Search

A new electrically driven gas booster is described as an alternative to the classical air-driven gas boosters known for their poor energetic efficiency. These boosters are used in small scale Hydrogen storage facilities and in refueling stations for Hydrogen vehicles. In such applications the overall energy count is of significance and must include the efficiency of the compression stage. The proposed system uses an electric motor instead of the pneumatic actuator and increases the total efficiency of the compression process. Two mechanical principles are studied for the transformation of the rotational motion of the motor to the linear displacement of the compressor pistons. The strongly fluctuating power of the compressor is smoothed by an active capacitive auxiliary storage device connected to the DC circuit of the power converter. The proposed system has been verified by numeric simulation, including the thermodynamic phenomena, the kinetics of the new compressor drive and the the operation of the circuits of the power smoothing system. [ABSTRACT FROM AUTHOR]

Maintaining a fuel cell (FC) system in correct operating conditions when subjected to fast load changes requires good system control. The best results are typically achieved using model-based control strategies. This paper elaborates a control-oriented proton exchange membrane FC system model in two distinct steps. First, the FC auxiliary systems (i.e., air and hydrogen supply along with thermal management) are described in a state-space approach linking user input to FC operating conditions. A steady-state FC stack model then describes the effect of those operating conditions on system performance. The model then allows the implementation of advanced control strategies such as multivariable control with decoupling, actuator sensitivity analysis or maximum efficiency tracking algorithms. Index Terms--Fuel cell (FC), modeling, state-space control.

The transient and static behavior of an insulated gate bipolar transistor (IGBT) are analyzed through finite elements simulations and physically based equations. The standard model using a bipolar transistor driven by a MOSFET is abandoned for three partial voltage drops in series, each with its specific static and dynamic behavior. One voltage drop on the internal MOSFET, one on the base and one on the collector-base junction. It is found that the dynamic model can be drastically simplified by focusing on the equivalent electron density. This takes into account the most important phenomena related to the carrier mobilities, necessary for an accurate transient modeling. The specific behavior of the gate-collector capacitance in soft switching conditions is discussed. An equation set based on semiconductor physics is developed to determine the static operating points for each contribution. The importance of the minority carriers transit time in soft switching conditions is then shown. The similarity observed between the waveforms obtained through a finite element simulation and the waveforms obtained using the developed IGBT model within various external structures validates the proposed approach. Index Terms--Insulated gate bipolar transistor (IGBT).

Control structures and strategies have a critical influence on a power electronic converter's behavior during disturbances. Most of the previous works in the field of pulsewidth modulation voltage-source converter (VSC) operation under unbalanced conditions propose dual vector controllers with dc bus voltage optimization strategies, which have been proven to be well adapted for rectifier applications. In this paper, two major contributions are made. On the one hand, a new optimized operation strategy based on exchanged power maximization is proposed for vector control structures, which permits the extension of optimized operation to other VSC applications (e.g., flexible alternating current transmission system and distributed generation interfaces). On the other hand, a scalar control structure is proposed based on resonant controllers, together with three adapted optimized operation strategies, namely: 1) dc bus voltage optimization; 2) power exchange maximization; and 3) a hybrid strategy (an intermediary mode between the other two strategies). Their main advantage is their simplicity and the lack of real-time symmetrical component extraction techniques. This scalar controller and the proposed optimized operation strategies are compared to conventional vector controllers. It is proven through experimental analysis that the proposed scalar controller offers very good performances with simpler structures and bigger flexibility in terms of operation modes. Index Terms--Current control, pulsewidth modulation (PWM) converters, voltage sag (dip), voltage unbalance.

The aim of this paper is to present a universal power quality conditioning system (UPQS) named after unified power quality conditioner, which is extended by adding a shunt active filter at the load side. Its main purpose is to compensate for both supply voltage and load current imperfections, such as: sags, swells, interruptions, imbalance, flicker, harmonics, reactive currents and current unbalance. Such system has better harmonic compensation characteristic, since there are no problems associated with passive filter operation. Converter and control analysis is presented, together with results showing the UPQS modes of operation. Index Terms--Active filter, converter, harmonics, power conditioning, power quality.

