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Nonlinear Voltage Regulation of an Auxiliary Energy Storage of a Multiport Interconnection

Felipe Morales, Rafael Cisneros, Romeo Ortega, Antonio Sanchez-Squella

TL;DR

The paper tackles nonlinear voltage regulation in a multiport interconnection comprising a bidirectional two-stage buck-boost DC-DC converter connected to a supercapacitor and a current-source load. It introduces a novel partially cascaded control strategy that decomposes the system into two subsystems and employs a dynamic reference extension to achieve regulation of the downstream port voltage while keeping the remaining states bounded. Controllers are derived for each subsystem, with an implementable realization that avoids sensitive open-loop differentiation. The overall control law guarantees asymptotic regulation of the targeted voltage, practical regulation of the auxiliary voltage, and bounded signals, as validated by both simulations and experimental tests. The approach is relevant for renewable energy systems and electric vehicle powertrains where fast, robust, bidirectional energy exchange is required between energy storage and loads.

Abstract

In this article, we propose a nonlinear voltage control to ensure power exchange in a multiport interconnected system, which consists of a bidirectional DC-DC converter and generating-storing devices. The converter topology under consideration is two-stage, composed of an interconnection of a buck with a boost converter. The motivation for this work is the explosive increase in the use of DC-DC converters due to the massification of renewable energies, electric vehicles powertrains, and energy storage systems, where fuel cells or batteries can be used as power backup or high-power support during transient phenomena. The converter's voltage step-up and step-down capabilities allow the use of supercapacitors with voltage limits that exceed those required by the load, thus enabling its use in a broader range of applications. The control design for this system does not correspond to that in standard applications involving power converters. As it is known, the latter consists of finding a control law such that the closed-loop system has an asymptotically stable equilibrium point fulfilling the voltage regulation objectives. Instead, in this application, the state does not tend to an equilibrium value in order for the system to be regulated. The converter voltage is regulated at desired some setpoint whereas the other variables are only required to be bounded. To achieve a dynamic response that best adapts to changes in system demand and ensure stability over the defined wide operating range we propose a novel control strategy that exploits the partially cascaded structure of the system. Numerical and experimental results validate our approach.

Nonlinear Voltage Regulation of an Auxiliary Energy Storage of a Multiport Interconnection

TL;DR

The paper tackles nonlinear voltage regulation in a multiport interconnection comprising a bidirectional two-stage buck-boost DC-DC converter connected to a supercapacitor and a current-source load. It introduces a novel partially cascaded control strategy that decomposes the system into two subsystems and employs a dynamic reference extension to achieve regulation of the downstream port voltage while keeping the remaining states bounded. Controllers are derived for each subsystem, with an implementable realization that avoids sensitive open-loop differentiation. The overall control law guarantees asymptotic regulation of the targeted voltage, practical regulation of the auxiliary voltage, and bounded signals, as validated by both simulations and experimental tests. The approach is relevant for renewable energy systems and electric vehicle powertrains where fast, robust, bidirectional energy exchange is required between energy storage and loads.

Abstract

In this article, we propose a nonlinear voltage control to ensure power exchange in a multiport interconnected system, which consists of a bidirectional DC-DC converter and generating-storing devices. The converter topology under consideration is two-stage, composed of an interconnection of a buck with a boost converter. The motivation for this work is the explosive increase in the use of DC-DC converters due to the massification of renewable energies, electric vehicles powertrains, and energy storage systems, where fuel cells or batteries can be used as power backup or high-power support during transient phenomena. The converter's voltage step-up and step-down capabilities allow the use of supercapacitors with voltage limits that exceed those required by the load, thus enabling its use in a broader range of applications. The control design for this system does not correspond to that in standard applications involving power converters. As it is known, the latter consists of finding a control law such that the closed-loop system has an asymptotically stable equilibrium point fulfilling the voltage regulation objectives. Instead, in this application, the state does not tend to an equilibrium value in order for the system to be regulated. The converter voltage is regulated at desired some setpoint whereas the other variables are only required to be bounded. To achieve a dynamic response that best adapts to changes in system demand and ensure stability over the defined wide operating range we propose a novel control strategy that exploits the partially cascaded structure of the system. Numerical and experimental results validate our approach.
Paper Structure (14 sections, 5 theorems, 42 equations, 16 figures, 4 tables)

This paper contains 14 sections, 5 theorems, 42 equations, 16 figures, 4 tables.

Table of Contents

  1. Introduction
  2. System Description, Modelling and Control Objective
  3. Two Suitable Decompositions of the Overall Systems
  4. First decomposition for the controller design
  5. Decomposition as feedback interconnection of two passive systems
  6. Controller Design
  7. Controller for the subsystem $\Sigma_1$
  8. Controller for the subsystem $\Sigma_2$
  9. An implementable realization of the controller of $\Sigma_2$
  10. Control Law for the Overall System
  11. Simulation and Experimental Results
  12. Simulation Results
  13. Experimental Results
  14. Concluding Remarks and Future Research

Key Result

Lemma 1

The system sys admits the representation of Fig. 3 where, for all control signals $u_1$ and $u_2$, the operator $\bar{\Sigma}_1^M: v \to y$ is output strictly passive and the operator $\bar{\Sigma}_2: -y \to x_2$ is a strictly positive real (SPR) transfer function, hence it is strictly passive. As a

Figures (16)

  • Figure 1: Considered topology.
  • Figure 2: Feedback interconnection representation of the system \ref{['sys']}
  • Figure 3: Representation of the system \ref{['sys']} as a feedback interconnection of two passive systems.
  • Figure 4: Alternative representation of the system \ref{['sys']}
  • Figure 5: System $\Sigma_1$: impact of the controller gains on $x_4$ when $x_4^\star$ varies in simulation.
  • ...and 11 more figures

Theorems & Definitions (10)

  • Remark 1
  • Lemma 1
  • Remark 2
  • Lemma 2
  • Remark 3
  • Lemma 3
  • Remark 4
  • Corollary 1
  • Remark 5
  • Proposition 1