一种具有低共模电压的三电平逆变器中点平衡算法

针对非隔离型三相三电平光伏逆变器的中点平衡及共模电压问题,提出一种具有低共模电压的三电平逆变器中点平衡算法,即在十三矢量调制策略基础上添加共模电压小的小矢量对中点电位进行控制,并根据此思想进一步提出一种基于零序电压注入的载波实现方法,该方法不需进行扇区判断和复杂的几何运算,因算法简单易于工程实现。实验结果证明本调制策略在降低共模电压的同时可实现中点平衡控制。     

弱电网下基于模型预测控制的NPC三电平LCL型并网逆变器谐振抑制方法研究

为了抑制弱电网下NPC三电平LCL型并网逆变器系统存在的谐振,提高输出电能质量,同时抑制直流侧中点电压波动,建立了弱电网下三电平LCL型并网逆变器的逆变器侧电流和直流侧中点电压的预测模型.针对LCL型滤波器存在的谐振问题,从预测模型角度出发,提出了采用电容电压基频分量的MPC-i1uc_f谐振抑制策略,消除了谐振分量对...     

三电平变频器水冷散热器温度场的计算与分析

针对三电平静止频率变换装置(SFC)功率器件温升难以确定的问题,以1台2 MW/3.3kV三电平SFC为例,建立了其功率器件水冷散热器温度场的三维数学模型和有限元计算模型,并对三电平SFC在额定负载运行时水冷散热器的温度场进行了计算,结果表明:各测量点的计算值与测量值能较好地吻合,证明该计算模型是合理的.在该温度场计算模型的基础上,分析了冷却水流量对水冷散热器温度场的影响,结果表明:冷却水流量对水冷散热器的温度分布影响显著,随着流量的增加,水冷散热器的最高温度和最低温度都有所降低.     

一种基于模型预测控制的T型三电平逆变器中点电位平衡控制方法

中点电位的平衡控制是T型三电平光伏并网逆变器系统首要解决的问题。本文建立了T型三电平逆变器的主电路数学模型及负载模型,并分析了中点电位不平衡的主要原因,在传统预测电流控制方法的基础上,研究了一种基于模型预测控制的中点电位平衡控制方法:首先对负载电流进行采样,用采样值计算出预测值,同时检测直流母线中点电流,得到中点电位的偏差值;然后优化由预测电流与参考电流之间的平方误差及中点电位的偏差值构成的性能指标函数,选择使性能指标函数最小的开关状态,在下一个采样周期作用于逆变器,从而实现中点电位的平衡控制。最后采用Matlab/Simulink进行仿真验证,仿真结果表明,该方法具有快速的动态响应,实现了中点电位的平衡控制,且输出了高质量的电压波形。     

T型三电平逆变器模型预测多目标优化控制方法

该文建立T型三电平逆变器的主电路数学模型,研究一种T型三电平逆变器模型预测多目标优化控制方法,主要包含输出电压控制和中点电位平衡的控制:首先对负载电压电流进行采样,用采样值计算出输出电压预测值,得到使预测电压与参考电压之间的误差最小的开关状态,同时测量直流母线中点电流,得到中点电位的偏差值,根据此开关状态下对应的直流侧电容充放电情况,优化选择使中点电位偏差值减小的开关状态,在下一个采样周期作用于逆变器,从而实现输出电压控制和中点电位平衡控制。最后通过Matlab/Simulink仿真和实验进行验证,仿真和实验结果表明,该方法可很好地实现输出电压控制和中点电位平衡控制,且具有原理简单、易于数字化实现的特点。     

基于IWO-PSO混合算法的三电平逆变器SHEPWM仿真研究

针对传统粒子群优化(PSO)算法在求解三电平逆变器选择谐波消除脉宽调制(SHEPWM)技术的非线性超越方程组时存在局部收敛、收敛速度慢且计算精度不高的问题,提出了一种基于入侵杂草优化和粒子群优化混合算法(IWO-PSO)的SHEPWM方程组计算方法,该混合算法结合IWO算法的广度和PSO算法的深度,通过合理选择算法参数,有效地解决了计算结果局部收敛和收敛速度慢的问题,并以三电平中点箝位型(NPC)逆变器为例,利用Matlab/Simulink进行仿真试验。结果表明,IWO-PSO算法可行、有效,实现了三电平NPC逆变器在线SHEPWM控制。     

