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Alleviation Technique for Thermal Concentration on Specific Switching Devices in Zero‐Speed Driving of PMSM

In this paper, a technique is proposed for alleviating the thermal concentration on specific switching devices by using a zero‐sequence voltage in a three‐level inverter that drives a permanent magnet synchronous motor (PMSM) in a zero‐speed and high‐torque condition. The use of the PMSM in home electronics and industrial products has become widespread, since it can realize miniaturization and a high efficiency drive. However, a large DC current flows when the PMSM is used in a zero‐speed and high‐torque condition, for example, in the hill‐start of electric vehicles, start or stop of elevators, or servo lock of servo pressing machines, and so on. In these cases, the current flows in the specific switching devices and heat generation is locally concentrated. This problem is unavoidable in a conventional two‐level inverter. A technique that can change the current path in a three‐level inverter and control the losses generated in the switching devices is proposed. We evaluated the effects of the proposed technique through a circuit simulation in which the electrical characteristics of a commercially available power device were applied. The proposed technique can reduce the highest loss of the switching devices in the three‐level inverter by about 40% as compared to that in a conventional inverter. Moreover, a method is proposed that suppresses the neutral point potential variation between the power supplies. This method can also reduce the maximum loss of the specific switching devices by about 30%.