In addition to the high-capacity storage facilities based on hydropower technologies, electrochemical solutions are today's candidate for storage for renewable energy sources support. However, sustainability and limited life cycles of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, which is mainly based on compressed air, where the storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted mean power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. This paper describes the concept of the system, the power-electronic interface circuits, and especially the maximum efficiency point tracking (MEPT) algorithm and the strategy used to vary the output power. In addition, this paper presents the characteristics of high-efficiency storage systems where the pneumatic machine is replaced by an oil-hydraulic and pneumatic converter, which is used under isothermal conditions. Practical results are also presented, which are recorded from a low-power pneumatic motor coupled to a small dc generator as well as from the first prototype of the final hydropneumatic system. Index Terms--Compressed air, energy storage, maximum efficiency point tracking (MEPT), supercapacitors.

Air-magnetic circuit breakers are widely used for short-circuit protection in dc electric railways or industrial plants. The well-known drawbacks of these breakers are mainly a slow breaking action, a short lifetime, and high maintenance costs due to the destructive effects of the arc. The use of power semiconductors in a full-static circuit breaker configuration allows the elimination of these disadvantages but is limited by excessive conduction losses. The paper will present the study of a so-called hybrid breaker, drawing its name from the combination of a high-speed mechanical switch and a bi-directional integrated gate-controlled thyristor assembly connected in parallel. The paper also includes experimental results from a prototype real scale. Index Terms--Arcless interruption, fault current limiter, hybrid high-speed circuit breaker, integrated gate-controlled thyristor (IGCT), mechanical switch, metal-oxide varistor.

In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage industrial drives. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase. To keep the power part simple and the efficiency high, the subinverters have no feeding from the net and can only supply reactive power. This is a very interesting solution in terms of power quality, efficiency, reliability, and cost. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an online nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behavior in steady state and during transients. Precharging of the nonsupplied capacitors is also an issue to consider. This paper proposes a startup method that charges them in parallel with the supplied ones, without any additional equipment. Measurements show its successful application in the proposed drive system. Index Terms--Converters, motor drives, multilevel systems, optimal control, power electronics, predictive control.

A supercapacitive-storage-based substation for the compensation of resistive voltage drops in transportation networks is proposed. It allows to feed as a current source in any voltage conditions of the line. The system has been designed as a compensation substation to be placed at weak points like end-of-fine stations, instead of additional feeding substations. A dedicated power-electronic converter with an associated control system for the stabilization of the voltage level at the point of coupling in case of strong perturbations is proposed. Practical results are also presented, which have been recorded from a reduced size prototype. Index Terms--Energy storage, supercapacitors, transportation networks, voltage drop compensation.

In recent years, power variations and energy criteria have been the main motivations for developing regenerative drive converters for elevators [1]. A better performing solution for power smoothing can be easily found by using a supercapacitor-based storage device, connected to the intermediary circuit of a variable-speed-drive system. In this paper, power and energy considerations are being accounted for in the design of the storage tank and regarding the maximum power demand from the feeding network. For the power-conversion circuit, which is necessary to compensate the voltage variations of the supercapacitors during charge and discharge, a high-efficiency converter topology is proposed, which allows the bidirectionnal energy flow under soft-commutation conditions. Additionally it offers a good flexibility for the optimal sizing of the supercapacitor voltage level. The typical behavior of the special converter is given, together with an analysis of the advantages related to the specific application. Index Terms--Energy storage, load leveling, medium-frequency transformers, supercapacitors.

This paper proposes two frequency based methods for parallel active filtering of current harmonics in utility grids. Active filter (AF) reference prediction and AF current control are the two key-points to obtain high performances. This paper deals with the AF reference prediction. The two proposed methods are based on the Fourier Series and its implementation on Dsp. They. belong to two prediction structures: 1) the open-loop structure which predicts the reference currents from the load currents; 2) the closed-loop structure which predicts the reference currents from the grid currents. Fourier Series based methods are very flexible and have several interesting properties. These two methods have been successfully implemented and tested. The latter method cancels permanent errors and results in better performances. Both methods are very flexible. Index Terms--Active power filtering, closed loop, FFT.