Optimized switching control strategy for current-fed half-bridge converter

A switching control strategy is proposed for current-fed half-bridge converters. An active switch based voltage doubler circuit at the secondary side of the isolation transformer is used to obtain zero-current-switching at turn-off and zero-voltage-switching at turn-on in the primary side switches of the current-fed half-bridge converter. The operation of the current-fed half-bridge converter with the proposed switching control strategy is explained using the equivalent circuit during each sub-interval of operation. The operation of the current-fed halfbridge converter is simulated using MATLAB/Simpower and PSIM to verify the feasibility of the switching control strategy. Experimental results are provided to validate the converter's operation.

Design of mode switching scheme for low-voltage ride-through of doubly fed induction generators

A mode switching doubly fed induction generator (MSDFIG) scheme is proposed for the purpose of achieving low-voltage ride-through for wind turbines. The MSDFIG operates as a doubly fed induction generator (DFIG) under normal condition but upon the detection of a low-voltage incident, the generator is to smoothly transfer to operate under the induction generator mode through the switching in of a set of stator-side crowbar. The MSDFIG automatically reverts back to the DFIG mode when network voltage recovers. A new strategy on the control of the crowbar resistance is included. Analysis shows that the proposed MSDFIG scheme can ride through the complete low-voltage and voltage recovery stages. Effectiveness of the scheme is demonstrated through simulation and experiment studies.

Doubly Fed Induction Generators : Overview and Intelligent Control Strategies for Wind Energy Conversion Systems

Adjustable speed induction generators, especially the Doubly-Fed Induction Generators (DFIG) are becoming increasingly popular due to its various advantages over fixed speed generator systems. A DFIG in a wind turbine has ability to generate maximum power with varying rotational speed, ability to control active and reactive by integration of electronic power converters such as the back-to-back converter, low rotor power rating resulting in low cost converter components, etc, DFIG have become very popular in large wind power conversion systems. This chapter presents an extensive literature survey over the past 25 years on the different aspects of DFIG. Application of H8 Controller for enhanced DFIG-WT performance in terms of robust stability and reference tracking to reduce mechanical stress and vibrations is also demonstrated in the chapter.

Soft-switching single inductor current-fed push-pull converter for PV applications

A switching control strategy is proposed for single inductor current-fed push-pull converter with a secondary side active voltage doubler rectifier or a voltage rectifier used in photovoltaic (PV) grid interfacing. The proposed switching control strategy helps to turn-on and turn-off the primary side power switches with zero-voltage and zero-current switching. The operation of the push-pull converter is analyzed for two modes of operation. The feasibility of the proposed switching control strategy is validated using simulation and experimental results.

HFL PV micro-inverter with front-end current-fed converter and half-wave cycloconverter

A high-frequency-link micro inverter is proposed with a front-end dual inductor push-pull converter and a grid-connected half-wave cycloconverter. Pulse width modulation is used to control the front-end converter and phase shift modulation is used at the back-end converter to obtain grid synchronized output current. A series resonant circuit and high-frequency transformer are used to interface the front-end and the back-end converters. The operation of the proposed micro-inverter in grid-connected mode is validated using MATLAB/Simpower simulation. Experimental results are provided to further validate the operation.

Comparison of stool microbiota compositions, stool alpha1-antitrypsin and calprotectin concentrations, and diarrhoeal morbidity of Indonesian infants fed breast milk or probiotic/prebiotic-supplemented formula

Aim The composition of faecal microbiota of babies is known to be influenced by diet. Faecal calprotectin and α1-antitrypsin concentrations may be associated with mucosal permeability and inflammation. We aimed to assess whether there was any difference after consumption of a probiotic/prebiotic formula on faecal microbiota composition, calprotectin and α1-antitrypsin levels, and diarrhoea in comparison with breast milk-fed Indonesian infants. Methods One hundred sixty infants, 2 to 6 weeks old, were recruited to the study. They were either breastfed or formula fed (80 per group). Faecal samples were collected at recruitment and 3 months later. Bacterial groups characteristic of the human faecal microbiota were quantified in faeces by quantitative polymerase chain reaction. Calprotectin and α1-antitrypsin concentrations were measured using commercial kits. Details of diarrhoeal morbidity were documented and rated for severity. Results The compositions of the faecal microbiota of formula-fed compared with breast milk-fed children were similar except that the probiotic strain Bifidobacterium animalis subsp. lactisâ€...DR10 was more abundant after 3 months consumption of the formula. Alpha1-antitrypsin levels were higher in breastfed compared with formula-fed infants. The occurrence of diarrhoea did not differ between the groups of babies. Conclusion Feeding Indonesian babies with a probiotic/prebiotic formula did not produce marked differences in the composition of the faecal microbiota in comparison with breast milk. Detrimental effects of formula feeding on biomarkers of mucosal health were not observed.

