基于模糊控制的三电平逆变器中点电位平衡策略

Research on Neutral Point Potential Balance of Three-Level Inverter Based on Fuzzy Logic Control Strategy

中点电位平衡是设计三电平逆变器变频调速系统要考虑的问题,中点电位的不平衡增加了功率器件的电压应力,同时使逆变器输出谐波含量增大。首先由三电平逆变器的电路拓扑出发,建立三电平逆变器中点电位的数学模型,然后对中点电位失衡的原因进行了分析,在此基础上研究了一种基于模糊控制的中点电位平衡策略,通过检测直流侧电容电压的大小,把两电容电压的偏差与偏差的变化率作为模糊控制器的输入,根据中点电位不平衡程度,通过模糊规则实时调整输出正负小矢量的作用时间,从而达到中点电位的动态平衡。仿真和实验结果验证了所提控制方法的可行性。

The neutral point potential is an important problem when designing three-level inverter AC driving system. The imbalance of neutral point potential not only increases voltage stresses of power device, but also results in harmonic distortion of output waveform. In this paper, firstly, the neutral point potential model is set up, and reasons of imbalance of neutral point potential are analyzed, then a method based on fuzzy logic control is proposed. The method is based on the measurement of two capacitor voltages, then the errors of the voltages and errors change rates of voltages are as input for the fuzzy logic control, by changing fuzzy rule according to the degree imbalance, the duration of small voltage vector action can be obtained. At last, the simulation and experiment results verifies the feasibility of the proposed method.