A wavelet‐based piecewise approach for steady‐state analysis of power electronics circuits

Simulation of steady‐state waveforms is important to the design of power electronics circuits, as it reveals the maximum voltage and current stresses being imposed upon specific devices and components. This paper proposes an improved approach to finding steady‐state waveforms of power electronics circuits based on wavelet approximation. The proposed method exploits the time‐domain piecewise property of power electronics circuits in order to improve the accuracy and computational efficiency. Instead of applying one wavelet approximation to the whole period, several wavelet approximations are applied in a piecewise manner to fit the entire waveform. This wavelet‐based piecewise approximation approach can provide very accurate and efficient solution, with much less number of wavelet terms, for approximating steady‐state waveforms of power electronics circuits. Copyright © 2006 John Wiley & Sons, Ltd.     

A wavelet approach to fast approximation of steady‐state waveforms of power electronics circuits

Waveforms arising from power electronics circuits often contain slowly changing segments with high‐frequency details concentrated near the switching instants. Such a feature is consistent with the localization property of wavelets which are known in the signal processing literature to be highly suitable for describing fast changing edges embedded in slowly varying backgrounds. This paper considers the application of wavelet approximation to the steady‐state analysis of power electronics circuits. The basic procedure of wavelet approximation is reviewed, and an improved approach by mixing wavelets of different levels is described. When applied to power electronics circuits, the method yields efficient solutions because only a relatively small number of wavelets are needed and the proposed algorithm involves only matrix operations, permitting the steady‐state waveforms to be found fast. Copyright 2003 John Wiley & Sons, Ltd.     

Steady‐state solutions of a voltage source converter with dq‐frame controllers by means of the time‐domain method

A voltage source converter (VSC) is one of the most widely used power converters in a power system. In this paper, a time‐domain‐based accelerated steady‐state method is proposed to solve for a closed‐loop pulse‐width modulated (PWM) VSC with dq‐frame controllers, which is able to account for the harmonic interactions between the converter and the rest of the power network, between the AC and DC sides of a VSC, and between the converter and its controllers. The proposed time‐domain method is based on the modified time‐domain shooting method, where the Jacobian matrix is updated by the quasi‐Newtons method. This will drastically increase the computation efficiency as it avoids re‐evaluating and inverting the Jacobian matrix, whose size is usually very large for a PWM‐VSC due to high number of times of switching. All the results are shown to be consistent with those obtained by a PSCAD/EMTDC model, which has been validated with the experiment in a previous publication. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Studies on steady‐state stability of looped power systems and stabilization by SMES

With the increasing number of dispersed power sources interconnected to the power supply system, power systems can take a form similar to that of a longitudinal system. Also, they can become looped, with both ends of the longitudinal system connected to each other. In the present paper, the steady‐state stability of longitudinal power systems and looped power systems is analyzed by means of the mode analysis method via eigenvalue and eigenvector calculation, and power system stabilization by SMES (Superconducting Magnetic Energy Storage) for looped systems is examined relative to that for longitudinal systems. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 48–54, 2000     

Enhancement of steady‐state visual evoked potential‐based brain–computer interface systems via a steady‐state motion visual stimulus modality

Steady‐state visual evoked potential (SSVEP)‐based brain–computer interface (BCI) systems are among the most accurate assistive devices for patients with severe disabilities. However, existing visual stimulation patterns lead to eye fatigue, which affects the system performance. Therefore, in this study, we propose two improvements to SSVEP‐based BCI systems. First, we propose a novel visual stimulator that incorporates a visual motion stimulus for the steady‐state visual stimulus to reduce eye fatigue while maintaining the advantages associated with SSVEPs. We also propose two corresponding feature extraction algorithms, i.e. SSVEP detection and visual attention detection, to capture the phenomena of steady‐state motion visual stimulus responses. The accuracy of the test was ∼83.6%. Second, we propose a novel hybrid BCI‐SSVEP system and a motion visual stimulus hybrid BCI system to enhance the SSVEP‐based BCI system during a state of eye fatigue. Participants used the SSVEP system until reaching a fatigued state and then began using a hybrid motion visual stimulus. The accuracy of the proposed system was ∼85.6%. The proposed improvements can be incorporated into practical BCI systems for wheelchair control. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Parallel processing and genetic algorithm‐based efficiency optimization for multiconverter power system

