University of Technology Sydney. Faculty of Engineering and Information Technology.Currently, most pure electric vehicles (EVs) in the commercial market are equipped with a single-speed transmission. However, this configuration presents some disadvantages such as compromised driveability performance and lower overall efficiency due to the limited freedom in determining optimal states for motor drives. Therefore, using multi-speed transmission (MST) in EVs is regarded as a viable scheme to improve the EV performance further. This thesis focuses on the control of a dual motor-based multi-speed transmission. More specifically, the thesis centres on the following three research topics: 1) powertrain modelling and model-based torque observer design; 2) high-performance motor control including position/speed sensorless operation, controller and observer design under low pulse ratio, and closed-loop control based on synchronized pulse width modulation; 3) gearshift control including coordinated torque and speed control of two motors, speed synchronization and active vibration damping control.
The first part of this thesis introduces the configuration of the studied MST, its advantages and the issues need to be addressed. Additionally, the detailed transmission and motor models are developed for theoretical analysis and controller design. The requirement of the motor drive in an EV involves more than the satisfactory steady-state performance but also fast dynamic response and high battery-to-motor efficiency. The control of motor drive is the fundamental based on which an EV can be driven efficiently, comfortably and safely. Therefore, the second part of this thesis work develops control schemes for the induction motor (IM) and permanent magnet synchronous motor (PMSM) which are currently the main choices for EVs. The improved observers are designed to achieve position/speed sensorless control. The impact of discrete-time implementation is investigated to ensure stability and fast dynamic response under low pulse ratio. Simulation, experimental tests and comparative studies with the prior methods were carried out to validate the superiority of the proposed methods. Finally, a closed-loop torque control scheme along with active vibration damping is proposed to achieve high-quality gearshift. Considering the measurement of shaft torque is not feasible in practical application, a discrete-time sliding-mode torque observer is further designed to provide the feedback signal for the proposed controller.
Owing to the sophisticated structure design and advanced control schemes, not only the driving comfort but also the reliability and efficiency of the whole system can be greatly improved. The feasibility and effectiveness of the proposed methods are confirmed by simulation and/or experimental tests
