A full compensating system for general loads, based on a combination of thyristor binary compensator, and a PWM-IGBT active power filter

A full compensating system for distribution networks, able to eliminate harmonics, correct unbalanced loads, and generate or absorb reactive power, is presented. The system is based on a combination of a thyristor binary compensator (TBC), and a pulsewidth-modulation insulated gate bipolar transistor active power filter (APF) connected in cascade. The TBC compensates the fundamental reactive power and balances the load connected to the system. The APF eliminates the harmonics and compensates the small amounts of load unbalances or power factor that the TBC cannot eliminate due to its binary condition. The TBC is based on a chain of binary-scaled capacitors and one inductor per phase. This topology allows, with an adequate number of capacitors, a soft variation of reactive power compensation and a negligible generation of harmonics. The capacitors are switched on when the line voltage reaches its peak value, avoiding inrush currents generation. The inductor helps to balance the load, and absorbs reactive power when required. The APF works measuring the source currents, forcing them to be sinusoidal. The two converters (TBC and APF) work independently, making the control of the system simpler and more reliable. Simulations show that the system is able to respond to many kinds of transient perturbations in no more than a couple of cycles. The paper analyzes the circuit proposed, the way it works and shows some experimental results obtained under operation.     

Using compositional mixed-effects models to evaluate responses to amino acid supplementation in milk replacers for calves

The consequences of supplementing Lys, Met, and Thr in milk replacers (MR) for calves have been widely studied, but scarce information exists about potential roles of other AA (whether essential or not). The effects on growth performance of supplementation of 4 different AA combinations in a mixed ration (25.4% crude protein and 20.3% fat) based on skim milk powder and whey protein concentrate were evaluated in 76 Holstein male calves (3 ± 1.7 d old). The 4 MR were as follows: CTRL with no AA supplementation; PG, supplying additional 0.3% Pro and 0.1% Gly; FY, supplying additional 0.2% Phe and 0.2% Tyr; and KMT, providing additional 0.62% Lys, 0.22% Met, and 0.61% Thr. All calves were fed the same milk allowance program and were weaned at 56 d of study. Concentrate intake was limited to minimize interference of potential differences in solid feed intake among treatments. Animals were weighed weekly, intakes recorded daily, and blood samples obtained at 2, 5, and 7 wk of study to determine serum urea and plasma AA concentrations. Plasma AA concentrations were explored using compositional data analysis, and their isometric log-ratio transformations were used to analyze their potential influence on ADG and serum urea concentration using a linear mixed-effects model. We detected no differences in calf performance and feed intake. Plasma relative concentration of the AA supplemented in the KMT and PG treatments increased in their respective treatments, and, in PG calves, a slight increase in the proportion of plasma Gly, Glu, and branched-chain AA was also observed. The proportions of plasma branched-chain AA, His, and Gln increased, and those of Thr, Arg, Lys, and Glu decreased with calves' age. A specific log-contrast balance formed by Arg, Thr, and Lys was found to be the main driver for lowering serum urea concentrations and increasing calf growth. The use of compositional mixed-effects models identified a cluster formed by the combination of Arg, Thr, and Lys, as a potential AA to optimize calf growth.     

Stated Preferences in Modelling Accessibility

The stated preference (SP) experimental design problem in measuring and representing the role of accessibility in modelling urban residential location is considered. The preferences of households between certain accessibility attributes and the monthly rent of the house, ceteris paribus with respect to the rest of the location attributes, is analysed in order to isolate the effects of interest. A review of the conceptual definition of accessibility, its relationship with the transportation system, its functionality and the different measures used up until now, allowed generation of an SP data collection instrument. This was employed to subject a sample of households to the location decision based on several transport system variables. The experiment made several novel contributions. First, the whole household was considered as the choice-making entity, with decisions shared by all its members. Second, the alternatives considered different accessibility levels without modifying the household's current location. Using the data gathered, models were estimated with consistent parameters in terms of their signs and significance tests, and some functional forms associated with the perception of the access concept were defined. Furthermore, a valuation of time index was generated and this allowed a new discussion to be opened regarding its relation to the subjective value of time traditionally derived from mode-choice models.     

Japan's integrated residential policy

Japan has experienced rapid and continuous industrial and economic development which few will term as less than spectacular. However, this development has left behind a sequel of urban and regional problems, particularly environmental ones, which can no longer be ignored. As the country moves rapidly into the next phase of development it intends, through an ‘integrated residential policy’, to bring about an improved population distribution, a rise in the standard of living, and an improvement in its environment. This article discusses some of the issues and efforts involved in such a programme, as well as some of the outcomes and initial results to date.     

Electric Vehicle Using a Combination of Ultracapacitors and ZEBRA Battery

The sodium–nickel chloride battery, commonly known as ZEBRA, has been used for an experimental electric vehicle (EV). These batteries are cheaper than Li-ion cells and have a comparable specific energy (in watt–hours per kilogram), but one important limitation is their poor specific power (in watts per kilogram). The main objective of this paper is to demonstrate experimentally that the combination of ZEBRA batteries and ultracapacitors (UCAPs) can solve the lack of specific power, allowing an excellent performance in both acceleration and regenerative braking in an EV. The UCAP system was connected to the ZEBRA battery and to the traction inverter through a buck–boost-type dc–dc converter, which manages the energy flow with the help of DSP controllers. The vehicle uses a brushless dc motor with a nominal power of 32 kW and a peak power of 53 kW. The control system measures and stores the following parameters: battery voltage, car speed to adjust the energy stored in the UCAPs, instantaneous currents in both terminals (battery and UCAPs), and present voltage of the UCAP. The increase in range with UCAPs results in more than 16% in city tests, where the application of this type of vehicle is being oriented. The results also show that this alternative is cheaper than Li-ion powered electric cars.      

Santiago's metro

The Santiago metro system, which carried its first passengers in 1975, has proved an expensive and only partly successful method of responding to the city's public transport needs. Not only has expenditure on the metro far exceeded original estimates, but the diversion of a substantial proportion of the national budget to a transport system only servicing residents of Santiago has led to a regional imbalance between Santiago and Chile's other urban areas.     

Voltage-source active power filter based on multilevel converter and ultracapacitor DC link

A new topology for active power filters (APF) using an 81-level converter is analyzed. Each phase of the converter is composed of four three-state converters, all of them connected to the same capacitor dc link voltage and their output connected in series through output transformers. The main advantages of this kind of converter are the negligible harmonic distortion obtained and the very low switching frequency operation. The single-phase equivalent circuit is analyzed and their governing equations derived. The dc link voltage control, based on manipulating the converter's voltage phase, is analyzed together with the circuit's characteristics that determine the capability to draw or deliver active and reactive current. Simulation results for this application are compared with conventional pulsewidth-modulated (PWM) converters, showing that this filter can compensate load current harmonics, keeping better-quality sinusoidal currents from the source. The simulated configuration uses a 1-F ultracapacitor in the dc link, making it possible to store energy and deliver it during short voltage dips. This is achieved by applying a modulation control to maintain a stable ac voltage during dc voltage drops. A prototype of the filter was implemented and tested, and the obtained current waveforms showed to be as good as expected.