Hamid Ben Ahmed

Sizing Optimization Methodology of a Surface Permanent Magnet Machine-Converter System Over a Torque-Speed Operating Profile: Application to a Wave Energy Converter

This paper sets forth a sizing optimization methodology of a surface permanent magnet machine-converter system over a torque-speed operating profile. The two optimization objectives are to minimize the cost of the machine-converter system and to minimize (or maximize) electrical energy consumption (or generation). The optimization parameters serve to describe both the machine geometry and the electrical ratings of the electronic power converter. Each operating point of the profile is treated independently, and current control is optimized at every operating point to not only minimize machine drive losses but also satisfy several constraints and then implicitly considering flux-weakening possibility. This optimization methodology is generic and is applied to a particular case: a direct-drive conversion chain for a wave energy converter (WEC). We show that taking into account both the sizing parameters of the converter and the flux-weakening control, in addition to the classical sizing parameters of the machine, has a strong impact on the machine-converter system optimal results. Moreover, the strong coupling with the WEC through damping parameters plays also a crucial role on the sizing results.

Dynamical Electromechanical Model for Magnetic Bearings

Magnetic bearings are electromechanical systems. From a mechanical point of view, their modeling is plainly related to general rotor dynamics modeling. But the forces acting between the rotor and the stator are of an electromagnetic nature. This paper presents the analysis of the potentially unstable dynamical behavior of magnetic bearings. It adopts an electromechanical point of view and represents the forces acting on the system by dampers, springs, and an electrical phase shift. The coefficients of the model are found by parameter identification with a finite-element model of the system.

Enhanced Aging Model for Supercapacitors Taking Into Account Power Cycling: Application to the Sizing of an Energy Storage System in a Direct Wave Energy Converter

This paper proposes an original model for supercapacitors that takes into account both calendar aging and cycling aging. A state variable is used to quantify the state of aging. This model is based on a series of recent experiments conducted in various research laboratories on the same technology (Maxwell Technology) and serves to represent the degradation of equivalent series resistance and capacitance. This model is particularly useful in an aging-aware life-cycle cost analysis. We show that an accurate aging model is critical to the design of an energy storage system that optimizes the economic life-cycle cost. Such an optimization is particularly applicable for smoothing in offshore systems such as direct wave energy converters, which require both cost reduction and high reliability. The influence of an aging model in the sizing process is investigated toward the end of this paper.

Influence of control strategy on the global efficiency of a Direct Wave Energy Converter with electric Power Take-Off

The choice of control strategy for Direct Wave Energy Converters (DWEC) is often discussed without taking into account the limitations of electric Power Take-Off (PTO): limits of torque or force and power, as well as losses in the electric chain. These assumptions leads to large and expensive electric systems, that prevent leading to a global minimization of the per-kWh cost. We propose herein a simple loss model in order to design a better control strategy.

Aging-aware NaS battery model in a stochastic wind-storage simulation framework

Dispatchability of wind power is significantly increased by the availability of day-ahead production forecast. However, forecast errors prevent a wind farm operator from holding a firm production commitment. An energy storage system (ESS) connected to the wind farm is thus considered to reduce deviations from the commitment. We statistically assess the performance of the storage in a stochastic framework where day-ahead forecast errors are modeled with an autoregressive model. This stochastic model, fitted on prediction/production data from an actual wind farm captures the significant correlation along time of forecast errors, which severely impacts the ESS performance. A thermo-electrical model for Sodium Sulfur (NaS) batteries reproduces key characteristics of this technology including charging/discharging losses, state-dependent electrical model and internal temperature variations. With help of a cost analysis which includes calendar and cycling aging, we show trade-offs in storage capacity sizing between deviation from commitment and storage costs due to energy losses and aging.

Influence of IGBT current rating on the thermal cycling lifetime of a power electronic active rectifier in a direct wave energy converter

Direct Wave Energy Converters offer high reliability potential, which is a key factor in offshore environments, yet their electrical power produced is strongly pulsating. The thermal cycling of their power electronic switches (considered here to be Insulated Gate Bipolar Transistors, IGBT) may reduce the lifetime of the power electronic converter. This study proposes a generic design method for choosing both the IGBT current rating and the heatsink thermal resistance in order to satisfy a reliability constraint. A parametric electro-thermal model has thus been developed to determine the junction temperature time series. Moreover, a rainflow cycle counting method is introduced for the reliability analysis and lifetime prediction using two aging models, one for wire bonds, the other for the solder joint of the chip.

New multi-rod linear actuator for direct-drive, wide mechanical bandpass applications

In this paper, a new multi-rod linear actuator is presented. This actuator has been developed for high thrust density and wide mechanical bandpass applications. The multi-air-gap concept is first illustrated and explained. Its advantages are highlighted thanks to finite-element method optimizations. Next, the multi-rod prototype technology is discussed. Lastly, experimental measurements for prototype forces are provided.

Micro-kinetic generator: Modeling, energy conversion optimization and design considerations

This article focuses on a micro-kinetic generator, which is used in Autoquartz watches designed by the Swiss manufacturer ETA (part of the Swatch Group). This original electromechanical system, incorporating an intermediate energy storage located in a spring, is based on harnessing the energy from movement. We have built an electromechanical model using the Matlab Simulink application and proceeded with its experimental validation on various movement profiles. Our research has highlighted the existence of an optimal transfer of energy (obtained by either influencing generator design or regulating output voltage of the active rectifier connected to the generator) that helps maximize energy recovery. Finally, this paper presents the results of a system resizing study for the purpose of studying potential system productivity at other scales, and highlights the existence of an optimal set of parameters maximizing energy recovery.

Electromagnetic resonant generator

In this paper, the authors present the energy production potential of a mechanically-resonant electrical generator system, which makes use of natural human walking movements. The characteristics associated with the human walk is discussed first, followed by the electromechanical modeling approach employed. The choice of electromechanical architecture is justified and the permanent magnet and moving coil structure can then be modeled and optimized. A demonstration device has also been generated and tested in order to validate the concept developed as well as the theoretical models derived.

Sizing Optimization of Tubular Linear Induction Generator and Its Possible Application in High Acceleration Free-Piston Stirling Microcogeneration

We usually find applications of rotary induction generator, direct-drive tubular linear permanent-magnet generator, etc. for the mechanoelectrical conversion process within Stirling microcogenerator systems. This paper presents the design optimization investigation for a direct-drive tubular linear induction generator for a dual free-piston Stirling microcogenerator system. On the one hand, a high oscillating frequency and a relatively long pistons travel bring about a very high acceleration of the generators moving part, up to 1018 m/s 2. On the other hand, the tubular linear induction generator offers many interesting assets in this application: low weight mover, appearance of levitation force, no mechanical spring, low mechanical losses, no cogging force, easy manufacture, very low investment and maintenance cost, and so on. However, the tubular linear induction generator is sparsely used, because of its a priori relatively low energetic efficiency. This paper presents a sizing optimization approach for maximizing the performance and demonstrates that, with an astute arrangement of electrical devices, the tubular linear induction generator can constitute a well adapted solution for free-piston Stirling microcogenerator systems.