Hybrid renewable energy systems (HRES) are becoming popular for remote area power generation applications due to advances in renewable energy technologies and subsequent rise in prices of petroleum products. Economic aspects of these technologies are sufficiently promising to include them in developing power generation capacity for developing countries. Research and development efforts in solar, wind, and other renewable energy technologies are required to continue for, improving their performance, establishing techniques for accurately predicting their output and reliably integrating them with other conventional generating sources. The paper describes methodologies to model HRES components, HRES designs and their evaluation. The trends in HRES design show that the hybrid PV/wind energy systems are becoming gaining popular. The issues related to penetration of these energy systems in the present distribution network are highlighted.

Modeling of hybrid renewable energy systems

Overview of energy storage in renewable energy systems

Flywheel Energy Storage System (FESS) is an electromechanical energy storage system which can exchange electrical power with the electric network. It consists of an electrical machine, back-to-back converter, DC link capacitor and a massive disk. Unlike other storage systems such as the Battery Energy Storage System (BESS), FESS is an environmentally-friendly short- or medium-term energy storage system, which has the capability of numerous charge and discharge cycles. These characteristics make the FESS a suitable choice for different applications in the power system such as power quality improvement, power smoothing, renewable energies integration support, stability improvement, etc. This paper presents an overview on the structures and applications of FESS in power system and Microgrid (MG) and also challenges, problems and future works discussed. It can be a driver for development of FESS applications and also recommends suggestions to use its advantages in other areas. Investigation of different studies shows that FESS, as a developing technology, can play an effective role in the operation of the present and future power system and MG.

Review of Flywheel Energy Storage Systems structures and applications in power systems and microgrids

Passivity-based sliding-mode control design for optimal power extraction of a PMSG based variable speed wind turbine

This paper proposes a new outer-rotor permanent-magnet (PM) vernier machine for direct-drive wind power generation, which can offer low-speed operation to directly capture wind power, and enable high-speed rotating field design to maximize the power density. Compared with its mechanical gear counterpart, the proposed machine can eliminate the mechanical wear and tear as well as gear transmission loss, thus improving the generation reliability and efficiency. The key is to newly introduce the flux-modulation poles which can effectively modulate the high-speed rotating field of the armature windings and the low-speed rotating field of the PM outer rotor. By using the time-stepping finite-element method, the proposed machine can be accurately analyzed. Hence, its performances are quantitatively compared with other PM vernier machines, thus verifying its validity.

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A New Efficient Permanent-Magnet Vernier Machine for Wind Power Generation

Modelling, control and simulation of an overall wind energy conversion system

In this paper, we propose to study an electromagnetic actuator which involves linear and/or rotary movements. The studied device is constituted of permanent magnets, iron teethed armature and concentrated coils with a simplified design. The aim of this paper is to study the main electromagnetic features of the actuator using 3D finite element method (FEM). First, the actuator is described and the design choices are given and discussed. Then, the electric and magnetic behaviors (fluxes, forces, etc.) are studied thanks to 3D-FEM analyses. Results are given and compared to measurements.

Modeling of A Linear and Rotary Permanent Magnet Actuator

This paper presents a modulated hysteresis direct torque control (MHDTC) applied to an induction generator (IG) used in wind energy conversion systems (WECs) connected to the electrical grid through a back-to-back converter. The principle of this strategy consists in superposing to the torque reference a triangular signal, as in the PWM strategy, with the desired switching frequency. This new modulated reference is compared to the estimated torque by using a hysteresis controller as in the classical direct torque control (DTC). The aim of this new approach is to lead to a constant frequency and low THD in grid current with a unit power factor and a minimum voltage variation despite the wind variation. To highlight the effectiveness of the proposed method, a comparison was made with classical DTC and field oriented control method (FOC). The obtained simulation results, with a variable wind profile, show an adequate dynamic of the conversion system using the proposed method compared to the classical approaches.

Improved direct torque control of an induction generator used in a wind conversion system connected to the grid.

Vector control of autonomous induction generator taking saturation effect into account

In this paper, the performance of an isolated self-excited induction generator driven by a wind turbine under unbalanced loads is studied. First, the whole system, including the induction generator, the capacitors, and the loads, is modeled. The model used for the isolated induction generator is a diphase one obtained, using the Park transformation. This model allows the saturation effect to be taken into account, assuming certain simplifying hypotheses. Then, the developed model is validated comparing simulation and experiment results at no load and for balanced load cases. Finally, the same model is used to study the performance of the isolated induction generator under unbalanced load cases. Compared to the experiments, the simulation results show a good prediction of the electrical variable waveforms. Furthermore, it can be seen that the magnitude and frequency of the voltages do not vary a lot even if the load is hardly unbalanced.

Abdelmounaïm Tounzi

Papers

Modelling, control and simulation of an overall wind energy conversion system

Modeling of A Linear and Rotary Permanent Magnet Actuator

Improved direct torque control of an induction generator used in a wind conversion system connected to the grid.

Vector control of autonomous induction generator taking saturation effect into account

Performance of an Isolated Induction Generator Under Unbalanced Loads