Estimating state of charge for HEVs and EVs

  • 15-Mar-2010 10:40 EDT
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Much of IFP's R&D effort is centered on powertrain electrification and electrical energy storage

The technical and commercial success of hybrid-electric and electric vehicles (HEVs and EVs) is strongly related to the efficiency of the vehicle supervisory controller that manages the power flows between the multiple energy sources. Regardless of the control technique adopted, information essential to the supervisor is the state of the electric-energy storage system.

Several techniques are currently used or have been proposed for the state of charge (SoC) estimation. Due to the physical basis of the estimation, France-based IFP, a public-sector research and training center focusing on energy and mobility-industry technologies, proposed an integrated approach. Improved electrochemical and thermal lumped-parameter modeling to the vehicle application is seen as an innovative, promising alternative to popular equivalent circuit models to predict battery behaviors.

This process results in a high precision of advanced 0D electrochemical modeling for both voltage and temperature prediction of battery packs, under currents ranging from zero to strong, while covering the wide thermal window of vehicle applications. The approach translates into a close correlation to 1D models, while keeping the same level of complexity of standard 0D models and avoiding excessive computational time.

Validated against experiments in nominal and extreme operating conditions, these models are of primary interest to study battery performance evolution, during aging, to develop control-law for the battery management system (BMS) or to design and optimize the vehicle architecture on a vehicle/system simulator.

IFP proposes an innovative approach with information and communication technology (ICT) integration to optimize the onboard energy of hybrid/electric vehicles: complete offline optimization of vehicle behavior, system architecture design, optimization of the energy demand (speed profiles), thermal management, consumption/emissions compromise, etc.

Software-in-the-loop (SiL) and hardware-in-the-loop (HiL) simulation platforms and a semi-virtual powertrain test bench (HyHiL) are used for rapid prototyping of in-house energy management control laws and other model-based controllers (engine control, electric machine control, battery management and transmission control).

IFP’s current developments focus on the evaluation of onboard heat recovery systems, with the help of numerical tools, to assess heat recovery potential vs. driving cycle (transient evaluation).

For example, in the case of Rankine cycle-based systems, IFP expertise covers steady-state system predimensioning, real-time system simulation and system testing at the engine test cell (control algorithm, Rankine loop behavior, heat exchanger development, fluid optimization).

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