Fast and Reliable Primary Frequency Reserves From Refrigerators with Decentralized Stochastic Control

Due to increasing shares of renewable energy sources, more frequency reserves are required to maintain power system stability. In this paper, we present a decentralized control scheme that allows a large aggregation of refrigerators to provide Primary Frequency Control (PFC) reserves to the grid based on local frequency measurements and without communication. The control is based on stochastic switching of refrigerators depending on the frequency deviation. We develop methods to account for typical lockout constraints of compressors and increased power consumption during the startup phase. In addition, we propose a procedure to dynamically reset the thermostat temperature limits in order to provide reliable PFC reserves, as well as a corrective temperature feedback loop to build robustness to biased frequency deviations. Furthermore, we introduce an additional randomization layer in the controller to account for thermostat resolution limitations, and finally, we modify the control design to account for refrigerator door openings. Extensive simulations with actual frequency signal data and with different aggregation sizes, load characteristics, and control parameters, demonstrate that the proposed controller outperforms a relevant state-of-the-art controller.Comment: 44 pages, 17 figures, 9 Tables, submitted to IEEE Transactions on Power System

Hypothyroidism conversion to hyperthyroidism: it's never too late.

Primary hypothyroidism is a common endocrine condition, most commonly caused by autoimmune thyroiditis (Hashimoto's disease) while Graves' disease is the most common cause of hyperthyroidism. Hypothyroidism is usually a permanent condition in most patients requiring lifelong levothyroxine treatment. Transformation from Hashimoto's disease to Graves' disease is considered rare but recently been increasingly recognised. We describe a case of a 61-year-old lady who was diagnosed with hypothyroidism approximately three decades ago and treated with levothyroxine replacement therapy. Approximately 27 years after the initial diagnosis of hypothyroidism, she started to become biochemically and clinically hyperthyroid. This was initially managed with gradual reduction in the dose of levothyroxine, followed by complete cessation of the medication, but she remained hyperthyroid, ultimately requiring anti-thyroid treatment with Carbimazole. This case highlights that there should be a high index of suspicion for a possible conversion of hypothyroidism to hyperthyroidism, even many years after the initial diagnosis of hypothyroidism. To our knowledge, this case illustrates the longest reported time interval between the diagnosis of hypothyroidism until the conversion to hyperthyroidism. Learning points: Occurrence of Graves' disease after primary hypothyroidism is uncommon but possible.In this case, there was a time-lapse of almost 28 years and therefore this entity may not be as rare as previously thought.Diagnosis requires careful clinical and biochemical assessment. Otherwise, the case can be easily confused for over-replacement of levothyroxine.We suggest measuring both anti-thyroid peroxidase (TPO) antibodies and TSH receptor antibodies (TRAB) in suspected cases.The underlying aetiology for the conversion is not exactly known but probably involves autoimmune switch by an external stimulus in genetically susceptible individuals

No universal support for solar glare as an evolutionary driver of malar stripes in falcons

The paired dark malar or moustachial stripes of falcons (Falco spp.) are putatively adaptive plumage features whose function and evolutionary significance are poorly understood, and have rarely been investigated in published literature. A popular hypothesis for the function of falcon malar stripes is that they serve as antiglare devices, with the dark pigment absorbing visionimpeding solar glare and thereby improving the falcon's ability to visually detect and target prey in bright conditions. Correlative evidence from Peregrine Falcons (Falco peregrinus) provides support for this hypothesis, with a previous study finding that the size and prominence of malar stripes in this species correlate positively with solar radiation across the species' geographic range. In the present study, I extend the methodology used in this previous research to all extant species in the genus Falco, to determine both whether other falcon species display similar intraspecific trends, and whether differences in solar radiation conditions, in conjunction with species ecology, explain interspecific variation in falcon malar stripe characteristics. My results indicated that malar stripe characteristics were not positively related to solar radiation in the majority of species, with only the Peregrine Falcon showing reliable trends towards larger and darker malar stripes in individuals inhabiting regions of higher solar radiation. Likewise, solar radiation was not positively related to interspecific variation in falcon malar stripe characteristics, even after accounting for differences in body size, agility, prey base, and habitat between species. These results suggest that falcon malar stripes do not universally function as antiglare devices, at least in species other than the Peregrine Falcon. Malar stripes thus likely evolved in falcons for a different purpose (such as crypsis or social signaling), but may have become exapted for solar glare reduction in Peregrine Falcons owing to the species' cosmopolitan distribution and high degree of specialization on agile bird prey