The Effect of Recombinant Bovine Somatotropin on Patterns of Milk Production, Lactational Milk Estimates and Net Farm Income

Bovine somatoropin (bST) alters total milk production and production patterns in dairy cows and understanding the economic benefits of bST for the dairy producer are critical. Holstein cows (n = 555) from four Michigan dairy farms were randomly assigned as untreated controls or to receive 500 mg of bovine somatotropin (PosilacR) administered every 14 days beginning at 63 to 69 days of lactation and continuing until approximately 21 days prior to the end of lactation or until the animal was removed from the herd. Average peak milk production was 50.8 kg / day and occurred at an average of 113 9 days of lactation for bST-treated cows while average peak production was 48.9 kg / day occurring at an average of 86.4 days of lactation for control cows; both parameters were significantly greater for bST-treated cows compared to controls. Study cows treated with bST were significantly more persistent in lactation (7% greater lactational persistency) compared to control cows. All DHIA estimates and actual milk produced were not significantly different between the study treatment groups for any of the four comparisons made (first, second, third monthly tests after bST treatment initiation and final (305-day) DHIA production estimates); however, the accuracy of DHIA production estimates was significantly affect by the amount of time elapsed since bST but became non-significant by the third DHIA test date. The use of bST changed NFI for each of the four study farms by $96.21,$3.57, $78.71 and ($7.15) per bST-treated cow, respectively during the trial period (from 63 to 305 days of lactation). The overall average change in NFI attributable to bST was $43.01 per bST-treated cow. 2 Profitability of bST use was observed to be quite variable between farms studied because many factors were found to affect the change in NFI per cow resulting from bST use; the level of production response and the price received for milk had the largest effects on the change in NFI associated with bST use; by contrast, price paid for bST itself and feed had only minimal effects on bST-associated profitability. Diseases that may be associated with bST may reduce the profitability of this product and need to be considered as a cost of bST use if present.bovine somatotropin, dairy, net farm income, Farm Management, Livestock Production/Industries, Productivity Analysis, Research and Development/Tech Change/Emerging,

Modeling of MMCs With Controlled DC-Side Fault Blocking Capability for DC Protection Studies

The fault current characteristics in dc systems depend largely on the response, and hence also the topology, of the ac-dc converters. The presently used ac-dc converter topologies may be categorized into those with controlled or uncontrolled fault blocking capability and those lacking such capability. For the topologies of the former category, generic models of the dc-side fault response have not yet been developed and a characterization of the influence of control and sensor delays is a notable omission. Therefore, to support accurate and comprehensive dc system protection studies, this paper presents three reduced converter models and analyzes the impact of key parameters on the dc-side fault response. The models retain accurate representation of the dc-side current control, but differ in representation of the ac-side and internal current control dynamics, and arm voltage limits. The models were verified against a detailed (full-switched) simulation model for the cases of a full-bridge and a hybrid modular multilevel converter, and validated against experimental data from a lab-scale prototype. The models behave similarly in the absence of arm voltage limits, but only the most detailed of the three retains a high degree of accuracy when these limits are reached

Thyristor-Bypassed Sub-Module Power-Groups for Achieving High-Efficiency, DC Fault Tolerant Multilevel VSCs

Achieving DC fault tolerance in modular multilevel converters requires the use of a significant number of Sub-Modules (SMs) which are capable of generating a negative voltage. This results in an increase in the number of semiconductor devices in the current path, increasing converter conduction losses. This paper introduces a thyristor augmented multilevel structure called a Power-Group (PG), which replaces the stacks of SMs in modular converters. Each PG is formed out of a series stack of SMs with a parallel force-commutated thyristor branch, which is used during normal operation as a low loss bypass path in order to achieve significant reduction in overall losses. The PG also offers negative voltage capability and so can be used to construct high efficiency DC fault tolerant converters. Methods of achieving the turn-on and turn-off of the thyristors by using voltages generated by the parallel stack of SMs within each PG are presented, while keeping both the required size of the commutation inductor, and the thyristor turn-off losses low. Efficiency estimates indicate that this concept could result in converter topologies with power-losses as low as 0.3% rated power, whilst retaining high quality current waveforms and achieving tolerance to both AC and DC faults

