1.为了研究电网电压跌落对永磁同步电机风电系统的影响,进行了实验室实验并构建永磁直驱风电系统的仿真模型,分别对永磁同步发电机和变流器进行控制,分析当电网电压跌落30% (2 s)、跌落50% (0. 5s)以及跌落85% (0. 2 s)三种情况时电机和变流器的运行情况。实验结果和MATLAB R2007a/SimuLink仿真结果表明,永磁同步发电机转速跟踪很好;发电机侧输出电流近似正弦;在电网电压跌落的同时还能对电网提供一定的无功支持,直驱式永磁同步电机风电系统具有较强的低电压穿越能力。
In order to study the influence of grid voltages dip on permanent magnet synchronous motor of wind power system, laboratory experiments and simulation system of direct-driven permanent wind power system were carried out, which were to control the permanent-magnet synchronous generator, commentator motor and analysis three operation conditions when grid voltages dip by 30% (2 seconds), 50% (0. 5 seconds) and 85% (0. 2 seconds). The result of experiment and simulinked by MATLAB R2007a/SimuLink indicated that permanent-magnet synchronous generator speed tracked well current output from the generator-side approximated sinusoidal When the grid voltages dip, it could provide some of reactive power supporting. The direct-driven permanent-magnet synchronous generator of wi
nd power system had a strong low-voltage penetration capability.
2.风机变流器是风电机组实现低电压穿越的关键部件，其控制性能的提升有利于提高风电机组的低电压穿越能力。基于变流器功率平衡控制思想，提出了网侧变流器改进型负载前馈控制策略，提升了网侧变流器的稳压与能量转移能力，缓和了电网故障期间的系统能量失衡，改善了风机变流器及风电机组的低电压穿越能力。控制系统的小信号模型分析结果表明，上述控制策略的稳压与能量转移能力优于传统控制策略。永磁同步风力发电机组系统仿真进一步证明了上述理论分析的正确性。
Wind turbine converter (WTC) is a key component of wind turbine generation system (WTGS) to implement low voltage ride through (LVRT), so the improvement of its control performance is favorable to enhance LVRT ability of WTGS. Based on the thinking of power balance control of converter, an improved load feed-forward control strategy for grid-side converter is proposed to enhance voltage stabilization and energy transfer ability of grid-side converter as well as to mitigate the energy unbalance of power grid during voltage sag and improve LVRT ability of WTC and WTGS. Analysis results of small-signal model for
control system show that the ability of voltage stabilization and energy transfer of the proposed control strategy is better than traditional control strategy. The correctness of above-mentioned theoretical analysis is proved by simulation results of direct-drive permanent magnet synchronous wind power system.
3. 在分析变速变桨距风力发电机组基本控制策略的基础上,提出一种扩大过渡区的改进控制
策略,用来消除额定功率运行点附近切换造成的功率波动及突变载荷等不利影响。依据改进的控制策略设计了3个控制器平滑过渡方案,实现对该策略的最佳跟踪。运用MATLAB仿真平台模拟了改进控制策略下的风力发电机组运行特性,结果表明了改进控制策略的正确性及控制器设计的有效性。
Abstract:Based on an analysis of basic control strategy for variable-speed pitch controlled wind turbine driven generator system, an improved control strategy of enlarging the transition region is proposed to mitigate the harmful effects caused by controller switch near the rated power point, such as power fluctuation and sudden load change. A three-controller smooth transition scheme is designed to fulfill the optimal tracking to the improve
d control strategy. The operation characteristics of the generator system with the improved control strategy are simulated on the MATLAB simulation platform, and the results prove the correctness and effectiveness of the improved control strategy. This work is supported by Natural Science Foundation Project of CQ CSTC
4. 电网电压不平衡会导致双馈感应发电机组(DFIG)定、转子电流出现较大不平衡,使发电机
功率和电磁转矩发生振荡,从而恶化机组运行状况。分析了串联网侧变换器抑制不平衡电网电压对DFIG系统影响的机理,利用并联网侧变换器的控制及静止坐标系下的比例谐振控制器,提出了基于串联网侧变换器的DFIG在不平衡电网电压条件下的控制策略;在实现DFIG电磁转矩、直流母线电压及系统总输出有功功率无2倍频波动的同时,使DFIG定、转子三相电流平衡。所述方法具有不改变转子侧变换器的控制策略、无需求解复杂高阶矩阵的特点。对一台基于串联网侧变换器的2 MW DFIG系统进行了仿真,验证了所提出控制策略的正确性和有效性。
In a hybrid AC-DC transmission grid, DC bias and commutation failure have adverse effects on the behavior of transformer differential protection. With the model of an actual hy
brid AC-DC transmission grid in northwest of China, the performance of differential protection under these two situations are discussed. Simulation results show that the second order harmonic produced by DC bias may cause miss-operation of differential protection in the event of minor internal faults. The results also reveal that under the circumstances of commutation failure, where the current of the AC system can be seen as a harmonic source, the differential protection may refuse operation when internal faults happen because of the high second order harmonic. The protection scheme based on fault component integrated impedance is used to solve these problems. Theoretical analysis and simulation results show that the scheme is with high sensitivity and reliability even when minor internal faults happen under the situation of DC bias or commutation failure.
5. 双馈感应发电机(DFIG)因其对电网故障的敏感性,其低电压穿越运行控制技术备受关注。文中针对定子侧加装串联网侧变换器的新型DFIG风电系统,详细研究了其低电压穿越运行特性,提出了一种适用于新拓扑下发电系统的运行控制方案:通过控制串联网侧变换器抑制定子磁链暂态直流分量及电网电压负序分量对发电机转子侧的不良影响;通过控制转子侧变换器进一步限制故障时发电机的定、转子电流,从而实现发电系统的低电压穿越运行。仿真结果表明:
采用所提出的控制方案,可实现电网故障时DFIG风电系统的零电压穿越运行;采用新拓扑的DFIG风电系统具有优良的电网对称及非对称短路故障穿越能力
Doubly-fed induction generator (DFIG) is sensitive to the grid faults, and its low voltage ride-through (LVRT) operation and control technology attracts more and more research interests. The LVRT operation characteristics of doubly-fed induction generator wind turbines with a series grid-side converter in the stator are investigated, and an operational control strategy is proposed. To restrain the stator and rotor currents during the grid fault, the series grid-side converter is controlled to suppress the transient DC flux component in the stator flux and the negative component in the grid voltage. In the mean time, a successful LVRT under the grid fault is realized by also controlling the rotor-side converter. Simulation results show that the proposed control strategy can make the DFIG system achieve zero voltage ride-through, and the generation system with the new topology has the excellent fault ride-through capability under symmetrical and unsymmetrical faults.
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