基于功率平衡算法的NPC三电平变换器 中点电压控制

分析了中点钳位型三电平变换器的中点电压数学模型,推导出三相功率与零序电压的传递函数。提出一种新型的注入零序电压控制方案,该方案通过控制中点处的零序总功率为0,来实现中点电压的平衡控制。具体方案是,通过计算中点处的三相功率偏差,经PI调节器输出零序电压调制波,经过3 s/2 r坐标变换,叠加至三相基波调制波,并采用SVPWM调制算法实现。仿真显示,方案能够实现中点电压的平衡控制,具有较好的动态响应。     

新能源并网三电平逆变器并联系统中点电位平衡及环流抑制

虽然三电平并网逆变器并联系统可以提高功率等级,但存在中点电位不平衡及零序环流问题。文章在分析中点电位波动及零序环流产生机理的基础上,提出了基于双调制波载波脉宽调制(DWMPWM)配合零序环流控制器的综合调制算法。通过PI闭环控制零序环流,将所得到的偏置量注入到调制波之中,并将每相调制波进行正负分解得到两组调制波,增加了零状态占空比的调节自由度,解决了零序环流问题和高调制度及任意功率因数范围内的中点电位不平衡问题;无须进行空间矢量调制(SVPWM)的复杂矢量计算,算法更为简单。在Simulink和RTDS中分别搭建了仿真模型,仿真结果表明,采取双调制波载波配合环流控制器综合调制算法,可以快速地使中点电位趋于平衡,有效抑制零序环流。文章所提算法可用于解决高电压、大功率新能源并网三电平逆变器并联系统中点电位平衡问题及零序环流问题。     

用于提高发电机-变流器组出口电压的新型风电变流器及其特性分析北大核心CSCD

文章提出一种新型中低压混合拓扑的风电变流器,该变流器机侧采用两电平变流器级联,网侧采用三电平变流器,提高了网侧变流器电压等级,减少了电缆的数量。首先对新型风电变流器的电压特性进行Simulink仿真验证,表明新拓扑结构不需要提升发电机绝缘要求;然后,对网侧变流器中点电位平衡进行了分析,并提出了一种改进的虚拟空间矢量调制策略,该策略能够在较高调制度下实现中点电位平衡,并通过RTLAB硬件在环实验验证了其中点电位平衡能力;最后,对新型风电变流器的效率与成本进行了分析,指出同功率等级下,新型风电变流器较低压并联型风电变流器有显著的效率与成本优势。     

永磁直驱风电机组的三电平升压变流技术

对于额定功率为2 MW或更高容量的变流器,背靠背(BTB)中点钳位型(NPC)变流器可以降低系统的成本、体积以及复杂性。文章提出一种新型拓扑结构,该结构采用二极管整流,三电平升压(TLB)和中点钳位型变流器,能够进一步降低系统的成本和体积。该结构在直流侧完成最大功率点跟踪(MPPT)控制计划,使TLB解决MPPT和直流侧电容平衡问题,为中点钳位控制提供更大的灵活性。最后以3 MW永磁风力发电系统为仿真对象,仿真结果验证了该拓扑结构和控制策略的正确性。     

燃气轮机发电机组静止变频启动装置研究

近年来我国进口了数十套燃燃气轮机发电机组,它们利用发电机及相应的变频启动装置启动。而变频启动装置由于采用可控硅（SCR）整流再逆变原理,其输出电压电流波形差,致使输出效率低、力矩小;另外,谐波分量大,不能满足国家相关标准要求。为此,利用绝缘栅双极型功率晶体管（IGBT）器件替代可控硅元件设计了一种新技术装置。结果表明,后者输出的谐波非常理想,性能指标远远超过前者,可全面满足国家相关标准。     

基于构件技术的电力系统MIS模型

提出一种基于构件技术的MIS三层模型,可以大大提高 电力系统应用软件的重要性、开发效率和安全可靠性,并实现应用软件系统中构件工程部署最优化和便于扩充与管理。     

Use of a static frequency converter for rapid load response inpumped-storage plants

