Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Fault diagnosis in neutral point indirectly grounded system basedon information fusion

In neutral point indirectly grounded systems, phase-to-ground fault is putting new demands on fault diagnosis technology. Information fusion is applied to detect the phase-to-ground fault, which integrates several sources of information, including line current, line voltage, zero sequence current and voltage, and quintic harmonic wave component. This method is testified through the simulation of Matlab. Simulation results show that the precision and reliability of the detection has been greatly increased.

A Study on Neutral Point Earthed Method of Power System

This paper mainly is study on power system working state with neutral point different grounded methods, when the power system is normal working and the single-phase grounding. And further analysis of the different operating modes of voltage and current relationships, expounds the different operation occasions and characteristics.

Combination Operation for Neutral Point of 35 kV Power Grids in Mountainous Area

Based on a lot of measurement and analysis,this paper find that the unbalanced nature of 35 kV grids due to unsymmetrical capacitance values gives difficulty in neutral point operation in mountainous area.Improving compensation of Petersen coil can rectify imbalance of voltage but bring up new problem that Petersen coil can not extinguish grounding arc effectively in fault.To put down contradiction mentioned above,this paper proposes a combination operation for neutral point of 35 kV grids as neutral point insulated in routine operation and grounding through Petersen coil in fault,then EMTP simulation is carried out.Simulation indicates that new neutral operation method can improve lightning withstand level and decrease trip-out rate of grids.

Low-complexity model predictive control of a four-level active neutral point clamped inverter without weighting factors

The four-level active neutral point clamped(ANPC)inverter has become increasingly widely used in the renewable energy indus-try since it offers one more voltage level without increasing the total number of active switches compared to the three-level ANPC inverter.The model predictive current control(MPCC)is a promising control method for multi-level inverters.However,the conven-tional MPCC suffers from high computational complexity and tedious weighting factor tuning in multi-level inverter applications.A low-complexity MPCC without weighting factors for a four-level ANPC inverter is proposed in this paper.The computational burden and voltage vector candidate set are reduced according to the relationship between voltage vector and neutral point voltage balance.The proposed MPCC shows excellent steady-state and dynamics performances while ensuring the neutral point voltage balancing.The efficacy of the proposed MPCC is verified by simulation and experimental results.

Adaptive Neuro Fuzzy Inference System Based Decoupled Control for Neutral Point Clamped Multi Level Inverter Fed Induction Motor Dri

The presence of an integrator in a reference model of a rotor flux-based model reference adaptive system(RF-MRAS)and non-linearity of the inverter in the output voltage degrade the speed response of the sensorless operation of the electric drive system in terms of DC drift,initial value issues,and inaccurate voltage acquisition.To improve the speed response,a compensating voltage component is supplemented by an amending integrator.The compensating voltage is a coalition of drift and offset voltages,and reduces DC drift and initial value issues.During low-speed operation,inaccurate voltage acquisition distorts the stator voltage critically,and it becomes considerable when the stator voltage of the machine is low.Implementing a three-level neutral point clamped inverter in speed-sensorless decoupled control of an induction motor improves the performance of the drive with superior quality of inverter output voltage.Further,the performance of the induction motor drive is improved by replacing the proportional-integral(PI)controller in the adaption mechanism of RF-MRAS with an adaptive neuro-fuzzy inference system(ANFIS)controller.A prototype model of the three-level neutral point clamped inverter(3L-NPC)-fed induction motor drive is fabricated in a laboratory,and its performance for a RF-MRAS,modified RFMRAS,and modified RFMRAS using ANFIS are compared using different benchmark tests.

Evaluation Method of Output Waveform Quality for Neutral⁃Point⁃ Clamped Three⁃Level Converter

An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency error caused by neutral point voltage ripple and high frequency error introduced by space vector synthesis were both taken into account,and the unified error model of output current ripple was established.By taking continuous and discontinuous modulation strategies as examples,the unified error model was validated through Fourier analysis of the experimental results.The proposed evaluation method will be helpful for the switching sequence optimization and the modulation strategy selection.

