一种零序注入的三电平中点钳位型变换器中点电位平衡控制策略

A Novel Zero Sequence Injection Scheme for Three-Level NPC Converters Considering Neutral-Point Potential Balance

对三电平的两种调制方法空间矢量脉宽调制(SVPWM)和虚拟空间矢量脉宽调制(VSVPWM)进行深入比较,详细分析VSVPWM方法线电压dv/dt高和谐波含量大、功率器件开关损耗大以及中点电压平衡动态响应特性慢等问题的本质原因。为克服SVPWM和VSVPWM的不足,提出一种零序注入的载波调制方法。该方法将一种适用于两电平的零序注入法引入到简化的三电平空间矢量图的小六边形中,在每个小六边形中建立中点电流与零序分量之间严格准确的数学关系,并结合6个小六边形开关函数符号特点,只需一路载波和6个等式即可实现三电平载波调制和中点电位平衡控制,且具有计算量小,执行时间短,中点电压平衡动态响应快等优点。最后,本文方法与SVPWM和VSVPWM的实验对比,验证了提出方法的可行性和有效性。

An in-depth comparison of two methods(SVPWM and VSVPWM)for the three-level converter is presented in this paper,and the disadvantages are analyzed such as high dv/dt of the lineto-line voltage,high harmonic contents,high power device switching losses,and slow neutral-point voltage-balancing dynamics of VSVPWM.In order to overcome the drawbacks of the two methods,a novel zero sequence injection carrier-based modulation scheme is proposed.Firstly,a zero sequence injection method for the two-level converter is introduced into a small hexagon of the simplified three-level space vector diagram,then the relationship between the neutral-point current and the zero sequence component is studied mathematically in each small hexagon.In addition,combined with the signs of switching functions in six small hexagons,the carrier-based modulation and the potential balancing control can be achieved with only one carrier wave and six expressions.The proposed method has the advantages of small calculation amount,short execution time and fast voltage-balancing dynamics.Finally,a comparison among three kinds of strategy(the proposed method,SVPWM,and VSVPWM)is presented,which verifies the feasibility and validity of the proposed method.