Most pumped-storage power plants have the capability to operate as synchronous condensers. As such, they can be brought online very quickly to support power system load requirements. However, one of the effects of making a rapid transition from synchronous condenser operation to turbine/governor operation is an initial reverse power flow into the machine. This reverse power flow can be very undesirable at a time when the power system is calling for load support. On weak or isolated power systems, this reverse power flow can lead to objectionable voltage and frequency dips in the power system. With the proper utilization of a static frequency converter (SFC) and its associated controls and auxiliary switchgear systems, the reverse power flow resulting from a transition from synchronous condenser operation can be eliminated. This paper describe a method by which an SFC system can be used to make this rapid load response in pumped-storage power plants without incurring a reverse power flow and to provide additional instantaneous short term power to support the grid     

Electric powertrain modeling of a fuel cell hybrid electric vehicle and development of a power distribution algorithm based on driving mode recognition

This paper proposes a novel fuzzy controller based on an adaptive membership function for optimum power management of a fuel cell hybrid electric vehicle (FCHEV). In the first phase, an electric powertrain model of the FCHEV is derived and a fuzzy controller is proposed. Then, the fuzzy controller is optimized using a genetic algorithm. The optimization process is accomplished through simulation for a given driving cycle. Since, however, the optimized result may vary according to the applied driving cycle for optimization, it is impossible for one optimized result to cover various driving cycles. In the second phase, an adaptive membership function based on a stochastic approach is proposed to guarantee optimum performance from the presented fuzzy controller, even though the driving cycle changes. This controller is referred to as the ‘Stochastic fuzzy controller’ (SFC) in this study. The SFC employs a stochastic approach where membership functions can be transformed statistically using a probability evaluated from driving pattern recognition. Then, driving cycle analysis is performed through off-line simulation and hardware in a loop simulation (HILS) test for four driving cycles. Finally, the SFC shows the best performance in terms of minimum fuel consumption and state-of-charge (SoC) maintenance.     

The Influence of Collector Fluid Inlet Temperature on the Performance of a Solar-Assisted Absorption System Using Step-Finned Flat-Plate Collector

In the present work, an extensive analysis is developed for an evaluation of the thermal performance of a solar-powered H₂O/LiBr absorption cooling system using a step-fin flat-plate collector (SFC). The performance parameters, namely, collector efficiency factor, heat removal factor, and collector efficiency, for the SFC is derived. A system simulation model has been developed to analyze the system performance—that is, to identify an operating criterion as a function of the collector fluid inlet temperature (T _FI). It has been observed from the results that the performance of the system depends strongly on T _FI. Simulation results show that the system operates optimally (maximum coefficient of performance) at an optimal T _FI. When the system runs at this optimal value of T _FI, minimum collector material is required. Thus, when using SFC in place of a rectangular-fin flat-collector, thirty-five percent or more collector material can be saved. However, it has been observed that the effect of thermal conductivity on the plate volume of SFC has a marginal effect.     

Optimization and study of performance parameters in an engine fueled with hydrogen

Engine performance parameters, including fuel conversion efficiency (FCE), power, torque and specific fuel consumption (SFC), can be affected by variables such as ignition timing (IGT), injection timing (IT) and hydrogen volume fraction (H2%). In this paper an engine fueled with different H2/CNG blend rations from 0 to 50% volume under ignition and injection timing at different speeds were investigated. For model validation, the engine operating conditions were simulated using the AVL fire software and compared with experimental results. The statistical comparison showed that there was no significant difference between them. Also, a support vector machine (SVM) was used to study the engine's behavior according to the variables studied. The SVM model predicted the FCE, power, torque, SFC and CO with error of less than 4%. The Genetic Algorithm (GA) was used to find optimal IGT, IT and H2% values to achieve optimum engine performance. Therefore, the results showed that the optimum engine operating conditions depend on the engine speed. Also, the results showed that independent variables (IT, IGT and H2%) maximize the engine performance and minimize SFC and CO emission. So that the optimum use of hydrogen in this research at different engine speeds was between 20% and 30%.     

Experimental study of the functionality of a semisubmersible wind turbine combined with flap-type Wave Energy Converters

In the present paper the functionality of the Semisubmersible wind energy and Flap-type wave energy Converter (SFC) is examined experimentally. In order to study the functionality of the SFC, the focus is on operational environmental conditions. SFC is a combined concept that utilizes offshore wind energy and ocean wave energy for power production. Details are presented as far as the physical modelling of the wind turbine with the use of a redesigned small-scale rotor and of the Power Take-Off mechanism of the Wave Energy Converters (WECs) with the use of a configuration that is based on a mechanical rotary damper. Tests with quasi-static excitation, motion decay, regular and irregular waves without and with wind that is uniform are conducted on an 1:50 scale physical model. The experimental data are compared with numerical predictions obtained by a fully coupled numerical model using Simo/Riflex tool. A good agreement is observed between experimental and numerical predictions. The combined operation of WECs doesn't affect the tension of mooring lines nor the acceleration of nacelle and the bending moment in tower's base. The produced power of the WECs of the SFC and consequently the functionality of the SFC is estimated.     

