Real-Time Energy-Efficient Traction Allocation Strategy for the Compound Electric Propulsion System

Abstract

This paper presents the development of a novel compound electric propulsion system for the ground vehicle with the emphasis on real-time, energy-efficient traction control strategy. The proposed compound electric propulsion system employs an induction motor (IM) and two permanent magnet synchronous motors (PMSM) to provide traction forces for the front and rear wheels, respectively; such design is aimed to improve energy efficiency and vehicle dynamics performance of conventional electric vehicles using IM traction systems by exploiting complementary power characteristics of IM and PMSMs and dynamic traction allocation on all wheels. In this study, a practical traction allocation method, which is based on the power fusion and instantaneous power minimization (IPM) concepts, is proposed to dynamically control the torque loads for the IM and PMSMs, such that all motors can be operated in respective high efficiency regions. The optimal operating points (torque, speed) of IM and PMSMs are searched offline through the IPM process, and the efficiency maps of the IM and PMSMs are combined and transformed into an optimal efficiency map of the compound electric propulsion system. To verify the feasibility and efficacy of the proposed traction allocation strategy, hardware in the loop simulation experiments were conducted with an active motor dynamometer, IM and PMSM, and a vehicle simulator.

Existing System

Optimization controller for induction motor drives.

Proposed System

In this paper, a novel electric propulsion system for the four-wheel EV is presented. The system, dubbed compound electric propulsion system, combines an induction motor (IM) and two PMSMs to provide traction forces for all wheels. The IM drives the front wheel axle through a speed reduction gearbox, and two PMSMs drive rear wheels, independently. Such EV compound powertrain system design is aimed to improve energy efficiency of the IM traction system through propulsion fusion of complimentary PMSMs as well as to enhance the vehicle dynamics and stability control performance through independent control of the rear wheel motors, such as differential traction/regenerative braking for yaw stabilization control. Finally, the energy consumption tests are performed using HiLS/CiLS techniques. The superior energy economy of the proposed EV powertrain system over the conventional IM traction system is verified. In addition, the feasibility and effectiveness of the proposed real-time traction allocation method for the compound electric propulsion system are evaluated.

Architecture

Configuration of the compound electric propulsion system

Schematic plot of the EV powertrain HiLS/CiLS platform