• Energy Research

Abstract Machine Emulation (ME) is one of the main applications of Power-Hardware-In-the-Loop (PHIL) simulations. The performance and cost of an ME system depends heavily on the type of Power Amplifier (PA) it employs. Linear Power Amplifiers (LPAs) produce ripple free outputs and offer high bandwidths but are costly. Switch-Mode Power Amplifiers (SMPAs) are more affordable, with higher power density, but produce switching harmonics that yield distorted waveforms and reduce the closed loop bandwidths. In order to get a compromise between these technologies for ME, this paper proposes an ME based on a Hybrid Power Amplifier (HPA), with parallel LPA and SMPA. A new current control scheme for the HPA, suitable for voltage-in current-out machine models, is proposed to reduce the required current rating, and thus the cost, of the LPA. A design procedure for the control scheme of the HPA is presented and illustrated for the emulation of a direct-online start-up of an Induction Machine (IM). Simulation results evaluate and compare systems built exclusively with SMPA or LPA for ME. Experimental results are shown to validate the proposed control scheme for the parallel HPA in ME systems. Besides, the impact of the bandwidths of the control loops of the LPA and SMPA and the switching frequency of the SMPA, on the accuracy of the ME system and on the current requirement of the LPA are highlighted.

Abstract This paper addresses a problem that occurs in many small appliances. As such, it is an important problem of energy utilization. To improve the performance of a single phase capacitor start/run induction motor, FET type power transistors could be used to replace a SCR H bridge. Such a configuration can lead to a simpler and more inexpensive circuit for the electronically controlled capacitor. In this paper, ICs and an OP-AMP are used to design an electronically controlled capacitor for a single phase induction motor. The design can compensate for the input voltage fluctuations that are present in the normal operation of the motor. In addition, an improvement in its performance can be obtained. At present, the use of a tachometer can be considered a disadvantage of the proposed scheme. Thus, a configuration that enables removal of the tachometer, while maintaining reasonable cost, is desirable. In addition, replacing the ac capacitor with one rated for dc can lead to a system reduction, in addition to a considerable reduction in the size of the circuit due to the use of integrated circuits.

Abstract A model for pressure-retarded osmotic (PRO) power systems is described. The model considers several non-ideal phenomena including internal and external concentration polarization, local variation due to mass transfer, pressure losses along membrane surfaces and other losses throughout the system. This provides an overview of many of the major dynamics that must be considered in PRO power modeling. The model is validated by comparison to experimental data available in the literature. The model is used to investigate the effect of feed and draw flow rates, and of hydraulic pressure difference on PRO system performance. These parameters can be controlled by the system operator and can be set so as to minimize competing non-ideal effects. Improvements in net power of up to 7× are observed when best operating parameters are used as opposed to other values used in the literature.

The need to mitigate the adverse environmental impacts of fossil fuel usage, the volatility of fuel prices and enhancement of national energy security, have largely driven a phenomenal growth, around the world, in renewable energy (RE) generation (particularly grid-connected), over the past two decades. The necessity to apply policy support instruments to promote the dissemination of these technologies is now a universally accepted norm. Different countries and societies depending on the prevailing socio-economic environment draft and apply their policy frameworks differently and debates abound as to which mechanisms should have been most suitable under which circumstance. Most of these debates, however, assume the existence of an intrinsic political environment in favour of the process. In South Africa the current political environment is not very conducive to the development of a sustainable RE industry. This paper explores some of the anomalies and barriers and suggests possible options for a way forward to a viable RE industry in the country.

This paper first reviews three internationally standardized core loss measurement methods: Epstein frame, toroids and single sheet testers. A comparison of the Epstein frame and toroid test results is presented for annealed and unannealed steel. Two methods are used to predict core losses under nonsinusoidal supplies. The first method uses the Fourier series and an improved loss separation algorithm to predict core losses under equivalent brushless DC motor flux waveform with known spectrum. For lower harmonics, superposition yielded results close to the measured values. The second method uses the form factor concept and an improved loss separation algorithm to predict core loss. The combination of the improved loss separation algorithm and the form factor concept was found to yield results close to the measured losses under high frequency supplies, such as pulse width modulated waveforms. An Epstein frame with commercial 0.0140-inch electrical steel was used for direct core loss measurements; the methods and test bench used are detailed in the paper, along with test results.

Microgrid (MG) is attracting considerable attention as a solution to energy deficiency, especially, in remote areas. A MG is defined as a group of interconnected loads and multiple distributed generators that are usually integrated via voltage source convertors (VSC) and is able to operate in both grid-connected or island-mode. In order to enhance power quality and power energy management reliability, MG needs optimization in terms of control and size reduction of components. To make some contributions, this paper analyzes three aspects: 1) developing a new approach of active damping technique based on mathematical model of VSC without any additional sensors; 2) reducing the size of the output LC filter by shifting the frequency and adjusting the active damping coefficient; and 3) building a strong fuzzy logic supervisor for smart power management. The simulation and experimental results demonstrate excellent performance of the proposed design and control approaches.

This paper is concerned with the development and implementation of an improved algorithm for dip classification. It can determine the type of dip based on the difference in phase angle between the measured voltages using Zinari's Algorithm. The improved algorithm overcomes the shortcomings of existing conventional dip classification methods which are based solely on the duration and magnitude of the voltage deviation. A software program was developed using Matlab/Simulink and the performance of the algorithm was checked over the full range of phase shift and dip magnitude. Moreover, the algorithm was implemented in a laboratory set up, and various dip types were simulated and then classified using the improved algorithm.

Abstract This paper proposes a novel approach of estimating the symmetrical component into a network. The power grid development and deployment offer several advantages regarding the overall system performance of the electrical system. Currently, through the smart metering system, the symmetrical components problems can be resolved in real-time by extracting, tracking and detecting any issue related to power disturbance on the grid. An adaptive method to estimate symmetrical components in the framework of the power systems is presented. The proposed method is based on a nonlinear adaptive tracking of amplitude, phase and frequency of a non-stationary sinusoidal waveform in real-time. The method offers structural simplicity while maintaining performance robustness and controllable speed and accuracy. Experimental results are presented to verify the performance of the proposed method. The results show that the method can provide an accurate estimation of the symmetrical components in the presence of amplitude and angle variations, as well as in the presence of harmonics. The simplicity of the structure and ease of the parameter settings render the proposed method suitable for both software and hardware implementation. Two scenarios are analysed to validate the proposed algorithm.

Abstract The chemical potential difference of two liquids with dissimilar salinities can produce electrical energy using salinity gradient power (SGP). The pressure-retarded osmosis (PRO) concept can be used to generate SGP across a semi-permeable membrane. This work describes a mathematical model for evaluating PRO processes at both the bench scale and the commercial scale. The effect of concentration polarization is considered, including concentrative external polarization. Bench scale simulation results show agreement with published experimental data. At the commercial scale axial variations in flow rates and concentrations are considered. The model is used to evaluate performance of membranes that have previously only been considered at the bench scale. Commercial-scale simulation results show power densities of up to 5.6 W/m 2 .

Electrical energy can be produced from the chemical potential difference of two liquids with dissimilar salinities. This source of energy is known as salinity gradient power. In this paper, the theory, the technologies used to exploit the power, the major challenges, and their development trends are first presented. Then a modeling of fluxes across semi permeable membranes is proposed and validated. Next, an energy balance study is done in order to estimate the power potential for a given salinity gradient system. By applying this study to several rivers in Quebec, the salinity power gradient potential is estimated to 45 TWh/yr based on the minimal flow rate of each river.