A Comparison Study Between Two Parallel Hybrid Control Concepts

Two parallel HEV control concepts: ‘thermostat’ and ‘power split’ are compared in this paper. To achieve a substantial improvement in fuel economy, the ‘thermostat’ or ‘on/off’ control technique intended to improve the fuel efficiency of a series HEV has been adopted and designed for parallel HEV. Among different ‘power split’ concepts developed for parallel hybrids only the ‘electrically assist’ algorithm is considered in this paper. These two control concepts are compared for three parallel HEV architectures: pre-transmission, post-transmission and continuous variable transmission hybrids. The comparison study also includes the effect of hybridization factor-the ratio of the electric power to the total propulsion power. The matrices of comparison are level of performance, energy consumption and exhaust emissions. The SAE J1711 partial charge test procedure is followed. The full hybrid propulsion system is simulated using two EV-HEV software packages: ‘V-ELPH’ developed by Texas A&M University and ‘ADVISOR’ from NREL. Based on the simulation results, the paper defines an optimum range of hybridization factor for the two control concepts.