双馈风力发电系统串电阻低电压穿越控制研究

发布时间：2019-03-01 14:33

【摘要】：能源危机和环境污染，，加大了人类对可再生能源的需求，近年来风力发电技术作为主流新能源之一获得了突飞猛进的发展。随着风电机组容量的日益增大以及风电渗透率的不断提高，风电与电网之间的相互影响引起了广泛的重视。DFIG作为当前两大主流机型之一，因其结构原因在电网电压出现跌落故障时，会出现转子过电流和过电压、直流母线电压波动等问题，严重时风机的解列还可能造成电网的大面积瘫痪。因此，电网故障条件下保证双馈风电机组的不脱网运行成为新的研究热点。本文以电网电压跌落条件下的双馈风电系统为研究对象，设计了外接保护装置和优化DFIG励磁策略的低电压穿越方案，并通过仿真和实验对方案的可行性进行了验证。首先，基于PSCAD/EMTDC软件搭建了双馈风力发电系统的数学模型，并在此基础上分析了双馈感应发电机的工作原理及其矢量控制策略。之后，对电网电压严重跌落情况下双馈感应电机的电磁暂态特性进行了理论的分析和仿真验证。其次，提出了一种适用宽功率因数范围的串接连续可调电阻的硬件保护方案。设计的保护装置采用三单相结构，串接在风机升压变压器高压侧和汇流母线之间，每相装置均由功率二极管构成的不控整流电路及并联IGBT的电阻共同组成。考虑电网故障初始时引起的暂态现象最为严重，采用全幅值补偿策略计算等效电阻初值，保证了电网电压跌落时刻机端电压的稳定。同时设计了低功率因数优化控制策略，提升了保护装置在低功率因数工作环境的稳压效果。然后，提出了基于滑模定子磁链观测器的灭磁控制策略。采用滑模磁链观测器对DFIG定子磁链进行跟踪，将观测到的磁链与其经50Hz带通滤波器后得到的交流分量作差，获取定子磁链的直流分量。之后，控制机侧变流器励磁电流，使之建立与磁链直流分量反向的漏磁场，加速了暂态直流分量的衰减。对灭磁控制策略的仿真结果验证了该方案的有效性。最后，搭建了包含小型风电系统网侧变换器和电阻保护装置的实验平台，进行了电网电压跌落故障的低电压穿越实验研究。串接电阻的低电压穿越保护装置采用DSP2812作为主控芯片，调节PWM占空比，实现串接的等效电阻阻值调节。最后模拟了三相电压对称跌落跌落故障，串入电阻保护装置后使得机端电压维持在期望范围，验证了所设计的电阻保护装置的有效性，同时再次验证了理论研究的正确性。
[Abstract]:Energy crisis and environmental pollution have increased human demand for renewable energy. Wind power generation technology as one of the mainstream new energy has been developed by leaps and bounds in recent years. With the increasing capacity of wind turbine and the increasing permeability of wind power, the interaction between wind power and power grid has attracted extensive attention. DFIG, as one of the two mainstream models at present, has attracted more and more attention. Due to its structural reasons, the overcurrent and overvoltage of the rotor and the voltage fluctuation of the DC bus will occur when the voltage drop occurs in the power network. In serious cases, the unwinding of the fan may also cause the large area paralysis of the power network. Therefore, it is a new research hotspot to ensure the operation of doubly-fed wind turbine under the condition of power grid failure. Taking the doubly-fed wind power system under the condition of voltage sag as the research object, this paper designs an external protection device and a low voltage traversal scheme to optimize the excitation strategy of DFIG. The feasibility of the scheme is verified by simulation and experiment. Firstly, the mathematical model of doubly-fed wind power generation system is built based on PSCAD/EMTDC software, and the working principle and vector control strategy of doubly-fed induction generator are analyzed. Then, the electromagnetic transient characteristics of doubly-fed induction machine under the condition of serious voltage sags are analyzed theoretically and verified by simulation. Secondly, a hardware protection scheme, which is suitable for wide power factor range, is proposed. The designed protection device adopts a three-phase structure, connected in series between the high-voltage side of the fan-boost transformer and the bus. Each phase device is composed of an uncontrolled rectifier circuit composed of a power diode and a resistance of the parallel IGBT. Considering the transient phenomenon caused by the initial fault of the power network, the full-amplitude compensation strategy is used to calculate the initial value of the equivalent resistance to ensure the stability of the terminal voltage at the time of the voltage drop. At the same time, the optimal control strategy of low power factor is designed to improve the voltage stabilization effect of the protection device in the low power factor working environment. Then, a sliding mode stator flux observer based demagnetization control strategy is proposed. A sliding mode flux observer is used to track the stator flux of DFIG. The DC component of stator flux is obtained by the difference between the observed flux and the AC component obtained by 50Hz bandpass filter. After that, the excitation current of the converter is controlled to establish the leakage magnetic field which is opposite to the DC component of the flux chain, and the attenuation of the transient DC component is accelerated. The simulation results of the demagnetization control strategy verify the effectiveness of the proposed scheme. Finally, an experimental platform consisting of a network-side converter and a resistance protection device for a small wind power system is built, and an experimental study on the low voltage traversal of the voltage sag fault in the power grid is carried out. DSP2812 is used as the main control chip to adjust the duty cycle of the PWM to realize the equivalent resistance adjustment of the serial resistance in the low voltage traversing protection device of the serial resistance. Finally, the three-phase voltage symmetry sag fault is simulated, and the terminal voltage is maintained in the desired range after connecting to the resistance protection device. The validity of the designed resistance protection device is verified, and the correctness of the theoretical research is verified again.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM614

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