电网故障情况下三相光伏三电平逆变器的控制技术研究

发布时间：2018-10-10 11:21

【摘要】：如今随着新能源的发展，大量光伏发电系统并网连接。由于线路短路等电网故障造成的电网电压跌落使得并网控制策略出现了很多问题亟待解决，这就需要并网光伏系统在电网故障期间需要满足许多诸如逆变器快速准确的电网同步技术、不平衡电流控制、无功支撑、功率因数矫正和电网故障穿越等并网标准。然而，公共耦合点非线性负载和电网中常见的两相短路和单相短路都会导致电网电压的不平衡和非正弦畸变，使得逆变器同步电网的相位、瞬时有功功率和无功功率、直流侧电压、并网电流和电压的正负序分量都会产生影响逆变器性能的二倍频振荡。本文在三电平中点钳位式逆变器拓扑基础上，提供了很多可以解决电网故障情况下并网变量振荡和电网故障穿越能力等问题的控制方案。首先，为了解决三电平中点钳位式拓扑在实际运行中易造成中点电位不平衡的问题，文中采用了基于电容电荷守恒原理来改变逆变器开关状态的直流侧中点电位控制。其次，为了解决电网发生不对称故障时的电网同步问题，本文采用了一种基于新型解耦双同步参考坐标系锁相环的正序电压相位检测技术，这种方法可以完全消除普通同步参考坐标系锁相环的相位检测误差，并且能准确分离出不平衡电网电压的正序和负序分量。在设计电网不对称故障条件下的电流控制策略时，本文采用了一种新的基于交叉解耦双同步参考坐标系下PI控制电流环的正负序并网电流控制方案，这种方案可以抵消由电流正负序分量造成的电流分量上的二倍频振荡。然而，在电网发生故障期间，光伏系统为了把光伏电池产生的功率全部传输给电网必然会增大并网电流从而导致由过流引起的光伏并网系统解列。为了解决这个问题，本文采用了基于正负序控制的带电流限制的功率控制算法与光伏电池定功率跟踪控制方案相结合的控制策略。最后，，本文推导了一系列计算瞬时有功功率和无功功率中功率振荡的方案，可以根据实际电网故障情况来选择最合适的方案来消除功率振荡。本文基于DSP与FPGA控制系统，在带LCL滤波的三电平中点钳位式并网逆变器实验平台上验证了部分理论与实验研究，实验结果验证了理论的正确性。
[Abstract]:Now with the development of new energy, a large number of photovoltaic power systems connected to the grid. Because of the voltage drop caused by circuit short circuit and other network faults, there are many problems to be solved urgently in the grid-connected control strategy. Therefore, grid-connected photovoltaic systems need to meet many grid-connected standards such as inverter fast and accurate synchronization technology, unbalanced current control, reactive power support, power factor correction and fault traversing. However, the common coupling point nonlinear load and the common two-phase and single-phase short-circuit in the power network will lead to the unbalanced and non-sinusoidal voltage of the power network, which makes the inverter synchronize the phase, instantaneous active power and reactive power. The positive and negative sequence components of DC side voltage, grid-connected current and voltage will produce double frequency oscillation which affects the performance of inverter. Based on the topology of three-level neutral-point clamped inverter, this paper provides many control schemes which can solve the problems of grid-connected variable oscillation and power network fault traversing ability. Firstly, in order to solve the problem that the three-level neutral-point clamping topology is prone to cause the neutral point potential imbalance in practical operation, the DC side neutral point potential control based on the principle of capacitance charge conservation is adopted to change the switching state of the inverter. Secondly, in order to solve the problem of power network synchronization in the event of asymmetric fault, this paper uses a novel decoupled double-synchronous reference coordinate system phase-locked loop to detect the positive sequence voltage and phase. This method can completely eliminate the phase detection error of the common synchronous reference coordinate PLL and can accurately separate the positive and negative sequence components of unbalanced grid voltage. In the design of current control strategy under asymmetrical fault condition, a new current control scheme based on PI control current loop in cross-decoupled double-synchronous reference coordinate system is proposed in this paper. This scheme can counteract the double frequency oscillation on the current component caused by the positive and negative sequence components of the current. However, in order to transmit all the power generated by photovoltaic cells to the grid during the power grid failure, the grid-connected current will be increased, which will lead to the de-listing of the grid-connected photovoltaic system caused by overcurrent. In order to solve this problem, a new power control algorithm with current limitation based on positive and negative sequence control and a fixed power tracking control scheme for photovoltaic cells are proposed in this paper. Finally, a series of schemes to calculate the instantaneous active power and reactive power oscillation are derived. The most suitable scheme can be selected to eliminate the power oscillation according to the actual power network fault situation. Based on DSP and FPGA control system, this paper verifies some theoretical and experimental research on the three-level neutral-point clamped grid-connected inverter with LCL filter, and the experimental results verify the correctness of the theory.
【学位授予单位】：燕山大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

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