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Improved selective harmonic elimination pulse-width modulation strategy in multilevel inverters

机译：多电平逆变器中改进的选择性谐波消除脉冲宽度调制策略

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摘要

In the standard selective harmonic elimination (SHE)-pulse-width modulation (PWM) technique for multilevel converters, in order to eliminate N 2 1 non-triplen odd harmonics of the ac-side voltage and to regulate the output voltage amplitude, N switching angles need to be determined. Therefore a set of N non-linear transcendental equations must be solved to find the desired switching angles for any value of the modulation index. However, solutions to the non-linear equations are not feasible for the entire range of modulation region. This study proposes a modified SHE-PWM technique that extends the standard modulation region and generates a stepped voltage waveform within a wide range of modulation indices. As compared with the standard SHE-PWM technique, the constraint associated with elimination of the harmonic with the highest order is relaxed and the corresponding equation is disregarded. Consequently, a reduced number of transcendental equations are employed to find the N desired switching angles. Since the switching frequency remains constant, converter's efficiency does not change. However, in order to produce a pure sinusoidal waveform, a higher order filter is required. A genetic algorithm is used to solve the equations and to determine the switching angles. The proposed technique can generate stepped voltage waveforms with a wide range of modulation indices. Performance of the proposed SHE-PWM technique for a seven-level cascaded H-bridge converter, based on simulation studies, is evaluated and experimentally verified.
机译：在用于多电平转换器的标准选择性谐波消除（SHE）-脉宽调制（PWM）技术中，为了消除ac侧电压的N 2 1非三重奇次谐波并调节输出电压幅度，N开关需要确定角度。因此，必须解决一组N个非线性先验方程，以找到任何调制指数值所需的开关角度。但是，非线性方程的解决方案在整个调制区域范围内都不可行。这项研究提出了一种改进的SHE-PWM技术，该技术扩展了标准调制区域并在宽调制指数范围内生成阶跃电压波形。与标准SHE-PWM技术相比，放宽了与消除最高次谐波相关的约束，并且忽略了相应的方程式。因此，减少数量的先验方程被用于找到N个期望的切换角。由于开关频率保持恒定，因此转换器的效率不变。然而，为了产生纯正弦波形，需要更高阶的滤波器。遗传算法用于求解方程式并确定开关角度。所提出的技术可以产生具有宽调制指数范围的阶跃电压波形。基于仿真研究，对提出的SHE-PWM技术在七级级联H桥转换器中的性能进行了评估和实验验证。

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