Sensitivity Analysis and Optimal Design of a Dual Mechanical Port Bidirectional Flux-Modulated Machine

This paper presents an optimal design methodology of a dual-mechanical-port bidirectional flux-modulated machine for electric continuously variable transmission in hybrid electrical vehicles. The machine utilizes bidirectional flux modulation effect to combine two rotors and one stator together, aiming to realize electrical and mechanical power flexible split and combination. Due to the complexity of the machine structure, conventional optimization methods using analytical model are inapplicable. Therefore, an effective and practical method that combines the genetic algorithm and finite-element method (GA-FEM) is proposed to optimize the design of the machine in this paper. Since the computational cost increases exponentially with the increasing of number of design parameters, to reduce the computational cost in the optimization process, the design parameters are divided into two levels basing on a sensitivity analysis. And, then, the sensitive parameters are optimized using the GA-FEM coupled method. Finally, a prototype is fabricated to verify the effectiveness of the optimal design.

I. Introduction

Nowadays, planetary gear unit is widely used in commercial successful hybrid electric vehicles (HEVs), such as Toyota Prius series and Cadillac CT6. The planetary gearbox is a core component of the electronic continuously variable transmission (E-CVT) system in HEVs, which can split and combine the mechanical power from the internal combustion engine (ICE) and the electrical power from battery to drive the wheels efficiently. In Toyota Prius, the ICE couples with the carrier or planetary gear, the sun gear is connected with Motor/Generator I and the ring gear couples with both Motor/Generator II and the final drive. Recently, to reduce maintenance costs and improve the fuel economy, the dual-mechanical-port permanent-magnet (DMP-PM) machine and its application in HEVs have attracted increasing attention [1]–[4] . The DMP-PM machine proves to be a potential option to substitute the planetary gear unit in E-CVT system. The novel E-CVT system with a DMP-PM machine is more compact, M/G I and M/G II are integrated into one compound machine frame and the planetary gearbox is not required. Compared with the conventional gear box based E-CVT system, the E-CVT system with DMP-PM machine has many advantages, such as high reliability, low mechanical vibration, and low audible noise.