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Arctic marine mammals live in a rapidly changing environment due to the amplified effects of global warming. Pacific walruses (Odobenus rosmarus divergens) have responded to declines in Arctic sea‐ice extent by increasingly hauling out on land farther from their benthic foraging habitat. Energy models can be useful for better understanding the potential implications of changes in behavior on body condition and reproduction but require behavior‐specific metabolic rates. Here we measured the resting metabolic rates (RMR) of three captive, adult female Pacific walruses through breath‐by‐breath respirometry when fed and fasted resting out of water (sitting and lying down) and while fed resting in water. RMR in and out of water were positively related with pretrial energy intake when not fasted and 25% higher than RMR when walruses were fasted and out of water. Overall, RMR was higher than previously estimated for this species. Fasting RMR out of water was only 25% lower than subsurface swimming metabolic rates suggestive of relatively efficient swimming in adult females. Our results identify the importance of considering feeding status and species‐specific differences in affecting metabolic costs. Further research is needed to better understand potential energetic costs of thermoregulation at temperatures experienced by wild walruses. [ABSTRACT FROM AUTHOR]

This paper presents the definition of the virtual vectors for the general case of an n-level two-leg diode-clamped converter, suggests guidelines for designing virtual-vector pulsewidth modulation (PWM) strategies, and provides the mathematical expressions of the leg duty-ratio waveforms corresponding to this family of PWMs. Modulations defined upon these vectors guarantee the dc-link capacitor voltage balance in every switching cycle under any type of load and enable the use of these topologies with passive front ends. The performance of these multilevel converters operated with the proposed PWMs is compared to the performance of alternative designs through analysis, simulation, and experiments. Index Terms--Capacitor voltage balance, diode clamped, multilevel, pulsewidth modulation, virtual vector.

Several pulsewidth modulation (PWM) strategies have been proposed for the three-level three-phase diode-clamped dc-ac converter. Among them, the nearest-three virtual-space-vector PWM guarantees the dc-link capacitor voltage balance under any operating condition, provided that the addition of the three phase currents equals zero. This paper extends this modulation concept to the four level converter. The new virtual vectors are presented and a simple modulation solution is defined. Conventional nearest-three space vector PWM cannot comprehensively achieve balanced and stable dc-link voltages. The proposed modulation solution enables the practical use of the four-level converter since it guarantees the dc-link capacitor voltage balance for any operating condition and load, provided that the addition of the three phase currents equals zero. Simulation and experimental results prove the goodness of the presented approach. Index Terms--Capacitor voltage balance, diode-clamped, multilevel, pulsewidth modulation (PWM), virtual vector.

In photovoltaic (PV) power systems where a set of series-connected PV arrays (PVAs) is connected to a conventional two-level inverter, the occurrence of partial shades and/or the mismatching of PVAs leads to a reduction of the power generated from its potential maximum. To overcome these problems, the connection of the PVAs to a multilevel diode-clamped converter is considered in this paper. A control and pulsewidth-modulation scheme is proposed, capable of independently controlling the operating voltage of each PVA. Compared to a conventional two-level inverter system, the proposed system configuration allows one to extract maximum power, to reduce the devices voltage rating (with the subsequent benefits in device-performance characteristics), to reduce the output-voltage distortion, and to increase the system efficiency. Simulation and experimental tests have been conducted with three PVAs connected to a four-level three-phase diode-clamped converter to verify the good performance of the proposed system configuration and control strategy. Index Terms--Four-level three-phase diode-clamped dc-ac converter, multilevel, photovoltaic-array (PVA) voltage control, photovoltaic (PV) energy, pulsewidth modulation, renewable energy, virtual vectors.