeling. All the detailed simulations are carried out in the MATLAB/Simulink environment using the SimPowerSystems toolbox.

• Proceedings of the KAIS Fall Conference
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• 2004.06a
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• pp.193-197
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• 2004

The four-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. In this paper a novel line interactive Uninterruptible Power Supply(UPS) using the two four-leg VSCs is proposed. One VSC is in parallel with the ac link reactor of the power source side, and the other is in series with the load. The parallel four-leg voltage source inverter controls the three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series four-leg voltage source inverter compensates the line voltage and allows it to be balanced and harmonic-free. Both of the parallel and series four-leg voltage source inverters always act as independently controllable voltage sources, so that the three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulations results.