基于重复控制原理的LCL型并网逆变器的研究

发布时间：2018-11-08 08:06

【摘要】：随着分布式发电系统的广泛应用，与并网变换器电能质量相关的问题受到了越来越多的关注。逆变器并网时会受到众多因素的干扰，而其中以周期性扰动居多。为了抑制周期性扰动，通常采用基于内模原理的重复控制技术，在控制环节中通过前馈一个延时时间为电网基波周期的延时环节，构成重复控制内模，从而实现对并网电流中基波信号的无静差跟踪。然而在实际应用场合，数字控制中的延时时间只能为系统采样周期的整数倍，一旦实际电网频率发生变化，系统采样频率和电网频率的比值就不能保持为整数。此时若仍然采用重复控制技术，系统的稳态跟踪性能和谐波抑制能力将会明显降低。针对传统重复控制的缺点，本文研究了一种以FIR滤波器为内模参数的改进型重复控制系统，并研究一种新型的FIR滤波器参数设计方法。以该方法设计的FIR滤波器在中低频段具有线性相频特性和低通滤波特性，能够模拟非整数延时环节，，从而使重复控制系统内模的谐振频率始终能够跟随电网的基波和谐波频率，使得改进重复控制系统能够在中低频段逼近理想重复控制的控制效果。在上述理论分析的基础上，利用MATLAB仿真软件进行仿真，验证本文提出的改进型重复控制方法的有效性。最后，搭建了一台由DSP控制的LCL型三相并网逆变器实验平台，在此平台上对改进型重复控制方法进行了实验验证。实验结果表明，该方法不仅能够在三相平衡系统及带非线性负载的三相平衡系统下有效的降低系统的稳态跟踪误差和消除入网电流中的谐波，还能够在频率变比不固定的情况下使控制系统依然具有比较理想的控制效果，弥补了传统控制方法频率适应能力不足的缺点。
[Abstract]:With the wide application of distributed generation system, more and more attention has been paid to the problems related to the power quality of grid-connected converters. Inverter grid-connected will be disturbed by many factors, among which the periodic disturbance is the most. In order to suppress the periodic disturbance, the repetitive control technique based on the internal model principle is usually used. In the control link, the repetitive control internal model is formed by feedforward a delay link in which the delay time is the fundamental wave period of the power network. Thus, the tracking of fundamental signal in grid-connected current without static error is realized. However, in practical applications, the delay time in digital control can only be an integer multiple of the sampling period of the system. Once the actual power network frequency changes, the ratio of the system sampling frequency to the power network frequency cannot be maintained as an integer. In this case, the steady-state tracking performance and harmonic suppression ability of the system will be significantly reduced if the repetitive control technique is still adopted. Aiming at the shortcoming of traditional repetitive control, an improved repetitive control system with FIR filter as internal mode parameter is studied in this paper, and a new design method of FIR filter parameter is studied. The FIR filter designed by this method has the characteristics of linear phase frequency and low pass filter in the low and medium frequency band, which can simulate the non-integer delay link, so that the resonant frequency of the internal model of the repetitive control system can always follow the fundamental and harmonic frequencies of the power network. The improved repetitive control system can approach the control effect of ideal repetitive control in low and medium frequency band. Based on the above theoretical analysis, the MATLAB simulation software is used to verify the effectiveness of the improved repetitive control method proposed in this paper. Finally, an experimental platform of LCL type three-phase grid-connected inverter controlled by DSP is built, and the improved repetitive control method is verified by experiments on this platform. The experimental results show that the proposed method can effectively reduce the steady-state tracking error and eliminate the harmonics in the three-phase balance system and the three-phase balanced system with nonlinear load. It can also make the control system have ideal control effect under the condition that the frequency changing ratio is not fixed, which makes up for the shortcoming of the traditional control method which has insufficient frequency adaptability.
【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

【参考文献】