Analysis and simulation of efficiency optimized IPM drives in constant torque region with reduced computational burden


Abstract: Moving from internal combustion engine based towards electric based transportation is crucial for wide societies as they facilitate the use of green energy technologies such as wind and solar. Interior mounted permanent magnet (IPM) machines, also known as salient brushless alternating current (AC) machines, are commonly employed in traction applications as they have superior features, such as high efficiency operation, high torque, and power densities. The efficiency optimization in IPM drives is achieved by obtaining and operating at accurate and unique current angle for a certain electromagnetic torque demand. In conventional drives, the optimum current angle is obtained by online utilization of iterative techniques. However, these techniques result in increased burden on the processor. In addition, accuracy of the generated current commands, and hence, the drive efficiency may significantly reduce if the number of iterations is not adequate. More importantly, online zero divisions issue may result in instability of the drive system at certain operating points in real life experiments. This paper proposes an efficiency optimized IPM drive with smooth output torque production addressing the aforementioned issues. The optimum operating points as a function of electromagnetic torque demand are computed offline by Newton-Raphson approximation technique in the paper, and they are stored in the controller as look-up tables, which are then employed to achieve optimum efficiency operation at a wide range. The superiority of the proposed drive is validated through extensive simulation of a 4.1 kW prototype IPM machine designed and manufactured for traction applications and the results are discussed in detail. The paper also presents detailed high efficiency control analysis of permanent magnet machines and hence it would be quite insightful for new researchers on the topic.

Keywords: Control of interior mounted permanent magnet (IPM) machines, interior permanent magnet synchronous motor (IPMSM), maximum torque per ampere (MTPA), efficient drives, alternating current (AC) drives

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