Energy Management in Electric Vehicle based on Frequency sharing approach, using Fuel cells, Lithium batteries and Supercapacitors

This paper deals with an energy management improvement based on frequency sharing approach for an electric vehicle. In order to satisfy the traction/propulsion system requirement, the Fuel cell (FC) system is assisted by lithium-ion batteries and Supercapacitors (SC). Bidirectional Buck Boost converters link the batteries and Supercapacitors to the DC-Bus. The FC stack is connected to the DC-Bus by an interleaved Boost DC-DC converter. The traction/propulsion motor is a permanent magnet synchronous motor (PMSM) coupled to a DC motor in order to emulate the vehicle's load and energy requirements during the driven cycle. The DC-Bus feeds the permanent magnet synchronous motor via a bidirectional DC-AC converter. The contribution of this study involves EV's energy effort sharing between Supercapacitors, Fuel cells and Lithium-ion batteries, taking into account the dynamic responses and electrical performances of each energy sources. The effectiveness of the control is verified through simulations performed on Matlab/Simulink software.

I. Introduction

Fully electric multi-source systems are an attractive solution for a wide range of applications, for example microgrids, hybrid electric boats and electric vehicles etc. On the one hand, these systems are fully electric which means that the environmental impact is greatly reduced, on the other hand these systems use mainly electricity, an energy qualified cleanliness and easily controllable [1] [3]. In this paper, this type of system is investigated for electric vehicles applications. For electric vehicle applications, the energy requirement is very fluctuating and strongly depends not only on the driving conditions but also on the driver’s behavior. Depending on the number and type of sources contained in the multi-source system, the energy demand must be well shared over the different sources according to their dynamic performance. In fact, the main source, which is generally an energy source, cannot ensure fluctuating demands, it will cause the deterioration of its state of health and subsequently the reduction of its life span. Generally, the main source is assisted by other types of sources having much greater dynamics and good response to power peaks as well as rapid load solicitations. The configuration of the considered multisource system is presented in Fig.1, where the Fuel cell system is connected to the DC-Bus via an interleaved Boost converter and the energy storage devices (Batteries and Supercapacitors banks) are linked to the DC-Bus through Buck-Boost converters. The traction/propulsion system is composed of a PMSM coupled to a DC motor, a two-level inverter links the PMSM to the DC-Bus, and it allows to controls the synchronous machine in terms of speed and torque. The DC machine emulates the vehicle loads (weight, resistant forces, driving conditions, etc.). Energy management based frequency sharing method is the main contribution of this paper. This approach reduces the impact of the load power fluctuations on the main source (the Fuel cells in this case), it makes possible to benefit from the characteristics of each used sources in terms of dynamic response, and finally it reduces the size of the main source by reducing the amount of energy stored [2].