Search

In the traditional random switching frequency pulsewidth modulation (RSFPWM), the frequency range should be set large enough to make the harmonics evenly distributed without spikes, which may also disperse the harmonics to the lower frequency band that is hard to be filtered. To avoid the low-frequency harmonics induced by widening the frequency range, a double frequency-band random pulsewidth modulation (DFB-RPWM) strategy is proposed in this article, to form a more uniform harmonic distribution in a narrower frequency range. In this strategy, each harmonic cluster is divided into two harmonic peaks, and the relative position of the two harmonic peaks influences the harmonic dispersion effect. By adopting the harmonic dispersion theory of the frequency spectrum, the condition that makes lower harmonic amplitudes and more uniform harmonic distribution can be determined. The simulation and experiment are conducted to verify the effectiveness of the DFB-RPWM, showing a better performance than the RSFPWM.

The cross-coupling effect is the magnetic coupling effect of the flux caused by direct-axis current and quadrature-axis current due to nonlinear characteristics of core material. The knowledge of the cross-coupling inductance is of particular importance in order to obtain the angle deviation of magnetic axis from geometric axis of the rotor lamination, which will contribute to the minimization of rotor position estimation error. However, the cross-coupling inductance varies with operating conditions and is often ignored in rotor position estimator. This article proposes a general online method for sensorless predictive direct torque control identifying angle deviation of magnetic axis from geometric axis caused by the cross-coupling effect. Only intrinsic electrical signals for machine drives are employed to build response points distribution graph and implement the angle deviation identification. Experimental results verify that the proposed graphical method online identifies the angle deviation and effectively suppresses the estimation error in the rotor position estimator caused by the cross-coupling effect.

As a modulation technology for low electromagnetic interference, random pulsewidth modulation has been increasingly applied to inverter power supply for three-phase motors. This article proposes a random triangular carrier wave space vector pulse width modulation (RTCW-SVPWM) strategy with dual random parameters, which are subject to a uniform distribution. In this strategy, the shape of the triangular carrier wave changes with random carrier frequency and random pulse center position while the duty cycle of the pulse is the same as that in the conventional SVPWM. 2-D Fourier analysis is used to describe the basic principle of the harmonic dispersion effects in the proposed strategy. The simulation and experimental results show that the dominant harmonics of the output voltage at the integral multiples of the carrier frequency are scattered to their sidebands. Therefore, the prominent harmonic peaks can be greatly attenuated and the harmonics in the high-frequency band are evenly distributed.

This study investigates a short primary double-side six-phase linear induction motor (LIM) operating in non-periodic transient conditions. The main purpose is to solve the problems arising from the dynamic end effect. The equivalent circuit method is used for intensively studying the transient time-varying law of eddy current and excitation inductance, and the finite element method is adopted for verification. The calculation of eddy current loss leads to an expression of secondary equivalent resistance. Then, a mathematical model is established for the six-phase LIM involving the dynamic end effect. Furthermore, the matrix reconstruction method is adopted for the coupling of windings. Based on the time-varying characteristics of the model, an improved vector control method that can update the velocity-related correction coefficients through on-line calculation is proposed. During the transient process, the slip frequency and the torque current are modified in real-time to achieve the maximum output thrust of the motor. This approach can compensate for the thrust drop caused by the dynamic end effect, thereby improving the control precision. Simulations and experiments show that the related theory and the proposed control method are feasible and effective.