Eric Berthelot

An Innovative Control Strategy of a Single Converter for Hybrid Fuel Cell/Supercapacitor Power Source

In this paper, an innovative control strategy for hybrid power sources dedicated to automotive applications is detailed. First, an analysis of classical hybrid architectures using fuel cell (FC)/supercapacitors is presented. Then, an analysis of load requirements for automotive applications is proposed. A new control strategy of a single converter, based on a cascaded control loop with a decoupling strategy in the frequency domain, is fully explained. Finally, experimental results on a Ballard proton exchange membrane FC are presented to illustrate the effectiveness of the proposed method.

Speed and rotor flux estimation of induction machines using a two-stage extended Kalman filter

This paper presents an effective implementation of an extended Kalman filter used for the estimation of both rotor flux and rotor velocity of an induction motor. An algorithm proposed by Hsieh and Chen in [Hsieh, C.S., & Chen, F.C. (1999). Optimal solution of the two-stage Kalman estimator. IEEE Transactions on automatic control, 44(1), 194-199] for linear parameter estimation is extended to non-linear estimation, where parameters such as the velocity of an induction machine are present in the transition matrix and in the augmented state space. Compared to a straightforward implementation of an extended Kalman filter, our modified optimal two-stage Kalman estimator reduces the number of arithmetic operations by 25%, allowing higher sampling rate or the use of a cheaper microcontroller.

Diagnosis of Speed Sensor Failure in Induction Motor Drive

A large number of adjustable - speed drives in industry and emerging applications such as automotive (EV or HEV) require high dynamic performances, robustness against parameter variation and also reliability, parameter detuning and mechanical speed sensor faults lead to a deterioration of the performances and even to instability, therefore condition monitoring is becoming mandatory in those sensitive applications. the objective of this contribution is to study the feasibility of detection and diagnosis of the mechanical speed sensor faults in an induction motor drive, using knowledge of the motor condition, the proposed technique based on fuzzy logic is applied to discriminate load and parameter variations from the speed sensor faults, both simulation and experimental results are presented in terms of accuracy in the detection of speed sensor faults and knowledge extraction feasibility.

Supercapacitors for power assistance in hybrid power source with fuel cell

This paper deals with the use of supercapacitors as ancillary power supply in transport applications powered by a PEM fuel cell. These applications are known for strong transient power demand which makes supercapacitors a relevant choice. The aim of this association and its associated power management is to guarantee load requirements as well as to minimize fuel consumption and to ensures that each component constraint is satisfied (lifetime, reliability, high efficiency, …). The designed strategy uses a cascade control allowing a frequency decomposition of the power demand cycle: supercapacitors supply the high band of the load power frequency spectrum whereas low frequencies are provided by the fuel cell which contributes to the longterm autonomy. An experimental 1 kW power test bench has been designed to illustrate the effectiveness of the proposed method. Experimental results are presented demonstrating that this approach provides improvements in terms of a significant energy savings when ancillary power supply is implemented.

Voltage Regulation of a Boost Converter in Discontinuous Conduction Mode: A Simple Robust Adaptive Feedback Controller

Ideal switches in power converters are typically implemented using unidirectional semiconductor devices that may lead to a new operation mode generically called discontinuous conduction mode (DCM). The DCM arises when the ripple, that is, sustained oscillations of small amplitude, is large enough to cause the polarity of the signal (current or voltage) applied to the switch to reverse. Due to the presence of diodes, switches are assumed to operate unidirectionally, but in DCM this unidirectionality assumption is violated. In classicalconverter topologies, DCM appears very frequently in low load operating modes. More interestingly, to achieve high performance some new converters are purposely designed to operate all the time in DCM [1].

A model-based method for the characterisation of stress in magnetic materials using eddy current non-destructive evaluation

A precise knowledge of the distribution of internal stresses in materials is key to the prediction of magnetic and mechanical performance and lifetime of many industrial devices. This is the reason why many efforts have been made to develop and enhance the techniques for the non-destructive evaluation of stress. In the case of magnetic materials, the use of eddy current (EC) techniques is a promising pathway to stress evaluation. The principle is based on the significant changes in magnetic permeability of magnetic materials subjected to mechanical stress. These modifications of magnetic permeability affect in turn the signal obtained from an EC probe inspecting the material. From this principle, a numerical tool is proposed in this paper to predict the EC signal obtained from a material subjected to stress. This numerical tool is a combination of a 3D finite element approach with a magneto-mechanical constitutive law describing the effect of stress on the magnetic permeability. The model provides the variations of impedance of an EC probe as a function of stress. An experimental setup in which a magnetic material subjected to a tension stress is inspected using EC techniques is tailored in order to validate the model. A very good agreement is found between experimental and modelling results. For the Iron-Cobalt alloy tested in this study, it is shown that a uniaxial tensile stress can be detected with an error lower than 3 MPa in the range from 0 to 100 MPa.

