Modular input-parallel-output-series DC/DC converter control with fault detection and redundancy

Large offshore wind farms will require an extensive sub-sea power network to provide internal interconnection. Present solutions are based around conventional medium-voltage AC architectures. This paper proposes an alternative DC collection network based around modular DC/DC converters with input-parallel-output-series (IPOS) connection. Small-signal analysis of the converter is presented, to assist in control scheme development for the converter input and output stages. A Lyapunov controller is embedded within the conventional output voltage sharing control loop. A master-slave control scheme is proposed to ensure power sharing under a range of operating conditions, and provides fault-tolerant operation since the status of 'master' can be reallocated in the event that the present 'master' module fails

Suppression of allergic airway inflammation by helminth-induced regulatory T cells

Allergic diseases mediated by T helper type (Th) 2 cell immune responses are rising dramatically in most developed countries. Exaggerated Th2 cell reactivity could result, for example, from diminished exposure to Th1 cell–inducing microbial infections. Epidemiological studies, however, indicate that Th2 cell–stimulating helminth parasites may also counteract allergies, possibly by generating regulatory T cells which suppress both Th1 and Th2 arms of immunity. We therefore tested the ability of the Th2 cell–inducing gastrointestinal nematode Heligmosomoides polygyrus to influence experimentally induced airway allergy to ovalbumin and the house dust mite allergen Der p 1. Inflammatory cell infiltrates in the lung were suppressed in infected mice compared with uninfected controls. Suppression was reversed in mice treated with antibodies to CD25. Most notably, suppression was transferable with mesenteric lymph node cells (MLNC) from infected animals to uninfected sensitized mice, demonstrating that the effector phase was targeted. MLNC from infected animals contained elevated numbers of CD4(+)CD25(+)Foxp3(+) T cells, higher TGF-β expression, and produced strong interleukin (IL)-10 responses to parasite antigen. However, MLNC from IL-10–deficient animals transferred suppression to sensitized hosts, indicating that IL-10 is not the primary modulator of the allergic response. Suppression was associated with CD4(+) T cells from MLNC, with the CD4(+)CD25(+) marker defining the most active population. These data support the contention that helminth infections elicit a regulatory T cell population able to down-regulate allergen induced lung pathology in vivo

Fault blocking converters for HVDC transmission : a transient behaviour comparison

A thorough comparison of the transient behaviours of two state-of-the-art converters suitable for HVDC transmission is presented. The Alternate Arm and Mixed-Cell Modular Multilevel Converter topologies both have DC fault blocking capability and are selected for the comparison. Converter performance is evaluated and compared under various transient conditions including charging sequence, unbalanced operation, and DC fault recovery. The study is conducted using high-fidelity converter simulation models, integrating detailed controllers that reflect real-scale projects. The main findings of the study assist in the selection of the most suitable converter, given specific performance specifications such as capacitor voltage ripple, cell capacitor requirements, and response during transient operation

State Policy Response to the Taxpayer Relief Act of 1997

The Taxpayer Relief Act of 1997 (TRA 1997) is the largest single increase in federal funding for higher education since the GI Bill. This chapter explores the impact of this new federal law on state higher education policy and offers options and recommendations for state response. These recommendations are based on the belief that programs which support both access and affordability are necessary to advance the larger national policy of college opportunity, but that affordability should not be allowed to supersede access as a policy goal

The Sensitivity of Auditory-Motor Representations to Subtle Changes in Auditory Feedback While Singing

Singing requires accurate control of the fundamental frequency (F0) of the voice. This study examined trained singers’ and untrained singers’ (nonsingers’) sensitivity to subtle manipulations in auditory feedback and the subsequent effect on the mapping between F0 feedback and vocal control. Participants produced the consonant-vowel /ta/ while receiving auditory feedback that was shifted up and down in frequency. Results showed that singers and nonsingers compensated to a similar degree when presented with frequency-altered feedback (FAF); however, singers’ F0 values were consistently closer to the intended pitch target. Moreover, singers initiated their compensatory responses when auditory feedback was shifted up or down 6 cents or more, compared to nonsingers who began compensating when feedback was shifted up 26 cents and down 22 cents. Additionally, examination of the first 50 ms of vocalization indicated that participants commenced subsequent vocal utterances, during FAF, near the F0 value on previous shift trials. Interestingly, nonsingers commenced F0 productions below the pitch target and increased their F0 until they matched the note. Thus, singers and nonsingers rely on an internal model to regulate voice F0, but singers’ models appear to be more sensitive in response to subtle discrepancies in auditory feedback

Modular input-parallel output-series DC/DC converter control with fault detection and redundancy

Large offshore wind farms require extensi ve sub-sea cables within the collection network. Present solutions are based aro und medium-voltage AC collection networks. Recent studies have highlighted the poten tial benefits of DC collection networks. However, achieving DC/DC conversion at th e required voltage and power levels presents a significant challenge for wind-tu rbine power electronics. This paper proposes an alternative DC collection network based around a modular DC/DC converter with input-parallel output-series (IPOS) connection. This modular topology can overcome the limitations imposed by semiconduct or voltage ratings and provides fault-tolerant operation. Small-signal analysis of the converter is presented to be used to facilitate controller design for the converter inpu t and output stages. A new master- slave control scheme and distributed voltage sharin g controllers are proposed that ensure power sharing under all operating conditions , including during failure of a master module. This control scheme achieves fault-t olerant operation by allowing the status of master module to be reallocated to any he althy module. The proposed control scheme is validated using simulation and experiment ation, considering active power sharing between modules with parameter mismatch