基于微电网阻抗在线辨识的并网逆变器增益调度自适应控制

Since micro grid is weak grid, equivalent impedance of micro grid can affect the grid-connected inverter performances such as controlling specification, robustness and the stability etc. In general, the grid impedance is changed with operation condition, if the grid impedance varies too far, the behavior of the grid-connected inverter with fixed parameter PI or PR regulator may be deteriorated or even instable. By using the gain-scheduling adaptive control strategy in the PLL(phase locked loop) of the grid-connected inverter, or in the adaptation feedforward voltage regulator, the system performance can be improved, but the further investigations of the gain-scheduled current regulator for grid-connected inverters were still to be needed. In this project, based on the constructed photovoltaic grid-connected inverters and distributed generation power system, the identification of micro-grid impedance and the gain-scheduling control scheme of the grid-connected inverter were further investigated. Firstly ,an impedance online identification algorithm based on the pseudo random sequence injection was proposed, the power spectrum of this pseudo random sequence can be specified by the user, so this online identification algorithm is effected for the local identification or the global identification. Secondly, the optimization gain-scheduled current control strategy for grid connected inverter was investigated in which the other controlling specifications were taken into consideration based on the main specification. Finally the bumpless control strategy was further studied, in which the micro-grid impedance was divided into different region, and the gain-scheduling controller can be simplified. The investigation can provide a better solution for the system stability, optimal control and robustness.

微电网是弱电网，其等效阻抗会影响并网逆变器的稳定性、控制性能和鲁棒性。微电网阻抗是实时变化的，如果微电网阻抗变化过大，采用固定参数的PI或者PR调节器的并网逆变器性能指标会恶化，甚至会失稳。增益调度自适应控制已应用到并网逆变器的锁相环和电压前馈控制中，改善了系统的性能，但在并网逆变器电流调节器方面的研究有待于进一步深入。本项目拟在前期建立的光伏并网发电系统研发平台上，进一步探索微电网阻抗辨识方法及并网逆变器增益调度自适应控制策略。首先，拟进行基于功率谱可以设定伪随机序列信号注入，获得实时辨识微电网阻抗算法，对整体及局部的阻抗进行有效辨识。其次，探讨以某一特定性能指标最优，兼顾其他性能指标，优化并网逆变器电流调节器的增益调度控制策略。最后，划分适当的阻抗区间，探讨无扰切换控制优化设计的机理，简化了增益调度控制器。项目研究为微电网和并网逆变器的稳定性、最优控制和鲁棒性提供一个解决途径。

项目以TI公司的TMS320F28335DSP处理器为控制核心，分别构建功率容量3kW的单相并网逆变器和功率容量6kW的三相并网逆变器，单相并网逆变器和三相并网逆变器，都可以采用自然坐标（a、b、c），（α、β）坐标 和（d 、q）坐标分别进行控制，在此基础上，进行阻抗在线辨识方法的研究和并网逆变器控制器的研究。.在微电网阻抗辨识方面，采用三种方法进行了微电网阻抗快速准确的辨识：①利用注入基波信号非整数倍的低频小电流信号进行辨识；②利用高频载波信号（逆变器开关频率信号）进行辨识；③注入DIBS（Discrete Interval Binary Sequence）电流扰动信号进行微电网阻抗辨识。.结果表明：三种方法均能实现微电网阻抗快速准确的辨识。.在并网逆变器控制方面，在常规的PI控制器，准谐振的PR控制器的基础上，进行增益调度自适应控制器的研究，探讨无扰切换策略实现，并进行自适应比例复数积分控制器的研究，PI加状态反馈的控制器研究等等。.结果表明：①自适应比例复数积分，易于实现特定频率处的高增益，达到零稳态误差的控制效果，也易于实现谐振频率的调整，且整体控制性能优于比例谐振控制器。.②采用逆变侧电流反馈的三相不平衡并网逆变器的解耦控制策略，结合 PI 控制可以无静差跟踪直流量，重复控制周期性的补偿死区效应的控制方法，可以降低并网电流谐波含量。③将控制延时当成增广状态，建立离散增广状态空间表达式，设计带延时估计的状态观测器，基于状态反馈，可实现LCL的有源阻尼，在消除并网电流的稳态误差的同时，可以补偿控制延时。.项目已取得的成果和后续的研究为微电网和并网逆变器的稳定性、可靠性和鲁棒性提供了一个可能的解决方案。