Efficiency Mapping of Electrically Excited Synchronous Motors with Different Control Strategies

Electrically excited synchronous motors (EESMs) have gained significant attention in the transportation sector due to their ability to eliminate the need for rare-earth materials. One critical tool for evaluating and optimizing the performance of EESMs is the efficiency mapping, which provides insights into the motor’s behavior across a wide range of operating conditions. This paper presents a comprehensive methodology for generating efficiency maps of EESMs based on the machine flux and loss maps, readily obtainable through finite element simulations or direct prototype measurements. Additionally, the proposed methodology accounts for multiple control strategies enabled by the three degrees of freedom offered by the rotor current and the stator d- and q-axis currents. Indeed, while traditional approaches focus on minimizing total losses to optimize overall efficiency, alternative strategies - such as reducing rotor losses, maximizing power factor, or minimizing d-axis current - can offer targeted advantages, including improved thermal management and optimized inverter design. To demonstrate the effectiveness of this approach, an electric motor equipping a commercially available vehicle is used as a case study, with efficiency maps computed for five distinct control strategies. The findings highlight the adaptability of EESMs to meet different performance requirements, making them a versatile solution for electrified powertrains.