电网不平衡条件下永磁风力发电系统网侧变流器控制

发布时间：2018-12-10 14:47

【摘要】：风力发电技术已成为国内外学者研究热点,在大电网三相电压平衡时传统风电机组已实现并网发电。然而在微网或小型孤网中存在三相电压不平衡及不对称故障的情况,给风电机组锁相、并网发电带来了一系列困难。针对上述问题,本文对风电机组网侧变流器在电网三相电压不平衡及不对称故障下的控制策略展开了深入研究。首先,对风电机组网侧变流器以及三相电压不平衡电网建模。研究了网侧变流器在电网三相电压平衡下的数学模型,并分析了网侧变流器稳态运行特性。并为进一步研究电网三相电压不平衡下网侧变流器的运行特性,推导了三相电压不平衡下的网侧变流器数学模型。然后,针对电网三相电压不平衡直接导致传统的网侧变流器锁相不准确问题,对传统的电网锁相方法进行了改进。基于现有的三相电压不平衡下同步参考坐标系的软件锁相方法,增加陷波器,改进二阶广义积分器,从不平衡电网中提取出正负序分量,然后分别计算出正负序相位角。进一步在MATLAB/Simulink中搭建了仿真模型,在电网电压不平衡度为10%的工况下,对所提出的改进锁相方法进行验证。通过仿真结果看出,所用方法可以快速、准确地提取出网侧电压正负序分量及相位信息。其次,由于直接功率控制策略具有算法简单、响应性能好等特点,在网侧变流器中采用了直接功率控制。但传统基于PI控制的空间矢量直接功率控制(SVM-DPC)无法满足电压不平衡下非线性系统的高频开关控制,为了实现上述目的,提出一种基于滑模变结构的空间矢量直接功率控制,通过内外环的协调控制,抑制了直流母线电压二倍频分量,并增加了陷波器,实现了无功功率无差调节,消除了二次谐波影响,保证了直流母线电压稳定。并在单相接地和两相电流短路故障工况下,分别对传统与改进控制策略进行仿真对比,对所改进控制策略的正确性进行了验证。最后,搭建了基于DSP28335网侧变流器硬件平台。设计了网侧变流器的主电路、控制电路及外围保护电路,测试了各部分电路的正确性。利用硬件平台中控制电路部分与RTLAB半实物仿真平台,在不同单相负载增加工况下,对采用传统基于PI控制的SVM-DPC与所提出的基于滑模变结构的SVM-DPC的网侧电压、电流进行了对比,对改进控制策略的有效性进行了验证。
[Abstract]:Wind power generation technology has become a hot topic for scholars at home and abroad. When the three-phase voltage balance of large power grid, the traditional wind turbine has realized grid-connected generation. However, there are three phase voltage imbalance and asymmetric faults in microgrid or small isolated grid, which brings a series of difficulties for wind turbine to phase lock and grid connection. In order to solve the above problems, the control strategy of wind turbine grid-side converter under the unbalance and asymmetry of three-phase voltage is studied in this paper. First, the wind turbine grid side converter and three-phase voltage imbalance network are modeled. The mathematical model of grid-side converter under three-phase voltage balance is studied, and the steady-state operation characteristics of grid-side converter are analyzed. In order to further study the operation characteristics of grid-side converter under three-phase voltage imbalance, the mathematical model of grid-side converter under three-phase voltage imbalance is derived. Then, aiming at the inaccurate phase locking problem of traditional grid-side converter caused by unbalanced three-phase voltage, the traditional power grid phase-locked method is improved. Based on the existing software phase-locking method of synchronous reference coordinate system under unbalanced three-phase voltage, the notch filter is added, the second-order generalized integrator is improved, the positive and negative sequence components are extracted from the unbalanced power network, and the phase angles of positive and negative sequence are calculated respectively. Furthermore, the simulation model is built in MATLAB/Simulink, and the improved phase-locked method is verified under the condition of voltage imbalance of 10%. The simulation results show that the proposed method can extract the positive and negative sequence components and phase information of the voltage on the grid side quickly and accurately. Secondly, because the direct power control strategy has the characteristics of simple algorithm and good response performance, direct power control is used in the grid-side converter. But the traditional space vector direct power control (SVM-DPC) based on PI control can not satisfy the high frequency switching control of nonlinear system under voltage imbalance. A space vector direct power control based on sliding mode variable structure is proposed. Through the coordinated control of internal and external loop, the double frequency component of DC bus voltage is restrained, and the notch filter is added to realize reactive power reactive difference regulation. The second harmonic effect is eliminated and the DC bus voltage is stable. Under the condition of single-phase grounding and two-phase current short-circuit fault, the traditional control strategy and the improved control strategy are simulated and compared, and the correctness of the improved control strategy is verified. Finally, the hardware platform based on DSP28335 converter is built. The main circuit, control circuit and peripheral protection circuit of the grid-side converter are designed, and the correctness of each circuit is tested. Using the control circuit part of the hardware platform and the RTLAB hardware-in-the-loop simulation platform, under different single-phase load increasing conditions, the grid-side voltages of the traditional SVM-DPC based on PI control and the proposed SVM-DPC based on sliding mode variable structure are studied. Compared with the current, the effectiveness of the improved control strategy is verified.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46;TM614

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