Band 21, Heft 6

This paper presents two unique smart branch controller for compensating several power quality disturbances. The first proposed intelligent branch controller comprises a series transformer with its indirectly controlled impedance by secondary voltage injection. Further, the smart controller is made adaptive and flexible. It is installed at the point of common coupling (PCC), where PCC voltage & load current can be locally acquired without the presence of a communication channel, which then tracks its references as pure sinusoidal waveforms. Therefore without any filter requirement, harmonic elimination is done by the smart branch controller. The proposed smart controller can be applied in microgrids (MGs) for multi-objective optimization of power quality (PQ). For proper elimination of harmonics and to enhance the quality of power supply, the smart branch is optimized by a droop controller, which delivers power to a constant current source and eliminates harmonics by providing an appropriate quantity of harmonic voltage to the inverter voltage. The total harmonic distortion (THD) becomes 23.06% for the voltage and 6.24% for the current with droop controller, whereas, with an only smart branch into the power network, the THD becomes 26.47% for the voltage and 12.30% for the current. The simulation result concludes that the discussed optimized smart branch-based droop controller reduces drastically THD. Also, a separate study has been performed on the improvement of PQ by second proposed smart controller called as Photovoltaic Distribution Static Compensator (PV-DSTATCOM) grid-tied system using an adaptive reweighted zero attracting (RZA) control algorithm with perturbation and by applying maximum power point tracking technique (MPPT) for a three-phase system. The converter with PV array along with an active filter feature known as PV-DSTATCOM is required to convert the DC voltage into AC and for the improvement of the PQ by limiting harmonic distortions. It is concluded from the simulation results that the use of the RZA strategy presents an excellent steady state and transient response. The proposed PV grid-tied system is capable of working round the clock for both constant and variable irradiation and linear loads. The system is termed as smart as it can perform both modes automatically sensing the PV power and is capable of multi-directional power flow. The proposed method performs dual functions of improving PQ by working as DSTATCOM and also transfers power to the load and the grid obtained from PV array.

An efficient and economic scheduling of power plants relies on an accurate demand forecast especially for the short-term due to its tight relation to power markets and trading operations in interconnected power systems. A slight deviation of load prediction from real demand could engender the start-up of a conventional power station which could be either time-consuming or requiring expensive combustible, a deviation that could interfere as well with renewables intermittency and demand response strategies. Hence, load forecasting still a challenging subject because of the various transformations that the energy sector undergoes and that directly impact the demand profile shape. Therefore, conceiving dynamic load demand forecast approaches will permit utilities save money in different vertical structures and regulation schemes. In this paper, we propose a novel approach for short-term demand prediction valid for normal and special days to address the impact of climate changes along with events occurrence on forecast accuracy. This approach is based on the prediction of hourly loads, established on the daily peak load prediction using backpropagation combined to chi-squared method for weighting historical data to enhance the training process. Obtained results from extensive testing on the Moroccan’s power system confirm the strength of the developed approach, that improved the forecast accuracy by a range of 1.1–4% compared to the existing methods.

Microgrid system stability is a major source of concern due to the rapid increase in load demand and a high level of renewable energy penetration. During the grid- connected mode, the microgrid power quality is mainly affected by the level of connection strength with the host grid. Thus, this paper aims to investigate the impact of the implemented control strategy in the microgrid, on frequency response when its level of connection strength is weak, that is, the frequency and voltage are not dominantly controlled by the grid. A control scheme based on a fuzzy logic-based self-tuning PID controller (fuzzy-PID) is used to maintain the frequency within the acceptable range. Simulations illustrate that the frequency dynamic response of the microgrid guarantees a good performance using the fuzzy-PID controller despite a large drop in grid inertia and the presence of disturbances whereas the classical PID controller cannot maintain the frequency within the acceptable range.

The comprehensive energy-saving potential evaluation method of the energy-saving schemes of a distribution network considering the power uncertainty of source and load is studied in this paper. The K-means clustering method is firstly employed to extract typical scenarios of distribution network, and the forward-push back method is used to calculate the power flow in typical scenarios, then energy-saving reconstruction schemes are formulated according to the power flow calculation results. A comprehensive energy saving potential evaluation index system that consists the improvement rate of network loss, line loss rate, transformer loss rate, annual electricity saving cost, annual equipment investment cost, annual maintenance cost and voltage quality improvement rate is built, and the comprehensive evaluation method based on DEMATEL-ANP-TOPSIS mixed decision model is used to evaluate the comprehensive energy-saving potential of the energy-saving reconstruction schemes regarding the index system. Finally, the optimal reconstruction scheme is selected based on the evaluation results of energy saving potential in multiple scenarios. The effectiveness of the proposed method is verified by an example in IEEE-33 node distribution network.

In this study, a methodology for partial eigenstructure assignment (PEVA) is applied to dampen electromechanical oscillations in electrical multi-machine power systems. The approach is anchored in allocating a small number of undesirable eigenvalues, for example, which are poorly damped, preserving the other eigenvalues in the system - the so-called no-spillover spectrum. The new position of the selected eigenvalues is carried out based on the partial controllability analysis of the system, in order to minimize the control effort. Simulation examples using a system with 68 buses, 16 generators and five areas showed that the presented methodology is efficient in dampening the local and inter-area oscillation modes when compared to the classic power system stabilizers (PSS). The quality of the solution is illustrated through computer simulations, eigenvalues tables and mode-shapes.

High-speed surface-mounted permanent magnet synchronous machine is often used in micro gas turbine generation system due to its high rotor strength and high efficiency. The electrical machine in this kind of generation system needs to integrate two functions of starter and generator. Therefore, its comprehensive performance, including starting performance and generating performance, has become a comprehensive standard to measure machine performance. In this paper, a 40 kW, 20,000 r/min high-speed machine is taken as an example, the influence of magnets magnetization direction on the machine comprehensive performance is studied. The machine models with different magnets magnetization directions are established by using finite element method and the correctness of the models is verified by comparing the experimental data with the finite element calculation data. On this basis, the influence of different magnetization directions on the performance of the machine, such as generation loss, torque ripple, output voltage, start-up time and maximum starting ability, is analyzed. Furthermore, based on the Fourier decomposition of air gap flux density and the decoupling analysis of starting torque, the influence mechanism of magnetization direction on the performance of the machine is revealed. The presented results provide a reference for the selection of a suitable magnetization direction for high-speed surface-mounted permanent magnet machines.

Buildings account for much of the world’s energy consumption; thus, it is important to develop ways, not just to harness more of the energy in the universe, but also to make system of devices in buildings more energy-efficient. Occupancy-based illumination is an emerging trend in energy management, but research in this field has mostly been focused on illumination of rooms and workspaces in building interiors. To the best of the authors’ knowledge, there is virtually no literature on the energy optimisation of depersonalised spaces such as passageways. This paper explores the development and evaluation of a controller-based model for illumination of passageways in buildings, where relatively-large number of depersonalized luminaires are usually found and automation might prove especially beneficial. After development, testing and scaled-up simulations, results show that occupancy-based illumination of exterior corridors and semi-covered passages in buildings is feasible, economical, has significant energy savings, and is worthy of consideration for modern buildings.