An efficient optimization approach based on parallel processing and genetic algorithm for a multiconverter power system is presented in this paper. The system consists of several clients and one server. The genetic algorithm helps the system to reach maximum efficiency over the entire load range. Meanwhile, WiFi is employed to achieve high‐speed data transfer. Also, a benefit from the parallel processing and structure is that the optimization time has been exponentially reduced. The experimental results show that the prototype can achieve optimal efficiency over the entire load range, and the optimizing process is accelerated five times in average because of the parallel processing © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Calculation of steady‐state solution of parallel‐connected buck converters with active current sharing and its parameter sensitivity

In this paper, the effect of active current‐sharing control on the steady‐state operation of parallel‐connected buck converters is investigated. The system under study consists of N voltage‐mode‐controlled buck converters connected in parallel. Three kinds of active current‐sharing schemes are considered, namely, master–slave scheme with automatic master, master–slave scheme with dedicated master, and democratic scheme. Using the principle of charge balance, the mechanism of the operating point drift arising from active current sharing is examined. A general formulation of the steady‐state solution under active current sharing is derived. Moreover, detailed parameter sensitivity analysis is performed to evaluate the effect of parameters' variation on the operating point. The results from sensitivity analysis can be used to categorize parameters for facilitating practical design. Computer simulations are presented to verify the analytical results. Copyright © 2010 John Wiley & Sons, Ltd.     

Steady‐state stability of shaft torsional oscillation in an ac‐dc interconnected system with self‐commutated converters

Recent progress in power electronics technology makes it possible to consider applying self‐commutated converters using gate turn‐off thyristors (GTOs) to HVDC transmission systems. Since the self‐commutated converter can be operated stably without depending on ac‐side voltage, the magnitude and the phase angle of the converter output voltage can be controlled independently. Therefore, this type of converter will improve voltage stability at its ac side. On the other hand, shaft torsional oscillation of a thermal power plant caused by the interaction between the shaft‐generator system and the control system of the self‐commutated converter is still an open problem. In this paper, a linearized model for eigenvalue analysis of a power system, including HVDC interconnection with self‐commutated converters, is described to analyze the effect of the self‐commutated converter on the shaft torsional oscillation of a thermal power plant. Then, numerical results from the eigenvalue analysis of the shaft torsional oscillation are presented. Results obtained by the frequency response method are also reported. The numerical results make it clear that parameter regions of DC‐AVR and ACR control systems of self‐commutated converters exist where the shaft torsional oscillation may be caused. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 25–37, 1999     

Fast algorithm for multiple time-scale simulation of power system using parallel processing

Power system analysis is the basis of operation and planning. Since power systems are very large and complex, however, long computation time is required for the analysis. Development of a fast calculation method for stability analysis is desirable. Recently, the method using multiple time-scale numerical integration algorithm was developed for analyzing long-term dynamics. This method has the problem of calculation time since the coefficient matrix is very large. It is expected that calculation time can be shortened using parallel processing. In order to increase the efficiency of parallel processing, the coefficient matrix must be divided since solution of a set of linear equations is the main part of stability analysis. In this paper, coefficient matrix is converted into BBDF matrix for effective calculation of parallel processing. Each subnetwork block can be divided again since it is sparse. The algorithm discussed in this paper was implemented on the nCUBE2S parallel processing computer system. The computing time is measured so that it can be compared to the computer time of a single-processor system. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 14–22, 1997     

Time domain and steady‐state sensitivity of periodic switched networks to element changes

Switched periodic networks are widely used in power engineering and sensitivities of their steady‐state to element changes are of interest to the designers. The paper develops a method to obtain steady‐state sensitivities for networks in which semiconductor and other switching devices are modelled as ideal short circuits without additional elements. Such modelling has the advantage that switching transients need not be calculated and correct initial conditions after switching are obtained with only four integration steps. It is also shown that sensitivities need not be calculated during the process of reaching the steady‐state. Once the steady‐state is available, integration over two additional periods is sufficient to provide time domain steady state sensitivity to the element changes. Copyright © 1999 John Wiley & Sons, Ltd.     