Micro inverter with a front-end current-fed converter

The reliability of micro inverters is an important factor as it would be necessary to reduce cost and maintenance of the small and medium scale distributed PV power conversion systems. Electrolytic capacitors and active power decouple circuits can be avoided in micro inverters with the use of medium voltage DC-link. Such a DC-link based micro inverter is proposed with a front-end dual inductor current-fed push-pull converter. The primary side power switches of the front-end converter have reduced switching losses due to multi-resonant operation. In addition, the voltage and current stresses on the diodes of the secondary diode voltage doubler rectifier are reduced due to the presence of a series resonant circuit in the front-end converter. The operation of the proposed micro inverter is explained using an in-depth analysis of the switching characteristics of the power semiconductor devices. The theoretical analysis of the proposed micro inverter is validated using simulation result.

Load-Commutated SCR Current-Source-Inverter-Fed Induction Motor Drive With Sinusoidal Motor Voltage and Current

Current source inverter (CSI) is an attractive solution in high-power drives. The conventional gate turn-off thyristor (GTO) based CSI-fed induction motor drives suffer from drawbacks such as low-frequency torque pulsation, harmonic heating, and unstable operation at low-speed ranges. These drawbacks can be overcome by connecting a current-controlled voltage source inverter (VSI) across the motor terminal replacing the bulky ac capacitors. The VSI provides the harmonic currents, which results in sinusoidal motor voltage and current even with the CSI switching at fundamental frequency. This paper proposes a CSI-fed induction motor drive scheme where GTOs are replaced by thyristors in the CSI without any external circuit to assist the turning off of the thyristors. Here, the current-controlled VSI, connected in shunt, is designed to supply the volt ampere reactive requirement of the induction motor, and the CSI is made to operate in leading power factor mode such that the thyristors in the CSI are autosequentially turned off. The resulting drive will be able to feed medium-voltage, high-power induction motors directly. A sensorless vector-controlled CSI drive based on the proposed configuration is developed. The experimental results from a 5 hp prototype are presented. Experimental results show that the proposed drive has stable operation throughout the operating range of speeds.

A Current Source Inverter Fed Induction Motor Drive with Power Factor Angle Control Using Microprocessor

This paper describes a method of adjusting the stator power factor angle for the control of an induction motor fed from a current source inverter (CSI) based on the concept of space vectors (or park vectors). It is shown that under steady state, if the torque angle is kept constant over the entire operating range, it has the advantage of keeping the slip frequency constant. This can be utilized to dispose of the speed feedback and simplify the control scheme for the drive, such that the stator voltage integral zero crossings alone can be used as a feedback for deciding the triggering instants of the CSI thyristors under stable operation of the system. A closed-loop control strategy is developed for the drive based on this principle, using a microprocessor-based control system and is implemented on a laboratory prototype CSI fed induction motor drive.

Using Alkanes to Predict Voluntary Intake, Faecal Output and Digestibility of Buffel Grass Hay Fed to Steers

The cuticular waxes of forage plants contain long chain n-alkanes with odd carbon chain lengths in the range C25-C37 which are quantitatively recovered in faeces. When these concentrations are used with the concentrations of administered synthetic even chain length alkanes, the voluntary intake (VI), faecal output (FO) and digestibility (DMD) of forages can be estimated (Dove and Mayes 1991, 1996).

A DC-link Capacitor Voltage Balancing with CMV Elimination using only the Switching State Redundancies for a Reduced Switch Count Multi-Level Inverter fed IM Drive

Common mode voltage (CMV) variations in PWM inverter-fed drives generate unwanted shaft and bearing current resulting in early motor failure. Multilevel inverters reduce this problem to some extent, with higher number of levels. But the complexity of the power circuit increases with an increase in the number of inverter voltage levels. In this paper a five-level inverter structure is proposed for open-end winding induction motor (IM) drives, by cascading only two conventional two-level and three-level inverters, with the elimination of the common mode voltage over the entire modulation range. The DC link power supply requirement is also optimized by means of DC link capacitor voltage balancing, with PWM control., using only inverter switching state redundancies. The proposed power circuit gives a simple power bits structure.

