【作者】 陈倩；

【导师】 罗利文； 陆昱；

【作者基本信息】 上海交通大学 ， 电气工程（专业学位）， 2015， 硕士

【摘要】 如今,将太阳能作为能源的光伏发电系统并入配电网中后,一定程度上能有效地缓解用电日趋紧张的问题。分布式光伏发电供电方式灵活:在光伏并网满足用户用电需求时,多余的电量会并入配电网对配电网侧负载进行供电;在光伏并网满足不了用户用电需求时,配电网会对用户侧进行补足供给。这样供电成本相对较低并且还能缓解供电压力,但同时给配电网带来了诸如谐波污染、孤岛效应、直流注入、剩余电流等电能质量的问题。本文根据分布式光伏发电的运行方式、输出功率等方面的不同,对配电网侧的电流和电压产生的影响,来分析其对配电网的电能质量的影响。首先介绍了光伏电网的主要组成部分,对各部分设备的工作原理进行了分析。搭建了分布式光伏发电装置通过LC滤波后并入配电网的模型,用户侧负载不论如何变化,光伏并网电流始终与电压保持同频率同相位。接着介绍了无功功率和谐波,对谐波的污染及对策进行了说明,这是衡量电能质量的主要标准之一。根据仿真模型计算出逆变器在额定功率下工作时,电流总谐波畸变率(THD)为4.92%,当逆变器在10%的额定功率下工作时,电流THD会剧增到7.63%。所以在光伏发电并网时,逆变器应尽量在额定功率状态下运行。根据光伏并网及配电网的拓扑结构说明了孤岛效应会对输配电网产生很大的影响,并对目前常用的检测方法进行了说明。根据建立仿真模型的结果表明,在孤岛状态前,整个电网处于稳定工作状态,配电网的电压和电流符合标准;在孤岛效应发生后,电网中的电压和电流可能会产生突变,给输配电网和光伏电网带来很大的压力,甚至会引起电网的崩溃。然后从数学的角度来阐述直流分量的定义,说明其由来和控制方法。直流分量的存在,使得配电变压器的铁芯产生直流偏磁造成过度饱和,导致输出的电压波形在峰值处缺失,同时电流有突变脉冲量存在,对整个配电网有很大的冲击。最后对剩余电流的定义、影响和产生进行简要的说明。以单相全桥逆变器为例,根据其等效电路详细分析建立了仿真模型,对配电网侧的电流和电压以及剩余电流进行了分析。更多还原

【Abstract】 Nowadays, the photovoltaic(PV) power grid, which is feeding on solar energy, can incorporate into distribution network. It can relieve the situation of power emergency effectively. The distributed PV generation has flexible power supply mode. When PV gird produces more electricity than users consume, the rest of electricity will be exported to distribution network. When PV gird produces less electricity than users consume, the lack of electricity will be imported by distribution network. Although the technique has lower costs and release of energy emergency, it brings some power quality problems at the same time, such as harmonic pollution、islanding effect、DC injection、residual current, etc. According to the operation and output power of distribution network, this paper analyzes the impact on power quality of distribution network under its voltage and current influence.First, the main component of PV grid is simply introduced, and its principles are analyzed. Based on distributed PV device model, there comes the conclusion: PV grid current always maintains the same frequency and phase with the voltage no matter how the changes of user load.Second, reactive power and harmonic is introduced. This is one of the main measures of power quality. Based on the simulation model, the current total harmonic distortion(THD) is 4.92% under the rated power of inverter. When the inverter operates at 10% rated power, the current THD will be increased to 7.63%. So the inverter must be operated under rated power.Third, islanding effort is illustrated according to the topological structure of PV grid and distribution network. Its common detection methods are simply introduced. Based on the simulation model, before the island state, the gird is under stable operation as well as its voltage and current are in standard permission scope. Under the island state, the bad change of voltage and current would bring a lot of pressure to operation of PV grid and distribution network, even breakdown.Then the definition of DC component is introduced by mathematical method. And its origin and control methods are explained. The existence of DC component causes the supersaturation of DC magnetic bias in the distribution transformer. Therefore the output voltage waveform will loss at its peak, meanwhile the output current waveform has a pulse. The entire grid would be impacted.Finally, the definition and influence of residual current are briefly described. Based on the simulation model of single-phase full-bridge inverter, the current and voltage of distribution network and residual current of the inverter are analyzed.更多还原