A novel SVPWM strategy considering neutral-point potential balancing for three-level NPC inverter

This paper proposes a novel SVPWM （space vector pulse width modulation） strategy for the three-level neutral-point-clamped voltage source inverter, based on the particular disposition of all the redundant voltage vectors. The new modulation approach shows superior performance for harmonic voltage and balancing control of neutral-point potential compared to the popular eight-stage centered SVPWM. It realizes suppression of inverter neutral-point potential variation by accurately modifying redundant factor of small vectors pairs, only requiring information of DC-link capacitor voltages and three-phase load currents. This is convenient to apply and is compatible of digital computer realization. Feasibility of the proposed control approach is verified by simulation and experimental results.

Fixed Points and Asymptotic Properties of Neutral Stochastic Delay Differential Equations

This paper discusses a linear neutral stochastic differential equation with variable delays. By using fixed point theory, the necessary and sufficient conditions are given to ensure that the trivial solution to such an equation is pth moment asymptotically stable. These conditions do not require the boundedness of delays, nor derivation of delays. An example was also given for illustration.

Study on Over-Voltage of 220 kV Transformer＇s Neutrals and Protection Strategy

In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.

Periodic Points on the Parabolic Domain

The papers proves that there is one and only one rational neutral periodic points on the bound ary of any parabolic domain.

Periodic Solutions for a Kind of Second-Order Neutral Differential Equation on Time Scales

In this paper,the existence of periodic solutions and nonnegative periodic solutions for a kind of second-order neutral differential equation on time scales is considered.The partial increment is a fixed constant if the time scale is the real number set and is a multiple of the periodic of the time scale if the time scale is not the real number set.By means of a fixed point theorem due to Krasnoselskii,some sufficient conditions are obtained.

适用于中点箝位型三电平逆变器的多目标调制策略

为同时实现中点箝位型三电平逆变器的中点电压平衡和共模电压降低,分别分析了基于载波脉宽调制(CBPWM)和基于虚拟空间矢量脉宽调制(VSVPWM)的中点电压平衡和共模电压降低方法。基于CBPWM提出一种可以降低共模电压的载波脉宽调制(RCMV_CBPWM)策略,可将大多数工作区域的共模电压限制在直流侧电压的1/6以内。为了实现上述2个目标,同时不过分增加开关损耗,在RCMV_CBPWM基础上提出了一种多目标调制(MOPWM)策略,在全调制度和全负载功率因数范围内,共模电压可限制在直流侧电压的1/6以内并实现中点电压平衡,且其开关损耗低于VSVPWM。比较了MOPWM、RCMV_CBPWM和VSVPWM在中点电压控制、共模电压降低和开关损耗降低方面的性能。实验结果验证了MOPWM的可行性和优越性。

PROBLEM OF PERIODIC SOLUTIONS FOR NEUTRAL FUNCTIONAL DIFFERENTIAL EQUATION

The problem of periodic solutions for a kind of kth-order linear neutral functional differential equation is studied. By using the theory of Fourier expansions, a sufficient and necessary condition to guarantee the existence and uniqueness of periodic solution is obtained. Further, by applying this result and Schauder's fixed point principle, a kind of kth-order nonlinear neutral functional differential equation is investigated, and some new results on existence of the periodic solutions are given as well. These results improve and extend some known results in recent literature.

