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This paper studies different switching schemes for loss reduction in a traction motor drive. The system under examination is composed of a battery, a 2 level Voltage Source Inverter, and an Interior Permanent Magnet motor. Discontinuous PWM (DPWM) control strategy is widely used in this type of motor drive for the reduction of losses. In some publications, the effect of the DPWM modulation scheme is compared to the reduction of the switching frequency which can also cause a reduction in switching losses of the inverter. Extensive studies have examined the effect of variation of the switching frequency on the motor and inverter losses. However, the effect of applying both switching schemes simultaneously has not been explored. This paper will use a system that is operated at a fixed switching frequency as the baseline. Afterwards, three different switching schemes will be studied and compared to the baseline.

In an interior permanent magnet machine, magnet temperature plays a critical role in determining optimal current control trajectory. Monitoring magnet temperature is a challenging task. In lab and various specialized applications, infrared sensors or thermocouples are used to measure the temperature. But it adds cost, maintenance issues and their integration to electric machine drives could be complicated. To tackle issues due to sensor based methods, various sensorless model based approaches are proposed in the literature recently such as flux observer, high-frequency signal injection, and thermal models, etc. Although magnet temperature monitoring received a lot of attention of researchers, very few papers give a detailed overview of the effects of magnet temperature on motor control from a controls perspective. This paper discusses the impact of magnet temperature variation on Maximum Torque per Ampere control and Flux Weakening Control trajectory.

For high performance motor controls applications such as electric vehicles, accurate motor parameter knowledge is required. Motor parameters like d-axis inductance, q-axis inductance, resistance and permanent magnet flux linkage are difficult to obtain and measure directly. These four parameters can be reduced to three parameters resistance, d-axis and q axis flux linkage. In this paper, a new scheme is proposed to approximate d-axis and q-axis flux linkage using measured torque, dq-axis measured current, and dq-axis voltage commands to the inverter. d-axis and q-axis flux linkages are estimated over a range of d-axis and q-axis currents that fully map the desired motor operation region.