Design and Control of A Low Power DC-DC Converter fed by a Photovoltaic array

In this paper, we present a DC-DC converter fed by a PV array for stand alone applications up to 50 W. It is dedicated to rural areas in countries having abundant sunshine and where there is no grid connection to the utility network or the power supply is weak as in many underdeveloped countries. Using a single PV array of 50 W as typical power, the aim is to have a simple system, robust, free- maintenance and highly efficient. The design of the structure has led to a double boost for the DC-DC module (325 V as output voltage) where a high gain is needed ( the input rated voltage is approximately 17 V). Using simulation packages, we have extracted the required characteristics of the power components (switches and diodes) and set the switching frequency. The natural switching behavior of the boost converter is particularly adapted to the use of a sliding mode controller which has been studied. A linear controller based on a linearized model of the DC-DC converter has also been designed and tested. Both controllers have been implemented and the results in terms of dynamic and static performances, robustness and efficiency are promising.

Real-Time Optimal Control of a 3-Phase PMSM in 2-Phase Degraded Mode

This paper aims to optimize real-time control for the degraded mode of a fault-tolerant power architecture but not the fault detection and isolation procedure itself. Such power architecture is dedicated to electric vehicles in which it performs the three following essential functions: traction, battery charging, and electric-grid assistance. For safety reasons, in the degraded mode, power control is limited to the traction mode. Thus, for a given torque, the proposed innovative strategy uses a novel current/voltage transform that leads to efficient real-time control of the torque. The key idea is to drive the current without a priori restrictions on its waveform, while minimizing Joule losses, i.e., the effective value of the current. It has been validated on a laboratory test bench. The studied system is based on a three-phase open-end-winding synchronous machine powered by an inverter with three full H-bridges. The last section of the paper analyzes the comparison between the classic sinusoidal current waveforms and the proposed sinusoidal current waveforms while operating on the two remaining motor phases. It results in a 14% increase of the torque produced by the permanent-magnet machine under test and a 14% decrease of the global system losses in traction mode. As a result, the new control strategy enhances traction performance in degraded mode and increases electric-vehicle autonomy in a postfailure condition.

Sensorless control of Switched Reluctance Machine

The Switched Reluctance Machine is one of the most promising electrical machine in variable speed applications because of its intrinsic robustness and its fault tolerant capability. However, the performances of the machine are deteriorated when a defect affects the position sensor. This paper describes a sensorless control for the switched reluctance machine: two methods based on the characteristics of the machine are proposed to eliminate the requirement of the position sensor. The first one utilizes the phase inductance characteristic to determine the rotor position by injecting a test signal while the phase winding is non-energized. The second one utilizes the flux characteristic to estimate the position by measuring the phase voltage and current. Both methods are evaluated through intensive simulation and the results show their good performance respectively in low speed and high speed region. The flux-based method, implemented in a FPGA, has been evaluated on a test bed. The experimental results confirm the simulation ones with an average position estimation error of around 2° mechanical in the range between 1/3 and the rated speed.

Adaptive Control of the Boost Converter in Discontinuous Conduction Mode

Abstract In this brief note we are interested in the problem of voltage regulation of a classical boost converter operating in discontinuous conducting mode. The system does not admit a (continuous–time) average model approximation, hence is a bona fide hybrid system where the control objective is the generation of a periodic orbit and the actuator commands are switching times. The standard procedure to solve the problem relies on approximations of the solution of the differential equations, which may lead to below par performances (or, as shown here, even instability). Our main contribution is a simple adaptive algorithm that gives explicit formulas for the switching times without approximations and estimates all the uncertain parameters. Simulation and experimental results that illustrate the robustness of the scheme, as well as performance comparisons with current practice, are presented.