异步电机模型预测三电平直接电流控制

三电平逆变器为控制系统提供了更多的电压矢量,相对于传统两电平逆变器能够使得直接电流跟踪控制变得更加精确,能进一步减小电流纹波。但是三电平逆变器存在中点电压平衡问题,如果不对中点电压进行控制会使得电机无法正常工作,同时在大容量三电平逆变器中一般需要其降低开关频率。因此,提出一种具有中点电压平衡和降低开关频率功能的模型预测直接电流控制方案:通过对中点电压进行预测控制,在模型预测直接电流控制的价值函数中加入开关切换次数的约束,能将中点电压有效控制在给定的范围内,并同时实现逆变器开关频率的降低;针对控制延时导致定子电流在参考值附近振荡并增加电流纹波和转矩脉动,采用延时补偿提高控制系统性能。仿真和实验结果验证了所提方法的有效性和可行性。

Model Predictive Direct Current Control of Induction Machines Fed by a Three Level Inverter

Compared with the two-level inverter, the three-level inverter provides more voltage vectors to the control system. Thus, the current can be controlled accurately, and the current ripple can be reduced effectively. But the three-level inverter has a problem about the neutral point voltage balance. That is, the motor cannot work properly if the neutral point voltage is not controlled. Moreover, the reduction of the switching frequency of the three-level inverter is required in medium-voltage drive field. To address this problem, a model predictive direct current control method considering neutral point voltage balancing and switching frequency reduction is proposed in this paper. This method can carry out predictive control to the neutral point voltage, and introduce the constraint of power semiconductor switching number to the cost function of the model predictive direct current control (MPDCC). Accordingly, the neutral point voltage can be controlled and the switching frequency of the inverter is reduced significantly by introducing the constraint of the power semiconductor switching number to the cost function of the MPDCC. The time delay arising from the computational time will cause the stator current to oscillate around its reference and increase the current and the torque ripples. The delay compensation method is then adopted. Both the simulation and experimental results verify the proposed method.