Search

Random pulsewidth modulation (RPWM) with variable carrier frequency generally disperses the dominant PWM harmonics more effectively than the RPWM with constant carrier frequency. But variable carrier frequency results in variable sampling frequency, which changes controller parameters and makes RPWM difficult to use in closed-loop applications. To significantly disperse dominant harmonic clusters located nearby the PWM frequency and its multiples, while maintaining constant sampling frequency, in this article, N-state random pulse position space vector pulsewidth modulation is proposed. This method randomly selects one of the N selected carrier patterns with equal probability in each carrier period, resulting in N different pulse position states. By applying two-dimensional Fourier analysis, the additional multiplication factor in the derivation results, named harmonic dispersion coefficient in this article, can intuitively explain the principle from the perspective of mutual cancellation of complex vectors in different directions. All dominant PWM harmonics are significantly dispersed except those located nearby the Nth PWM frequency and its multiples when using the proposed method. Besides, power losses and switching counts are detailed discussed. Both simulation and experimental results verify the effectiveness of the method at last. [ABSTRACT FROM AUTHOR]

Considerable vibration and acoustic noise limit the further application of Switched Reluctance Machine (SRM) due to its structural characteristics and working principle. An improved SRM model with double auxiliary slots (DAS) was proposed, in which the direction of the magnetic line of force was adjusted, and the radial magnetic density in the air gap was reduced by changing the local tooth profiles of the stator and the rotor. The effects of initial rotor position and turn-on angle and turn-off angle on radial Electromagnetic Force (EMF) and maximum torque were investigated. The results indicate the radial EMF and torque increase significantly with the advancement of the turn-on angle or the delay of the turn-off angle. In the orthogonal experimental design, initial rotor position, turn-on angle, and turn-off angle were taken as the factors, and the optimal set of parameters that minimized radial EMF was determined according to a greater output torque. In contrast to conventional SRM, the radial EMF of the SRM with DAS significantly reduces when the optimal set is applied. [ABSTRACT FROM AUTHOR]

The common method to mitigate the slot-frequency vibration and noise of the permanent magnet (PM) motors is skewing the stator slot or skewing the PM. However, the limitation of this method in pole-frequency vibration reduction exists. In this article, one method by adopting the piecewise stagger PM pole with a continuous skew edge is proposed to reduce the pole-frequency and slot-frequency vibration for surface-mounted permanent magnet (SPM) synchronous machines. First, the analysis of the radial force acting on the stator teeth is conducted. Basing on this, the limitation of the skewing slot method in reducing the vibration is revealed. In order to solve this problem, a piecewise stagger PM pole with a continuous skew edge for pole-frequency and slot- frequency vibration reduction is proposed and its principle of vibration reduction is presented in detail. The finite element models of three 6-pole/36-slot SPM motors are built to simulate the radial force. Finally, two 6-pole/36-slot SPM motors are manufactured and the experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The analytical methods are widely used to predict the vibration and noise of the permanent magnet motors in industry applications. In the traditional analytical method, the influence of the teeth is ignored and a large error of vibration calculation will occur in the slotted motor. In this article, a high-precision analytical method is proposed for vibration calculation of motors based on tooth modeling. First, the electromagnetic forces on each tooth of stator of the motor under no load and load are calculated. Then, the transfer function from the force acting on the teeth to the vibration on the surface of the shell is derived and verified by finite-element method (FEM). Next, the superposition method is introduced and used to superimpose the vibration excited by the force of all teeth to calculate the total vibration acceleration of the motor surface. Finally, the FEM and experiments are conducted to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]