Electrical-Continuously Variable Transmission System Based on Doubly Fed Flux-Bidirectional Modulation

A brushless power split system is presented in this paper. The proposed system offers an electric solution for continuously variable transmission (CVT) in hybrid electrical vehicles (HEVs). The key contribution is to use a doubly fed flux-bidirectional-modulation (DF-FBM) machine with two electric ports and two concentric mechanical ports to realize power combination and split in HEV. The torque distribution relationship between two rotors is derived from the mathematical model of the DF-FBM machine and verified by simulation using finite-element method (FEM) and experiment results. This electric CVT system not only integrates the merits of the dual rotor machine and flux modulation machine but also enjoys additional benefits such as high torque density and low-cost partial-scale converter. The operation principle, flux modulation principle, and steady performance of the machine are investigated. Control strategy with dual rotor position feedback is developed. Time stepping FEM is used to analyze the dynamic performance of the proposed system. A prototype is fabricated and the experimental results verify the validity of the mathematical model and simulation results.