Application of time‐frequency analysis for EMC study of a power conversion system

In recent years, the harmonics and EMI noise sent out from an electric power conversion system have attracted a great deal of attention in electromagnetic environment problems, so that the above considerations have become important. Therefore, there is a need for a detailed frequency analysis, for example, of transient phenomena during switching. We thus have proposed an analytic technique using the wavelet transform, in which it is possible to detect a phenomenon in terms of both time and frequency. In this paper, we perform an analysis using a wavelet transform on actual measured data at the switching interval. Then, based on the results obtained, we demonstrate the high validity of the wavelet transform and its application to the field of power electronics. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 48–56, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1170     

Real-time digital simulator for power system analysis

To understand a number of power system phenomena and to predict critical conditions in system operation, such as voltage collapse, a real-time simulator able to model the dynamic behavior of large power systems has been needed for a long time. The need for real-time simulations stems from the fact that in many practical situations it is desirable to test new equipment and analyze the dynamic behavior of a large power system using the actual pieces of equipment. A new digital simulator was developed based on a hypercube-type massively parallel computer to achieve this objective. The new simulator features: (1) real-time simulation of a large power system which covers transient stability through long-term behavior with constant accuracy level; (2) user-friendly man-machine interfaces which mimics an actual operating environment and realtime data presentation on a CRT; and (3) high-speed digital/analog conversion interfaces which connect the digital simulator to actual equipment.     

Planning the optimal installation of a solar power station through wind‐state analysis

Wind‐state analysis is required for the installation planning of a solar power station, since the wind's cooling effect controls the photovoltaic cell temperature. In this study, a large‐scale solar power system and the configuration of the target installation location are digitized based on open data from the Geographical Survey Institute of Japan's Ministry of Land, Infrastructure, Transport and Tourism. A method for obtaining the temperature distribution of the photovoltaic array is proposed by applying heat fluid analysis (wind‐state analysis), including heat transmission analysis using the above data. Furthermore, as a case study, we plan the installation of a large‐scale solar power system in Hamamasu, Shinshinotsu, and Chitose, which fall under the jurisdiction of the Ishikari Development and Promotion Bureau of Hokkaido. The distribution of the wind and heat flow in the photovoltaic array's circumference is determined, as well as the temperature distribution and the average conversion efficiency, considering the actual photovoltaic array configuration. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Development of an eigenvalue estimation method (Mode Coupling Method) for small signal stability analysis of power system

An eigenvalue estimation method for small signal stability analysis of electric power systems is proposed. The method, called the Mode Coupling Method, is used to estimate efficiently the nonlinear change of the eigenvalue with respect to the change of parameter. The eigenvalue sensitivity analysis method, which has been used to estimate the change of the eigenvalue, is a method of linear estimation of the change of the eigenvalue. However, the eigenvalue frequently shows a strong nonlinear change, and therefore the calculation efficiency and speed were insufficient in the conventional method. In the Mode Coupling Method, the most important modes and those most related to the major mode under consideration are first selected. Next, these two or more selected modes are coupled and the new eigenvalues of the coupled matrix are calculated, providing good estimation of the new eigenvalues. The size of the coupled matrix is very small. We can consider mutual interaction between important modes. Thus, this is a powerful method in which nonlinear estimation of eigenvalues is possible. When the QR method is used, the calculation time for eigenvalue analysis is proportional to the third power of the size of the matrix. The size of the matrix used for the mode coupling method is approximately 1/6 of the original value. Therefore, the computing time for eigenvalue estimation becomes less than 1% of the original computing time. The computational accuracy of the proposed method is verified with the IEEJ EAST30 standard power system model. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 10–16, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/ eej.21037     

Fixed‐point steady‐state analysis of adaptive filters

The steady‐state performance of adaptive filters can vary significantly when they are implemented in finite precision arithmetic, which makes it vital to analyse their performance in a quantized environment. Such analyses can become difficult for adaptive algorithms with non‐linear update equations. This paper develops a feedback and energy‐conservation approach to the steady‐state analysis of quantized adaptive algorithms that bypasses some of the difficulties encountered by traditional approaches. Copyright © 2003 John Wiley & Sons, Ltd.     

