Effect of diacid stabilizers on kinetics of hydrolytic polymerization of ϵ‐caprolactam in industrial reactors

The rate constants in hydrolytic polymerization of ε‐caprolactam are dependent on the concentration of carboxylic acid groups in the reaction medium. Therefore, the use of diacid stabilizers for regulating molecular weight are likely to have favorable effect on the kinetics of polymerization compared to monoacid stabilizers, which are traditionally used in such polymerizations. To understand the kinetics of polymerization in the presence of diacid stabilizer compared to monoacid stabilizer, mathematical kinetic models were developed using the end group approach. These models were used to quantify the effect of both stabilizers on nylon‐6 synthesis in a closed isothermal batch reactor at different temperatures in the range of 245–265°C. The kinetic model for the diacid‐stabilized system was then extended to an industrial VK tube reactor using the process model developed earlier for the monoacid stabilized system. Both the mathematical modeling and experimental results showed that the presence of diacid stabilizer could significantly enhance the overall kinetics of the reaction compared to the monoacid stabilized system and in turn, resulted in reduction of the polymerization time by about 20–25%. The study suggests that diacid stabilizers may be used preferably over monoacid stabilizers in synthesis of nylon‐6 to reduce the cost of polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of cathode active materials produced by a wet-type jet mill on lithium cell performance

We prepared slurries by dispersing LiMn₂O₄ and LiCoO₂ into toluene or NaPO₃ aqueous solution. The slurries were then milled with a high-pressure wet-type jet mill to form fine particles. In estimating the performance of Li cells containing the materials, we found that the cell capacity improved with a decrease in the materials’ particle size. Maximum cell capacity was obtained using materials produced by milling NaPO₃ slurry to reduce the particle diameter to 2-3 μm. Such the maximum value was disappeared by treating the materials with toluene. The treatment, however, did not provide remarkable increase in the cell capacity. We found that the cell cycle life tended to increase with a decrease in the mean diameter of the material particles.     

Position sensorless control for ultrasonic motors based on input voltage information

This paper presents a method of position sensorless control of ultrasonic motors (USM). The position sensorless control method is useful for reducing the cost and size of drive system. The position estimation method is based on the input voltage information of the ultrasonic motor. The characteristic of input voltage versus rotor position is expressed by a quadratic function which is used to estimate a rotor position based on input voltage information. This estimation method, which uses only the drive voltage of the ultrasonic motor, is a very simple algorithm and shows good estimation ability. The parameters of the quadratic function are adjusted by using the recursive least squares method and are obtained on‐line. Since it can correspond to parameter change, the estimated rotor position shows good agreement with the measured rotor position against load torque and motor temperature changes. Sensorless position control is achieved by using the estimated rotor position instead of the measured rotor position. The validity of the proposed method is confirmed by experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 57–64, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20626     

A novel calculation method for iron loss resistance suitable in modeling permanent-magnet synchronous motors

This paper proposes a calculation method for iron loss resistance, suitable for modeling permanent-magnet synchronous motors. The proposed method is based on the linear feature between semi-input power and square of speed electromotive force. The iron loss resistance is calculated from the slope of this linear function in the offline manner. The advantage of the proposed method is that the iron loss resistance can be calculated directly without any measurements related to mechanical loss. In addition, the proposed method can be executed at any load conditions. The validity of the proposed method is experimentally confirmed by the comparison between the actual torque and the calculated torque containing the iron loss resistance.     

Torsional torque suppression of decentralized generators using H∞ observer

The output power fluctuations of renewable energy plants such as wind turbine generators and photovoltaic systems cause frequency deviations and terminal voltage fluctuations. Furthermore, these power fluctuations also affect the turbine shaft of diesel generator and gas-turbine generators which are usually the main electric power systems in isolated islands. This paper presents a control strategy that achieves torsional torque suppression and power system stabilization. Since the measurement of the torsional torque is technically difficult and there is uncertainty in mechanical constants of the shaft torsional system, the torsional torque is estimated by using a H_∞ observer. The simulation results validate the effectiveness of the proposed control system.     

Torsional torque suppression of generator based on H∞ control theory in isolated power system

Renewable energy power plants, such as wind turbine generator and photovoltaic system, have been introduced in isolated power system recently. The output power fluctuations of wind turbine generator and load deviations result in frequency deviation and terminal voltage fluctuation. Furthermore, these power fluctuations also affect the turbine shafting of diesel generators and gas‐turbine generators, which are the main components of power generation systems in isolated islands. For stable operation of gas‐turbine generator, the torsional torque suppression as well as power system stabilization should be considered. In this paper, the control strategy that achieves torsional torque suppression and power system stabilization is presented based on H_∞ control theory. The effectiveness of the proposed control system is validated by numerical simulation results. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimal operation of DC smart house system by controllable loads based on smart grid topology

From the perspective of global warming mitigation and depletion of energy resources, renewable energy such as wind generation (WG) and photovoltaic generation (PV) are getting attention in distribution systems. Additionally, all-electric apartment houses or residence such as DC smart houses are increasing. However, due to the fluctuating power from renewable energy sources and loads, supply-demand balancing of power system becomes problematic. Smart grid is a solution to this problem. This paper presents a methodology for optimal operation of a smart grid to minimize the interconnection point power flow fluctuation. To achieve the proposed optimal operation, we use distributed controllable loads such as battery and heat pump. By minimizing the interconnection point power flow fluctuation, it is possible to reduce the electric power consumption and the cost of electricity. This system consists of photovoltaic generator, heat pump, battery, solar collector, and load. To verify the effectiveness of the proposed system, results are used in simulation presented.     

Balancing control method by dispersed generators based on H∞ control theory in DC power feeding system

Recently, dispersed generators have been installed in distribution network to supply power to commercial facilities. Renewable energy generation contains output power fluctuations and distributed generator produces sluggish response for power demand. In order to overcome these problems, an ultra capacitor energy storage system is used for compensating the instantaneous power imbalance. However, use of a large capacity ultra capacitor energy system increases system cost. In addition, PPSs (Power Producer and Supplier) that own these generators are supposed to achieve 30-min balancing control for stable supply of electric power. This paper proposes a control system to achieve both 30-min balancing control and interconnection point power flow control by using a fuel cell and an ultra capacitor based on the H_∞ control theory. Besides, remaining storage energy of the ultra capacitor is controlled to be constant to maintain compensation capability. Effectiveness of the proposed control system is verified by using simulation results.     

Erratum to “Steady-state analysis of PV supplied separately excited DC motor fed from IDB converter” [Sol. Energy Mater. Sol. Cells 71 (4) (2002) 493–510]

Interleaved dual boost converter is capable of extracting more amount of power from the photovoltaic source than the conventional boost converter. Power extraction capabilities of the conventional boost and interleaved dual boost converters from the photovoltaic array are verified through experimental studies. As an application the effectiveness of this interleaved dual boost converter for PV supplied separately excited DC motor is studied through simulation. Extensive studies are made by formulating the mathematical models for photovoltaic source, interleaved dual boost converter, DC motor and load. Steady-state performance of the motor coupled to centrifugal pump load is analyzed for maximum power, gross mechanical energy operations. From the simulation studies, it is found that the motor performance is improved with gross mechanical energy output operation as compared to maximum power operation of solar cell array. Furthermore, the use of interleaved dual boost converter reduces the ripple content both in the source and load waveforms, thus resulting in reduced filtering requirements and improved photovoltaic array performance.