S. Pierfederici

Application of SMC With I/O Feedback Linearization to the Control of the Cascade Controlled-Rectifier/Inverter-Motor Drive System With Small dc-Link Capacitor

The necessity of the compactness of the converters in many applications imposes the reduction of the size of their different components when it is possible. In this paper, a control method allowing the use of a small size dc-link capacitor (C o) for the cascade of voltage controlled-rectifier/inverter-motor drive system is proposed. This is achieved by adding the power balance equation in the systems model and the application of an exact I/O feedback linearization technique in a way that the rectifier controller compensates any sudden change in the inverter load, which is here an induction motor. Since the exact I/O feedback linearization technique is sensitive to the uncertainties over system parameters, a robust control strategy based on sliding mode controller (SMC) is proposed. By this approach, the dc-link voltage (v dc) becomes almost insensitive to the load variations. As a result, the level of v dc could be stabilized with a small C o. Without any considerations of the RMS current stress on the C o, a calculation method of a minimum dc-link capacitor C o(min) based on its storage energy is proposed. All the investigations are shown by computer simulations and the performance of controlled system is verified by experimentation results.

High voltage ratio non-isolated DC-DC converter for fuel cell power source applications

In this paper, a non-isolated DC-DC converter with high voltage ratio is proposed for power source like fuel cell. To take into account the low voltage - high density characteristics of power sources, a cascaded structure composed by two sub-converters in cascade has been chosen and allows obtaining a high voltage ratio. The choices of each sub-converter are based on the requirements of the source and its performances. Consequently, we have chosen a two-interleaved boost converter as the 1st sub-converter whereas the 2nd sub-converter is a two-level boost converter. The control of the whole system is realized thanks to energetic trajectories planning based on flatness properties of the system. The control of both the currents and the balance of voltage across the output serial capacitors of the two-level boost converter is ensured by nonlinear controllers based on a new nonlinear model. Experimental results allow validating the proposed power architecture and its associated control.

Nonlinear control of an inverter motor drive system with input filter — large signal analysis of the DC-link voltage stability

The objective of this paper is to detail an analytical method allowing the large signal stability analysis of an electric system constituted by an input filter connected to an actuator (inverter - permanent magnet synchronous motor or induction motor). The proposed approach supposes that a nonlinear control is used to drive the actuators. The studied control allows decoupling the control of torque from the variations of the DC-link voltage and those for any operating point. In many studies, the design of the dc-link capacitance is based on a first order modeling of the system and is realized to ensure only the asymptotic stability around the operating point. The stability is then proved around the operating point. Nevertheless the behavior of the system in case of large disturbances is unknown. In fact the state trajectory goes away from the operating point and behavior of the state trajectory is not foreseen by the modeling. If the state trajectory stays in its attraction region, then it will converge towards the operating point. The present work explains a method based on the takagi sugeno theorem which generates a quadratic lyapunov function which allows the determination of an attraction domain for a given operating point. The knowledge of such a set allows estimating the robustness properties of the control and provides a tool to design the dc-link capacitance value thanks to an estimation of the attraction domain.

New fixed frequency AC current controller for a single phase voltage source inverter

The performance of AC current supplies depends on the characteristic of the current controller technique. In this paper, we propose a new AC current control method with constant switching frequency. This controller is a hybrid controller using both sliding mode control and peak current control. The sliding mode controller generates robustness properties according to the load parameter variations and the peak controller method ensures rapid dynamic response and a fixed switching frequency, well adapted to the current tracking issues like harmonic filtering. In addition, its implementation is relatively simple. To explain the irregular current comportment not foreseen by the high frequency average model a mathematical analysis adapted to chaos theory is developed. Both simulations and experimental results are given to validate theoretical modeling.

Modelling and design of an hybrid modulated hysteresis current controller application to a single phase voltage source inverter

A new hybrid non-linear current controller for imposing the output current of single-phase voltage source converters is proposed and studied. This hybrid controller, called “modulated hysteresis” controller, combines in one hand the robustness properties of a hysteresis controller and on the other hand the zero static error of a linear PI controller. In addition it allows the fixed frequency operation of the converter. To model the proposed non-linear current controller, different tools are developed. In a first step, a high frequency average model to study the average dynamic properties (bandwidth, time response, overflow) is proposed. To investigate the behavior of the current ripple due to the switching effect, a second model, based on the construction of a three-dimensional bifurcation diagram and the definition of a form function, is developed. It allows determining the nature of each cycle by studying the state trajectory during the corresponding switching period. Design rules of the parameters of this hybrid non-linear current controller are explained and its robustness properties are tested by numerical simulation and experimentation.

