Emmanuel Godoy

Experimental validation with a control point of view analysis of the SEPIC converter

This paper presents a theoretical study with experimental validation carried out on a DC-DC SEPIC converter operating in continuous conduction mode (CCM). Two dynamic modeling techniques are adopted and various aspects of the converters operating modes are analyzed. Simulations of transient and frequency responses are verified with experimental results. A PI control law is used to validate responses to load and reference voltage variations with parasitic losses taken into account. An in-depth analysis of the effects of unstable zeros of the transfer function, from the duty cycle to the output voltage, on the implementation of control laws is also presented. The frequency behavior of the converter along with the stability margins are found to be widely influenced by load resistance and duty cycle variations.

RST-Controller Design for Sinewave References by Means of an Auxiliary Diophantine Equation

The RST-design of discrete-time controllers is a very handsome method, that brings the solution almost automatically, once the discrete model of the process is known and a model transfer function for the closed loop has been chosen. The cancellation of steady state errors in response to reference signals has been solved a few years ago for polynomial reference signals of any order by the introduction of an auxiliary Diophantine equation. This method has now been extended to sinusoidal references as well, even to a combination of references of both types.

A control strategy to stabilize PWM dc-dc converters with input filters using state-feedback and pole-placement

LC filters at the input of dc-dc converters can lead to instabilities due to filter interactions with the converter control. Conventional methods to remedy this issue usually employ external resistors to damp filter oscillations. However such dissipative damping of input filter degrades the converter efficiency. In this paper we propose an alternate solution to this problem using a full state-feedback controller combined with a PI-control. This control algorithm assures stability of the system without using any passive components in the filter circuit and thus avoiding any undesirable losses. Moreover it guarantees adequate level of performance using a varying gain state-feedback and pole-placement. Simulation studies are carried out to confirm the effectiveness of the suggested control strategy under large perturbations.

Suppression of periodic disturbances in the continuous casting process

In the continuous casting process, the steel level in the mold is controlled using a stopper rod as the flow control actuator and a level sensor. Various control strategies are used in order to reduce the mold level fluctuations which strongly affect the surface quality of the final product. Indeed, under certain casting conditions, the plant is often disturbed by periodic phenomena, in particular bulging or clogging-unclogging generating fluctuations over the free surface, which cannot be efficiently rejected by current controllers. This paper proposes a control architecture based on the introduction of compensation actions in the mold level regulation loop to cancel periodic disturbances occurring on the system. For that purpose, an observer is first designed which estimates disturbances signals. Due to the existence of a time delay within the system, these estimates are further predicted in order to be used as a feed-forward action acting in the control loop. The proposed method combining observer and feed-forward actions is finally validated in simulation, compared with the behavior without anticipative terms.

Formal approach to compute hybrid automata models for linear physical systems with switches

This paper considers the computation of a hybrid automaton that models the behaviour of a switching linear physical system using energy considerations. The system is represented in a compositional way with bond graphs that include switches. In a first step the switches are considered from a functional point of view. This allows to determine the locations that are associated to consistent configuration of switches, the continuous activities and the jumps. In a second step elementary models of switches are introduced and allow to determine the invariants and the guards of transitions. The approach is exemplified with a simple electronics circuit

Nonlinear sliding mode observer and control of high order DC-DC converters

In this paper, the application of the Sliding Mode Theory, in terms of observer and control design, to the DC-DC Single-Ended Primary Inductor Converter (SEPIC) is investigated. The choice and influence of the sliding surface regarding the state vector is presented. Usual sliding surfaces chosen to control other high order DC-DC converters are found not to work on the SEPIC. Thus, other surfaces are proposed here and which require the presence of more than one state variable. Also, an extended sliding mode observer is proposed to estimate the state vector. Results are experimentally validated.

PI Stabilization of Power Converters With Partial State Measurements

In a recent paper a procedure to design globally asymptotically stabilizing linear proportional plus integral controllers for switched power converters was proposed. The construction requires the measurement of the full state of the system, which is often unavailable in practice. In this note we identify a class of converters for which an asymptotically convergent reduced order observer, preserving the aforementioned stability property of the closed-loop, can be designed. The class is characterized by a simple linear matrix inequality. The new controller is illustrated with the widely-popular, and difficult to control, single-ended primary inductor converter, for which simulation and experimental results are presented.

Explicit model predictive control of buck converter

This article proposes a model predictive control (MPC) design to control a fixed frequency DC-DC power converter in a defined operating domain. The prediction model used for the control synthesis is a piecewise affine approximation (PWA) that covers the whole operating range of the converter. Based on the obtained hybrid model a constrained optimal control problem is formulated and solved. The explicit form of the control law is derived offline as an affine state feedback controller. This explicit controller is stored in a look-up table for implementation. The experimental results show the potential advantages of this control approach in comparison with a static state-feedback or a classic PI controller.

A double resonance generator simulation using a hybrid approach

By using a hybrid approach the authors present the modelling of a double resonant DC/DC converter. This kind of generator is used for medical imagery applications, requiring high tensions, typically 40 kV to 200 kV, associated with high powers (about 100 kW). The proposed methodology can constitute an effective method allowing a structured and systematic approach of the dynamic systems modelling

Energy management and control of a fuel cell/supercapacitor multi-source system for electric vehicles

This article presents a control strategy of a multi-source system dedicated to automotive applications, aiming to maximize the global system efficiency. A parallel-architecture of the multi-source system is considered, composed of a fuel cell as a primary power source, a supercapacitor as a secondary storage element, which provides peak power in fast transients, and power converters for the power sources interconnection to the DC bus. The power management is realized as a two-level control structure. The first level contains inner control loops for fuel cell/supercapacitor currents and a DC bus voltage control loop, designed using PI controllers. The higher level consists of an energy management supervision system based on the equivalent consumption minimization strategy. The fuel cell power demand is computed by minimizing the hydrogen mass consumption with respect to system physical constraints. The performances of the proposed control structure are evaluated in simulation, in terms of fuel economy, using an urban driving cycle.