Exact sampled‐data analysis of quasi‐resonant converters with finite filter inductance and capacitance

Previous models of quasi‐resonant converters generally use averaging and assume infinite filter inductance and capacitance to reduce circuit complexity, but at the expense of accuracy. In this paper, exact sampled‐data modelling is used. A general block diagram model applicable to various topologies of quasi‐resonant converters is proposed. Large‐signal analysis, steady‐state analysis and small‐signal analysis are all studied. They agree closely with the experimental results in the literature. Compared with the averaging approach, the sampled‐data approach is more systematic and accurate. Copyright © 2001 John Wiley & Sons, Ltd.     

Digital filter design with state space method for 1‐bit signal processing based on delta‐sigma modulation

One‐bit signal processing based on delta‐sigma modulation has been studied for hardware implementation of signal processing systems. In the 1‐bit signal processing, finite word‐length problems such as overflow and coefficient quantization error occur. To solve the problems, a new design method with state space is proposed in this paper. Digital filters are designed to show the feasibility of the method. First, the L₁/L₂‐sensitivity is shown to evaluate coefficient quantization error and L₂ scaling constraints to prevent overflow. Second, a state space equation is presented and the L₁/L₂‐sensitivity and L₂‐scaling constraints are extended to take the filter structure and oversampling effects into account. Finally, the proposed method is shown to attain a higher SNR than conventional ones. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 48–56, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21075     

Optimization method of P+ ω PSS parameters for stability and robustness enhancement in a multimachine power system

Recent steady increase of electric power demand causes power sources to be large and far from cities. Wide area power interchanges lead to larger and more complex power systems. This makes the network susceptible to poor damping power swing oscillations of relatively low frequencies which influence the whole system. This paper describes a newly developed generator's double input signal PSS (P+ ω input PSS) design method. Several power system conditions (power flow and/or power patterns) are considered to satisfy a well‐stabilized power system for each system condition. Major features of this method are: (1) Weighting factor for eigenvalue sensitivity of the oscillation mode is considered when the parameters of the PSS are updated during the optimization process. (2) The new method provides good results for the generator's local and interarea oscillation modes under peak and off‐peak power flow conditions. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 19–31, 2000     

Multi‐command SSAEP‐based BCI system with training sessions for SSVEP during an eye fatigue state

This paper proposes a steady‐state auditory stimulus modality and a detection algorithm to replace steady‐state visual evoked potential (SSVEP )‐based brain–computer interface (BCI ) systems during visual fatigue periods. The optimal speaker position for the steady‐state auditory evoked potential (SSAEP )‐based BCI system and possible electrode positions are investigated. Using the proposed system, an accuracy of 85% for two commands was achieved based on the T3–T5 and T4–T6 electrode positions using only one speaker. SSAEP is a promising BCI modality for mitigating the problem of eye fatigue that often occurs during the use of SSVEP ‐based BCI systems. However, SSAEP ‐based BCI systems suffer from low accuracy. To increase accuracy, we propose a new enhanced SSAEP training method. The training process was enhanced by instructing users to control their attention levels while simultaneously detecting an auditory stimulus frequency. Furthermore, we propose a corresponding single‐frequency, multi‐command BCI paradigm for the proposed training method. With the proposed paradigm, four commands can be detected using only one auditory stimulus frequency. The proposed training system yielded an accuracy of ∼81% compared to 66% for sessions performed without the proposed training method. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Maximum‐power‐point tracking method of photovoltaic power system using a single transducer

This paper describes a novel strategy of maximum‐power‐point tracking for photovoltaic power generation systems. A unique feature of this method is the capacity to see the maximum power point using only a single transducer, that is, a Hall‐effect CT or an isolation amplifier. Output power of the photovoltaic can be estimated with an average value and ripple amplitude of the detected reactor current or the capacitor voltage. A conventional hill‐climbing method is employed to seek the maximum power point, using the output power estimated with only the current or voltage transducer. In this paper, not only a theoretical aspect of the proposed method is discussed, but also experimental results are presented to prove the feasibility of the method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 79– 86, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20275