Study of AC modulated hysteresis current controller for a single phase voltage source inverter

The performances of AC current supplies depend on the characteristics of its current controller. In this paper, we study a large bandwidth AC-current controller combining the robustness properties of a hysteresis controller with constant switching frequency of PWM technique. A high frequency average model is proposed for this modulated hysteresis regulator to study its dynamic properties. A second approach of modeling, based on the construction of a three-dimensional bifurcation diagram allows studying the nature of the cycle described by the state trajectory and to prove that the system operates with a fixed switching frequency. Design rules of control parameters of this controller are explained and its robustness properties are tested by numerical simulation.

Implementation of a Flatness Based Control for a Fuel Cell-Ultracapacitor Hybrid System

A flatness based control of a hybrid system composed of a fuel- cell and an ultracapacitor is investigated and implemented in this paper. For this purpose, at first, the system is provided to be flat and an expression which takes into account the power losses in converters is extracted to control variables. Three control methods, sliding mode, state feedback and classical PI controllers are considered to ensure the control of the flat outputs to their references. The dSPACE-based implementation results are presented to validate operation of each control method in the purposed hybrid system.

Application of SMC with I/O Feedback Linearization to the Control of the Cascade Controlled-Rectifier/Inverter-Motor Drive System with a Small DC-Link Capacitor

The necessity of the compactness of the converters in many applications imposes the reduction of the size of their different components when it is possible. In this paper a control method allowing the use of a small size DC-link capacitor for the assembly voltage controlled-rectifier/inverter-motor drive system is proposed. This is achieved by adding the power balance equation in the systems model and the application of an exact I/O feedback linearization technique in a way that the rectifier controller compensates any sudden change in the inverter load, which is here an induction motor. Since the exact I/O feedback linearization technique is sensitive to the uncertainties over system parameters, a robust control strategy based on sliding mode controller (SMC) is proposed. By this approach, the DC-link voltage becomes almost insensitive to the load variations. As a result, the DC-link voltage level is stabilized with a small DC-link capacitor. The robust property of the overall controlled system to the variation of the rotor time constant of the induction motor is investigated when an opened loop flux observer is used. The simulation and experimentation results can confirm the performance of the control system

Performance Investigation and Comparison of Two Different Electrical Hybrid System Structures

Two different topologies of an electrical hybrid system composed of a fuel cell as main source and an ultracapacitor as auxiliary source are investigated in this paper. To control these hybrid systems, a flatness-based control method which eliminates algorithm commutation in different operating modes is employed and its operation is studied in each structure. After simulating model of the structures, system efficiency in steady states is calculated while all ohmic, switching and conduction losses are considered. The simulation results show well performance of the proposed control method in both topologies and allow comparing operation of the systems in different situations.

Load power compensations for stabilized DC-link voltage of the cascade controlled rectifier/inverter-motor drive system

The necessity of the compactness of the converters in many applications imposes the reduction of the size of their different components when it is possible. In this paper, the cascade of a grid connected voltage controlled rectifier and an inverter supplying a motor is considered and the effect of diminution of DC-link capacitor (C/sub 0/ on Fig.1) on the stability of the DC-link voltage is investigated using small-signal linearization and impedance criterion. The output impedance of the controlled rectifier is studied in both cases of DC-link voltage control (DC-VC) and DC-link energy control (DC-EC). The input impedance of the inverter-motor stage, for which the control is based on the classical field orientation, is also explained. In ideal case, if the power delivered by the controlled rectifier can track the load power, the DC-link voltage remains almost constant even in transitory state. Under this condition a low value of C/sub 0/ could ensure the stability of the DC-link voltage. Then, three methods of power load compensation, i.e. a decoupling matrix, a nonlinear feedback compensation and the feedback linearization technique, are proposed and studied for stabilizing the DC-link voltage. The results are illustrated by means of digital computer simulations of complete induction motor and controlled rectifier models with full order linear closed loop flux observer.