【作者】 骆坚；

【导师】 陈燕东； 方旺林；

【作者基本信息】 湖南大学 ， 电气工程（专业学位）， 2020， 硕士

【摘要】 随着传统化石能源的大量消耗,能源紧缺、环境污染等问题变得日益严重,风能、太阳能等新能源因具有清洁和可再生等特性而在国内外得到了广泛的开发利用。新能源发电通常需通过并网逆变器转换成稳定的工频交流电后接入弱电网或通过离网逆变器为本地用户供电。随着接入弱电网和给本地用户供电的逆变器数量不断增加,宽频带振荡现象频现,严重影响供电系统稳定性。目前阻抗分析法因其分析简便性成为研究交互系统稳定性的重要手段,阻抗分析法只需要知道逆变器的等效输入阻抗模型、弱电网和用户负荷的等效输出阻抗模型就可以分析研究新能源发电系统的宽频带振荡机理。因此,本文研发了380V/150k VA、测量频率范围为10Hz到1000Hz的宽频带阻抗测量装备,主要创新点如下:1.对平衡工况下新能源发电系统的并网逆变器和离网逆变器进行序阻抗建模,并通过Bode图直观地分析了锁相环、滤波器和直流侧电压对两种逆变器的序阻抗特性的影响。针对三相不平衡负载工况下离网逆变器输出电压不平衡的问题,提出了离网逆变器采用正负序双支路控制的序阻抗建模方法,对比分析了传统V/F控制模式和正负序双支路控制模式下逆变器的序阻抗特性和输出电压、电流。传统V/F控制模式下,逆变器在基频的正序阻抗幅值较小,但负序阻抗幅值较大,使得不平衡负载引起的负序电流在逆变器阻抗上产生的电压降落较大;正负序双支路控制模式下,逆变器在基频的正负序阻抗幅值均很小,使得负序电流在逆变器阻抗上产生的电压降落很小,因此对逆变器三相输出电压的平衡性影响很小。2.提出了一种低压宽频带阻抗测量装备的整体拓扑结构,其中电压扰动串联注入单元采用变压器、PWM整流器、PWM逆变器和LC滤波器的结构,可发出宽频带、低畸变率的小扰动电压正弦波。PWM整流器采用电压外环PI控制、电流内环无差拍控制的双闭环控制来获得稳定的直流侧电压,PWM逆变器采用电压外环改进重复控制、电流内环比例控制的双闭环控制以得到波形良好的输出电压。最后通过Matlab仿真软件对无源负载、并网逆变器和离网逆变器等进行了宽频带阻抗测量,验证了本文所提阻抗测量装备的拓扑结构和测量方法的正确性。3.研制了一台380V/150k VA宽频带在线阻抗测量实验装备,测量频率范围为10Hz～1000Hz,详细介绍了阻抗测量装备的软硬件设计。基于Lab VIEW在工控机上设计了方便人机交互的序阻抗测量程序,并对无源负载进行了序阻抗特性测量实验。通过实验证明了本文所提的宽频带阻抗测量方法与装备设计的合理性。更多还原

【Abstract】 With the massive consumption of traditional fossil energy sources,energy shortages,environmental pollution and other problems have become increasingly serious.New energy sources such as wind energy and light energy have been rapidly developed and utilized at home and abroad due to their clean and renewable characteristics.New energy power generation usually needs to be converted into stable power-frequency AC through grid-connected inverters and off-grid inverters,and then connected to a weak grid or provide power to local users.As the number of inverters connected to the weak power grid and supplying power to local users continues to increase,wide-band oscillations frequently occur,seriously affecting the stability of the power supply system.At present,the impedance analysis method has become an important method for studying the stability of interactive systems because of its simplicity of analysis.The impedance analysis method only needs to know the equivalent input impedance model of the inverter and the equivalent output impedance model of the weak power grid and user load to analyze and study broadband oscillation mechanism of new energy power generation system.Therefore,this paper developed a 380V/150 k VA,measurement frequency range of 10 Hz to 1000 Hz broadband impedance measurement equipment.The main innovations are as follows:1.The sequence impedance modeling of grid-connected and off-grid inverters in the new energy power generation system under equilibrium condition is carried out,and the influences of phase-locked loop,filter and dc side voltage on the characteristics of the sequence impedance of the two inverters are analyzed intuitively by Bode diagram.Aiming at the problem of unbalanced output voltage of off-grid inverters under three-phase unbalanced load conditions,a sequential impedance modeling method for off-grid inverters with positive and negative sequence dual branch control is proposed.The inverter sequence impedance characteristics and output voltage and current in traditional V/F control mode and positive and negative sequence dual branch control mode are compared and analyzed.In the traditional V/F control mode,the amplitude of the positive sequence impedance of the inverter at the fundamental frequency is small,but the amplitude of the negative sequence impedance is large,Therefore,the negative sequence current caused by the unbalanced load has a large voltage drop on the inverter impedance;The positive and negative sequence impedance amplitudes of the inverter in the mode of positive and negative sequence double-branch control are very small,so the small voltage drop generated by the negative sequence current on the inverter impedance has little effect on the output voltage balance of the inverter.2.An overall topology of low-voltage wide-band impedance measurement is proposed,in which the voltage disturbance series injection device adopts the structure of a transformer,PWM rectifier,PWM inverter and LC filter,which can emit a small disturbance voltage sine wave with a wide frequency band and low distortion rate.PWM rectifier adopts double closed-loop control to obtain stable dc side voltage,in which the outer voltage loop adopts the deadbeat control and the inner current loop adopts PI control.The PWM inverter adopts double closed-loop control to obtain the output voltage with good waveform,in which the outer voltage loop adopts the improved repetitive control and the inner current loop adopts the P control.Finally,the broadband impedance measurement of passive load,grid-connected inverter and off-grid inverter was carried out through Matlab simulation software,and the correctness of the impedance measurement equipment topology and measurement method proposed in this paper were verified.3.A 380V/150 k VA broadband online impedance measurement experimental equipment was developed with a measurement frequency range of 10 Hz to 1000 Hz.The software and hardware design of the impedance measurement equipment was introduced in detail.Based on Lab VIEW,a sequence impedance measurement and calculation procedures designed to facilitate human-computer interaction is designed on the industrial computer,and the sequence impedance characteristic measurement experiment was carried out on the passive load.Experiments have proved the rationality of the wide-band impedance measurement method and equipment design proposed in this paper.更多还原