A compound current limiter and circuit breaker

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The protection of sensitive loads against voltage drop is a concern for the power system. A fast fault current limiter and circuit breaker can be a solution for rapid voltage recovery of sensitive loads. This paper proposes a compound type of current limiter and circuit breaker (CLCB) which can limit fault current and fast break to adjust voltage sags at the protected buses. In addition, it can act as a circuit breaker to open the faulty line. The proposed CLCB is based on a series L-C resonance, which contains a resonant transformer and a series capacitor bank. Moreover, the CLCB includes two anti-parallel power electronic switches (a diode and an IGBT) connected in series with bus couplers. In order to perform an analysis of CLCB performance, the proposed structure was simulated using MATLAB. In addition, an experimental prototype was built, tested, and the experimental results were reported. Comparisons show that experimental results were in fair agreement with the simulation results and confirm CLCB’s ability to act as a fault current limiter and a circuit breaker

Control of MMC-based STATCOM as an effective interface between energy sources and the power grid

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This paper presents a dynamic model of modular multilevel converters (MMCs), which are considered as an effective interface between energy sources and the power grid. By improving the converter performance, appropriate reactive power compensation is guaranteed. Modulation indices are calculated based on detailed harmonic evaluations of both dynamic and steady-state operation modes, which is considered as the main contribution of this paper in comparison with other methods. As another novelty of this paper, circulating current control is accomplished by embedding an additional second harmonic component in the modulation process. The proposed control method leads to an effective reduction in capacitor voltage fluctuation and losses. Finally, converter’s maximum stable operation range is modified, which provides efficiency enhancements and also stability assurance. The proficiency and functionality of the proposed controller are demonstrated through detailed theoretical analysis and simulations with MATLAB/Simulink

A multi-inductor h bridge fault current limiter

© 2019 by the authors. Current power systems will suffer from increasing pressure as a result of an upsurge in demand and will experience an ever-growing penetration of distributed power generation, which are factors that will contribute to a higher of incidence fault current levels. Fault current limiters (FCLs) are key power electronic devices. They are able to limit the prospective fault current without completely disconnecting in cases in which a fault occurs, for instance, in a power transmission grid. This paper proposes a new type of FCL capable of fault current limiting in two steps. In this way, the FCLs’ power electronic switches experience significantly less stress and their overall performance will significantly increase. The proposed device is essentially a controllable H bridge type fault current limiter (HBFCL) that is comprised of two variable inductances, which operate to reduce current of main switch in the first stage of current limiting. In the next step, the main switch can limit the fault current while it becomes open. Simulation studies are carried out using MATLAB and its prototype setup is built and tested. The comparison of experimental and simulation results indicates that the proposed HBFCL is a promising solution to address protection issues

Unit commitment optimisation of hydro-thermal power systems in the day-ahead electricity market

Unit commitment is one of the serious major problems encountered in power system operation, control and coordination. It is a complex non-linear problem used in the schedule of operation of generating units at minimum operating cost. This paper presents a new formulation and classical exhaustive enumeration search method for the well-known unit commitment problem for scheduling thermal and hydroelectric power generating units in a day-ahead electricity market. In the study, the two objective functions formulated are minimisation of total production cost and maximisation of the energy consumption. To effectively deal with the constraints of the problem, the difficult minimum up/down-time constraints of thermal generation units and the turbine operating constraint of hydropower stations are embedded in the binary strings that are coded to represent the on/off-states of the generating units. The Nigeria 330 kV power system containing four thermal and three hydropower plants is studied under different scenarios for a 24 h horizon to show the effectiveness of the proposed algorithm. Although the approach is not really computationally efficient compared to some methods, a high accuracy of optimal solution is guaranteed. The results obtained in the study are compared with the ones reported in the literature, which confirm the effectiveness of the proposed technique

Effective Remote Control of Several Outdoor Security Lights by SMS and Wifi Technology

The aim of this study was to design and develop a control system using Short Message Service (SMS) and wireless networking (WiFi) technology to remotely control outdoor security lights in large organisations. The device comprises four main units, namely: the mobile phone or a computer system, the Global System for Mobile communication (GSM) modem, the switching unit and the WiFi module. One feature that makes the developed system better than other related existing works is its ability to use two means of control. It makes use of WiFi when the operator is within the coverage area of the network of about 100 m to the device, at no cost, otherwise it uses SMS containing certain codes to control the lights. A Subscriber Identity Module (SIM) card is placed in the GSM modem and SMS from the transmitter are sent to that mobile number. The module is also constantly checked by the microcontroller unit, processes the information, extracts the message and command from the GSM modem and WiFi module respectively and then acts accordingly. Owing to its simplicity, C programming is used to programme the microcontroller. The developed device when tested with three lighting points operating on 230V power supply, gives an impressive performance in terms of accuracy and promptness with both SMS and WiFi technology