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论文作者作者单位	*专业名称
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论文研究方向学位授予单位学位级别文献类型	培养单位答辩日期 *论文语言
导师1姓名导师2姓名导师3姓名论文来源	*导师1单位导师2单位导师3单位
论文内容
*中文标题：光伏微网并联逆变器环流抑制技术研究
*英文标题： Research on Circulation Suppression Technology of Photovoltaic Microgrid Parallel Inverter
*中文关键词（关键词用逗号分隔）：光伏微网并联逆变器，基波环流，谐波环流，鲁棒下垂控制，虚拟谐波阻抗
*英文关键词（关键词用逗号分隔）： photovoltaic microgrid parallel inverter,fundamental wave circulation,harmonic circulation,robust droop control,virtual harmonic impedance
*中文文摘：随着光伏微网交流侧负荷的增长需求，常将多台小容量光伏逆变电源以共交流母线方式并联为负荷供电，以解决单台大容量逆变器成本高、可靠性低、运行维护困难等问题。然而，由于各逆变器存在输出电压矢量不一致、线路阻抗差异等因素，导致光伏微网并联逆变器间产生较大的环流，从而加快器件损耗、降低系统效率，严重时将影响系统稳定运行。因此，本文针对光伏微网并联逆变器环流抑制技术展开以下研究。首先，以三相三线制式电压型并联逆变器拓扑结构作为研究对象，对比分析了不同坐标系下逆变器系统数学模型的优缺点。确定了逆变器工作在两相静止坐标系，并在该坐标系下设计了QPR-P型电压电流双闭环基本控制策略，实现了光伏微网并联逆变器输出电压的无静差跟踪。其次，针对光伏微网并联逆变器基波环流问题，提出了一种基于虚拟复阻抗的改进鲁棒下垂控制方法，引入虚拟复阻抗调节基波域等效连线阻抗呈感性，消除了有功和无功功率耦合；通过增设逆变器输出电压初始值与改进积分系数，求解关于基波电压的一阶非齐次线性微分方程，减小基波电压到达稳态的时间以提升环流抑制速度；通过设定下垂系数与额定容量成反比、下垂功率标准值按各逆变器额定容量比例分配，利用终值定理计算各逆变器输出功率，使稳态时输出功率达到功率标准值，消除了相同和不同额定容量逆变器在负荷投切后的母线电压偏差，有效抑制了因各逆变器输出电压矢量不一致造成的基波环流。仿真结果表明，当逆变器额定输出功率为10KW时，基波环流经0.13s即达到最大抑制效果，基波环流抑制到0.65A以下，并且稳态时母线电压稳定在220V/50Hz，有效提升了环流抑制速度与系统稳定性。最后，针对光伏微网并联逆变器谐波环流问题，提出了一种基于自适应虚拟谐波阻抗和多准比例复数积分（MQPCI）控制方法，通过引入由虚拟电阻和主要次谐波电流构成的虚拟阻抗，使谐波域等效连线阻抗呈阻性的同时，利用谐波电流与阻抗值的反比关系自适应补偿等效连线阻抗差异，消除了非线性负载下等效连线阻抗不一致引起的谐波环流；通过设计MQPCI控制器调节5次和7次谐波频率处控制器增益和带宽，使谐波电压很好的跟踪零指令电压，从谐波电压抑制角度消除了电源端输出谐波电压分量不一致引起的谐波环流。仿真结果表明，加入MQPCI控制器后的各逆变器输出电压THD降低到0.52％和1.56％，对电源端引起的谐波环流抑制达到90％；引入自适应虚拟谐波阻抗控制后，并联逆变系统谐波环流由0.7A降低到0.063A，对负载端引起的谐波环流抑制达到91％。
*英文文摘： With the increasing demand of AC load in photovoltaic microgrid， multiple small capacity photovoltaic inverters are often connected by the form of common AC bus in parallel for load power supply， so as to solve the high cost， low reliability and difficult maintenance problems of single large capacity inverter. However， the output voltage vector and the line impedance of each inverter are inconsistent， which will lead to larger circulation between photovoltaic microgrid parallel inverters. Circulation will accelerate the device loss， reduce the system efficiency， and seriously affect the stable operation of system. Therefore， the circulation suppression technology of photovoltaic microgrid parallel inverters is studied as follows in this paper.Firstly， the topology of three-phase three-wire voltage parallel inverter is studied， and the advantages and disadvantages of mathematical models are compared and analyzed under different coordinate systems. In two-phase static coordinate system， the QPR-P control strategy of voltage and current double closed-loop is designed to realize the output voltage non-static tracking of photovoltaic microgrid parallel inverters.Secondly， an improved robust droop control method based on virtual complex impedance is proposed aiming at the fundamental wave circulation problem of photovoltaic microgrid parallel inverters. The equivalent line impedance in fundamental wave domain is sensitive by introducing the virtual complex impedance， so as to eliminate the coupling of active and reactive power. The first order linear non-homogeneous differential equation about fundamental wave voltage is solved by adding the initial value of inverter output voltage and improving the integral coefficient. It reduces the fundamental wave voltage time of arrival in steady state to improve the circulation suppression speed. The output power of each inverter is calculated by final value theorem by setting the droop coefficient inverse with the rated capacity and the droop power standard value distribute with the inverter rated capacity ratio. It makes the steady-state output power reach power standard value to eliminate the bus voltage deviation of inverters with the same or different rated capacity after load switching and suppress the fundamental wave circulation effectively which is caused by inconsistent output voltage vector. The simulation results show that the maximum suppression effect is achieved in 0.13s of fundamental wave circulation and the fundamental wave circulation is suppressed below 0.65A. At the same time， the bus voltage is stable at 220V/50Hz in steady-state. Therefore， this method can effectively improve the circulation suppression speed and system stability.Finally， a control method based on adaptive virtual harmonic impedance and multi-quasi proportional complex integral is proposed aiming at the harmonic circulation problem of photovoltaic microgrid parallel inverters. The equivalent line impedance in harmonic domain is assumed to be resistive by introducing the virtual impedance composed of virtual resistance and the main harmonic current. The difference of equivalent line impedance can be compensated adaptively next by using the inverse relation between harmonic current and impedance. It eliminates the harmonic circulation caused by the inconsistent of equivalent line impedance under nonlinear load. The harmonic voltage can track the zero instruction voltage well by designing MQPCI controller to adjust the gain and bandwidth of controller at the 5th and 7th harmonic frequencies. It eliminates the harmonic circulation caused by the inconsistent output harmonic voltage components from harmonic voltage suppression aspect. The simulation results show that the output voltage THD of each inverter is reduced to 0.52％ and 1.56％ after adding MQPCI controller， and the suppression effect of harmonic circulation caused by power reaches 90％. The harmonic circulation of parallel inverter is reduced from 0.7A to 0.063A after the introduction of adaptive virtual harmonic impedance control， and the suppression effect of harmonic circulation caused by load reaches 91％.
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