In this paper, a model predictive direct power control (MP-DPC) with power compensation and circulating current reduction is proposed for modular multilevel converter under unbalanced grid conditions. The main objectives of this paper are to achieve the circulating currents reduction and the power ripples elimination under unbalanced grid-side voltage conditions. In order to realize the aforementioned objectives, a triple-stage MP-DPC method based on a decoupled mathematical model of circulating current and DC-link current components is presented, which results in the elimination of weighting factors. Meanwhile, a power compensation term is embedded in the proposed design so as to eliminate the power ripples. In this sense, the power compensation terms are expressed by grid voltages and their quadrature signals without the complex positive/negative sequences extraction of grid voltage/currents and phase-locked loop. The proposed methodology can not only relieve the effect of circulating currents but also eliminate the active and reactive power ripples while remaining computationally feasible under unbalanced grid conditions. Additionally, a reduced switching frequency approach is introduced to decrease the power loss. Finally, the effectiveness of the proposed MP-DPC method is validated by both simulation and experimental results.

针对不平衡电网条件下的模块化多电平变换器，提出了一种具有功率补偿和循环电流降低的模型预测直接功率控制（MP-DPC）。本文的主要目的是在不平衡的电网侧电压条件下实现降低循环电流和消除电源纹波的目的。为了实现上述目的，提出了一种基于循环电流和直流母线电流分量解耦数学模型的三级MP-DPC方法，消除了加权因子。同时，在设计方案中嵌入了功率补偿项，以消除功率纹波。在这个意义上说，功率补偿项由电网电压及其正交信号表示，而无需对电网电压/电流和锁相环进行复杂的正/负序列提取。所提出的方法不仅可以减轻循环电流的影响，而且可以消除有功和无功功率波动，同时在不平衡的电网条件下仍具有计算上的可行性。另外，引入了降低的开关频率方法以减少功率损耗。最后，通过仿真和实验结果验证了所提出的MP-DPC方法的有效性。所提出的方法不仅可以减轻循环电流的影响，而且可以消除有功和无功功率波动，同时在不平衡的电网条件下仍具有计算上的可行性。另外，引入了降低的开关频率方法以减少功率损耗。最后，通过仿真和实验结果验证了所提出的MP-DPC方法的有效性。所提出的方法不仅可以减轻循环电流的影响，而且可以消除有功和无功功率波动，同时在不平衡的电网条件下仍具有计算上的可行性。另外，引入了降低的开关频率方法以减少功率损耗。最后，通过仿真和实验结果验证了所提出的MP-DPC方法的有效性。