Hervé Cormerais

Comparison of Hybrid Control Techniques for Buck and Boost DC-DC Converters

Five recent techniques from hybrid and optimal control are evaluated on two power electronics benchmark problems. The benchmarks involve a number of practically interesting operating scenarios for fixed-frequency synchronous dc-dc converters. The specifications are defined such that good performance can only be obtained if the switched and nonlinear nature of the problem is accounted for during the design phase. A nonlinear action is featured in all methods either intrinsically or as external logic. The designs are evaluated and compared on the same experimental platform. Experiments show that the proposed methods display high performances, while respecting circuit constraints, thus protecting the semiconductor devices. Moreover, the complexity of the controllers is compatible with the high-frequency requirements of the considered application.

On the stabilisation of switching electrical power converters

This paper considers the control of switching power converters which are a particular class of hybrid systems. Such systems, which are controlled by switches, can be modeled using physical principles. Taking advantage of the energetical properties of their models, a Lyapunov function is proposed. This function, which has not to be computed but is systematically deduced from the physical model, allows to derive different stabilizing switching sequences. From a theoretical point of view, asymptotic stability can be obtained, but it requires null intervals between switching times. In order to ensure a minimum time between switchings, this Lyapunov function has to be increasing for a small duration by using a delay or a dead zone. A control law principle that guarantees the invariance of a specified domain with respect to state trajectories is proposed. Two examples are provided at the end of this paper that demonstrate the efficiency of the proposed approach.

Analysis of the bond graph model of hybrid physical systems with ideal switches

Abstract This paper deals with the modelling of hybrid physical systems. The bond graph technique is used to establish their knowledge model, based upon an ideal representation of the switches. These components are modelled either by flow or by effort sources according to their state and therefore modify the circuit topology at switching times. The paper shows the usefulness of the implicit representation to derive a unique implicit state equation with jumping parameters, to analyse the model properties, to derive an implicit state equation with nilpotency index one for each configuration and to compute the discontinuities. Also, a comparison between the chosen ideal modelling approach and the more common non-ideal approach is carried out using singular perturbations theory. After a presentation of the whole study in the most general context, its results are applied to power converters, which constitute a particular class of hybrid physical systems where switches only commutate in pairs. Finally, an example is developed.

Hybrid Control Techniques for Switched-Mode DC-DC Converters Part I: The Step-Down Topology

Several recent techniques from hybrid and optimal control are evaluated on a power electronics benchmark problem. The benchmark involves a number of practically interesting operating scenarios for a fixed-frequency synchronous step-down DC-DC converter. The specifications are defined such that good performance only can be obtained if the switched and nonlinear nature of the problem is respected during the design phase.

Hybrid control of a three-level three-cell dc-dc converter

This paper compares three synthesis methods for controlling a three-level three-cell dc-dc converter. The main contribution of this paper is to analyse different strategies: i) The Passivity Based Control that uses the notion of average model, ii) A stabilizing method in which a unique Lyapunov function is introduced and iii) A new predictive control approach, which relies on the use of optimization procedures.

Modelling and Passivity Based Control of switched systems from bond graph formalism: Application to multicellular converters

This paper addresses the modelling and control of switched systems with Boolean inputs. A generalization of Passivity Based Control (PBC) is proposed and fitted to bond graph formalism. The state equations of the equivalent average model are first deduced from the original bond graph using the notion of commutation cells and then interpreted according to Port Controlled Hamiltonian formalism. The whole approach is presented in a formal way. This method is then applied on a multicellular serial converter, which is widespread in power systems and of growing interest. The application of PBC associated to a modelling approach using commutation cells on a non-trivial example shows its efficiency to determine a generic controller, the number of elementary cells being considered as a parameter.

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

A GENERIC PASSIVITY BASED CONTROL FOR MULTICELLULAR SERIAL CONVERTERS

Abstract Multicellular converters appeared for a few years in order to palliate some drawbacks of the classical structures. Such structures allow to reduce the voltage throughout the switches and the number of discrete values of the voltage in the load is directly related to the number of commutation cells. In opposing view, the control of a multicellular converter is more complex. In this paper a generic controller for a multicellular serial converter is developed, based on a generalization of Passivity Based Control (PBC) fitted to bond graph formalism. The generic state equations are deduced from the original bond graph model using the notion of commutation cells. The whole approach is presented in a formal way and the performances of the controller realised will be tested on an example.

Extending passivity based control to dae systems with boolean inputs

Abstract This paper addresses the control of switching systems with Boolean inputs and state equations in DAE form. A generalization of Passivity Based Control is proposed and fitted to bond graph formalism in the general case where derivative causality occur in the models. The state equations deduced from the original bond graph models are first made explicit via a special variable change, then interpreted according to Port Controlled Hamiltonian formalism. The whole approach is presented in a formal way, and illustrated on the example of a power converter.

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