Optimal frequency separation of power sources by multivariable LPV/H∞ control: Application to on-board energy management systems of electric vehicles

Abstract

In this paper a multi-variable LPV/H∞ control approach is applied to design a strategy for power source coordination within a multi-source energy system. Three different kinds of power sources - fuel cell, battery and ultracapacitor - compose the power supply system of an electric vehicle. All sources are current-controlled and paralleled together with their associated DC-DC converters on a common DC-link coupled to vehicle's electrical motor and its converter. DC-link voltage must be regulated in spite of load power variations representing the driving cycle image. To this end, a MIMO LPV/H∞ provides the three current references so that each source operates in its most suitable frequency range as either high-energy-density or high-power-density source: low-frequency, the mean power is provided by the fuel cell, the ultracapacitor supplies/absorbs the instantaneous variations of power demand and the battery operates in between the two other sources. Selection of H∞ weighting functions is guided by a genetic algorithm whose optimization criterion expresses the frequency-separation requirements. The nonlinear multi-source system is simulated in MATLABP® /Simulink® using the driving cycle of IFSTTAR (Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux) as load profile, whose frequency content is richer than the one of Normalized European Driving Cycle (NEDC). Simulation results show good performance in supplying the load at constant DC-link voltage according to user-configured frequency-separation power sharing strategy.