Nonlinear optimal control for ship propulsion with the use of an induction motor and a drivetrain

Vasilios Siadimas,S. Koubias,S. Pantelakis,Masoud Abbaszadeh,Dimitrios Serpanos,Krishna Busawon,Pierluigi Siano,Gerasimos Rigatos

doi:10.1051/matecconf/201818805007

Abstract

A nonlinear optimal (H-infinity) control method is proposed for an electric ship's propulsion system that consists of an induction motor, a drivetrain and a propeller. The control method relies on approximate linearization of the propulsion system's dynamic model using Taylor-series expansion and on the computation of the state-space description's Jacobian matrices. The linearization takes place around a temporary equilibrium which is recomputed at each time-step of the control method. For the approximately linearized model of the ship's propulsion system, an H-infinity (optimal) feedback controller is developed. For the computation of the controller's gains an algebraic Riccati equation is solved at each iteration of the control algorithm.The stability properties of the control method are proven through Lyapunov analysis,

Highlights

Control of the propulsion of electric ships is a non-trivial problem due to the nonlinearities that characterize the associated state-space model and due to the system’s functioning under variable conditions [1]-[2]
The dynamic model of the propulsion system undergoes approximate linearization around a temporary operating point which is recomputed at each iteration of the control algorithm
A nonlinear optimal (H-infinity) control method has been developed for electric ship propulsion systems, comprising a three-phase induction motor, a drivetrain and a propeller

Summary

Introduction

Control of the propulsion of electric ships is a non-trivial problem due to the nonlinearities that characterize the associated state-space model and due to the system’s functioning under variable conditions [1]-[2]. In the present article, a nonlinear optimal control approach is developed for the propulsion system of electric ships, comprising a three-phase induction motor, a drivetrain. The dynamic model of the propulsion system undergoes approximate linearization around a temporary operating point (equilibrium) which is recomputed at each iteration of the control algorithm This operating point is defined by the present value of the propulsion system’s state vector and the last value of the control inputs vector that was applied to it. Conditions for the global asymptotic stability of the control scheme are provided

Dynamics of the mechanical part

Dynamics of the electrical part

Aggregate dynamics

Approximate linearization of the ship’s propulsion model

The nonlinear H-infinity control

H-infinity feedback control

Lyapunov stability analysis

Simulation tests

Conclusions