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This paper proposes a novel magnetization state (MS) control method to eliminate the unintentional demagnetization (UD) of low-coercive force permanent magnet (PM) for variable flux memory machine (VFMM). In the proposed method, the amplitude of demagnetization d-axis current pulse is determined from a look-up table with the relationship between the demagnetization d-axis current pulse and the intersections of torque-speed curves under different MSs, and subsequently used as the condition for the MS manipulation. A PM flux linkage observer is adopted to monitor the UD all the time and the amplitude of d-axis current is controlled without exceeding the amplitude of the demand demagnetization d-axis current pulse to avoid the UD in the whole speed range. The inverter nonlinearity is compensated to improve the estimation accuracy of the PM flux linkage. The experiment validation is conducted on a hybrid magnet memory machine system to illustrate the UD issue and to verify the PM flux linkage estimation method and the proposed MS control method.

This paper investigates the interaction effects of permanent magnet (PM) tolerances and rotor eccentricities of 12-slot/10-pole PM machines by finite element method (FEM) and phasor analysis. It is found that the relative location between diversified PMs and eccentric rotor have a significant effect on cogging torque. (a) When a weak (e.g., thin thickness) PM is close to the minimum airgap, rotor static eccentricity and PM tolerances have a strengthening effect to deteriorate cogging torque, but rotor dynamic eccentricity and PM tolerances have a weakening effect to reduce cogging torque. (b) When a strong (e.g., thick thickness) PM is close to the minimum airgap, rotor static/dynamic eccentricity and PM tolerances always have a strengthening effect to deteriorate cogging torque. The experiments verify the FEM-predicted cogging torques and the interaction effects between PM tolerances and rotor eccentricities on cogging torque in the 12-slot/10-pole PM machine.

This paper proposes a simple inductance asymmetry compensation method for minimizing the second-order harmonic current responses and the corresponding position errors in high frequency signal injection sensorless controlled dual three-phase interior permanent magnet synchronous machines (IPMSMs). It is found that the second-order harmonics of HF current responses in two sets of dual three-phase windings due to self-inductance asymmetry have opposite phase angles in the double dq control method. Thus, a simple current summation-based position error compensation method including an online calculation technique of harmonic amplitude ratio is proposed. The proposed compensation method can not only suppress the second-order position error effectively but also maintain a high signal-to-noise ratio of the sensorless control system. It is validated by experiments under different inductance asymmetry conditions.

This paper investigates the ability for elimination of unwanted magneto-motive force (MMF) harmonics in fractional slot dual m-phase single-layer PM machines. By doubling the number of slots and applying stator shifting, the 1st order and one unwanted higher order winding MMF harmonic can be suppressed. Then, through the addition of a second converter operating at a specified phase shift one higher order harmonic can be eliminated. This work identifies the required shift angle of the second winding set as well as converter phase shift in any dual m-phase machine to achieve elimination of an unwanted winding MMF harmonic. This methodology is validated by studying 3- and 5-phase machines through analytical modelling. Then two 3-phase machines, 12-slot/10-pole (12s/10p) and 12s/14p, are investigated using FEA. It is found that the 24s/10p dual 3-phase machine can achieve higher torque than the conventional 3-phase 12s/10p but the 24s/14p dual 3-phase performs worse. However, in both cases the significant suppression of unwanted harmonics reduces the rotor iron losses and PM eddy current loss. As a result, the efficiency of each machine is increased by about 3% over its initial 12-slot counterpart. In particular, the PM eddy current losses are reduced by over 95% leading to a substantial reduction in thermal demagnetization risk. The dual 3-phase single-layer machine is also found to achieve higher torque than two similar topology dual 3-phase double-layer machines while having equivalent PM eddy current losses. Both analytical and numerical results have been validated by a series of tests. A prototype machine has been manufactured to validate EMF, static torque, and efficiency measurements of the proposed machine.

With the aid of vector analysis and finite element method, this paper investigates the influence of slot and pole number combinations on cogging torque in permanent magnet (PM) machines with interactive effects between tooth bulge and rotor eccentricity, accounting for various slot/pole number combinations (Ns/2p), e.g., 2p = Ns ± m where m is an integer (including 2p = Ns ± 1 and 2p = Ns ± 2), Ns/2p = 12/8, and Ns/2p = 12/4. It is firstly found that m greatly influences the interaction of two tolerances on cogging torque. The degree of interaction is reduced with m, and it is larger in “−m” than in “+ m” machines. Secondly, for the machines having 2p = Ns − m, there is a weakening interaction of cogging torque when the static eccentric rotor is close to outward bulged teeth, whilst there is a strengthening interaction of cogging torque when the static eccentric rotor is close to inward bulged teeth, but vice versa for 2p = Ns + m machines. However, in both 2p = Ns ± m machines, cogging torques due to dynamic eccentricity and tooth bulge always have a strengthening interaction. The measured cogging torques of the prototypes verify the predicted results.

This paper investigates the influence of arbitrary self-inductance asymmetries in one set three-phase windings on high-frequency pulsating sinusoidal signal injection based sensorless control of dual three-phase interior permanent magnet synchronous machine and the adaptive notch filter is utilized to compensate arbitrary inductance asymmetries. It is found that the demodulated current responses in both two sets generate 2nd- and 4th-order positive and negative sequence error signals because of arbitrary self-inductance asymmetries in one set three-phase windings. These current error signals cause 2nd- and 4th-order estimated position errors in high frequency pulsating sinusoidal signal injection-based sensorless control method. The adaptive notch filter based compensation method can suppress both 2nd- and 4th-order estimated position errors. The compensation method for inductance asymmetries is validated by the measured results.