Loss-Minimizing Control of PMSM With the Use of Polynomial Approximations

Normally, lookup-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 lookup table, and the program size becomes bulky. In this paper, analytic methods for 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 with 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 and implemented in an inverter digtal signal processor. Experiments were done with a real PMSM developed for a sport utility fuel cell electric vehicle. The analytically derived minima were justified by experimental evidences, and the dynamic performances over a wide range of speed were shown to be satisfactory.