This paper proposed an online optimizing duty cycle control approach for three-phase active-front-end rectifiers, aiming to obtain the optimal control actions under different operating conditions. Similar to finite-control set model predictive control strategy, a cost function previously constructed based on the desired control performance is adopted here, which is essential for the solving process of the optimizing problem. On the other hand, differently, with respect to the proposed strategy, duty cycle signals are optimized, instead of possible switching states. The determination of optimal duty cycles is made by predicting the effect of duty cycles on instantaneous current variations and minimizing the cost function. Due to the adoption of behavior prediction, the proposed controller inherits the excellent dynamic characteristics of predictive controllers. Moreover, the application of optimal duty cycles determined by cost function minimization automatically ensures optimum operations of converters within each sampling period. Improved transient and steady-state features of the proposed strategy are confirmed by experimental validations and in-depth comparisons with linear controllers, deadbeat predictive controllers, and finite-control set model predictive control strategies.

In this paper, a current optimization control method for reducing torque ripple in brushless dc drives using integral variable structure control (IVSC) is proposed. The conventional current control method will result in torque ripple if the back electromotive force (EMF) is a nonideal trapezoidal waveform. Based on back-EMF waveforms, the proposed method can optimize the reference currents in both two-phase conduction mode and commutation mode. A Luenberger full-order estimator is designed in order to estimate back-EMF waveforms. During commutation, commutation control with two-phase or three-phase switching mode is employed to reduce torque ripple by controlling the currents of noncommutated windings to trace the optimized reference current, and a three-phase inverter is switched between the two switching modes according to the current rate of change and the difference between the reference current and the actual current. Current controllers using IVSC, which exhibits broadband noise-suppressing capacity and strong robustness against external disturbances, are designed to obtain optimal phase currents, and the experimental results validate the effectiveness of the proposed method.

Duty cycle model predictive torque control (Duty-MPTC) only uses zero vector as the second vector to form vector combinations, which restricts its torque control performance. This paper proposes a modified double vectors model predictive torque control (DVMPTC) by reasonably selecting active vector instead of zero vector. By analyzing the regulation of torque and flux of permanent magnet synchronous motor (PMSM), the torque and flux difference parameters are obtained, and then a second vector selection table is established to determine the best vector combination for torque ripple suppression. And based on the torque and flux difference parameters, the duty cycle calculation method is proposed to reduce the calculation burden of the control system. In order to verify the effectiveness of the proposed method, experiments with a 6-kW PMSM are carried out. Compared to Duty-MPTC, the proposed DVMPTC method can significantly reduce the torque ripples with good dynamic performance and relatively low average switching frequency.

In this paper, a predictive direct power control (DPC) method without sector information and voltage vector selection is proposed for three-phase grid-connected converters. Different from conventional predictive direct power controllers, the proposed strategy always adopts fixed voltage vectors, instead of selecting voltage vectors according to the angular information of the grid-voltage vector or the virtual-flux vector. The converter switching time is obtained by minimizing the squared errors of the instantaneous active and reactive power. Switch duty cycles are then calculated and equivalently reconstructed. The proposed strategy not only presents rapid dynamic response due to the use of the predictive controller, but also possesses excellent steady-state performance as a result of duty cycle reconstruction. The main advantage of the proposed control scheme, compared with the classical DPC strategies, is that it is unnecessary to use sector information of the grid-voltage vector, and selection of active voltage vectors is also not required here. Therefore, incorrect selection of voltage vectors and the resulting performance deterioration are surely avoided, without the need of any additional compensation measures. An in-depth comparison and experimental assessment are given to validate the effectiveness of the proposed strategy.

A novel synchronized space-vector pulsewidth modulation (SSVPWM) strategy is proposed for three-level inverters, which focuses on improving the output waveforms while reducing the device switching frequency. The modulation index m is segmented in linear modulation region reasonably, and the switching sequences are designed at each segmentation independently. The sequences for two reference vector distribution modes are designed, respectively, which ensure the synchronization and symmetry in output waveforms and the minimization of switching frequency. Then, the optimal sequence at each segmentation is selected from the two sequences (corresponding to the two modes) in terms of the weighted total harmonic distortion (THD) of line voltage. The proposed strategy is verified through simulation and experiment on a constant v/f open-loop induction motor drive, and the results show that both line voltage weighted THD and no-load stator current THD can be significantly reduced compared to conventional SSVPWM (CSSVPWM) and space-vector-based synchronized discontinuous PWM (SDPWM) in linear modulation region. Moreover, at a certain reference vector number, the switching frequency can be reduced by 33.3% compared to CSSVPWM and 13.3% to SDPWM. The proposed strategy can also be implemented in the overmodulation region.