级联型多电平逆变器最小总谐波失真阶梯调制策略研究

Staircase modulation strategy with minimum total harmonic distortion for cascaded multilevel inverters

为了降低级联型多电平逆变器的输出电压谐波分量,提出了一种新颖的基于KKT条件最优化方法的阶梯调制策略。利用KKT条件法,经过严格的数学推导,得到相应的导通角计算方法,所提出的阶梯调制策略能够在任意调制系数下最小化阶梯波输出的总谐波失真(THD)。另外利用牛顿-拉普逊迭代法来求取上述导通角计算中的关键参数。为了克服牛顿—拉普逊迭代法计算速度慢的缺点,提出了幂函数逼近法来简化计算复杂度。最后,对上述方法进行了仿真分析,得到了固定和可变调制系数下的级联逆变器输出电压波形和其频谱分布。仿真结果证实了调制策略的有效性。

In order to decrease the output-voltage harmonic components of cascaded multilevel inverter, this paper proposes a novel staircase modulation strategy based on Karush-Kuhn-Tucker （KKT） conditions. With KKT conditions and rigorous mathematical derivation, this paper acquires the corresponding calculation method of conducting angles, and the proposed staircase modulation strategy can minimize the total harmonic distortion （THD） under arbitrary modulation index. Furthermore, this paper takes advantage of Newton-Raphson iteration method to obtain the key parameter in the aforementioned conducting angle calculation method. To overcome the deficiency of slow calculation speed of Newton-Raphson iteration method, this paper proposes the power function approximation approach to simplify calculation complexity. Finally, thispaper undertakes simulation analysis and obtains the output voltage waveforrns and their frequency-domain distributions under both fixed and varying modulation indices. Simulation results verify the effectiveness of the modulation strategy.