一种三相双输出有源中点钳位型三电平变换器

该文基于有源中点钳位型三电平变换器(ANPC-TLC)结构,通过每相增加两个开关管形成一种具有两组三相交流电压输出端口的双输出有源中点钳位型三电平变换器(DOANPC-TLC)拓扑。该文详细介绍DO-ANPC-TLC的拓扑结构,对其工作原理进行分析,研究其不同开关状态下的电流路径、输出相电压电平和各开关的电压应力。针对DO-ANPC-TLC结构特点及工作原理,应用一种双输出虚拟空间矢量脉宽调制(DO-VSVPWM)方法,能够独立控制两组交流输出,并保持直流链路电容电压平衡。为了进一步简化控制过程,研究一种基于载波的简化双输出虚拟空间矢量脉宽调制(CB-VSVPWM)策略,在器件损耗和总谐波畸变率(THD)方面,对所提出DO-ANPC-TLC的性能进行分析。实验结果验证了所提拓扑的可行性和调制策略的有效性。

配电网相电压不对称动态变化下的高阻接地故障辨识

配电网单相高阻接地故障与相电压不对称动态变化间具有相似的中性点位移电压波形,易引起接地保护的误判。为此,该文建立不对称导纳矢量模型,通过分析相电压不对称动态变化的原因,揭示非故障条件下中性点位移电压的变化机理。同时建立故障电路全响应模型,刻画中性点位移电压随过渡电阻的变化轨迹,研究高阻接地故障和不对称导纳动态变化时的位移电压稳态重合区域及暂态特征差异。在论证二者稳态特征存在混叠的同时,揭示暂态过程中故障初相角对中性点位移电压直流衰减分量的影响规律。采用经验小波变换提取中性点位移电压直流衰减分量和高频分量,并利用直流衰减分量辨识故障;对于特定故障初相角导致的直流分量无法检测场景,提出基于方差贡献率的重心频率分布特征判断方法辨识接地故障。仿真分析表明,该方法为5 kΩ及以下的高阻接地故障与不对称导纳动态变化提供了明显的区分特征,为单相接地故障的准确辨识提供了新思路。

一种新型三电平变换器中点电压平衡调制策略

在大功率轨道交通装备领域中,三电平变换器因具有众多优点,在实际中得到广泛应用,但是也存在中点电压不平衡这一固有问题。为解决三电平中点箝位(NPC)型变换器存在的中点电压不平衡问题,减少输出相电流畸变情况,提高系统运行稳定性,文章提出了一种基于分析中点电荷量的双自由度新型中点电压平衡调制策略。该调制策略首先从数学分析的角度介绍了三电平变换器直流侧中点电压不平衡问题的原因;之后分析了在空间矢量脉宽调制(SVPWM)技术中,电压矢量输出序列对中点电压的影响;最后基于上述分析结果,改进传统的电压矢量输出序列,并基于改进序列的特点提出了一种新的双自由度中点电压平衡调制策略,通过双自由度的平衡因子调节作用时间。理论上,所提出的新型调制策略具有更多可控电荷量,相较于传统方法具有更良好的控制效果;仿真和试验结果验证了所提的新型调制策略对中点电压的控制效果具有更好的快速性和稳定性。综上所述,文章所提的新型双自由度调制策略可更有效解决三电平变换器存在的中点电压不平衡问题。

一种适用三电平并联系统的虚拟矢量调制策略

直流侧中点电位平衡和零序环流抑制是保证三电平逆变器并联系统正常运行的重要问题,然而基于冗余小矢量对调节的环流抑制方案进一步增加空间矢量脉宽调制(space vector pulse width modulation,SVPWM)中点电流无法对称消除的场景,加剧双机系统中点电位不平衡程度。该文基于虚拟矢量合成思路,提出一种满足零序环流抑制和中点电位平衡需求的双机虚拟矢量调制方法。该方法重新定义虚拟中矢量,通过缩短中矢量作用时间和增加参与合成的对称冗余小矢量以减少中点电流不平衡场景;分析不同扇区不同控制目标下虚拟矢量合成规则,利用相占空比法优化虚拟矢量的作用顺序,减少矢量合成过程中的开关次数。与传统SVPWM策略下中点电压变化量的对比分析表明,所提方法能够削弱环流抑制和中点电位平衡的耦合关系。最后,利用Starsim平台实验验证该策略的有效性。