Reliability Analysis of MMCs Considering Submodule Designs with Individual or Series-Operated IGBTs

The half-bridge-based modular multilevel converter (MMC) has emerged as the favored converter topology for voltage-source HVDC applications. The submodules within the converter can be constructed with either individual insulated-gate bipolar transistor (IGBT) modules or with series-connected IGBTs, which allows for different redundancy strategies to be employed. The main contribution of this paper is that an analytical method was proposed to analyze the reliability of MMCs with the consideration of submodule arrangements and redundancy strategies. Based on the analytical method, the relative merits of two approaches to adding redundancy, and variants created by varying the submodule voltage, are assessed in terms of overall converter reliability. Case studies were conducted to compare the reliability characteristics of converters constructed using the two submodule topologies. It is found that reliability of the MMC with series-connected IGBTs is higher for the first few years but then decreases rapidly. By assigning a reduced nominal voltage to the series valve submodule upon IGBT module failure, the need to install redundant submodules is greatly reduced

Dimensioning and Modulation Index Selection for the Hybrid Modular Multilevel Converter

The Hybrid MMC, comprising a mixture of fullbridge and half-bridge sub-modules, provides tolerance to DC faults without compromising the efficiency of the converter to a large extent. The inclusion of full-bridges creates a new freedom over the choice of ratio of AC to DC voltage at which the converter is operated, with resulting impact on the converter’s internal voltage, current and energy deviation waveforms, all of which impact the design of the converter. A design method accounting for this, and allowing the required level of derating of nominal sub-module voltage and up-rating of stack voltage capability to ensure correct operation at the extremes of the operating envelope is presented. A mechanism is identified for balancing the peak voltage that the full-bridge and halfbridge sub-modules experience over a cycle. Comparisons are made between converters designed to block DC side faults and converters that also add STATCOM capability. Results indicate that operating at a modulation index of 1.2 gives a good compromise between reduced power losses and additional required sub-modules and semiconductor devices in the converter. The design method is verified against simulation results and the operation of the converter at the proposed modulation index is demonstrated at laboratory-scale

Power-System Level Classification of Voltage-Source HVDC Converter Stations Based Upon DC Fault Handling Capabilities

status: publishe

Minimum-Uncertainty Angular Wave Packets and Quantized Mean Values

Uncertainty relations between a bounded coordinate operator and a conjugate momentum operator frequently appear in quantum mechanics. We prove that physically reasonable minimum-uncertainty solutions to such relations have quantized expectation values of the conjugate momentum. This implies, for example, that the mean angular momentum is quantized for any minimum-uncertainty state obtained from any uncertainty relation involving the angular-momentum operator and a conjugate coordinate. Experiments specifically seeking to create minimum-uncertainty states localized in angular coordinates therefore must produce packets with integer angular momentum.Comment: accepted for publication in Physical Review

The Extended Overlap Alternate Arm Converter:A Voltage Source Converter with DC Fault Ride-Through Capability and a Compact Design

The Alternate Arm Converter (AAC) was one of the first modular converter topologies to feature DC-side fault ride-through capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with an additional short overlap period) resulted in (i) substantial 6-pulse ripples in the DC current waveform, (ii) large DC-side filter requirements, and (iii) limited operating area close to an energy sweet-spot. This paper presents a new mode of operation called Extended Overlap (EO) based on the extension of the overlap period to 60 ◦ which facilitates a fundamental redefinition of the working principles of the AAC. The EO-AAC has its DC current path decoupled from the AC current paths, a fact allowing (i) smooth DC current waveforms, (ii) elimination of DC filters, and (iii) restriction lifting on the feasible operating point. Analysis of this new mode and EO- AAC design criteria are presented and subsequently verified with tests on an experimental prototype. Finally, a comparison with other modular converters demonstrates that the EO-AAC is at least as power efficient as a hybrid MMC (i.e. a DC fault ride-through capable MMC) while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume