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This paper describes a direct-power-controlled CVCF inverter and presents its experimentally examined operation characteristics. The most important feature of this strategy is the direct selection of the switching states of the CVCF inverter to restrict errors between the feedback and command values of active and reactive power. In addition, this paper presents a theoretical analysis of the relationship between the instantaneous power and the switching state, which is essential for deriving a switching-state table for the controller. The feasibility of the proposed method was verified through several computer simulations and experimental tests using a 2.0-kVA prototype setup. The output voltages were confirmed to be stable sinusoidal waveforms with a total harmonic distortion of 1.13% under nonlinear load conditions. Excellent voltage balance was achieved by the proposed strategy even under unbalanced load conditions. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 62-69, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21023 [ABSTRACT FROM AUTHOR]

In this paper, a learning algorithm combining memory-less learning and memory-based learning is proposed for agents operating under POMDP. In the first stage of the proposed algorithm, memory-less learning is applied. The stochastic gradient method is employed as a memory-less learning algorithm. In the first stage, a state-action set series that accomplishes the task is stored in memory. In the second stage, memory-based learning is applied. In this process, only the series obtained in the first stage is used, so that this method is able to reduce significantly the amount of required memory. The proposed algorithm is applied to three simulations for comparison with the memory-less learning algorithm. Through computer simulations, it is shown that the proposed algorithm works more effectively in POMDP than ordinary memory-less learning. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(1): 32–40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20963 [ABSTRACT FROM AUTHOR]

In a distribution system, in order to enhance the reliability of power supply, the distribution feeder is divided into several sections by installing sectionalizing switches, and then each of the sectionalized sections is connected to a different feeder. For example, one feeder is divided into three sections by two sectionalizing switches, and then each of the divided sections is connected to the other feeder through sectionalizing switch. Since a distribution system with many feeders has many sectionalizing switches, the system configuration is determined by states (opened or closed) of sectionalizing switches. Usually, a power utility tries to obtain distribution loss-minimum configuration among large numbers of configuration candidates. However, it is very difficult to determine the loss-minimum configuration such that the mathematical optimality is guaranteed, because it is well known that determination of a distribution system's configuration is to decide whether each sectionalizing switch is opened or closed by solving a combinatorial optimization problem. In this paper, the authors propose a determination method of loss-minimum configuration by which the mathematical optimality is guaranteed for a three-sectionalized three-connected distribution feeder network. A problem to determine the loss-minimum configuration is formulated as a combinatorial optimization problems with four operational constraints ( feeder capacity, voltage limit, radial structure, and three-sectionalization). In the proposed method, after picking up all partial configurations satisfied with radial structure constraint by using enumeration method, optimal combination of partial configurations is determined under the other operational constraints by using conventional optimization method. Numerical simulations are carried out for a distribution network model with 140 sectionalizing switches in order to examine the validity of the proposed algorithm in comparison with one of conventional meta-heuristics (tabu search). © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 56– 65, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20530 [ABSTRACT FROM AUTHOR]

We have proposed the multirate discrete Fourier transform (MR-DFT) as one of the DFT algorithms. The feature of the MR-DFT is that only one multiplication is used for each Fourier coefficient. Therefore, the number of multiplications can be decreased compared with the conventional DFT. In this paper, for applications of the MR-DFT, we consider how the noise affects the estimation performance of the MR-DFT. Then we propose two improved algorithms of the estimation performance, that is, a shifted multirate discrete Fourier transform (SMR-DFT) and a parallel shifted multirate discrete Fourier transform (PSMR-DFT). The SMR-DFT prevents an aliasing of the additive noise by a frequency modulation. The PSMR-DFT performs the parallel processing of the SMR-DFT with different sample points using the periodicity of an input signal. The estimation performances of the proposed algorithms are compared with MR-DFT by computer simulations. The SMR-DFT could prevent the degradation of the estimation performance of the MR-DFT in the lower components caused by the wide bandwidth noise. Hence its estimation variance could become 0.61 times that of the MR-DFT. Furthermore, the PSMR-DFT could improve the estimation variance of the SMR-DFT to 0.46 times. Comparing the number of operations of the proposed algorithms with the MR-DFT, the number of additions has increased, however, the number of multiplications has the same complexity. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 20–27, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20044 [ABSTRACT FROM AUTHOR]

There are many applications where it is necessary to estimate accurately the amplitude and phase of signals when the information regarding the frequencies is obtained in advance. This paper presents a new algorithm for estimating more accurately Fourier coefficients of a signal contaminated by additive noise where sinusoidal frequencies of interest are not distributed uniformly. In the proposed method, Fourier coefficients are adaptive parameters. It uses averaged gradient signals and has almost the same acquisition time as the conventional LMS algorithm with more accurate estimation. The performance analysis of the proposed method is presented and its validity and limits are verified under various conditions by computer simulations. It is shown that the proposed method has especially better performance than the LMS algorithm when both the number of frequencies and the step size parameter, µ, are large. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 52–60, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10362 [ABSTRACT FROM AUTHOR]

Active noise control systems that have been studied previously require a replica of the cancellation path to obtain the updating weight values, because the signals for the operation cannot be observed. In this paper we propose a structure and an adaptive algorithm for the active noise control system using an adaptive exponential filter that does not require any replica. The adaptive algorithm is based on the steepest descent method that can be easily realized and the updating weight value of the adaptive exponential filter is the correlation of the observable output signal of the adaptive system and the estimation error. The other adaptive filters are composed of the linear transversal system. It is proven that the transfer function after converging completely corresponds to the transfer function of the noise and the cancellation path under a certain condition. Finally, the convergence performance of the estimation accuracy and the tracking performance with respect to rapid changes of the noise and the cancellation paths are verified by computer simulation. [ABSTRACT FROM AUTHOR]

This paper presents a method to compensate voltage sags with minimum energy injection for a series-connected voltage restorer using a micro-SMES. A circuit for extracting the fundamental symmetrical components from sag voltages and a minimum energy injection algorithm is described. Simulations of voltage sag compensation have been carried out using PSCAD/EMTDC for various faults. The simulation results confirm the validity of the proposed method and show the possibility of reducing the size of energy storage devices. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 70–80, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10047 [ABSTRACT FROM AUTHOR]

Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than those of conventional motors. Thus the low synchronous reactance would be expected to improve the torque-ampere ratio stability and the overload capacity in case of the variable-speed drive system of a load-commutated inverter due to the small armature reaction. Moreover, the low subtransient reactance may contribute to lessen the voltage stress during the shortened commutating period, especially in current source-type inverter (CSI) systems. In this paper, after presenting analytical formulas needed for a machine design, one design algorithm is described, citing one example of an experimental CSI-fed superconducting motor of 30 kVA which will be fabricated. Further, the distinguished features in its operation, as expected in the foregoing, are verified by the computer simulation study in comparison with a conventional machine in terms of a high specific power density, an extension of stable power limit, and so on. [ABSTRACT FROM AUTHOR]