In this paper, the model predictive current control (MPCC) method using two vectors has been proposed to control output currents of three-phase voltage source inverters (VSIs) with small current errors and current ripples. Also, the proposed method can reduce switching losses by applying the vector pre-selection technique to the MPCC for the VSI. The VSI generates seven voltage vectors to control the output currents, but the proposed method uses four available voltage vectors with one switch, which are classified by the vector pre-selection method clamping one leg and conducting the largest output current among the three legs to reduce the switching losses. In the proposed method, selecting two future voltage vectors among the four voltage vectors and dividing them in a future sampling period are determined by an optimization process. The proposed method results in the lower total loss, better total harmonic distortion (THD), and smaller current errors than the conventional method with half the sampling period of the proposed method due to the optimal process. Simulation and experimental results of the three-phase VSIs are presented in order to verify the effectiveness of the proposed method.
This paper proposes a highly efficient single-phase three-level neutral point clamped (NPC) converter operated by a model predictive control (MPC) method with reduced commutations of switches. The proposed method only allows switching states with none or a single commutation at the next step as candidates for future switching states for the MPC method. Because the proposed method preselects switching states with reduced commutations when selecting an optimal state at a future step, the proposed method can reduce the number of switchings and the corresponding switching losses. Although the proposed method slightly increases the peak-to-peak variations of the two dc capacitor voltages, the developed method does not deteriorate the input current quality and input power factor despite the reduced number of switching numbers and losses. Thus, the proposed method can reduce the number of switching losses and lead to high efficiency, in comparison with the conventional MPC method.
This paper proposes a predictive control method with offset voltage injection for achieving a neutral point (NP) voltage balance of three-phase three-level neutral point clamped (NPC) inverter, without employing a weighting factor. In order to ensure the proper and reliable operation of the NPC inverter, the NP voltage balance should be regulated in addition to the sinusoidal output current. The conventional predictive control methods for NPC has suffered from tedious weighting factor selection. Besides, when the converter's parameters value and control condition changes, it is cumbersome to empirically redesign the weighting factor. Therefore, the proposed predictive control method without the weighting factor can successfully maintain the balance of NP voltage by utilizing an offset voltage, which is determined according to the difference between the upper and lower capacitor voltages. As a result, the proposed algorithm using the offset voltage injection can control the output currents and maintain the balance of NP voltage. Simulation and experiments are presented to prove the validity of the NP voltage balancing of the proposed control method. INDEX TERMS neutral point clamped (NPC) inverter, predictive control method, neutral point (NP) voltage balance, offset voltage injection
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