Electric vehicles (EV) are playing a momentous role to the wide society as they facilitate the use of clean energy technologies. Interior mounted permanent magnet (IPM) synchronous machines are commonly employed in EVs owing to their superior characteristics such as high efficiency and power density and a wide field weakening operating range. High efficiency motor operation extends EVs drive range with the same amount of energy. Advanced control techniques to achieve high efficiency operation and smooth output torque production are, therefore, highly important areas to be researched. This thesis deals with the state-of-art motor drives and further develops advanced control strategies for minimum loss operation with good torque control quality.
Modern AC drives can be classified in two groups, viz., field oriented control (FOC) and direct torque control (DTC). Whilst the former controls the phase currents for torque realization, the latter controls the torque directly. This thesis researches both and the novel advanced techniques are underpinned by extensive simulations and supported by experimental validations on a prototype motor designed for a specific class of EVs.
The biggest challenge associated with the FOC drives is to improve the efficiency due to highly nonlinear characteristics of IPM machines. It has been discovered that even if the machine parameters are accurately modelled and stored in controllers to achieve optimal efficiency operation in a great number of FOC based IPM drives, there is still much deviation from the ideal operating points. A novel approach for online efficiency optimisation is proposed and comprehensively analysed in this thesis.
The challenges pertinent to the DTC based IPM drives are to improve the observer quality and to reduce the strong coupling and the nonlinearity in the control loops. Novel observer structures, and the decoupled and linearized control techniques are among the novel contributions for DTC drives in this thesis. In addition, a comprehensive analysis of the relationship between stator flux vector and the torque has not been performed in the literature. The detailed analysis is made in this thesis and the maximum torque per voltage (MTPV) control theory for DTC drives is introduced.
It is noteworthy that this thesis is based on comparative studies between the state-of-art and the proposed techniques throughout, and hence offers an insightful understanding for modern IPM drives.
