Speed control of a PV powered dc motor driving a self-excited 3-phase induction generator for maximum utilization efficiency

Photovoltaic (PV) powered dc motors driving dedicated loads (e.g. water pumps) are increasingly used in the remote rural areas of many developing countries. The key to their success is simplicity (direct coupling, no dc-ac conversion, no storage batteries, etc.). Because of the relatively high cost of the PV array, the system designer is interested in maximizing its utilization efficiency. A PV powered dc motor can also be used to drive a three-phase self-excited induction generator (SEIG). This arrangement is useful as part of an integrated renewable energy system (IRES), which takes advantage of the inherent diversity of wind and solar energy in most developing countries to improve power quality. The SEIG is driven by a wind-turbine, dc motor, or both. Another advantage of this arrangement is its versatile control characteristics through the dc motor control. This paper describes a technique to maximize the utilization effeciency of the PV array by controlling the field current of the dc motor through a dc chopper. © 1996 IEEE.IEE

Scaffold-Free 3-D Cell Sheet Technique Bridges the Gap between 2-D Cell Culture and Animal Models

Various tissue engineering techniques have been created in research spanning two centuries, resulting in new opportunities for growing cells in culture and the creation of 3-D tissue-like constructs. These techniques are classified as scaffold-based and scaffold-free techniques. Cell sheet, as a scaffold-free technique, has attracted research interest in the context of drug discovery and tissue repair, because it provides more predictive data for in vivo testing. It is one of the most promising techniques and has the potential to treat degenerative tissues such as heart, kidneys, and liver. In this paper, we argue the advantages of cell sheets as a scaffold-free approach, compared to other techniques, including scaffold-based and scaffold-free techniques such as the classic systemic injection of cell suspension

Improved differential relay for bus bar protection scheme with saturated current transformers based on second order harmonics

Differential relays security to the external faults is affected by the saturation of branches’ current transformers (CTs). In this paper, a simple scheme is proposed to enhance the security of differential numerical relay by extracting the 2nd order harmonic using Fast Fourier Transform (FFT) to produce a restraint signal to inhibit the relay operation during external faults. The operation signal of differential relay is produced by comparing the vector addition of secondary currents of branches’ CTs (differential current) with pre-set value; the restraint signal is produced by comparing the algebraic sum of 2nd order harmonic of individual secondary currents with the 2nd order harmonic of differential current. The proposed scheme is investigated using PSCAD/EMTDC simulation and tested during internal and external faults for saturated CTs. The obtained results reveal how this scheme is effective and secure to the external faults for different suggested scenarios. The proposed scheme is using the simplest technique of signal processing compared to other proposed techniques. Keywords: Bus bar, Differential relay, CT saturation, 2nd order harmoni

Security Enhancement of Differential Protection of Power Transformers Based on Second Order Harmonics

International audienceDifferential relays are designed to protect the PTs (power transformers) from total damage when faults occur inside the PTs. Differential protection security of PTs is affected by external disturbances such as inrush currents, external faults, and over-excitation which cause undesired PT outage. In this work, a reliable algorithm is presented to improve the speed and security of PT protection. FFT (fast Fourier transform) method is used for taking out the second order harmonic of measured currents by CTs (current transformers) of the primary side and secondary side of PTs. The algorithm produces two signals: operating signal to disconnect PT during internal faults; and restraint signal to block the undesired action of the differential relay through external disturbances. The algorithm is inspected using PSCAD/EMTDC, where various abnormal conditions internal faults and external disturbances are simulated. The achieved results reveal that the proposed algorithm enhanced the speed and security of differential relay with simplest signal processing method compared to other techniques

Optimal Comfortable Load Schedule for Home Energy Management Including Photovoltaic and Battery Systems

Although the main concern of consumers is to reduce the cost of energy consumption, zero-energy buildings are the main concern of governments, which reduce the carbon footprint of the residential sector. Therefore, homeowners are motivated to install distributed renewable energy resources such as solar energy, which includes photovoltaics (PVs), solar concentrators, and energy storage systems (ESSs); these installations are intended to maintain the homeowners’ energy consumption, and the excess energy can be sold to the grid. In light of the comfort consumption suggestions made by users, this paper presents an optimal home energy management (HEM) for zero-energy buildings and low energy consumption. Firstly, this paper proposes a new optimization algorithm called random integer search optimization (RISO). Afterwards, we propose a new objective function to enable zero energy consumption from the grid and lower costs. Therefore, in this study, the primary energy resources for homes are PVs and ESSs, while the grid is on standby during the intermittency of the primary resources. Then, the HEM applies the RISO algorithm for an optimal day-ahead load schedule based on the day-ahead weather forecast and consumers’ comfort time range schedule. The proposed HEM is investigated using a schedule of habits for residential customers living in Hong Kong, where the government subsidizes the excess clean energy from homes to the grid. Three scenarios were studied and compared in this work to verify the effectiveness of the proposed HEM. The results revealed that the load schedule within the comfort times decreased the cost of energy consumption by 25% of the cost without affecting the users’ comfort