Ruminococcus bromii, identification and isolation as a dominant community member in the rumen of cattle fed a barley diet

Aims: To identify dominant bacteria in grain (barley)-fed cattle for isolation and future use to increase the efficiency of starch utilization in these cattle. Methods and Results: Total DNA was extracted from samples of the rumen contents from eight steers fed a barley diet for 9 and 14 days. Bacterial profiles were obtained using denaturing gradient gel electrophoresis (DGGE) of the PCR-amplified V2/V3 region of the 16S rRNA genes from total bacterial DNA. Apparently dominant bands were excised and cloned, and the clone insert sequence was determined. One of the most common and dominant bacteria present was identified as Ruminococcus bromii. This species was subsequently isolated using traditional culture-based techniques and its dominance in the grain-fed cattle was confirmed using a real-time Taq nuclease assay (TNA) designed for this purpose. In some animals, the population of R. bromii reached densities above 1010R. bromii cell equivalents per ml or approximately 10% of the total bacterial population. Conclusions: Ruminococcus bromii is a dominant bacterial population in the rumen of cattle fed a barley-based diet. Significance and Impact of the Study: Ruminococcus bromii YE282 may be useful as a probiotic inoculant to increase the efficiency of starch utilization in barley-fed cattle. The combination of DGGE and real-time TNA has been an effective process for identifying and targeting for isolation, dominant bacteria in a complex ecosystem.

Growth and carcass characteristics of cast-for-age Merino ewes fed sorghum-based feedlot diets

Grain feeding low bodyweight, cast-for-age (CFA) sheep from pastoral areas of eastern Australia at the end of the growing season can enable critical carcass weight grades to be achieved and thus yield better economic returns. The aim of this work was to compare growth and carcass characteristics for CFA Merino ewes consuming either simple diets based on whole sorghum grain or commercial feed pellets. The experiment also compared various sources of additional nitrogen (N) for inclusion in sorghum diets and evaluated several introductory regimes. Seventeen ewes were killed initially to provide baseline carcass data and the remaining 301 ewes were gradually introduced to the concentrate diets over 14 days before being fed concentrates and wheaten hay ad libitum for 33 or 68 days. Concentrate treatments were: (i) commercial feed pellets, (ii) sorghum mix (SM; whole sorghum grain, limestone, salt and molasses) + urea and ammonium sulfate (SMU), (iii) SMU + whole cottonseed at 286 g/kg of concentrate dry matter (DM), (iv) SM + cottonseed meal at 139 g/kg of concentrate DM, (v) SMU + virginiamycin (20 mg/kg of concentrate) for the first 21 days of feeding, and (vi) whole cottonseed gradually replaced by SMU over the first 14 days of feeding. The target carcass weight of 18 kg was achieved after only 33 days on feed for the pellets and the SM + cottonseed meal diet. All other whole grain sorghum diets required between 33 and 68 days on feed to achieve the target carcass weight. Concentrates based on whole sorghum grain generally produced significantly (P < 0.05) lower carcass weight and fat score than pellets and this may have been linked to the significantly (P < 0.05) higher faecal starch concentrations for ewes consuming sorghum-based diets (270 v. 72 g/kg DM on day 51 of feeding for sorghum-based diets and pellets, respectively). Source of N in whole grain sorghum rations and special introductory regimes had no significant (P > 0.05) effects on carcass weight or fat score of ewes with the exception of carcass weight for SMU + whole cottonseed being significantly lower than SM + cottonseed meal at day 33. Ewes finished on all diets produced acceptable carcasses although muscle pH was high in all ewe carcasses (average 5.8 and 5.7 at 33 and 68 days, respectively). There were no significant (P > 0.05) differences between diets in concentrate DM intake, rumen fluid pH, meat colour score, fat colour score, eye muscle area, meat pH or meat temperature.

Residue Potential of Norsesquiterpene Glycosides in Tissues of Cattle Fed Austral Bracken (Pteridium esculentum).

Austral bracken, Pteridium esculentum, occurs widely in Australian grazing lands and contains both the known carcinogen ptaquiloside and its hydroxy analogue, ptesculentoside, with untested carcinogenic potential. Calves were fed a diet containing 19% P. esculentum that delivered 1.8 mg of ptaquiloside and 4.0 mg of ptesculentoside per kilogram of body weight (bw) per day to explore the carcass residue potential of these compounds. Concentrations of ptaquiloside and ptesculentoside in the liver, kidney, skeletal muscle, heart, and blood of these calves were determined as their respective elimination products, pterosin B and pterosin G, by HPLC-UV analysis. Plasma concentrations of up to 0.97 mu g/mL ptaquiloside and 1.30 mu g/mL ptesculentoside were found, but were shown to deplete to <10% of these values within 24 h of bracken consumption. Both glycosides were also detected in all tissues assayed, with ptesculentoside appearing to be more residual than ptaquiloside. Up to 0.42 and 0.32 mu g/g ptesculentoside was present in skeletal muscle and liver, respectively, 15 days after bracken consumption ended. This detection of residual glycosides in tissues of cattle feeding on Austral bracken raises health concerns for consumers and warrants further investigation.