Boehme, T., Metwally, O., Becker, B., Meinhardt, N. et al., "A Simulation-Based Comparison of Different Power Split Configurations with Respect to the System Efficiency," SAE Technical Paper 2012-01-0438, 2012, doi:10.4271/2012-01-0438.
In power-split configuration, the input power is split into two parts, one of which is transmitted from the internal combustion engine through one or more planetary gear(s) to the wheels. The other part is generated as electricity and passes through an electrical variator to assist the driving torque. The latter has the characteristic of poor efficiency. In this simulation study, a comparison among the input power-split, compound power-split, and two mode power-split are discussed. Output power-split is not mentioned in this paper due to its limited applicability in specific vehicles. The idea of selection of the electrical machines is explained: the speed and torque of electrical machines was taken into consideration for the required transmission ratios spread.