海上风电通过柔性直流输电系统并网的控制策略研究

发布时间：2018-11-22 09:42

【摘要】：近年来,双馈式感应发电机(DFIG)越来越多地应用于海上风力发电系统中。而柔性直流输电系统(VSC-HVDC)又是远距离海上风电并网的典型结构。本文针对海上风电系统通过VSC-HVDC送出的控制策略做了以下几个方面的研究： (1)搭建了风电场由VSC-HVDC送出的数字仿真平台。风电场由基于DFIG的风力机组成,其中包含有风力机组模型,DFIG换流器模型以及桨矩角控制系统。对VSC-HVDC系统而言,风场侧换流器(WFVSC)主要控制海上风电交流系统的电压幅值和电网频率,以稳定交流电压；而网侧换流器(GSVSC)控制直流电压和与交流系统交换的无功功率。 (2)海上风电由VSC-HVDC送出系统是一个“低惯量”系统。故给出利用直流电容和DFIG转子动能去模拟同步电机惯量的协同控制策略。GSVSC通过直流电压滑差控制,在电网扰动下,直流电容将吸收或释放能量。两端VSC交流系统频率将通过WFVSC变频控制实现人工耦合,这样省去两端换流站之间的通讯。为响应WFVSC频率变化,DFIG功率控制器将调整功率指令值,使转子转速相应变化。通过一系列协同控制,海上风电场将参与电力系统频率控制。在允许的直流电压变化范围内,该协同控制策略可提供大范围的惯量,增加系统稳定性。 (3)分析了直流电容和GSVSC换流器电流控制器阈值对故障直流电压的影响。提出了海上风电由VSC-HVDC送出的故障穿越策略：当GSVSC侧系统故障,GSVSC首先处于限电流控制。然后,WFVSC感受到升高的直流电压,将其升高直流电压信号转化成升高的送端交流系统频率。最后,DFIG在感受到升高交流系统频率后,通过自身的降功率控制策略降低其发出的有功功率。并分析了利用频率偏差控制和频率-功率自定义曲线控制的DFIG自动降功率特性。
[Abstract]:In recent years, doubly-fed induction generator (DFIG) has been used more and more in offshore wind power system. Flexible direct current transmission system (VSC-HVDC) is a typical structure of wind power grid. In this paper, the control strategy of offshore wind power system through VSC-HVDC is studied in the following aspects: (1) the digital simulation platform of wind farm sent out by VSC-HVDC is built. The wind farm consists of wind turbine based on DFIG, including wind turbine model, DFIG converter model and propeller moment angle control system. For the VSC-HVDC system, the wind field side converter (WFVSC) mainly controls the voltage amplitude and the power network frequency of the offshore wind power AC system to stabilize the AC voltage. The grid side converter (GSVSC) controls DC voltage and reactive power exchange with AC system. (2) Offshore wind power supply system by VSC-HVDC is a "low inertia" system. Therefore, a cooperative control strategy using DC capacitance and DFIG rotor kinetic energy to simulate the inertia of synchronous motor is presented. The DC capacitance absorbs or releases the energy under the disturbance of the power grid through the DC voltage slip control. The frequency of VSC AC system at both ends will be manually coupled by WFVSC frequency conversion control, thus eliminating the communication between the two end converter stations. In response to the WFVSC frequency change, the DFIG power controller will adjust the power instruction value to make the rotor speed change accordingly. Through a series of cooperative control, offshore wind farm will participate in the frequency control of power system. Within the allowable DC voltage range, the cooperative control strategy can provide a wide range of inertia and increase the stability of the system. (3) the influence of DC capacitance and current controller threshold of GSVSC converter on DC voltage of fault is analyzed. A fault traversing strategy for offshore wind power from VSC-HVDC is proposed: when the GSVSC side system fails, the GSVSC is at the limit current control first. Then, the WFVSC senses the rising DC voltage and converts it into a higher AC system frequency. Finally, DFIG reduces the active power output by its own power reduction strategy after sensing the increase of AC system frequency. The automatic power reduction characteristics of DFIG using frequency deviation control and frequency-power custom curve control are analyzed.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

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