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Yap H.G.,Nanyang Technological University | Tseng K.J.,Berkeley Education Alliance for Research in Singapore
9th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2015-ECCE Asia | Year: 2015

DC power distribution is becoming more prevalent in buildings, starting in niche applications such as data centers and gradually moving into more mainstream applications. There is need for the DC network in the building (termed as nanogrid) to interface with the external AC utility grid for energy exchange, security and reliability. In this study, we examined the power electronic converter topologies available for this function, as well as how to integrate the secondary objectives of metering, protection, communications and energy efficiency optimization. A three-phase bidirectional buck rectifier is chosen as a case study to interface the external AC grid to the internal DC nanogrid. The output of the bidirectional rectifier is chosen to be 380Vdc, while having to fulfill the requirements of smooth DC output voltage, unity power factor and low THD. The implementation of space vector PWM for this rectifier gives good dynamic response during the power flow change-over. The increase in number of power semiconductor switches may however lower the reliability of this topology. To assess the reliability of this converter, the possible internal faults of this topology are visualized using a polar plot of output voltage against phasor of the source voltage from the AC grid. The fault mode can be then identified easily from the fault pattern in polar plot. Simulation results are presented to support the analysis and recommendations. © 2015 Korean Institute of Power Electronics.

Fadeyi M.O.,Berkeley Education Alliance for Research in Singapore | Fadeyi M.O.,Nanyang Technological University
Sustainable Cities and Society | Year: 2015

Presence of ozone in indoor environment has implications on creation of sustainable indoor environment. A material mass balance model is used to summarize outcome of the review exercise that was conducted to understand what 15 years has taught us, with regards to the chemistry and concentration of ozone in indoor environment, since after a similar review effort by Weschler in the year 2000. Additionally, key knowledge gained on the impact of ozone and its initiated chemistry products on human health and comfort are summarized. This paper is concluded with recommendations for future research directions. © 2015 Elsevier Ltd. All rights reserved.

Fadeyi M.O.,Berkeley Education Alliance for Research in Singapore | Fadeyi M.O.,Nanyang Technological University | Tham K.W.,National University of Singapore | Wu W.Y.,National University of Singapore
Indoor Air | Year: 2015

The impact of asthma, exposure period, and filter condition downstream of the mixing box of air-conditioning system on building occupants' perceptual response, work performance, and salivary α-amylase secretion during exposures to ozone and its initiated chemistry products is studied. The experiments were conducted in a field environmental chamber (FEC) (240 m3) simulating an office environment. Experiments were conducted during periods when the air-handling system operated with new or used pleated panel filters at constant recirculation (7/h) and ventilation (1/h) rates. Average ozone and secondary organic aerosols (ozone-initiated chemistry products) measured during non-asthmatic and asthmatic subjects' 3-h exposures in the FEC were in the ranges approximately 20-37 ppb and approximately 1.6-3 μg/m3, respectively. Asthmatic subjects' perceived odor intensity and sensory (eye, nose, and throat) irritation ratings were generally lower than those of non-asthmatic subjects, possibly explaining why asthmatic subjects accept perceived air quality more than non-asthmatic subjects. However, asthmatic subjects' perceived physiological-like symptom ratings (flu, chest tightness, and headache) and concentrations of secreted salivary α-amylase were generally higher than those of non-asthmatic subjects. Asthmatic subjects had significantly lower accuracy than non-asthmatic subjects in a task that required higher concentration although they had higher work speed. Filter condition did not make any significant difference for subjects' responses. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Yang B.,Berkeley Education Alliance for Research in Singapore | Yang B.,Nanyang Technological University | Schiavon S.,University of California at Berkeley | Sekhar C.,National University of Singapore | And 3 more authors.
Building and Environment | Year: 2015

In warm environments, isothermal cooling by deliberately enhanced air movement can maintain thermal comfort using less energy than compressor-based air conditioning. To evaluate the performance of a brushless direct current (DC) stand fan, the cooling fan efficiency (CFE) index was measured in a climatic chamber under four dry-bulb temperatures (24, 26, 28, and 30°C), six speed settings (corresponding to centreline speeds in the range 0.6-2.5m/s at 1m distance), two fan-manikin distances (1 and 2m) and two orientations (front, side). The CFE index is defined as the ratio of the whole-body cooling effect generated by non-uniform airflow from the fan to its power consumption (°C/W). The CFE index overcomes the limitations of assessing the cooling effect based just on a few air speed measurements. The results show that the CFE index is influenced by dry-bulb temperature, fan speed setting, and fan-manikin distance, but not by fan-manikin orientation. The lower the temperature and the closer the fan, the higher is the CFE index. Increasing fan speed setting simultaneously enhances whole-body cooling and increases power use. Consequently, the CFE has a non-monotonic relationship with fan speed setting and the peak value is reached for an intermediate speed. As compared with previous testing results using an alternating current stand fan, the CFE index of the DC fan we tested is three times higher. As a complement to air-conditioning, the tested stand fan is a suitable energy-efficient technology for providing thermal comfort in warm environments. © 2014 Elsevier Ltd.

Liu S.,Berkeley Education Alliance for Research in Singapore | Xie L.,Nanyang Technological University
2012 12th International Conference on Control, Automation, Robotics and Vision, ICARCV 2012 | Year: 2012

This paper considers the average consensus problem for multi-agent systems with continuous-time first-order dynamics. The communication channels among the agents are constrained in which the exchanged information is quantized. In this paper, logarithmic quantization is considered in the communication channels, and sampled-data based protocol is applied. It is shown that as long as the sampling interval is small enough, the consensus protocol is admissible under arbitrarily coarse quantization. To be specific, the consensus error is uniformly bounded and is proportional to the quantization error and averaged initial value. Numerical examples are given to demonstrate the effectiveness of the protocol. © 2012 IEEE.

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