三电平变流器的DPWM切换研究

Research on DPWM Switching of Three-level Converter

中点箝位型(NPC)三电平变流器在中压大功率系统中广泛应用。由于中压大功率系统的开关损耗较大,为了降低开关损耗,一般采用较低的开关频率,为进一步降低开关损耗,还可采用注入零序电压的方式实现断续脉宽调制(DPWM),它使得一相电平箝位其对应开关器件不动作,从而有效降低器件开关损耗。在此分析了DPWM注入不同的零序电压会对中点电位产生不同影响,为了控制直流侧中点电位平衡,提出了当系统出现直流侧中点电位偏移时通过不同DPWM方式切换来进行中点电位调节。最后,搭建了NPC三电平变流器仿真模型和3 kW NPC三电平变流器实验平台,仿真和实验验证了所提DPWM方式切换策略调节中点电位平衡的正确性和有效性。

Neutral-point-clamped(NPC) three-level converters are widely used in medium-voltage high-power systems.Due to the large switching loss of medium-voltage high-power systems,in order to reduce the switching loss,a lower switching frequency is generally used.In order to further reduce the switching loss,the injection of zero-sequence voltage to achieve discontinuous pulse-width modulation(DPWM) is used,which makes a phase level clamps its corresponding switching devices do not act,thereby effectively reducing device switching losses.It is analyzed that different zero sequence voltage injected into DPWM will have different effects on neutral point potential,and in order to control the balance of the neutral potential on the DC side,it is proposed to adjust the neutral potential by switching between different DPWM methods when the neutral potential on the DC side is shifted.Finally,the simulation model of NPC three-level converter and the experimental platform of 3 kW NPC three-level converter are built,and the simulation and experiment verify the correctness and effectiveness of the proposed DPWM mode switching strategy to regulate the neutral potential balance.