Modular multilevel converters (MMCs) will be widely applied in onboard integrated power systems due to their high levels of electric power output and good-quality sine waveform outputs. However, the capacitor voltage of MMCs fluctuates greatly because the charge–discharge process of the capacitor is continuous when the system is working. In order to reduce voltage ripples efficiently, a capacitor voltage ripple-suppression strategy employing a reversed PWM switching channel is proposed in this paper. For one pair of the upper and lower arm submodules, a switching channel is built. Then, the highest ripple voltage possible can be offset since the voltage fluctuation direction of the upper and the lower arm capacitors would be reversed. In addition, a clamping capacitor is added to the switching channel to further suppress the fluctuation voltage by 78%. Compared to traditional large capacitance suppression methods, only 12% capacitance is used in the proposed method. The reliability and power density of the proposed MMC both increased, and there are no additional losses compared with previous voltage ripple suppression methods. The effectiveness of the proposed voltage ripple suppression strategy is verified by simulation results.

Dual three-phase permanent-magnet synchronous motors (PMSM) have wide applications in electric vehicles due to advantages such as excellent control performance and outstanding fault tolerance capability. However, present fault-tolerant control of inverter single-leg open-circuit faults cannot make full use of each phase winding of the motor, which limits the torque-production capability. This paper proposes a torque superposition compensation (TSC) control which can minimize the stator copper losses while increasing the torque-production capability. The phase winding originally connected to the faulty inverter leg is then linked to the DC-link mid-point. Thus, the winding in the faulty phase can be utilized to generate an additional torque. The symmetric dual three-phase windings torque model and the asymmetric five-phase windings compensation torque model for Ud/2 voltage level are constructed according to the torque superposition, respectively. Then, the three-subplane decomposition transformation matrix for the post-fault dual three-phase PMSM is derived, and the decoupling model in the d-q subplane is constructed, which achieves the optimal enhancement of the torque-production capability. The simulation results verify the effectiveness of the proposed TSC fault-tolerant control.

The analysis of the voltage fluctuation and flicker is important to inhibit flicker. Mathematical morphology filter testing methods are proposed in this paper on the basis of Hilbert transform. Using Hilbert transform to extract flicker envelope, and the mathematical morphological filtering method is used to filter out high frequency noise of the grid. Simulation results show that this method can realize flicker signal detection, determine spectrum of flicker signal through mathematical morphology filtering method, and the measurement precision compared with spectrum amplitude of the signal with noise have larger increase.