为减少大功率变换器功耗,需降低器件开关频率,但将造成输出侧电流谐波含量显著增加,影响三电平逆变器中点电位控制精度. 为解决这一问题,以二极管箝位型三电平逆变器为对象,在分析低开关频率对中点电位影响的基础上,明确了三电平逆变器低开关频率分段调制的理论分界点. 针对低调制度区域所采用的常规SVPWM算法,提出了一种基于桥臂优化选取的中点电位控制方法,该方法只需判断中点电位差,无需引入输出侧电流,从而避免了低开关频率下电流畸变严重对电流极性的影响,有效保证了中点电位平衡. 仿真及实验验证了该中点控制方案在开关频率500 Hz时,仍能保持较好的中点电位误差在1%Vdc之内.%The switching frequency of the three-level inverters is usually kept low to reduce the dynamic losses of the high-power inverters and which results in an increase in the harmonic components of the out-put current, and affects the control difficulties of the neutral point potential. According to these prob-lems, the influence on the neutral point potential by the output current was analyzed, as well as the first proposing of the demarcation point for the subsection modulation. For low modulation index, the normal pulse width modulation would be more appropriate. A novel approach controlling the neutral point poten-tial for the low modulation index was proposed based on the optimal selection of the sub-bridges. This new method doesn' t need the output current as a feedback signal, which avoids the affect from the severe distortion of the output current at low switching frequency. Experimental results verify that method can maintain the neutral point potential balancing with the switching frequency as low as 500Hz.
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