Loss Minimizing Control of PMSM with the Use of Polynomial Approximations

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Normally, look-up table based methods are being utilized for loss minimizing control of permanent magnet synchronous motors (PMSMs). But, numerous repetitive experiments are required to make a look-up table, and the program size becomes bulky. In this work, analytic methods of finding the loss minimizing solution are studied. Since the solution lies either in the interior, or on the voltage limit boundary, two different cases are dealt separately. In both cases, fourth order polynomials are derived. To obtain approximate solutions, methods of order reduction and linear approximation are utilized. The accuracies are good enough for practical use. These approximate solutions are fused into a proposed loss minimizing algorithm (LMA), and implemented in an inverter DSP. Experiments were done with the real PMSM developed for a sport-utility fuel cell electric vehicle (FCEV). The analytically derived minima were justified by experimental evidences, and the dynamic performances over wide speed range were shown to be satisfactory.