Christophe Turpin

Interactions Between Fuel Cells and Power Converters: Influence of Current Harmonics on a Fuel Cell Stack

As fuel cells are likely to be used in many future applications, dedicated power converters must be developed and optimized. A thorough knowledge of the fuel cell operation is thus required for power electronics engineers. This paper proposes a theoretical and experimental study of the behavior of a fuel cell stack subject to current harmonics. The fundamental role of the internal double layer capacitor is demonstrated

Multicell converters: derived topologies

Multicell converters were introduced ten years ago and, over this period, their properties have been thoroughly analyzed. Since then, this concept has lead to some other innovative topologies which are briefly presented in this paper. Different ways to introduce soft switching in multicell converters are investigated. The concept of distributing power over several switches, giving more degrees of freedom and using less passive components, is extended further with the stacked multicell topology. Finally, direct AC-AC converters using the multicell approach are described.

Fault management of multicell converters

Component counts and oversimplified reliability rules may lead to the conclusion that multilevel converters are less safe than two-level converters, just because they use more components. A better approach might be to consider that they use a different arrangement of components and also that the consequence of faults may be very different. This paper is focused on the study of the consequences of faults in hard-switching and soft-switching multicell converters. Solutions to minimize the consequences of major faults are described.

Interactions between fuel cells and power converters influence of current harmonics on a fuel cell stack

As fuel cells are likely to be used in many future applications, dedicated power converters must be developed and optimized. A thorough knowledge of the fuel cell operation is thus required for power-electronics engineers. This paper proposes a theoretical and experimental study of the behaviour of a fuel cell stack subject to current harmonics. The fundamental role of the internal double layer capacitor is demonstrated.

Use of opposition method in the test of high-power electronic converters

The test and the characterization of medium or high-power electronic converters, under nominal operating conditions, are made difficult by the requirement of high-power electrical source and load. In addition, the energy lost during the test may be very significant. The opposition method, which consists of an association of two identical converters supplied by the same source, one operating as a generator, the other as a receptor, can be a better way to do these test. Another advantage is the possibility to realize accurate measurements of the different losses in the converters under test. In the first part of this paper, the characteristics of the method concerning loss measurements are compared to those of the electrical or calorimetric methods, then it is shown how it can be applied to different types of power electronic converters, choppers, switched mode power supplies, and pulsewidth modulation inverters. In the second part, different examples of studies conducted by the authors, and using this method, are presented. They have varying goals, from the test of soft-switching inverters to the characterization of integrated gate-commutated thyristor (IGCT) devices mounted into 2-MW choppers.

A Large-Signal and Dynamic Circuit Model of a

The authors propose a large-signal and dynamic circuit model for a proton exchange membrane fuel cell, which includes the following different main physical and chemical phenomena: activation, electrochemical double layer, gas diffusion through the gas diffusion and active layers, and ohmic losses. Be careful: this is not an impedance model. This model will be used in studying the interactions between fuel cells and power converters which are connected and, particularly, the fuel-cell behavior facing the perturbations created by the buck converter and the single-phase inverter.

\hbox{H}_{2}/\hbox{O}_{2}

The imbricated-cell multilevel converter is well suited to high power applications. It allows the series connection of n switches with natural voltage sharing between these switches enabled through the connection of n-1 flying capacitors. This paper deals with the application of soft-switching on this topology; to date, only the hard-switching mode has been studied. The use of soft switching enables an increase of the switching frequency (resulting in the size reduction of the flying capacitors) without a decrease of the converter efficiency. Of the soft switching methods considered, the Auxiliary Resonant Commutated Pole (ARCP) technique was chosen due to the relative ease in which it can be incorporated into the converter topology. Furthermore, this technique offers numerous advantages: loss reduction, no added stress to the switches and compatibility with PWM control. The main properties of the ARCP multicell converter are the same as the hard-switched topology: an increase of the apparent output switching frequency and natural self-balancing of the flying-capacitor voltages. This paper presents the results of both simulations performed and measurements taken from an experimental set-up in order to study the viable system functioning. The introduction of soft-switching strongly complicates the theoretical study of the balancing mechanisms, however. As a result, the authors depend on simulations to validate the natural balancing effect during soft switching. Lastly, a general method of loss measurement is presented. Results show that the converter losses are reduced by at least 30%.

PEM Fuel Cell: Description, Parameter Identification, and Exploitation

The auxiliary resonant commutated pole (ARCP) multicell converter is a soft-switched variant of the multicell converter. It is shown in this paper that the ARCP technique can be very efficiently used in multicell flying capacitor converters. The main properties of the resulting soft switching multicell converter are very similar to those of the hard-switched version. They are presented and validated by simulations as well as experimental results. In practice, due to the damping, the ARCP multicell converter can suffer from switching faults as in two-level ARCP inverters, but in the case of a multicell converter failures can occur in different cells. So, the main control strategies are evaluated and the switching process is discussed step by step, taking account of the main imperfections of actual control circuits. When they can occur, the switching faults are described and analyzed. Finally, an original quasisoft switching control that should give a high safety of operation is proposed. Experimental results obtained with a 900 V-100 A ARCP multicell inverter leg are given and the performances are compared with those of a hard-switched multicell inverter leg of the same rating.

A ZVS imbricated cell multilevel inverter with auxiliary resonant commutated poles

This paper proposes a structure and two strategies for hybridization of a RAT (Ram Air Turbine) with supercapacitor storage. The structure consists in coupling a High Voltage DC (HVDC) source (RAT) with a low voltage storage device through a specific topology of bidirectional DC-DC static converter. The energy management strategies consists in entrusting the storage with the “high frequency” harmonics of the load power while the RAT only produces the average power: the RAT sizing and its mass can then be reduced. Lab test bench architecture, control strategy, topology of the converter and experimental results are presented in this paper.

Switching faults and safe control of an ARCP multicell flying capacitor inverter

This paper proposes a diagnosis method of a hydrogen/air fuel cell using a quasi-static model coupled to a parameter identification method that are both described. An original statistical approach is proposed in an effort to obtain a certain guaranty on the validity of the identified parameters and raise in this way the associated “confidence index”. The analysis of the degradation of a fuel cell is afterwards achieved by comparing parameters identified before and after the degradation. A diagnosis is then presented based on the analysis of the different losses occurring within the fuel cell in an effort to monitor and control on-board systems.