State-of-art on permanent magnet brushless DC motor drives

Permanent magnet brushless DC (PMBLDC) motors are the latest choice of researchers due to their high efficiency, silent operation, compact size, high reliability and low maintenance requirements. These motors are preferred for numerous applications; however, most of them require sensorless control of these motors. The operation of PMBLDC motors requires rotor-position sensing for controlling the winding currents. The sensorless control would need estimation of rotor position from the voltage and current signals, which are easy to be sensed. This paper presents a state of art on PMBLDC motor drives with emphasis on sensorless control of these motors

PFC bridge converter for voltage-controlled adjustable-speed PMBLDCM drive

In this paper, a buck DC-DC bridge converter is used as a power factor correction (PFC) converter for feeding a voltage source inverter (VSI) based permanent magnet brushless DC motor (PMBLDCM) drive. The front end of the PFC converter is a diode bridge rectifier (DBR) fed from single phase AC mains. The PMBLDCM is used to drive the compressor of an air conditioner through a three-phase voltage source inverter (VSI) fed from a variable voltage DC link. The speed of the air conditioner is controlled to conserve energy using a new concept of voltage control at a DC link proportional to the desired speed of the PMBLDC motor. Therefore, VSI operates only as an electronic commutator of the PMBLDCM. The current of the PMBLDCM is controlled by setting the reference voltage at the DC link as a ramp. The proposed PMBLDCM drive with voltage control-based PFC converter was designed and modeled. The performance is simulated in Matlab-Simulink environment for an air conditioner compressor load driven through a 3.75 kW, 1500 rpm PMBLDC motor. To validate the effectiveness of the proposed speed control scheme, the evaluation results demonstrate improved efficiency of the complete drive with the PFC feature in a wide range of speed and input AC voltage

Wireless setups for improved remote area connectivity

Abstract. This thesis considers the problem of low radio frequency (RF) signal strength at remote locations where connectivity has been proven to be problematic. In such areas, the low signal strength makes it more difficult for the residents to establish reliable internet connections. Moreover, in addition to long distance between mobile user and the base station the signal is degraded due to natural obstacles such as hills or forests. The most straightforward solution to the signal deterioration in this case is both elevating user’s antenna and amplifying the received signal by means of dedicated devices. In this regard, we have proposed two configurations for improving the signal strength. The former one, described as fixed installation is installed at home. The elevated modem with the antenna together with the integrated router were used in order to facilitate proper reception for home-dwellers. The latter one, is referred to as semi-mobile installation, where the directional antenna is mounted on the vehicle in order to enable connectivity for users on the go. The measurement campaign was conducted at remote locations in Loppula and Rokua, Finland. The targeted long term evolution (LTE) signal was measured at band 20 at 800 MHz. In case of semi-mobile installation the performance of the inductive coupler was measured in terms of signal parameters received signal strength indicator (RSSI), reference signal received power (RSRP), reference signal received quality (RSRQ) and signal-to-noise ratio (SNR). For the fixed installation, the modem performance was measured in terms of data rate. In both cases, the installed set-up improved the quality of the signal, and thus can be recommended for users facing connectivity issues at remote locations

Doctor of Philosophy

dissertationThe present work reports studies of the ultrafast photoexcitations in various pristine n-conjugated polymers as well as compounds of polythiophene/fullerene blends, which act as the active layer of donor/acceptor in organic photovoltaic applications. The main technique used is the ultrafast (∼150 fs) transient photomodulation (PM) spectroscopy in the range of 0.25 to 2.5 eV using two different laser systems. In addition, two-photon-absorption and electroabsorption have also been complementary used. In organic photovoltaic studies, two different donor polymers namely, Regio-Regular-poly(3-hexylthiophene) (RR-P3HT) that forms lamellae, and Regio-Random-poly(3-hexylthiophene) (RRa-P3HT) that forms lamellae with lesser extent have been compared. The transient PM measurement of the most efficient RR-P3HT/fullerene blend shows that the decay of exciton does not result in the generation of polarons in the donor and acceptor materials, as assumed by the present model of charge dissociation in photovoltaic devices. On the contrary, the decay of exciton fits very well to the build-up of charge-transfer (CT) state in the fullerene phase, which indicates the migration of the photoexcited exciton in the polymer phase to the fullerene nano-domains. The transient PM measurement of RRa-P3HT/fullerene blend, which does not form phase-separated nano-domains, shows the formation of a CT state at the interface following by ultrafast geminate recombination. The transient PM measurement of poly(phenylene-vinylene) (PPV) derivatives show that in 2-methoxy-5-(2'-ethylhexyloxy) PPV (MEH-PPV) film there are two kinds of primary photoexcitations, namely, intrachain exciton and excimer, but only intra-chain exciton in other PPV derivative polymers. Furthermore the high-pressure study of MEHPPV film shows two kinds of polymer chain orders: isolated-chains and closely packed-chains. The high pressure mainly affects photoexcited excimers in the closely packed-chains. In contrast there is no pressure effect on the photogenerated intrachain excitons in the isolated-chains. The other π-conjugated polymers investigated in this dissertation are platinum(Pt)-containing conjugated polymers. The different parity excited states of these Pt-polymers are studied by electroabsorption and two-photon-absorption spectroscopies. These results show that, even after the incorporation of Pt atoms into the backbone of conjugated polymer, the behavior of the excited states is similar to regular π-conjugated polymers

Social Quality and Quality of Work Life Outline the Employees’ Quality of Life in Indian Public Sector: An Investigation

Many researchers have tried to identify the factors that determine quality of life and impact on these factors on social quality. The current research outlines the existing theory and provides an argument which suggests that the trust, loyalty and challenging works also can be part of the construct of social quality. Authors propose a model, supported by data, which suggests ways in which current social theories of trust, loyalty and challenging work may be incorporated within the quality of life framework.Design/Methodology/Approach- The study has two fold objectives. Firstly, to analyze the factors influencing employees social quality and quality of work life in Indian public sector and secondly, to understand the impact of identified variables on quality of life. The study is based on the primary data, collected from the employees of public sector of India. Data analysis was done using SPSS software. The statistical analysis method employed was descriptive analysis, factor analysis and multiple regressions