Keywords: maximum torque-per-ampere control, position sensorless vector control, permanent magnet synchronous motor, extended electromotive force This paper discusses a novel position sensorless vector control for permanent magnet synchronous motors. In this paper, we define a novel coordinate frame (hereafter, the maximum torque control frame), one axis of which is aligned with the current vector of the maximum torque-per-ampere (MTPA) control, and propose a sensorless control method for directly estimating the maximum torque control frame. In the conventional MTPA control method, the motor is operated with a current while the control frame (d-q frame) is estimated. The proposed method is robust against changes of motor parameter. In addition, the MTPA control is easily achieved. Fig. 1 illustrates the frames used in this paper. The estimated axes we propose are defined as the maximum torque control frame of dm-and qm-axes. The extended EMF model on the maximum torque control frame is represented in (1), and the second term on the right-hand side is defined as an extended EMF on the frame.where Therefore, the maximum torque control frame is estimated directly with this L qm . The MTPA control can be achieved with the control signal in the form of the γ-axis current (dm-axis current) remaining zero without considering the use of the reluctance torque. Fig. 2 shows L q and L qm against the q-axis current for the motor examined in consideration of magnetic saturation. The q-axis inductance L q was affected by magnetic saturation and markedly decreased with increasing q-axis current. On the other hand, the estimation parameter L qm did not change substantially. This indicated that the use of L qm , rather than the conventional L q , greatly reduces the effect of magnetic saturation on the position estimation. The reason is that L qm is less affected by the magnetic saturation caused by an increase in the q-axis current. Fig. 3 shows a current vector locus in the MTPA control and that in the proposed method, assuming L qm to be constant, when the magnetic saturation is considered. Excellent current vector loci are observed even when L qm is approximated by a constant value. Therefore the motor can be controlled thoroughly with almost MTPA control.

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In recent years, linear oscillatory actuators (LOAs) employing mechanical resonance have been researched aiming at highly efficient actuators. This paper considers a cylindrical moving magnet type LOA having spring characteristics for resonant oscillation in the actuator itself An equation to express the thrust of the proposed LOA is derived using a permeance model, and calculation results by the permeance analysis and magnetic field analysis are compared with actual measured results. The thrust constants by the permeance analysis and magnetic field analysis agree with the measurement, and the permeance analysis with a short calculation time is effective in calculation of the thrust constant. The magnetic field analysis is effective in the calculation of the spring characteristics of static thrusts. In addition, the optimization of the size of the proposed LOA based on the motor constant is investigated A relational equation of the size of the LOA and the motor constant is derived From calculation results on the motor constant using the permeance analysis and magnetic field analysis, the effectiveness of the permeance analysis with a short calculation time is confirmed. Moreover, by focusing on the motor constant below the same thrust constant, it is found that the coil resistance is effective as optimization indices identical to the motor constant.