电工技术学报2025，Vol.40Issue(8)：2573-2586,14.DOI:10.19595/j.cnki.1000-6753.tces.240520
中高调制度下NPC逆变器扇区重构型虚拟空间矢量脉宽调制及中点平衡策略
Sector Reconfiguration Virtual Space Vector Pulse Width Modulation and Neutral Point Balance Strategy of NPC Inverter in Medium and High Modulation Depth
摘要
Abstract
As a typical multilevel inverter,a neutral point clamped(NPC)three-level inverter is suitable for large-capacity and high-voltage converters,which can effectively reduce current harmonic content.However,the NPC three-level inverter has the problem of neutral point voltage imbalance due to the structural characteristics of capacitive voltage division.The traditional virtual space-vector pulse width modulation(VSVPWM)has limited ability to suppress neutral point voltage fluctuation.Correcting its offset is challenging,especially in the medium and high modulation depths.Therefore,this paper proposes a sector reconfiguration VSVPWM.By introducing equivalent medium vectors and reconstructing sectors in medium and high modulation depths,small and medium vectors can fully participate in neutral point balance adjustment while retaining fixed sector division.This method can effectively suppress the neutral point voltage fluctuation and accelerate the recovery of the neutral point offset.There is only one balance coefficient for each fixed sector,which is easy to implement. Firstly,the equivalent relationship between a large vector and a medium vector is analyzed.An equivalent medium vector with constant amplitude is then constructed.The equivalent medium vector can participate in the neutral point balance by adjusting the proportion of medium and large vectors.After that,a virtual vector group,including equivalent medium vectors,is constructed.Furthermore,an equivalent medium vector VSVPWM(EMV-VSVPWM)is proposed,which improves the neutral point adjustment ability in the sector with a medium vector.Secondly,the level of modulation depth is divided based on the operational sector position,and the neutral point margin of the EMV-VSVPWM strategy depths is analyzed in one modulation period.It is found that the regions with weaker capacity of neutral point balance exist in high modulation depth.Therefore,a sector reconstruction VSVPWM(SR-VSVPWM)is then designed.The sector boundary and vector selection boundary in the medium and high modulation depths are separated to increase the proportion of small and medium vectors in such regions,which can enhance the neutral point adjustment margin.Furthermore,the neutral point balance coefficient of small and medium vectors is unified to reduce the computational complexity.Meanwhile,the vector sequence is optimized according to the principle of constant switching state,and the switching loss is reduced. The initial neutral point voltage offset and modulation depth experiments are carried out on a hardware experimental platform in the loop.The results indicate that the SR-VSVPWM strategy can achieve the fast balance of the middle point in pure resistor load and resistor-inductance load conditions.Compared with the traditional VSVPWM single small vector adjustment,the neutral point voltage offset is eliminated,and the balance time in the high modulation depth is reduced by about 46%.In addition,the current harmonics are also reduced.When the experiment on variable modulation depth is considered,SR-VSVPWM still exhibits strong suppression of neutral point fluctuations and good current quality in high modulation depth.After the switching frequency is reduced to 5 kHz,the neutral point fluctuation level of SR-VSVPWM is 79.1%of the traditional VSVPWM.关键词
中点钳位(NPC)型三电平逆变器/虚拟空间矢量脉宽调制/中点电压平衡/扇区重构/等效中矢量Key words
Neutral point clamped(NPC)three-level inverter/virtual space vector pulse width modulation/neutral point voltage balance/sector reconstruction/equivalent medium vector分类
信息技术与安全科学引用本文复制引用
胡瀚林,赵咪,黄毅,闫海超,鲁敏..中高调制度下NPC逆变器扇区重构型虚拟空间矢量脉宽调制及中点平衡策略[J].电工技术学报,2025,40(8):2573-2586,14.基金项目
国家自然科学基金地区科学基金项目(62363030)和新疆维吾尔自治区科学技术厅重大科技专项项目(2022A01004-3)资助. （62363030）
