The bidirectional ac/dc converter is widely used to realize the power conversion between ac and dc microgrid, but the faults of switch devices and unbalanced grid voltages may lead to the decline of power quality and affect normal operation of the converter. The four-switch three-phase (FSTP) fault-tolerant structure is reconstructed from a six-switch three-phase structure with switch device fault. In order to reduce harmonic currents and output power fluctuations under unbalanced grid voltages, finite states model predictive direct power control (MPDPC) with power compensation method is proposed for FSTP structure and predictive power model of the bidirectional FSTP ac/dc converter is established. The power compensation values are expressed by grid voltages and their quadrature signals that lagging 90 electrical degrees in the αβ stationary coordinate system. Compared with the conventional method, phase-locked loop, pulse width modulation, and complex positive-/negative-sequence extraction of grid voltage are not required. Ripples of active power or reactive power under unbalanced grid voltages are eliminated. The proposed fault-tolerant MPDPC with power compensation method ensures the continuous and reliable operation of the bidirectional ac/dc converter with high power quality. Simulation and experimental results are presented to validate the proposed control strategy under symmetrical unbalanced grid voltages with switch device faults.

Strong parameter dependence and large current ripple are two shortcomings that obstruct the development of model predictive control for voltage source inverters (VSIs). To solve these problems, in this article,a double-vector model-free predictive control (MFPC) method for VSI with visualization analysis is proposed. First, the ultralocal model of the VSI is established and a full-order sliding model observer is designed to estimate the lumped disturbance. MFPC is achieved with enhanced parameter robustness. Then, a double-vector MFPC method is further proposed. By applying two vectors per control period, the current ripple is reduced significantly. A detailed visualization analysis method is proposed, which verifies the effectiveness of the proposed double-vector MFPC method in theory. Besides, the proposed visualization analysis method has the potential to be used to analyze the effectiveness of other types of multivector model predictive control method with different cost functions. Detailed comparative experimental studies verify the effectiveness of the proposed double-vector MFPC method.

To reduce the common-mode voltage (CMV) and eliminate the CMV spikes for 2-level voltage source inverters (2L-VSIs), an improved model predictive control (MPC) based CMV reduction method is proposed considering dead time effects. First, an improved voltage vector (VV) preselection strategy is proposed to reduce the CMV spikes caused by the dead time. Second, a new hybrid VV preselection strategy based on a delay compensation strategy and a modified current sector division strategy is proposed to completely eliminate the CMV spikes. As the proposed hybrid VV preselection based MPC strategy makes full use of the six nonzero VVs of the 2L-VSI, the current total harmonic distortions and ripples are reduced. The simulation and experiments are carried out to verify the effectiveness of the proposed strategy.

A model predictive control (MPC) strategy for grid-connected power converters is proposed in this paper to reduce the current ripples without using AC voltage sensors. Firstly, a sliding mode observer is designed to estimate the grid voltage with an adaptive compensation algorithm. Thus, grid voltage sensors are removed. The novelty of the proposed grid voltage observation method is that it is inherent frequency adaptive without using the accurate grid angular frequency. By implementing the MPC strategy using the estimated grid voltage, the current ripples are reduced, especially under distorted grid voltage conditions because of the low-pass filter used in the observer. Next, to further reduce the current ripples, a double-voltage vector (VV) based MPC strategy is proposed based on the principle of the modulated MPC. Detailed theoretical analyses are also carried out to show its effectiveness for the first time. Finally, experimental studies are carried out to verify the validity of the proposed AC voltage sensorless MPC strategy.

Hybrid electric bus (HEB) presents an emerging solution to exhaust gas emissions in urban transport. This paper proposes a multiport bidirectional switched reluctance motor (SRM) drive for solar-assisted HEB (SHEB) powertrain, which not only improves the motoring performance, but also achieves flexible charging functions. To extend the driving miles and achieve self-charging ability, photovoltaic (PV) panels are installed on the bus to decrease the reliance on fuels/batteries and charging stations. A bidirectional front-end circuit with a PV-fed circuit is designed to integrate electrical components into one converter. Six driving and five charging modes are achieved. The dc voltage is boosted by the battery in generator control unit (GCU) driving mode and by the charge capacitor in battery driving mode, where the torque capability is improved. Usually, an extra dc-dc converter is needed to achieve battery charging. In this paper, the battery can be directly charged by the demagnetization current in GCU or PV driving mode, and can be quickly charged by the PV panels and GCU/AC grids at SHEB standstill condition, by utilizing the traction motor windings and converter circuit, without external charging converters. Experiments on a three-phase 12/8 SRM confirm the effectiveness of the proposed drive and control scheme.

To suppress the common-mode voltage (CMV) and reduce the current total harmonic distortions (THDs) and ripples of two-level voltage source inverters (2L-VSIs), a hybrid voltage vector (VV) preselection based model predictive control (MPC) strategy is proposed in this paper. Six synthesized VVs (SVVs) are first defined based on the six nonzero VVs of the 2L-VSIs and a new SVV preselection strategy is proposed to reduce the CMV spikes caused by the dead time effects. Then, by dividing the three-phase current plane into seven sectors with an asymmetric hysteresis, a hybrid-VV preselection based MPC strategy is finally proposed by considering the one step delay effects to completely remove the CMV spikes. Moreover, to further improve the parameter robustness of the proposed method, a control error compensation algorithm is also designed in this paper. Simulation and experimental results show that the proposed hybrid-VV preselection based MPC strategy can not only completely restrict the CMV within $\pm$ udc/6, but also reduce the current THDs and ripples significantly. Additionally, the influences of the parameter variation on the proposed method are also reduced obviously.