单相光伏逆变器双闭环控制及并网稳定性研究

发布时间：2019-02-10 18:52

【摘要】：能源紧缺与环境污染形势不容乐观,大力发展光伏逆变技术是缓解危机的有效途径之一。目前中小型容量的单相光伏逆变器广泛使用锁相环或锁频环实现并网同步控制,但在实际电网中上述方法均存在跟踪误差较大导致逆变器功率因数变低的问题。另外,现有研究发现光伏逆变器在强电网下易达到稳定状态,而在弱电网下具有易失稳的现象,带来逆变器退出运行的严重后果。为解决光伏逆变器存在的上述问题,在双闭环控制的基础上,提出了使用锁相环和锁频环复合并网同步技术来提高跟踪精度改善逆变器功率因数的方法,理论分析了光伏逆变器独立使用锁相环或锁频环在同步控制过程中存在的优缺点,基于Matlab/simulink软件平台,分别搭建了在电网电压幅值跌落、频率和相角突变及谐波含量突增四种情况下的仿真模型,仿真对比研究了传统同步控制与复合控制方式在电网电压不稳定时对光伏逆变器输出特性的影响。针对弱电网下光伏逆变器易失稳的问题,提出在复合并网同步技术的基础上添加电压前馈控制策略提高逆变器输出阻抗的方法,构建了逆变器电流内环控制的结构框图,分析了逆变器输出阻抗与并网线路阻抗对逆变器在弱电网下运行稳定性的影响,研究了逆变器输出阻抗扰动成分的稳定性,搭建强弱电网切换下的仿真模型,对比分析了改变输出阻抗前后的并网效果,验证了对弱电网下增强光伏逆变器运行的稳定性的重要作用。得出了提高逆变器输出阻抗有利于增强逆变器在弱电网下的稳定性的结论。仿真结果表明:本文提出的基于复合并网同步技术的电压前馈控制策略,能够解决实际电网中跟踪误差较大和弱电网下具有易失稳的问题,避免逆变器功率因数变低和被迫退出运行的后果。
[Abstract]:The situation of energy shortage and environmental pollution is not optimistic. Developing photovoltaic inverter technology is one of the effective ways to alleviate the crisis. At present phase-locked loop or frequency locked loop is widely used in single-phase photovoltaic inverter with medium and small capacity to realize grid-connected synchronous control. However, in actual power grid, the tracking error is large and the power factor of inverter becomes lower. In addition, it is found that the photovoltaic inverter is easy to achieve stability under the strong grid, but unstable under the weak grid, which leads to the serious consequences of the inverter out of operation. In order to solve the above problems of photovoltaic inverter, based on the double closed loop control, a method of improving the tracking accuracy and improving the power factor of inverter by using PLL and FLOL combined grid-connected synchronization technology is proposed. The advantages and disadvantages of phase-locked loop (PLL) or frequency-locked loop (FL) in the synchronous control process of photovoltaic inverter are analyzed theoretically. Based on the Matlab/simulink software platform, the voltage amplitude drop in the power grid is built separately. The simulation model of frequency and phase angle mutation and harmonic increase is studied. The effects of traditional synchronous control and composite control on the output characteristics of photovoltaic inverter under the condition of voltage instability are compared. Aiming at the instability of photovoltaic inverter under weak grid, this paper proposes a method to increase the output impedance of inverter by adding voltage feedforward control strategy on the basis of combined grid-connected synchronization technology, and constructs the structure block diagram of inverter current inner loop control. The influence of inverter output impedance and grid-connected line impedance on the operation stability of inverter under weak grid is analyzed. The stability of the disturbance component of inverter output impedance is studied, and the simulation model of strong and weak power grid switching is built. The effect of grid connection before and after changing the output impedance is compared and analyzed, which verifies the important role of enhancing the stability of photovoltaic inverter under weak grid. It is concluded that increasing the output impedance of the inverter is beneficial to enhance the stability of the inverter under the weak grid. The simulation results show that the proposed voltage feedforward control strategy based on composite grid-connected synchronization technology can solve the problems of large tracking error and instability under weak electric network. Avoid the consequences of lower power factor and forced exit from operation of the inverter.
【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464;TM615

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