Voltage stabilization of VSI SMES capacitors and voltage sag compensation by SMES using novel switching strategies

This paper presents a novel and optimized switching strategy and control approach for a three-level two-quadrant chopper in a three-level Neutral point clamped (NPC) voltage source inverter (VSI) superconducting magnetic energy storage (SMES). Using the proposed switching strategy, the voltage of the inverter capacitors in SMES can be independently controlled; also, the minimum power and switching losses – as well as the proper convection – can be achieved using this same strategy. The simulation results indicate that when combined with a proportional-integral (PI) control approach the proposed switching strategy can be easily implemented in the power networks and can balance and stabilize the multi-level inverters’ capacitor voltage level. The voltage variation of the capacitors in the steady state condition is less than (0.062%) which is 15 times better than the IEEE standard requirement (1%). To investigate the effectiveness and reliability of the proposed approach in stabilizing capacitor voltage, SMES performance using the presented approach is compared with that of SMES when the capacitors of the three-level inverter are replaced with equal and ideal voltage sources. This comparison is carried out from the power-quality point of view and it is shown that the proposed switching strategy with a PI controller is highly reliable. Considering that the Space Vector Pulse Width Modulation (SVPWM) is highly effective in decreasing low order harmonics (LOH), this article utilizes this type of modulation when it is combined with the most optimized switching strategy.     

Combustion characteristics of CI engine fueled with WCO biodiesel/diesel blends at different compression ratios and EGR

The present study investigated the effect of compression ratio (CR) with the use of exhaust gas recirculation (EGR) technology on the performance of combustion characteristics at different CRs and engine loads; the brake thermal efficiency (BTE), specific fuel consumption (SFC), volumetric efficiency (VOL.EFF), exhaust gas temperature, carbon dioxide emission (CO₂), hydrocarbons (HC), nitrogen oxides (NOx), and oxygen content (O₂). The single-cylinder, four-stroke compression ignition engine was run on a mixture of diesel and biodiesel prepared from Iraqi waste cooking oil at (B0, B10, B20, and B30). A comparison has been achieved for these combustion characteristics at different blends, load, and CRs (14.5, 15.5, and 16.5) at 1500 rpm constant engine speed. The transesterification process is used to produce biodiesel and ASTM standards have been used to determine the physical and chemical properties of biodiesel and compare them to net diesel fuel. The preliminary conducting tests indicated that engine performance and emissions improved with the B20 mixture. Experimental test results showed an increase in BTE when CR increased by 17% and SFC increased by 23%. It also found a higher VOL.EFF by 6% at higher pressure ratios. A continuous decrease in BTE values and an increase in SFC were sustained when the percentage of biodiesel in the mixture was increased. Emissions of carbon dioxide, HC, and NOx increased by 12%, 50%, and 40%, respectively, as CR reached high values. NOx increased with the addition of biodiesel to 35%, which necessitated the use of EGR technology at rates of 5% and 10%. The results indicated that the best results were obtained in the case of running the engine with a mixing ratio of B20 with the addition of 10% EGR, NOx decreased by 47% against a slight increase in other emissions.     

Mitigation of harmonic disturbance at pumped storage power stationwith static frequency converter

This paper investigates the harmonic distortion problem and mitigation method at the Mingtan pumped storage power station in Taiwan, where six 300 MVA synchronous generator/motors are started by a static frequency converter (SFC) before the pumping stage. Since the SFC uses a 6-pulse rectifier technique, a large amount of harmonic currents are produced during the starting period. The harmonic distortion level at each bus of the power plant was very high. Especially, the total harmonic distortion (THD) of current at the lighting feeder reached up to 184%, so that power fuses were burned out. At first a 5 mH reactor was inserted in the SFC feeder and a 5th order and high pass filter was installed. However, the harmonic distortion levels were still too high, but there is no space for additional higher-order filters. Finally, the SFC is feeded with an individual transformer and the harmonic disturbance problem is avoided. This paper also gives computer simulations to investigate the harmonic distortion problems and verify the mitigation methods