不平衡条件下光伏并网逆变器控制研究

发布时间：2018-06-25 05:49

本文选题：光伏并网逆变器 + 电网电压不平衡　；参考：《中国矿业大学》2014年硕士论文

【摘要】：电网电压不平衡会恶化光伏并网逆变器的工作状况，如并网电流畸变加剧、MPPT过程受到干扰等。不平衡较为严重时，若不采取相应的措施，甚至可能烧毁逆变设备。本文分别以抑制直流电压2次谐波和抑制交流负序电流为目标，，研究了电网电压不平衡时的光伏并网逆变器控制。本文对电网电压不平衡下LCL滤波的并网逆变器进行了建模。建模结果显示，两相同步旋转坐标系下的模型较为复杂，而两相静止坐标系下的模型则相对简单。以常规定步长扰动观察法为例，本文定性分析了直流电压含有2次谐波对最大功率点跟踪的影响。分析结果表明，过大的直流电压2次谐波可能会干扰最大功率点跟踪过程，甚至导致跟踪失败。本文仿真分析比较了3种正、负序分离方法：1.基于陷波器的正、负序分离；2.采用基于解耦双同步旋转坐标系锁相环的正、负序分离；3.采用基于锁频环的双二阶广义积分器的正、负序分离。仿真结果显示：1.基于陷波器的正、负序分离方法动态响应较快，但对谐波的抑制能力弱；2.采用基于解耦双同步旋转坐标系锁相环或采用基于锁频环的双二阶广义积分器的正、负序分离动态响应较慢，但对谐波具有一定的抑制能力。基于扩展pq理论，本文研究了公共连接点处瞬时功率控制、变换器交流侧瞬时功率控制和抑制交流负序电流控制策略。其中，公共连接点处瞬时功率控制、变换器交流侧瞬时功率控制以抑制直流电压2次谐波为目标，抑制交流负序电流控制则以使网侧电流平衡为目标。考虑到在两相同步旋转坐标系中进行PI控制时解耦不易且控制器较多，选择在两相静止坐标系下采用PR控制。仿真和实验结果表明，这3种控制策略实现了各自的控制目标，且均能使并网逆变器在电网电压不平衡时正常工作，证明了控制策略的有效性。
[Abstract]:The unbalanced voltage of the grid will worsen the working condition of the grid-connected photovoltaic inverter, such as the distortion of grid-connected current is aggravated and the process of MPPT is disturbed. If the imbalance is serious, even the inverter equipment may be destroyed if the corresponding measures are not taken. In this paper, the control of photovoltaic grid-connected inverter with unbalanced voltage is studied, aiming at suppressing the second harmonic of DC voltage and restraining the negative sequence current of AC respectively. In this paper, the grid-connected inverter with LCL filter under unbalanced grid voltage is modeled. The modeling results show that the model in two-phase synchronous rotating coordinate system is more complex, while the model in two-phase stationary coordinate system is relatively simple. In this paper, the influence of the second harmonic in DC voltage on the maximum power point tracking is qualitatively analyzed by taking the constant step size perturbation observation method as an example. The results show that the second harmonic of DC voltage may interfere with the maximum power point tracking process and even lead to tracking failure. In this paper, three positive and negative sequence separation methods: 1. 1 are compared and simulated. A positive and negative sequence separation method based on notch filter is presented. A positive and negative sequence separation loop based on decoupled double synchronous rotation coordinate system is used. The positive and negative sequence separation of biquadratic generalized integrator based on frequency locked loop is presented. The simulation results show that: 1. The method of positive and negative sequence separation based on notch filter has a fast dynamic response, but its ability to suppress harmonics is weak. The dynamic response of positive and negative sequence separation of phase locked loop based on decoupled double synchronous rotating coordinate system or double second order generalized integrator based on frequency locking loop is slow, but it has certain ability to restrain harmonics. Based on the extended PQ theory, the strategies of instantaneous power control at common connection points, AC side instantaneous power control of converters and suppression of AC negative sequence current control strategies are studied in this paper. Among them, the instantaneous power control at the common connection point, the AC side instantaneous power control aims to suppress the second harmonic of DC voltage, and the suppression of AC negative sequence current control is to balance the grid side current. Considering that Pi control is not easy to decouple and there are many controllers in the two-phase synchronous rotating coordinate system PR control is adopted in the two-phase stationary coordinate system. The simulation and experimental results show that the three control strategies achieve their respective control objectives and can make the grid-connected inverter work normally when the voltage of the grid is unbalanced. The effectiveness of the control strategy is proved.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

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